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  • Articles  (583)
  • Column liquid chromatography  (344)
  • oxidation  (216)
  • Calcification
  • Springer  (583)
  • Nature Publishing Group
  • PANGAEA
  • 1995-1999  (565)
  • 1965-1969  (18)
  • 1
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    Springer
    Journal of applied electrochemistry 27 (1997), S. 1275-1282 
    ISSN: 1572-8838
    Keywords: Carbon monoxide ; Pt-Ru/C catalyst ; Tafel slopes ; oxidation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Electrical Engineering, Measurement and Control Technology
    Notes: Abstract CO electrooxidation on a Pt–Ru/C catalyst was investigated in sulphuric acid electrolyte. The physico-chemical properties of the Pt–Ru/C catalyst were studied by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The influence of temperature, CO partial pressure and proton concentration on the electrochemical oxidation rate was investigated by steady-state galvanostatic polarization measurements. The apparent activation energy decreased from 70 to 30kJmol−1 as the overpotential increased from 0.5 to 0.9V vs NHE. The reaction order with respect to carbon monoxide increased, passing from 0.4 to 1, with the increase of the overpotential from 0.5 to 0.7V vs NHE; a reaction order close to −1 with respect to the protonic concentration was observed, irrespective of the potential. Tafel slopes of about 136mVdec−1 were determined for oxidation of CO and CO/N2 mixtures.
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  • 2
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    Journal of applied electrochemistry 28 (1998), S. 607-612 
    ISSN: 1572-8838
    Keywords: SnO2 anodes ; doping ; high overvoltage anodes ; surface analysis ; oxidation ; water treatment
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Electrical Engineering, Measurement and Control Technology
    Notes: Abstract Doped tin dioxide electrodes have been prepared by a standard spray pyrolysis technique. The electrochemical behaviour of these electrodes has been investigated by cyclic voltammetry in sulphuric acid using the Fe2+/Fe3+ redox couple system as test reaction. Oxygen evolution has been used to study the stability of doped SnO2 electrodes. The SnO2 electrodes doped with antimony and platinum exhibit the highest stability. XPS analysis shows that the oxidation state of Sn, Sb and Pt are +4, +3 and +2, respectively, the probable species being SnO2, Sb2O3 and PtO.
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  • 3
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    Journal of chemical crystallography 28 (1998), S. 119-123 
    ISSN: 1572-8854
    Keywords: Azetidine ; azetine ; ring opening ; oxidation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract 1-Acetyl-3-bromo-3-phenylazetidine (1), C11H12BrNO, has been synthesized and characterized by spectroscopic methods and single crystal X-ray analysis. It crystallizes in the space group P2 1/c with a = 8.633(1), b = 7.461(1), c = 17.204(1) Å, β = 98.403(7)°, V = 1096.2(2) Å3, Z = 4, D calc = 1.540 g cm−3. The azetidine ring is nearly planar since the four atoms are within ±0.039(5) Å of the mean square plane calculated for the heterocycle. The attempt to obtain a highly strained 2-azetine derivative from the above compound gave, surprisingly, 1-phenyl-2-(N-acetyl-N-formyl)-aminoethanone (2), C11H11NO3. This compound has been also characterized by spectroscopic methods and single crystal X-ray analysis. It crystallizes in the space group P212121, with a = 5.4719(3), b = 8.3205(6), c = 23.298(3) Å, V = 1060.7(2) Å3, Z = 4, D calc = 1.286 g cm−3. The aminoethanone residue is in a near planar conformation where the torsion angles are 7(2)° for N–C–C–=O and −173(2)° for N–C–C–C(Ph).
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  • 4
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    Journal of polymers and the environment 3 (1995), S. 199-203 
    ISSN: 1572-8900
    Keywords: Chemiluminescence ; oxidation ; stability ; acrylonitrile-butadiene-styrene
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Energy, Environment Protection, Nuclear Power Engineering , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The thermal oxidative stability of various formulations based on emulsion-grade ABS was studied by the chemiluminescence technique. Emulsion products were found to be essentially less stable than ionic mass polymerization resins. Among the antioxidants studied, Santonox R is clearly more efficient than Irganox 1076 and Irganox 3114, and its superiority is reflected primarily in improved induction period values. The introduction of Tinuvin 770 and Tinuvin 328 UV stabilizers into emulsion resins does not change the durability of the products. In mixtures where both Irganox 1076 and UV stabilizers are present, a certain antagonistic effect was noted at high UV stabilizer concentrations.
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  • 5
    ISSN: 1572-8757
    Keywords: porous carbons ; activation ; oxidation ; surface oxygen groups ; LTPD
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Physics , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract A styrene/divinylbenzene copolymer has been used as precursor for making porous carbons with bimodal pore size distributions (i.e., with both microporosity and mesoporosity). Pretreatment of the as-received copolymer by mild oxidation in air, significantly increased the carbon yield after carbonization. Reactivity studies of the polymer-based chars to CO2 clearly show the influences of some important factors such as carbonization temperature, heating rate, soak time on char reactivities. Bimodal porous carbons were prepared by carbonization of the preoxidized styrene/divinylbenzene copolymer in N2, followed by activation in CO2 at different temperatures to different levels of burnoff. The pore structures of the porous carbons produced have been characterized by various techniques such as gas adsorption and mercury porosimetry. The surfaces of the porous carbons produced, and a commercial carbon adsorbent, have been modified with HNO3 and H2O2 treatment at various conditions. Characterization of the surface oxygen functionality, both quantitatively and qualitatively, has been achieved using techniques such as Linear Temperature Programed Desorption (LTPD) and selective neutralization of bases.
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  • 6
    ISSN: 1572-8765
    Keywords: carbonado ; diamond ; oxidation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The oxidation of carbonado type synthesized polycrystalline diamonds produced from graphite together with catalytic Ni-Mo alloy doped with TiB2 and BNcub was investigated. It was found that the addition of these boron compounds increases the oxidation resistance of the carbonado type synthesized polycrystalline diamonds. The oxidation mechanism acting on the carbonado type synthesized polycrystalline diamonds and the role of boron compounds in increasing the resistance to the oxygen reaction are discussed.
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  • 7
    ISSN: 1572-8773
    Keywords: acidophilic ; strain ; oxidation ; kinetics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract Recovery of metal values from sulfide ores by use of acidophilic microorganisms is gaining importance. A number of commercial/pilot plants are setup to find out the techno-economic feasibility of the overall process. The main drawback in the process is the slow kinetics of dissolution of metal values from the sulfide ores. To make the technology e attractive the kinetics should be improved considerably. There are various factors which determine the overall kinetics such as bacterial activity and concentration, iron and sulfur oxidation, oxygen consumption, reactor design and nature of ore. A brief review has been made dealing with the above parameters
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  • 8
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    Catalysis letters 37 (1996), S. 213-216 
    ISSN: 1572-879X
    Keywords: titanium silicalites ; oxidation ; amines ; hydrogen peroxide
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Titanium silicalite molecular sieves, TS-1 and TS-2 having MFI and MEL structures, respectively, catalyze the oxidation of secondary amines to the corresponding hydroxylamines using hydrogen peroxide as the oxidant. Higher concentrations of H2O2 lead to further oxidation of hydroxylamine to nitrone. Diffuse reflectance spectroscopy shows the formation of a titanium peroxo complex upon addition of hydrogen peroxide to the TS-1 catalyst. The titanium peroxo complex oxidizes the substrate and reforms to a titanyl group.
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  • 9
    ISSN: 1572-879X
    Keywords: oxidation ; cyclohexene ; polyoxometalate-intercalated hydrotalcite
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Cyclohexene was oxidized with molecular oxygen over transition-metal-substituted polyoxometalate-intercalated hydrotalcites to produce 2-cyclohexene-1-one and 2-cyclohexene-1-ol with high selectivity under mild reaction conditions.
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  • 10
    ISSN: 1572-879X
    Keywords: palladium metal ; oxidation ; toxic organics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract In water, metallic palladium was found to catalyze the deep oxidation of a wide variety of functional organics by dioxygen at 80–90°C in the presence of carbon monoxide. Several classes of organic compounds were examined: benzene, phenol and substituted phenols, aliphatic and aromatic halogenated compounds, organophosphorus, and organosulfur compounds. In every case, deep oxidation to carbon monoxide, carbon dioxide, and water occurred in high yields, resulting in up to several hundred turnovers over a 24 h period. Since the heterogeneous catalyst can be removed by simple filtration, simultaneous water purification and contaminant destruction becomes feasible. For those substrates that are insoluble in pure water, a mixture of water and perfluorobutyric acid was successfully employed as the solvent.
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  • 11
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    Catalysis letters 34 (1995), S. 31-40 
    ISSN: 1572-879X
    Keywords: palladium ; PdO ; alumina ; methane ; oxidation ; carbon ; XPS ; ellipsometry ; structure sensitivity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Samples of palladium supported onγ-alumina and a palladium foil were used as catalysts for methane oxidation at 550° C. The samples were quenched quickly in the reaction chamber to room temperature in flowing Ar and then transferred in vacuo for XPS analysis. Structure sensitivity was manifest from an increase in PdO stability and a decrease in carbon deposition relative to Pd with increasing particle size. The results were compared with recent ellipsometric data.
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  • 12
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    Catalysis letters 52 (1998), S. 25-29 
    ISSN: 1572-879X
    Keywords: metallosilicate ; mesoporous ; MCM-41 ; Mo-MCM-41 ; catalysis ; oxidation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Mo-incorporated MCM-41 has been prepared by direct hydrothermal synthesis. XRD and N2-adsorption measurements showed the characteristics of MCM-41. IR, FT-Raman and UV-VIS DR spectroscopic analyses gave the evidences for the incorporation of Mo in the framework of MCM-41. They are found to be stable and active for cyclohexanol and cyclohexane oxidation reactions with H2O2 as oxidant. Activity of this system has been compared with that of Ti-MCM-41 and molybdena impregnated on pure siliceous MCM-41.
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  • 13
    ISSN: 1572-879X
    Keywords: propane ; oxidation ; calcium-based catalysts ; tetrachloromethane
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The oxidation of propane has been investigated in the presence and absence of tetrachloromethane (TCM) on calcium hydroxyapatite (CaHAp), Ca3(PO4)2, CaSO4 and CaO at 723 K. In the absence of TCM, the conversion of C3H8 on CaHAp was 7.7–9.2% during 6 h on-stream while that on Ca3(PO4)2, CaSO4 and CaO was 0.6, 0 and 0.2–0.4%, respectively. The principal products on all catalysts in the absence of TCM were CO and CO2 with small selectivities to C3H6 and C2H4 (both 5–6%) observed on CaHAp. Upon addition of TCM, the selectivity to C3H6 on all catalysts and the conversion of C3H8 on CaSO4 increased while, with increasing time-on-stream, the changes in the conversion and selectivity were dependent upon the nature of the catalysts. XPS and XRD analyses provide evidence for the presence of chlorine in the surface and/or bulk of three of the catalysts, suggesting that chlorinated species on the solids play a role in the selectivity enhancement, but the absence of chlorine from the sulphate demonstrates the dissimilarities of the catalysts in their abilities to sorb and decompose TCM.
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  • 14
    ISSN: 1572-879X
    Keywords: methane ; oxidation ; strontium hydroxyapatite ; lead hydroxyapatite ; tetrachloromethane
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The oxidation of methane has been investigated on lead hydroxyapatite (PbHAp), strontium hydroxyapatite (SrHAp) and their binary mixtures at 873 K. PbHAp showed no activity for the oxidation of methane, while SrHAp produced carbon monoxide selectively at 2–4% conversion. On binary mixtures of the hydroxyapatites the conversion of methane and the selectivity to C2 compounds reached values higher than those of the separate constituents of the mixture. With tetrachloromethane in the feed stream a similar synergistic effect was observed with conversions of methane and selectivities to CH3Cl higher on the binary mixtures than those on either SrHAp or PbHAp. The strontium-containing hydroxyapatite appears to play a crucial role in the activation of methane, while the presence of the lead-containing analogue is apparently required for the minimization of undesirable processes involving methyl radicals.
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  • 15
    ISSN: 1572-879X
    Keywords: fluorination ; alumina ; platinum catalysts ; oxidation ; oxidation of benzene
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Platinum supported on fluorinated alumina is more active for the total oxidation of benzene than is the catalyst with the same Pt loading supported on hydrophilic unfluorinated alumina. The Pt-F/alumina catalyst contains well-dispersed small Pt particles, in contrast to Pt/alumina. The high dispersion is a consequence of a strong metal-support interaction.
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  • 16
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    Catalysis surveys from Japan 3 (1999), S. 55-60 
    ISSN: 1572-8803
    Keywords: acetic acid ; oxidation ; Pd ; heteropoly acid ; ethylene
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract A new process for acetic acid production by direct oxidation of ethylene which was established and commercialized is described. The catalyst system consisting of Pd and heteropoly acid exhibits excellent activity and selectivity. The addition of Se or Te to the catalyst system is effective to suppress the formation of carbon dioxide. This new process is applicable to a plant of a wide range of size corresponding to the local demand. Because this new process produces little waste water, it is very friendly to the environment.
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  • 17
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    Cellulose 5 (1998), S. 153-164 
    ISSN: 1572-882X
    Keywords: cellulose ; TEMPO ; polyglucuronic acid ; degree of polymerization ; oxidation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract Various cellulose samples were oxidized by 2,2,6,6,-tetramethylpipelidine-1-oxyl radical (TEMPO)-NaBr-NaClO systems, and the effects of oxidation conditions on chemical structures and degrees of polymerization of the products obtained were studied. In the case of regenerated and mercerized celluloses, almost all C6 primary alcohol groups were selectively oxidized to carboxyl groups, and water-soluble polyglucuronic acid (cellouronic acid) sodium salts were obtained almost quantitatively; the degrees of polymerization were influenced greatly by the amount of TEMPO added, and the oxidation time and temperatures. Cellouronic acids prepared from mercerized linter and kraft pulps had size exclusion chromatograms with two separate peaks due to higher and lower molecular weight fractions. On the other hand, only small amounts of carboxyl groups were introduced into native cellulose samples. Since polyglucuronic acids prepared from cellulose by the TEMPO–NaBr– NaClO systems regularly consist of the glucuronic acid repeating unit, differing from the conventional water-soluble cellulose derivatives, they may open new fields of cellulose utilization.
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  • 18
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    Catalysis surveys from Japan 2 (1998), S. 121-132 
    ISSN: 1572-8803
    Keywords: zeolite ; metallosilicate ; atom-planting ; modification ; catalysis ; acidity ; shape-selective alkylation ; oxidation ; hydrogen peroxide
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Atom-planting, a useful method to prepare some metallosilicates having zeolitic structure, was proposed. By treatment of highly siliceous zeolite with metal chloride vapor at selected temperature, metal cation could be introduced into the defect sites (hydroxyl nests) of zeolite framework. By the atom-planting method, some metallosilicates which are difficult to be synthesized by hydrothermal synthesis could be prepared. The vapor phase shape-selective alkylation of ethylbenzene with ethanol, and the liquid phase selective oxidation with hydrogen peroxide on the metallosilicates prepared by atom-planting method were reviewed.
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  • 19
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    Catalysis surveys from Japan 2 (1998), S. 31-44 
    ISSN: 1572-8803
    Keywords: porous heteropoly compounds ; Pt-promoted heteropoly compounds ; shape selectivity ; water-tolerant catalyst ; hydrogenation ; oxidation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract This paper attempts to review recent works on catalysis of porous heteropoly compounds. The salts of heteropolyacids having Keggin structure with large cations like Cs+ are porous materials. For Cs hydrogen salts, the pore width can be controlled by the Cs content. Cs2.5H0.5PW12O40 has the largest amount of protons on the surface among the acidic Cs salts and possesses pores with bimodal distribution in the micro and meso region. Efficient performances were demonstrated for acid-catalyzed reactions such as skeletal isomerization of η-butane in solid-gas system, alkylation and acylation in solid-liquid system, and hydrolysis and hydration in solid-water system. A microporous salt, Cs2.2H0.8PW12O40, exhibited reactant shape selectivity towards direct decomposition of esters. Furthermore, an ultramicroporous bifunctional catalyst, Pt–Cs2.1H0.9PW12O40 of which the pore width is around 5 Å, exhibits reactant shape selectivity for hydrogenation of alkenes and oxidation of hydrocarbons, and product shape selectivity for skeletal isomerization of η-butane.
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  • 20
    ISSN: 1572-879X
    Keywords: TiO2 ; heterogeneous photocatalysis ; oxidation ; substituted toluenes ; zeolites
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Photocatalytic oxidation of substituted toluenes was investigated on irradiated TiO2 and TiO2 combined with HY15 and HY20 zeolites. In all cases the oxidation occurred in the first step exclusively on either one substituent or the other, but never on both simultaneously. In the presence of a zeolite, photooxidation conversion was higher than that obtained without zeolite.
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  • 21
    ISSN: 1572-879X
    Keywords: Fischer-Tropsch synthesis ; cobalt catalysts ; deactivation ; oxidation ; reduction ; promoters ; rhenium
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The influence of water on alumina-supported cobalt catalysts has been studied. The deactivation of supported Co catalysts was studied in a fixed-bed reactor using synthesis gas feeds containing different concentrations of water vapour. Supporting model studies were carried out using H2O/H2 feeds in conjunction with XPS and gravimetry. Rapid deactivation occurs on Re-promoted CO/Al2O3 catalysts when H2/CO/H2O feeds are used, whereas unpromoted CO/Al2O3 shows more stable activity. The results from the gravimetric studies suggest that only a small fraction of the bulk cobalt metal initially present reoxidizes to cobalt oxide during reaction. However, the XPS results indicate significant reoxidation of surface cobalt atoms or highly dispersed cobalt phases, which is likely to be the cause of the observed deactivation. Rhenium is shown to have a marked effect on the extent of reoxidation of alumina-supported cobalt catalysts.
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  • 22
    ISSN: 1572-879X
    Keywords: perovskite ; La1−xSrxFeO3−δ ; dehydrogenation ; oxidation ; ethane
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Catalysts of the composition La1−xSrxFeO3−δ, 0⩽x ⩽1, have been tested for the oxidative dehydrogenation of ethane in the temperature range 300–800°C. The catalyst is active above 400°C, giving a maximum yield of 37% ethylene at 650°C. Above 650°C, synthesis gas was formed together with methane, suggesting that the reforming reaction and thermal cracking of ethane took place. The catalytic data are compared to conductivity measurements on the same material, and a good correlation between the activity and p-type conductivity has been found. In the phase diagram for the system LaFeO3-SrFeO3−δ, a phase separation to two types of (La, Sr)FeO3−δ perovskites was observed in the La/Sr binary composition in the temperature range below 800°C. The phase separation can elucidate the dependency of the catalytic activity on its p-type conductivity.
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  • 23
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    Catalysis letters 39 (1996), S. 205-208 
    ISSN: 1572-879X
    Keywords: oxidation ; hydroxyapatite ; carbon monoxide ; inhibition ; tetrachloromethane
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The introduction of tetrachloromethane (TCM) into the feedstream of CO and O2 inhibits the formation of CO2 on hydroxyapatite. TCM interacts with the surface of hydroxyapatite to form its chlorinated analogue, chlorapatite, which suppresses the oxidation of CO to CO2. Thus, in the oxidative coupling of methane the beneficial effects of the addition of TCM to the feedstream result, at least in part, from the suppression of the further oxidation of CO.
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  • 24
    ISSN: 1572-879X
    Keywords: platinum ; EXAFS ; catalysis ; catalyst deactivation ; oxidation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract With a new set‐up for in situ EXAFS spectroscopy the state of a carbon‐supported platinum catalyst during aqueous alcohol oxidation has been observed. The catalyst deactivation during platinum‐catalysed cyclohexanol oxidation is caused by platinum surface oxide formation. The detected Pt–O co‐ordination at 2.10 Å during exposure to nitrogen‐saturated cyclohexanol solution is different from what is observed for the pure oxidised platinum surface (2.06 Å).
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  • 25
    ISSN: 1572-879X
    Keywords: catalysis ; combustion ; oxidation ; formic acid ; STM ; molecular beams ; surface diffusion ; surface reactivity ; active sites ; reconstruction
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Using a combination of STM and molecular beam reactor data we summarise some important features of a model reaction (formic acid oxidation on Cu(110)) which is of general significance to surface reactivity and to catalysis. Three such features are highlighted here. The first concerns the role of weakly held species (possibly physisorbed) in surface reactions. These species, although of very short lifetime on the surface, can, nevertheless, diffuse over long distances to “find” a sparse distribution of active sites. Thus a very low coverage of oxygen on the surface of Cu(110) increases the sticking probability of all the formic acid molecules which strike the surface to high value (0.82), even though the clean surface is relatively unreactive. The important concept here is the “diffusion circle” or “collection zone” which represents the area of surface visited by the molecule in its short sojourn in the weakly held state. The second theme concerns the concept of the “flexible surface”. We show that the involvement of surface atoms in reactions directs the structure and reactivity for a particular reaction. For formic acid oxidation the liberation of Cu atoms during the removal of oxygen as water leads to gross restructuring of the surface and can lead to “compression” of one reactant (the oxygen in this case) into a lower area, higher local coverage, unreactive state (the c(6×2) oxygen structure). Thirdly, and finally, it is proposed that, for many surface reactions, the surface acts in an analogous way to a solvent, supporting a “dissolved” (highly mobile and fluxional) phase of intermediates at low coverage, which crystallise out above a critical coverage (the 2D “solubility limit”).
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  • 26
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    Catalysis letters 57 (1999), S. 109-113 
    ISSN: 1572-879X
    Keywords: superacid ; zirconia ; molybdenum oxide ; methane ; oxidation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract A series of zirconia-supported molybdenum oxide catalysts with different molybdenum loadings prepared using conditions reported to generate “superacidity” have been evaluated for their performance as catalysts for methane oxidation. A marked dependence of Mo content on activity has been observed, with the most active material being that with intermediate molybdenum content. 5 wt% MoO3/ZrO2 compares favourably with ZrxCe1-xO2 for methane combustion. The presence of MoO3 is observed to stabilise the tetragonal polymorph of ZrO2 and, as Mo content is increased, dispersed MoO3 crystallites are formed as evidenced by Raman spectroscopy. Temperature-programmed reduction studies evidence differences in the reduction behaviour of the materials as a function of loading. The results indicate that molybdenum oxide supported on monoclinic zirconia gives rise to the most active catalyst. It is tentatively suggested that the formation of a MoO3 monolayer during reaction may be of importance.
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  • 27
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    Catalysis letters 37 (1996), S. 79-87 
    ISSN: 1572-879X
    Keywords: methanol ; oxidation ; copper ; electron spectroscopy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The role of preadsorbed oxygen present at Cu(111), Cu(110) and polycrystalline surfaces in the oxidation of methanol has been investigated by X-ray and electron energy loss spectroscopies. In addition to the well established formation of methoxy species and its subsequent decomposition and desorption as formaldehyde, a second reaction pathway to surface formate is present. The latter is temperature dependent being undetectable at 260 K at a polycrystalline surface but occurs at a significant rate at 295 K and above. The limitations of experimental data for methanol oxidation by temperature programmed desorption and molecular beam techniques are discussed.
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  • 28
    ISSN: 1572-879X
    Keywords: synergistic effect ; carbon monoxide ; oxidation ; mixed oxides ; iron oxide ; tin oxide ; manganese oxide
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Based on the comparative evaluation of the catalytic activity of Fe2O3, Mn2O3 and SnO2 and their mixed oxides (Fe2O3+SnO2) and (Mn2O3+SnO2), it is shown that the system (Mn2O3+SnO2) shows strong synergistic effects during CO oxidation reaction. Such effects are not observed for the analogous system (Fe2O3+SnO2). Based on the calcination and reduction behaviour of these two mixed oxide systems and the redox potentials of the involved cations, the possible reasons for the observance of synergistic effects for the (Mn2O3+SnO2) system are discussed.
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  • 29
    ISSN: 1572-879X
    Keywords: non-uniform surface ; kinetics ; ethanol ; oxidation ; molybdenum oxide
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Temkin's theory of rates of catalytic reactions on non-uniform surfaces is extended to the MoO3-catalyzed oxidation of ethanol to acetaldehyde. Two types of sites are assumed to be present, an oxygen atom site that can be modeled with uniform properties and a metal atom site characterized by non-uniform properties both for ethanol chemisorption to an ethoxide intermediate and the conversion of this intermediate to acetaldehyde. The rate-limiting step is the cleavage of a C-H bond in the absorbed ethoxide intermediate. Non-uniform surface kinetics leads to a kinetic rate expression of the form $$v = kP_{C_2 H_5 OH}^{1 - m} P_{O_2 }^{(1 - m)/4} P_{H_2 O}^{ - (1 - m)/2} $$ . Such a rate expression, withm=0.14, is shown to provide a good fit to kinetic data for the selective oxidation of ethanol on a silica supported molybdenum oxide catalyst.
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    Catalysis letters 40 (1996), S. 47-50 
    ISSN: 1572-879X
    Keywords: Baeyer-Villiger ; titanium silicate molecular sieve ; oxidation ; rearrangement ; titanium peroxo ; triphase
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Titanium silicate molecular sieve TS-1 has been found to be an efficient catalyst for Baeyer-Villiger (BV) oxidation of cyclic and aromatic ketones under triphase conditions (solid catalyst along with two immiscible liquid reactants in the absence of any cosolvent), using dilute H2O2. Reactions studied are the oxidation of cyclohexanone and acetophenone. Whereas in the case of cyclohexane,ε-caprolactone, a BV product along with hydroxy and diketones is formed, in the case of acetophenone, phenyl acetate, a BV product along witho- andp-hydroxyacetophenone is formed. The acidic nature of titanium peroxo species, stabilised by water, is proposed to be responsible for such reactions under triphasic reaction conditions.
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    Catalysis letters 36 (1996), S. 31-36 
    ISSN: 1572-879X
    Keywords: ethanol ; kinetics ; oxidation ; oxydehydrogenation ; platinum ; structure sensitivity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The effect of the platinum particle size was investigated for the catalytic oxidative dehydrogenation of aqueous ethanol to ethanal at a temperature of 303 K, an ethanol concentration of 260 mol m−3, a partial oxygen pressure 60 kPa, a pH of 9, and an ethanal and ethanoate concentration of 20 mol m−3. A particle size effect on the turnover frequency was observed but only for particle sizes smaller than 2 nm. Hence, the reaction shows a limited structure sensitivity.
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  • 32
    ISSN: 1572-879X
    Keywords: oxidation ; metalloporphyrins ; hydroperoxide decomposition
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    Topics: Chemistry and Pharmacology
    Notes: Abstract A new family of metalloporphyrin complexes having perfluoroalkyl groups in the meso-positions of the ring are active catalysts for the oxidation of isobutane to tert-butyl alcohol, TBA, and for the decomposition of tert-butyl hydroperoxide to TBA. This discovery extends the limited number of meso-substituents that can be used to enhance catalytic activity and fits the postulate that groups that withdraw electrons from the porphyrin periphery give rise to active catalysts for alkane oxidation. The perfluoroalkyl groups also confer oxidative stability, hydrophobicity and lower cost to the catalyst.
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  • 33
    ISSN: 1572-879X
    Keywords: model catalysts ; spin coating ; Pt colloid ; AFM ; XPS ; Si wafer ; particle size ; oxidation ; reduction
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Platinum particles of 2 nm diameter have been immobilised on oxidised silicon wafers by spin coating with colloidal solutions and characterised by X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM). The coverage and dispersion of the Pt colloids on the Si wafer are controlled by varying the concentration and the spin speed. Under optimal conditions mono-dispersed Pt colloids on silicon wafers are prepared. For the Pt colloids immobilised on the Si wafer, the majority of the stabilising ligands are removed through a reduction (with H2 at 200°C) or an oxidation (in air at 300°C) procedure. AFM showed that particle sizes are retained after the reduction procedure, while significant sintering occurs after oxidation. The mechanism of ligand removal was studied using an in situ XPS reaction cell.
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    Catalysis letters 56 (1998), S. 199-202 
    ISSN: 1572-879X
    Keywords: cerium ; gas carbonic ; propane ; oxidation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The interaction between CO2 and CeO2 and its role in the surface reactivity of alumina-supported cerium oxide has been studied by programmed thermodesorption (TPD) of CO2 and FTIR spectroscopy. The performance of Ce/Al2O3 systems was then analyzed for the propane oxidation in presence of CO2. The results have shown that the catalytic activity decreased when carbonate species are formed at the surface of CeO2. This behavior was attributed to the presence of CO2 from three different sources: contamination before use, during the handling of the samples, contamination proceeding from the reactants and from CO2 produced by the reaction itself.
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    Catalysis surveys from Japan 3 (1999), S. 27-35 
    ISSN: 1572-8803
    Keywords: oxidation ; oxygen ; alkane ; N‐hydroxyphthalimide ; radical catalyst
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract A practical catalytic method to convert alkanes into the corresponding oxygen‐containing compounds with O2 under mild conditions using N‐hydroxyphthalimide (NHPI) in the presence or absence of a transition metal was developed. Thus, cyclohexane was successfully converted into adipic acid in good conversion and selectivity by a combined catalytic system consisting of NHPI and Mn(acac)2. Lower alkane such as isobutane was converted into t‐butyl alcohol (83%) under 10 atm of air by NHPI‐Co(OAc)2 system. Alkylbenzene such as toluene was oxidized to benzoic acid in high yield (81%) under normal temperature and pressure of dioxygen in the presence of a catalytic amount of NHPI and Co(OAc)2. ESR measurements showed that phthalimide‐N‐oxyl generated from NHPI under dioxygen atmosphere is a key species in this oxidation and functions as a radical catalyst.
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    Cellulose 2 (1995), S. 265-272 
    ISSN: 1572-882X
    Keywords: Hydrogen peroxide ; oxycellulose ; bleaching ; oxidation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract Peroxides are important bleaching agents, industrially, for cellulosic products. They are also used in detergents. Peroxides can degrade cellulose as well as decolorize it and remove stains. Both free radicals and perhydroxyl anions have been suggested as the intermediates in the reactions occurring between cellulosic products and hydrogen peroxide. The proposed mechanisms are reviewed with emphasis primarily on cotton cellulose. Further work is required to establish unequivocally the mechanism of degradation and decolorization of cellulose products.
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  • 37
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    Calcified tissue international 2 (1968), S. 296-298 
    ISSN: 1432-0827
    Keywords: Calcium ; Lipid ; Bacteria ; Calcification
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Description / Table of Contents: Résumé On a fait ce travail pour determiner si le facteur responsable pour la liaison de calcium par un calcifableBacterionema matruchotii est dans la fraction lipide de la cellule. Des cellules congelees et sechees ont ete extraites par le chloroform-methanol. La fraction de chloroform-methanol, les cellules extraites et les cellules non traitees ont ete examinees pour la liaison de calcium. La fraction du chloroform-methanol et les cellules non traitees avaient la liaison de calcium. Les cellules extraites n'en avaient pas.
    Abstract: Zusammenfassung Diese Arbeit wurde durchgeführt um festzustellen, ob sich der Faktor für die Calcium-bindung, durch das calcifizierendeBacterionema matruchotii, in der Lipoidfraktion befindet. Die lyophiilisierten Zellen wurden mit Chloroform-Methanol extrahiert. Die Chloroform-Methanol-Fraktion, die extrahierten Zellen, sowie die nicht behandelten Zellen wurden auf eine Calciumbindung hin untersucht. Die Chloroform-Methanol-Fraktion und die nicht behandelten Zellen demonstrierten eine Calciumbindung. Die extrahierten Zellen hingegen nicht.
    Notes: Abstract This work was done to determine whether the factor responsible for calcium binding by a calcifiableBacterionema matruchotii is in the lipid fraction of the cell. Freeze-dried cells were extracted with chloroform-methanol. The chloroform-methanol fraction, the extracted cells and untreated cells were examined for calcium binding. The chloroform-methanol fraction and the untreated cells bound calcium. The extracted cells did not.
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    Calcified tissue international 4 (1969), S. 260-268 
    ISSN: 1432-0827
    Keywords: Cartilage ; Histochemistry ; Staining ; Protein ; Polysaccharide ; Calcification
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Description / Table of Contents: Résumé Des coupes de cartilage épiphysaire frais de jeunes rats, effectuées à la main, sont colorées à pH=4,5 dans des solutions à 0,01% de divers colorants cationiques, appartenant aux groupes de la thiazine, oxazine, azine, triphénylméthane, acridine, et phthallocyanine. Les granules intracellulaires métachromatiques, mises en évidence antérieurement par le bleu de toluidine, sont également identifiées à l'aide de l'azur A, le bleu de méthylène et le bleu de crésyl. Les granules se colorent moins bien à la thionine, le rouge neutre, la safranine O, le bleu de toluylène et l'acridine orange. Dans les conditions utilisées, la matrice de la zone de réserve et la matrice de la zone hypertrophique inférieure (en voie de calcification) se colorent, alors que les matrices des zones prolifératives et hypertrophiques supérieures ne prennent pas les colorants. La gallocyanine, le violet cristal, la fuchsine basique, l'azocarmin B, le bleu de gallamine et la bleu alcian ne se colorent pas ou donnent des réactions colorées différentes de celles décrites ci-dessus. Il semble que le pK et le poids moléculaire des colorants jouent un rôle important, mais ils ne paraissent pas être les seuls facteurs intervenant dans la coloration des granules. Un changement, lié à la calcification, semble intervenir au niveau du matériel métachromatique (probablement des polysaccharides protéiques), aussi bien dans la matrice que les cellules cartilagineuses épiphysaires.
    Abstract: Zusammenfassung Handpräparierte Schnitte von frischem Epiphysenknorpel junger Ratten wurden bei einem pH von 4,5 in 0,01% igen Lösungen verschiedener kationischer Farbstoffe folgender Klassen gefärbt: Thiazin, Oxazin, Azin, Triphenylmethan, Acridin und Phthalocyanin. Die intracellulären β-und γ-metachromatischen Granula, erstmals mit Toluidinblau im frischen Gewebe nachgewiesen, konnten auch gut mit Azur A, Methylenblau und Brillantkresylblau dargestellt werden. Die Granula konnten ebenfalls, aber weniger gut, mit Thionin, Neutralrot, Safranin D, Toluylenblau und Acridinorange gefärbt werden. Unter diesen Färbungsbedingungen werden die inaktive Matrixzone und die untere hypertrophische (verkalkende) Matrixzone angefärbt, während die proliferative und die obere hypertrophische Matrixzone sich nicht färben. Gallocyanin, Kristallviolett, basisches Fuchsin, Azokarmin B, Gallaminblau und Alzianblau färbten entweder gar nicht, oder gaben ein anderes als das obenbeschriebene Färbemuster. Es wird vorgeschlagen, daß das pK und das Molekulargewicht der Farbstoffe wichtig aber nicht unbedingt die einzigen Faktoren sind, die die Färbung der Granula bestimmen. Die Resultate zeigen, daß eine Veränderung im metachromatischen Material (vermutlich Proteinpolysaccharide) vorliegt, und zwar sowohl in der Matrix als in den Zellen des Epiphysenknorpels; diese Veränderung scheint im Zusammenhang mit der Verkalkung zu stehen.
    Notes: Abstract Hand-cut sections of fresh epiphyseal cartilage from young rats were stained at pH 4.5 in 0.01% solutions of various cationic dyes of the thiazine, oxazine, azine, triphenylmethane, acridine, and phthallocyanin classes. The intracellular β-and γ-metachromatic granules, previously demonstrated in fresh tissues with toluidine blue, were also demonstrated well with azure A, methylene blue, and brilliant cresyl blue. The granules were also demonstrated, but not as well, by thionin, neutral red, safranin O, toluylene blue, and acridine orange. Under the conditions of staining, the reserve zone matrix and the lower hypertrophic (calcifying) zone matrix stained, whereas the proliferative and upper hypertrophic zone matrix did not stain. Gallocyanin, crystal violet, basic fuchsin, azocarmine B, gallamine blue, and alcian blue either did not stain, or gave a different pattern of staining from that described above. It is suggested that the pK and molecular weight of the dyes are important, but not necessarily the only factors in determining the staining of the granules. The results indicate that there is a change in the metachromatic material (presumably proteinpolysaccharide) in both the matrix and cells of epiphyseal cartilage, which appears to be related to calcification.
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    Calcified tissue international 4 (1969), S. 20-38 
    ISSN: 1432-0827
    Keywords: Calcification ; Epiphyseal Cartilage ; Bone ; Electrolytes ; Organic matrices
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Description / Table of Contents: Résumé Un procédé de dissection a été mis au point pour permettre l'analyse zonale du cartilage de l'épiphyse des os de la jambe d'un foetus bovin. Des échantillons de tissu complet et lavé venant des différentes zones ont été analysés pour déterminer leur contenu en électrolyte et en constituants organiques, ainsi que pour leur densité, cendres et humidité. Les résultats ont montré que lorsque la quantité de cendres et la densité augmentaient, l'eau contenu dans le tissu diminuait. Les quantités de cendres dans les zones de cartilage en voie de calcification étaient plus grandes qu'il avait été. Quand elles étaient exprimées comme un pourcentage du poids sec, elles étaient les plus importantes dans le cartilage lavé calcifié que dans le autre zones. Au début de la minéralisation du cartilage, la quantité de Na (m moles/l de tissu frais) diminuait tandis que celles du Ca et du P inorganique augmentaient. Les niveaux de Mg augmentaient pendant que la calcification se poursuivait, mais seulement à une faction du taux du Ca et du P. Les rapports Ca/P inorganique étaient les plus grands dans le cartilage au repos (Cartilage non-différentié hyalin), suggérant un lien initiale entre Ca et les chrondromucoprotéines. Cependant, au début de la calcification, pendant la prolifération du cartilage les rapports Ca/P étaient beaucoup plus petits (ca. 1.50) mais augmentaient graduellement avec l'advancement de la minéralisation. Des changements importants survenaient dans la composition de la phase organique, pendant la calcification endochondrale. Comme il a été déterminé par l'analyse de l'hydroxyproline la quantité de collagéne diminuait progressivement pendant la calcification du cartilage, mais augmentait rapidement pendant la formation d'os. Comme il a été déterminé par l'analyse de l'héxosamine et du sulfute les chrondromucoprotéines étaient aux niveaux les plus éléves pendant la prolifération du cartilage et diminuaient constamment au cours de la calcification. Cependant, bien que la calcification était déja très avancée dans le cartilage hypertrophique, de grandes quantites de mucopolysaccharides étaient encore présentes. Les rapports sulfure/hhéxosamine montraient un léger déclin pendant les premiéres étapes de la calcification, mais augmentaient beaucoup pendant le cours de la minéralisation. Les quantités d'acide sialique étaient plus grandes dans le cartilage de l'épiphyse que dans le cartilage au repos ou dans l'os. Les lipides augmentaient rapidement pendant la calcification du cartilage, mais étaient très réduites dans l'os complètement formé. La signification de ces résultats est discutée.
    Abstract: Zusammenfassung Eine Seziermethode, die eine Schichten-Analyse der Beinepiphysenplatte von Rinderfeten erlaubt, wurde entwickelt. Proben vor und nach Waschen des Gewebes der verschiedenen Schichten werden untersucht in bezug auf Elektrolyte und organische Bestandteile, als auch in bezug auf Dichte, Aschengehalt und Feuchtigkeit. Die Resultate zeigten eine Zunahme des Aschengehaltes und der Dichte, während der Wassergehalt abnahm. Unerwartet hoch waren die Aschenwerte im in Verkalkung begriffenen Knorpel. Ausgedrückt in Prozent Trockengewicht, ergab gewaschener, verkalkter Knorpel den höchsten Wert aller Zonen. In den Frühstadien der Knorpelmineralisation nahm der Natriumgehalt (m Mol/l Frischgewebe) ab, während Ca und anorganischer P zunahmen. Mit fortschreitender Verkalkung erhöhte sich auch der Magnesium-Spiegel, allerdings nur zu einem Bruchteil des Ausmaßes, in welchem Ca und P zunahmen. Die höchsten Ca/P anorg. Verhältnisse wurden im Ruheknorpel (undifferenzierter hyaliner Knorpel) gefunden, was auf eine initiale Bindung von Ca durch Chondromucoproteine hinweist. Die Ca/P-Verhältnisse proliferierenden Knorpels waren jedoch bei Verkalkungsbeginn viel tiefer (ca. 1.50). Diese nahmen allerdings mit fortschreitender Mineralisierung stetig zu. In der endochondralen Verkalkungsphase fanden markante Veränderungen in der Zusammensetzung des organischen Anteils statt. Basierend auf der Hydroxyprolinanalyse nahm der Collagengehalt in der knorpeligen Verkalkungsperiode fortschreitend ab, während er jedoch bei der Knochenbildung rasch zunahm. Die an Hand von Hexosamin- und Schwefelanalysen bestimmten Chondromucoproteingehalte ergaben Höchstwerte im proliferierenden Knorpel und fielen stetig ab mit zunehmender Verkalkung. Trotz der im hypertrophischen Knorpel schon weit fortgeschrittenen Verkalkung waren immer noch große Mengen an Mucopolysacchariden vorhanden. Die Schwefel/Hexosamin-Verhältnisse zeigten eine minimale Abnahme in den frühen Verkalkungsphasen, nahmen jedoch markant zu bei fortschreitender Mineralisation. Der Sialinsäurespiegel war im Epiphysenknorpel, verglichen mit demjenigen des Ruheknorpels oder Knochens, erhöht. In der knorpeligen Verkalkungsphase nahmen die Lipide rasch zu, während jedoch die Werte des vollständig ausgebildeten Knochens stark vermindert waren. Die Bedeutung dieser Ergebnisse wird besprochen.
    Notes: Abstract A dissection procedure has been devised to permit zonal analysis of the epiphyseal plate of fetal calf leg bones. Samples of whole and washed tissue from the various zones were analyzed for their content of electrolyte and organic constituents, as well as for density, ash and moisture. Results showed that as ash content and density increased, water content decreased. Ash levels in calcifying cartilage zones were unexpectedly high. When expressed as a percentage of dry weight, washed calcified cartilage had the highest content of any zone. In the early stages of the mineralization of cartilage, Na content (mmoles/l of fresh tissue) decreased as Ca and inorganic P increased. Magnesium levels increased as calcification proceeded, but only at a fraction of the rate of Ca and P. Ratios of Ca/inorganic P were highest in resting cartilage (non-differentiated hyaline cartilage), suggesting an initial binding of Ca to chondromucoproteins. However, at the onset of calcification in proliferating cartilage, Ca/P ratios were much lower (ca. 1.50), but gradually increased with advancing mineralization. Marked changes occurred in the composition of the organic phase during endochondral calcification. As determined by hydroxyproline analysis, collagen content progressively decreased during cartilaginous calcification, but increased rapidly during bone formation. As determined by hexosamine and sulfur analysis, chondromucoproteins were at highest levels in proliferating cartilage and decreased steadily as calcification increased. However, although calcification was already well advanced in hypertrophic cartilage, large amounts of mucopolysaccharide still were present. Sulfur/hexosamine ratios showed a slight decline during the early stages of calcification, but increased markedly with further mineralization. Sialic acid levels were elevated in epiphyseal cartilage over those in resting cartilage or bone. Lipids increased rapidly during cartilaginous calcification, but were greatly reduced in fully-formed bone. The significance of these findings is discussed.
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  • 40
    ISSN: 1432-0975
    Keywords: Key words Coral ; Calcification ; Biomineralisation ; Autoradiography ; Freeze-substitution
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences
    Notes: Abstract  The uptake of 45Ca and/or 14C by the skeleton of coral colonies has been commonly used to investigate the processes of calcification. This study reports the differential uptake of these tracers within different regions of the skeleton and tissues of individual corallites and polyps of the hermatypic coral Galaxea fascicularis. Incubation in 45Ca in the light resulted in 80 percent of the 45Ca taken up being deposited in the skeleton. Autoradiography of transverse and longitudinal slices of freeze-substituted polyps and corallites showed that in the light 45Ca was incorporated into the exsert septa, the outside of the thecal walls of the corallite and the inner edges of the septa. Incorporation did not occur in the costae. The radioactivity in the skeleton was considerably greater than in the tissues. In the dark, or in the presence of the photosynthetic inhibitor Diuron, 45Ca was taken up by the exsert septa and was patchily distributed in the corallite walls which suggests that it was not a result of isotopic exchange. The differential incorporation of 45Ca onto the exsert septa was confirmed by scintillation counting. Negligible radioactivity remained in the extrathecal coelenteron after a brief 5 min rinse in non-radioactive seawater. Only 0.1% of 14C taken up in the light was incorporated into the skeleton and this was confirmed by autoradiography. In the presence of Diuron or in the dark, very little 14C was incorporated into tissues or skeleton and in autoradiographs was either not evident in the skeleton or the distribution was similar to that seen in autoradiographs of 45Ca uptake. These results show that the deposition of 45Ca, and therefore calcium carbonate, occurs at specific loci on the skeleton of a corallite. In the dark, deposition occurs specifically at the growing points of the corallite. Differential deposition of calcium carbonate within individual corallites has not been previously reported.
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    Journal of solid state electrochemistry 3 (1999), S. 179-186 
    ISSN: 1433-0768
    Keywords: Key words Cathodic protection system ; Carbon ; oxidation ; Composite carbon/polymer anode ; Lifetime
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The suitability of a polymeric composite material for use as part of an anode structure in a cathodic protection system has been examined. The composite material was a conductive blend (volume resistivity typically 1.5 Ω cm) of carbon black in a polyethylene binder. A long operational lifetime for the material demands that the rate of carbon loss must be low. In the work reported here, electrochemical and in situ analytical techniques were employed to characterise the performance of the material over a wide range of anodic current densities in a variety of aqueous electrolytes. The predominant anodic electrochemical reaction on the polymeric material is CO2 formation in acid and neutral solutions, which causes loss of carbon from the surface and the development of a non-conducting layer of polyethylene. The characteristics of the reaction suggest that it occurs via the discharge of H2O. In alkaline pH, however, the anodic reactions are more complex. A high OH− concentration (pH 12 or higher) favours the formation of oxygen rather than CO2, particularly at low anodic potentials. The presence of CO3 2− in the electrolyte catalyses the evolution of oxygen at pH values as low as 9. The electrochemical formation of oxygen always occurs in parallel with the generation of some humic acid in the solution.
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    European journal of nutrition 36 (1997), S. 336-339 
    ISSN: 1436-6215
    Keywords: Amino acids ; protein ; metabolism ; meal feeding ; oxidation ; breath test ; Aminosäuren ; Protein ; Stoffwechsel ; Fütterung ; Oxidation ; Atemtest
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition , Medicine
    Description / Table of Contents: Zusammenfassung Die aktuellen Mengen an freien Aminosäuren im Blut reichen nur aus, um die Ganzkörper-Proteinsynthese für einige Minuten aufrecht zu erhalten. Das zeigt, daß die freien Aminosäurenkonzentrationen in der Zirkulation klein und konstant gehalten werden im Vergleich zu den Mengen der Aminosäuren, die täglich aufgenommen und über die Körperproteine umgesetzt werden. Das Verschwinden der Aminosäuren exogenen oder endogenen Ursprungs aus dem freien Aminosäuren-Pool, findet hauptsächlich durch die Proteinsynthese und den Aminosäurenabbau statt. Die Partitionierung der Nahrungs-Aminosäuren zwischen diesen beiden Prozessen im Kurzzeitbereich werden als bedeutsam für die Ökonomie der Ganzkörper-Aminosäuren angesehen. Eine Verbesserung der Aminosäurenökonomie könnte durch solche nutritiven Maßnahmen erreicht werden, welche die Clearance der Nahrungsaminosäuren durch die Proteinsynthese anstelle des Aminosäurenabbaus begünstigen. Diese nutritiven Maßnahmen sollten sich an den „Schwellenwerten“ des Abbaus der individuellen Aminosäuren orientieren.
    Notes: Summary Actual amounts of free amino acids in the blood are sufficient to support whole body protein synthesis for some minutes only. This indicates that the levels of free amino acids in the circulation are kept small and constant relative to the amounts of amino acids supplied by daily intake and turnover of body proteins. The clearance of the amino acids originating from either endogenous or exogenous sources is mainly due to protein synthesis and metabolic degradation. The partitioning of dietary amino acids between these processes, on the short term, is supposed to play an important role in whole body amino acid economy. Therefore whole body amino acid economy could be improved by nutritional measures that favour the clearance of dietary amino acids by protein synthesis instead of by metabolic degradation. These nutritional measures should to be focused on threshold values for metabolic degradation of individual amino acids.
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  • 43
    ISSN: 1436-5073
    Keywords: oxidation ; titanium aluminide ; SNMS ; niobium effect ; oxygen tracer
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The oxidation behaviour of γ-TiAl based alloys with different Nb contents (2–10 At.%) was investigated in air and in argon-20% oxygen at 900 °C using thermogravimetric analysis. The oxide scales were characterized by a combination of optical microscopy, SEM/EDX and X-ray diffraction analyses. Although in all studied cases the presence of niobium improves the oxidation resistance of γ-TiAl, the oxidation kinetics, scale morphology and composition in air differed strongly from that in argon-oxygen. In air the oxidation resistance increases with increasing niobium-content. In Ar/O2 the niobium dependence is far more complex because internal oxidation occurs which is favoured by the presence of niobium. SNMS analysis revealed that the differences in behaviour in the two atmospheres are related to the formation of Ti-rich nitride at the scale/alloy interface during air oxidation. The positive effect of niobium on the oxidation resistance of γ-TiAl is mainly caused by a decrease of the transport processes in the heterogeneous TiO2/Al2O3-surface scale. Nitride formation and/or niobium enrichment at the scale/alloy interface also affect the oxidation behaviour, however these factors are believed to be the result of the decreased transport processes rather than the main reason for the niobium effect.
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    Microchimica acta 125 (1997), S. 401-406 
    ISSN: 1436-5073
    Keywords: fullerenes ; intercalation ; oxidation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The investigation of structural and electronic properties of the novel family of fullerenes depends on the existence of pure reference materials. Sublimation of the van-der Waals solids is a suitable purification method. Little attention has been paid to the question about the air stability of such sublimed samples in form of crystals or thin films. A combination of thermal desorption spectroscopy, thermal analysis and diffuse reflectance FT-IR spectroscopy is used to show the extent to which oxygen from dry air is intercalated into fullerenes and which detrimental reactivity occurs from attempts to thermally remove („nneal”) air-exposed samples. The conclusion is that any fullerene sample exposed to air will be transformed in part into a polymeric non-fullerene carbon upon thermal treatment to above 400 K irrespective of its initial purity.
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    Nutrient cycling in agroecosystems 49 (1997), S. 91-95 
    ISSN: 1573-0867
    Keywords: greenhouse effect ; land use ; methane ; oxidation ; soils
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Intact core samples from soils with different textures and land use were tested for their capacity to oxidise methane. The soil cores were taken from arable land, grassland and forest. It was found that coarse textured soils (6.74–16.38 µg CH4 m-2 h-1) showed a higher methane uptake rate than fine textured soils (4.66–5.34 µg CH4 m-2 h-1). Increasing soil tortuosity was thought to reduce the methane oxidation rate in fine textured soils. The oxidation rate of forest soils (16.32–16.38 µg CH4 m-2 h-1), even with a pH below 4.5, was very pronounced and higher than arable land (11.40–14.47 µg CH4 m-2 h-1) and grassland (6.74–9.30 µg CH4 m-2 h-1). Within the same textural class arable land showed a faster methane uptake rate than grassland. In grassland with a fine texture, even methane production was observed. Nitrogen availability and turnover in these land use systems were thought to cause the different oxidation rates. Decreasing the moisture content slowed down the oxidation rate in all soils. This could be caused by an increased N turnover and a starvation of the methanotrophic bacteria.
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    Nutrient cycling in agroecosystems 49 (1997), S. 59-70 
    ISSN: 1573-0867
    Keywords: land use ; methane ; nitrogen fertilizer ; oxidation ; soil
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Aerobic soils are an important sink for methane (CH4) contributing up to 15% of annual global CH4 destruction. However, the sink strength is significantly affected by land management, nitrogen (N) fertilizers and acidity. We tested these effects on samples taken from the Broadbalk Continuous Wheat, Park Grass permanent grassland and Broadbalk and Geescroft Wilderness experiments at Rothamsted. The rates of uptake from the atmosphere of both enhanced (10 ppmv) and ambient (2 ppmv) concentrations of CH4 were measured in laboratory incubations of soil cores under controlled conditions. The most rapid rates of uptake were measured in soil from deciduous woodland at pH 7 (measured in water); acidic (pH 4) woodland soil showed no net CH4 oxidation. While disturbance of the cores used in the experiments did not affect the rate of CH4 uptake, extended (150 years) cultivation of land for arable crops reduced uptake rate by 85% compared to that in the soil under calcareous woodland. The long-term application of ammonium- (NH4) based fertilizer, but not nitrate- (NO3) based fertilizer, completely inhibited CH4 uptake, but the application for the same period of farmyard manure that contained more N than the fertilizer had no inhibitory effect. Although the effects of agricultural practice on the oxidation of CH4 in soil are significant, the differences in oxidation rates between land use types are even greater. The likely effects of forest clearance, agricultural intensification and anthropogenic emissions of CH4 over the last 2500 years have been estimated for the United Kingdom. The calculations indicate that 54% of the current CH4 uptake by UK soils is the result of increased CH4 mixing ratio. They also indicate that land use change has decreased the potential sink strength by 62% or 37 kt CH4 g-1. In countries with much larger land areas than the UK, such as China, aerobic soil is likely to be a more significant factor in calculating net fluxes of CH4. It is important that the impacts of different agricultural managements and land use systems are understood and quantified so that the best possible estimate of CH4 sinks is calculated for comparison with sources.
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  • 47
    ISSN: 1572-9508
    Keywords: X-ray ; calibration ; filters ; interference ; oxidation
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    Topics: Physics
    Notes: Abstract We report on UV/Visible transmission measurements of aluminum coated Lexan filters designed as UV blocking filters for soft x-ray detectors. Transmission of the filters in the 2300-8000 Å wavelength range is significantly higher than expected. It cannot be accounted for applying a simple slab model of the transmission and adopting material properties reported in the literature. We show that this is due to interference effects which are strongly dependent on the filter geometry, and to oxidation of exposed aluminum surfaces and/or chemical interaction with the plastic support. The results of this work have led to the redesign of the Advanced X-ray Astrophysics Facility High Resolution Camera UV blocking filters.
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    Calcified tissue international 3 (1969), S. 151-162 
    ISSN: 1432-0827
    Keywords: Calcification ; Physiologic ; Phosphonic Acids ; Phosphates ; Crystallization ; Electron Microscopy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Description / Table of Contents: Résumé On a étudié la formation de l'hydroxyapatite de calcium cristallin à partir de solutions d'ions de calcium et de phosphate et l'inhibition de la croissance de cristaux de l'hydroxyapatite de calcium au moyen de polyphosphonates et de polyphosphates. Les polyphosphonates, éthane hydroxy-1-diphosphonate-1,1 de disodium et dichlorométhanediphosphonate de disodium, sont inhibiteurs efficaces contre la croissance de cristaux de l'hydroxyapatite de calcium. Les polyphosphates sont aussi inhibiteurs efficaces contre la croissance de cristaux de l'hydroxyapatite de calcium tant que le niveau exigé de polyphosphate intact est présent dans le système. Cependant, à cause de leur instabilité hydrolytique, qui est soulignée par une température élevée, valeur de pH basse, et certaines enzymes, la concentration du polyphosphate diminue avec le tempsin vitro, et son activité comme inhibiteur est perdue. Au contraire aux polyphosphates, les polyphosphonates sont hydrolytiquement stables. Les polyphosphonates sont chimiosorbés sur la surface des microcristallites de l'hydroxyapatite de calcium, ainsi empêchant l'occurrence d'autre croissance de cristaux semblable à l'action d'autres poisons connus de croissance de cristaux. On propose l'extension de cette action sur la formation de l'apatite et cette stabilité des polyphosphonates aux applications médicales et dentaires concernant le metabolisme pathologique de calcium et de phosphate.
    Abstract: Zusammenfassung Die Bildung des kristallinen Calciumhydroxyapatit aus Lösungen, welche Calcium- und Phosphationen enthalten, und die Hemmung der Bildung von kristallinen Calciumhydroxyapatit durch Polyphosphonate und Polyphosphate wurden untersucht. Polyphosphonate, Dinatriumäthan-1-hydroxyl-1,1-diphosphonat und Dinatriumdichloromethandiphosphonate verhindern das Kristallwachstum des Calciumhydroxyapatits. Die Polyphosphate verhindern ebenfalls das Kristallwachstum des Calciumhydroxyapatits, solange die notwendige Konzentration des nicht hydrolysierten Polyphosphats vorhanden ist. Wegen ihrer hydrolytischen Unbeständigkeit, die durch hohe Temperatur, niedrige pH und bestimmte Enzyme erhöht wird, vermindert sich jedoch die Konzentration des Polyphosphats allmählichin vitro, und ihre Hemmungsaktivität geht verloren. Im Gegensatz zu den Polyphosphaten sind die Polyphosphonate hydrolytisch beständig. Die Polyphosphonate werden an der Oberfläche der Mikrokristallite des Calciumhydroxyapatits chemisorbiert und verhindern, wie andere bekannte Kristallwachstumsgifte, auf diese Weise weiteres Kristallwachstum. Die Beständigkeit der Polyphosphonate und ihre Chemisorption an dem Apatit empfehlen ihren Gebrauch in der ärztlichen und zahnärztlichen Praxis, soweit sie den pathologischen Calcium- und Phosphatstoffwechsel betreffen.
    Notes: Abstract The formation of crystalline calcium hydroxyapatite from solutions of calcium and phosphate ions and the inhibition of calcium hydroxyapatite crystal growth by polyphosphonates and polyphosphates have been studied. The polyphosphonates, disodium ethane-1-hydroxy-1,1-diphosphonate and disodium dichloromethane diphosphonate, are effective inhibitors of calcium hydroxyapatite crystal growth. The polyphosphates are also effective inhibitors of calcium hydroxyapatite crystal growth as long as the required level of intact polyphosphate is present in the system. However, because of their hydrolytic instability, which is enhanced by high temperature, low pH, and certain enzymes, the concentration of the polyphosphate decreases with timein vitro, and its activity as an inhibitor is lost. In contrast to the polyphosphates, the polyphosphonates are hydrolytically stable. The polyphosphonates are chemisorbed on the surface of the microcrystallites of calcium hydroxyapatite and, in the manner of other known crystal growth poisons, thus prevent further crystal growth. The stability of the polyphosphonates and their chemisorption on apatite suggest their use in medical and dental applications involving pathological calcium and phosphate metabolism.
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    Calcified tissue international 3 (1969), S. 184-193 
    ISSN: 1432-0827
    Keywords: Mitochondria ; Calcification ; Calcium ; Chondrocytes ; Growth plate
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Description / Table of Contents: Résumé Des cultures d'épiphyse prélevées sur des rats et des souris ont été étudiées sous le microscope électronique. Un profile de granules mitochondriques de densité électronique a été trouvé. Les chondrocytes dans la zone proliférative avaint peu de granules, alors que ceux des zones successives ont montré une augmentation progressive de leur nombre et densité jusqu'à ce que la zone de calcification provisoire ait été atteinte. Cette zone a montré une distribution périphérique de mitochondries et une réduction du nombre et de la densité des granules mitochondriques. Du calcium isotopique 47 a été utilisé autoradiographiquement pour déterminer la location de calcium dans ces cellules. Des grains ont été trouvés sur les membranes R.E. et sur la plupart des mitochondries. La preuve d'un profile de ces granules et de leur rapport spatial avec la face de minéralisation indique une action éventuelle de mitochondries dès le début de la calcification de la matrice.
    Abstract: Zusammenfassung Epiphysekulturen von Ratten und Mäusen wurden unter dem Elektronenmikroskop untersucht. Ein Profil von mitochondrischen Körnchen mit elektronischer Dichte wurde gefunden. Chondrozyten in der Proliferationszone wiesen wenig Körnchen auf, während die der nachfolgenden Zonen allmählich an Zahl und Dichte zunahmen, bis die Zone der provisorischen Verkalkung erreicht wurde. Diese Zone zeigte eine periphere Verteilung der Mitochondrien und eine Abnahme in Zahl und Dichte der mitochondrischen Körnchen. Isotopes Kalzium 47 wurde autoradiographisch verwendet, um die Lage des Kalziums in diesen Zellen zu bestimmen. Körnchen wurden auf den E.R.-Membranen und auf einem Großteil der Mitochondrien gefunden. Der Nachweis eines Profils dieser Körnchen und ihres räumlichen Verhältnisses zur Mineralisierungsfläche weist auf einen möglich Einfluß der Mitochondrien mit Beginn der Matrixverkalkung hin.
    Notes: Abstract Rat and mice epiphyseal growth plates were studied with the electron microscope. A gradient of mitochondrial electron-dense granules was found. Chondrocytes in the proliferative zone had few granules, while those of the succeeding zones showed a gradual increase in number and density until the zone of provisional calcification was reached. This zone showed a peripheral distribution of mitochondria and a decrease in the number and density of mitochondrial granules. Isotopic47calcium was used autoradiographically to determine the location of calcium in these cells. Grains were found over the endoplasmic reticulum membranes and over most mitochondria. The demonstration of a gradient of these granules and their spatial relation to the mineralization front suggests a possible involvement of mitochondria in the onset of matrix calcification.
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    Calcified tissue international 4 (1969), S. 78-83 
    ISSN: 1432-0827
    Keywords: Bone ; Calcification ; Osteomalacia ; Phosphorus ; Vitamin D
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Description / Table of Contents: Résumé Les effects d'une dose de 1 mg de vitamine D3 (40 000 Unités,) administrée par voie intra-veineuse, ont été étudiés sur l'histologie osseuse et le métabolisme du phosphore chez 19 sujets contrôles dont l'histologie était normale et 28 malades présentant les caractères histologiques de l'ostéomalacie par carence vitaminique D. L'administration de la vitamine D n'a entraîné aucune modification histologique ou biologique significative chez les sujets contrôles. Mais chez les ostéomalaciques, il est apparu en moins de sept jours une augmentation très significative du front de calcification à l'interface tissue-ostéoïde-tissue-calcifié. Cette modification s'accompagnait d'une ascension progressive de la phosphatémie et de la réabsorption tubulaire du phosphore atteignant dans le même délai des valeurs normales.
    Abstract: Zusammenfassung Bei 19 Patienten mit normaler Knochenhistologie und bei 28 Patienten mit histologisch gesicherter Osteomalacie wurde die Wirkung von 1 mg Vitamin D3 (40000 Iv) i.v. auf die Knochenhistologie und den Phosphatmetabolismus untersucht. Bei den Kontrollpatienten konnten keine signifikanten Änderungen nach Vitamin D festgestellt werden, wogegen die Osteomalacie-patienten innerhalb von 7 Tagen eine deutliche Zunahme der Verkalkungszone an der Grenze zwischen Osteoid- und Knochengewebe zeigten. Diese Änderung war von einer fortschreitenden Zunahme des Serum-Phosphates, verbunden mit einer gesteigerten renalen tubulären Rückabsorption des Phosphates begleitet; beide kehrten anschließend gleichzeitig wieder zur Norm zurück.
    Notes: Abstract The effect of a 1 mg dose of intravenous Vitamin D3 (40,000 i.u.) on bone histology and phosphate metabolism was investigated in 19 patients with normal bone histology and 28 patients with histological evidence of osteomalacia. No significant changes occurred in the control patients after Vitamin D but the patients with osteomalacia showed a marked increase, within seven days, in the proportion of osteoid having a calcification front. This was accompanied by a progressive rise in the serum phosphate, which was associated with an increase in the renal tubular reabsorption of phosphate to normal.
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    Calcified tissue international 4 (1969), S. 231-244 
    ISSN: 1432-0827
    Keywords: Calcification ; Pyrophosphate ; Inhibitors
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Description / Table of Contents: Résumé Les propriétés d'induction de calcification des liquides biologiques peuvent être mesurées, in vitro et in vivo, par leur possibilité de redurcir des blocs d'émail décalcifié. Cette propriété est exprimée par les concentrations de calcium (et de phosphate) de solutions synthétiques inductrices de calcification, de concentrations et d'activité connues. Un plasma humain typique a une activité inductrice correspondant à celle d'une solution contenant du calcium, 0,70 mM, Ca/P, 1,67 et fluorure, 0,05 mM. L'activité relativement peu élevée des sérums et des plasmas s'explique par la présence d'inhibiteurs ioniques. L'ion phosphate est l'un d'eux, mais ne peut rendre compte de l'inhibition totale. Des anions et des cations sont responsables de l'inhibition, avec un rôle majeur pour les cations. Les ions suivants, en concentration physiologique, jouent un rôle inhibiteur: P7O 7 4− , HCO 3 − , SiO 4 2− , CrO 4 2− , Mg2+, Zn2+. Un mélange de ces ions provoque une inhibition totale identique à celle du plasma.
    Abstract: Zusammenfassung Der Einfluß biologischer Flüssigkeiten auf den Verkalkungsvorgang kann in vitro und in vivo anhand ihrer Fähigkeit, enthärtete Blöcke von Zahnschmelz wieder zu härten, gemessen werden. Diese Aktivität wird ausgedrückt als Konzentration des Calciums (und Phosphates) synthetischer calcifizierender Lösungen mit bekannter Konzentration und Aktivität. Die Aktivität eines charakteristischen menschlichen Plasmas entsprach derjenigen einer Lösung folgender Zusammensetzung: Calcium 0,70 mM; Ca/P=1,67 und Fluorid 0,05 mM. Die relativ niedrige Aktivität von Serum und Plasma ist bedingt durch das Vorhandensein einer Anzahl ionischer Inhibitoren. Das Pyrophosphation ist ein solcher; er kann aber nicht für die gesamte Inhibition verantwortlich gemacht werden. Sowohl anionische als auch kationische Inhibitoren sind vorhanden, wobei die Kationen den Hauptanteil ausmachen. Folgende Ionen erwiesen sich in einer physiologischen Konzentration als Inhibitoren synthetischer Systeme: P7O 7 3− , HCO 3 − , SiO 4 1− , CrO 4 2− , Mg2+, Zn2+. Zusammengenommen verursachten diese Ionen eine Gesamtinhibition ähnlich derjenigen des Plasmas.
    Notes: Abstract The calcifying activities of biological fluids can be measured,in vitro andin vivo, by their ability to reharden softened blocks of tooth enamel. The activity is expressed in terms of the calcium (and phosphate) concentrations of synthetic calcifying solutions of known concentration and activity. A typical human plasma had an activity corresponding to that of a solution of the following concentration: calcium, 0.70 mM; Ca/P, 1.67 and fluoride, 0.05 mM. The relatively low activity of serums and plasmas was shown to arise from the presence of a number of ionic inhibitors. Pyrophosphate ion is one such inhibitor but cannot account for the major inhibition. Both anionic and cationic inhibitors were shown to be present, with the cations respresenting the major portion. The following ions at their reported physiological concentration were shown to be inhibitors in synthetic systems: P7O 7 4− , HCO 3 − , SiO 4 2− , CrO 4 2− , Mg2+, Zn2+. In combination, these ions caused a total inhibition similar to those for plasmas.
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    Calcified tissue international 3 (1969), S. 266-273 
    ISSN: 1432-0827
    Keywords: Calcification ; Arteries ; Membranes ; Elastic tissue
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Description / Table of Contents: Résumé Avec la modification d'une méthode de von Kossa nous avons macroscopiquement representé les dessins de calcification de la membrane élastique intérieure, ainsi que les grosses artères du bassin, des artères des extrémités inferieures, des artères du bras, de la rate et des reins. Dans les artères du type élastique, dans les A.a. ilicae communes et internae, se présentaient les dégénérations calcaires de la membrane élastique intérieure sous forme d'incrustations noires arrondies ou polygonales qui ont été formes en groupes. Elles étaient toujours présentes chez des enfants agés de plus de trois mois et chez des aux adultes. Dans les artères musculaires, se montraient les parties calcifiées de la membrane élastique intérieure en forme de «bandes de calcaire» noires et groupes en paires le long des bordures des fissures de la membrane. Dans le cas où existait une calcinose forcée, on pouvait montrer avec cette méthode tout le système de fissures de la mambrane élastique intérieure. Chez tous les morts âgés de 10 à 20 ans, nous avons trouvé des bandes de calcaire dans les artères musculaires des extrémités inferieures. Ces bandes de calcaire ont été constatées aussi dans des personnes plus âgées. Au point de la fusion des bandes de calcaire et des incrustations calcaire polygonales des dépôts calcaires en forme de feuille («feuilles de calcaire») se forment dans la membrane elastique. Les bandes de calcaire et les feuilles de calcaire représentent des points de cristallisation pour des dépôts calcaire granuleux. Ils se forment dans la plupart des cas sur le la côté externe tourné vers la media.
    Abstract: Zusammenfassung Mit einer modifizierten von Kossa-Methode wurden die Verkalkungsmuster der inneren elastischen Membran der großen Beckenarterien, der Arterien der unteren Extremität, der Oberarm-, Milz-und Nierenarterien makroskopisch dargestellt. In den Arterien vom elastischen Typ, i.e. in den Aa. ilicae communes et internae, erschienen die Verkalkungen der inneren elastischen Membran als schwarze rundliche oder polygonale Inkrustationen, die zu Gruppen angeordnet waren. Sie wurden häufig bereits bei Neugeborenen festgestellt. Bei Kindern, die älter waren als 3 Monate und bei Erwachsenen lagen sie stets vor. — In den muskulären Arterien traten die verkalkten Anteile der inneren elastischen Membran makroskopisch als schwarze paarweise angeordnete „Kalkbänder” entlang den Rändern vorgebildeter Membranspalten auf. Bei ausgeprägter Calcinose konnte mit der angewandten Methode das gesamte Spaltensystem der inneren elastischen Membran dargestellt werden. Kalkbänder wurden in den muskulären Arterien der unteren Extremität bei allen 10–20 Jahre alten Verstorbenen vorgefunden und waren auch in den nachfolgenden Altersstufen stets vorhanden. Beim Zusammenfluß von Kalkbändern und polygonalen Kalkinkrustationen entstehen in der inneren elastischen Membran folienartige Kalkablagerungen („Kalkfolien”). Die Kalkbänder und Kalkfolien stellen Kristallisationspunkte für körnige Kalkablagerungen dar, die zumeist an ihrer äußeren, der Media zugekehrten Seite entstehen.
    Notes: Abstract Calcification patterns of the internal elastic membrane of the main pelvic arteries, lower limb arteries, brachial, splenic and renal arteries were demonstrated grossly by a modified von Kossa technique. In the elastic segment in the common and internal iliac arteries, the membrane calcification appeared as groups of roundish or polygonal incrustations. They were found frequently in newborns, and were always present in infants of more than three months, as well as in adults. In the muscular arteries, the calcified parts of the internal elastic membrane appeared grossly as pairs of bands (“calcific bands”) along the edges of the pre-existing gaps in this membrane. When calcification was pronounced, the whole pattern of the membrane gaps could be demonstrated by the method used in this study. Calcific bands were found in the muscular arteries of the lower limbs in all 10–20 year-old subjects, and were always present in the older age groups. The confluence of calcific bands or polygonal membrane incrustations found in the iliac arteries lead to sheet-like membrane calcification. The calcific bands and sheets represent crystallizing points for grain-like calcific deposits, which appear later on the medial surface.
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    Calcified tissue international 3 (1969), S. 363-365 
    ISSN: 1432-0827
    Keywords: Calcification ; Mitochondria ; Protozoa
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    Calcified tissue international 3 (1969), S. 38-54 
    ISSN: 1432-0827
    Keywords: Epiphyseal cartilage ; Calcification ; Apatite crystals ; Organic/Inorganic relationships
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Description / Table of Contents: Résumé Les rapports entre composants organiques et inorganiques du cartilage ont été étudiés au niveau des épiphyses tibiales chez des rats de 5 jours et au niveau des jonctions costo-chondrales chez des cobayes d'un mois. Voici les principaux résultats auxquels on est parvenu: (a) Dans les zones où la calcification s'amorce les cristallites d'apatite sont susceptibles d'être facilement éliminés des coupes en araldite et en glycol methacrylate (GMA) après traitement pendant une heure par une solution d'acide formique au 2%. (b) Les zones décalcifiées sont douées d'une faible densité aux électrons et vont exemptes d'une structure quelconque. Seulement la fixation à l'osmium peut révéler du matériel amorphe. (c) Indépendemment du fixateur et du moyen d'inclusion, les coupes décalcifiées, traitées par l'acétate d'uranyl et/ou par le citrate de plomb, montrent de fines structures allongées dont l'aspect est semblable à celui des cristallites. (d) Ces structures ainsi qu'un fond dense interposé prennent l'acide phosphotungstique (PTA) dans les coupes en GMA, une méthode celle-ci qui met en évidence les polysaccharides. (e) Le fond dense ne prend plus le PTA après traitement par la hyaluronidase et en même temps les structures semblables au cristallites apparaissent plus faibles. Après traitement par l'acétate d'uranyl et le citrate de plomb, l'attaque par la hyaluronidase ne produit aucune modification appréciable. Au contraire l'aspect des structures semblables aux cristallites apparait modifié par la digestion à la papaïne. (f) Quand la décalcification à l'EDTA précéde l'enrobage, des amas de matériel fibrillaire se mettent en évidence dans les zones où la calcification s'était amorcée. L'ensemble de ces résultats permet d'établir la nature organique des structures semblables au cristallites et porte aussi à admettre que celles-ci soient formées par de fins filaments cylindriques (digérés par la papaïne) entourés, et probablement engainés par del polysaccharides (digérés par la hyaluronidase et prennant le PTA dans les coupes en GMA).
    Abstract: Zusammenfassung Die Wechselbeziehungen zwischen den organischen und inorganischen Substanzen des verkalkenden Knorpels wurden in der tibialen und femuralen Epiphyse 5 Tage alter Ratten und in den Rippen 1 Monat alter Meerschweinchen untersucht. Die Hauptergebnisse waren: a) Die Hydroxyapatitkristalle der Frühverkalkungszonen können in Araldit- wie auch in Glycolmethylacrilatschnitten (GMA) mit einer lstündigen Behandlung durch 1% ige Ameisensäure leicht entfernt werden. b) Die entkalkten Zonen haben eine sehr niedrige Elektronendichte und enthalten keine sichtbaren Festkörper. Nach Fixierung mit Osmiumsäure kann man darin ein formloses Material erkennen. c) Eine Färbung der Schnitte mit Uranacetat und Bleicitrat, welche von den Fixier- und Einbettungsmitteln nicht beeinträchtigt wird, zeigt feine, längliche Körper (“Kristallgeister”) an, welche morphologisch den Kristallen von Hydroxyapatit gleichen. d) Die Färbung der GMA-Schnitte mit Phosphowolframsäure (PWS), eine Methode welche Polysaccharide anzeigt, hob diese “Kristallgeister” besonders hervor und demonstrierte auch eine dichte dazwischenliegende Grundsubstanz. e) Diese Substanz ist nach Behandlung mit Hyaluronidase nicht mehr färbbar mit PWS; die Färbbarkeit der “Kristallgeister” wird dabei jedoch nur verringert. Die Hyaluronidasebehandlung verändert die Uranacetat- und Bleicitratfärbung nicht. Die Feinstruktur der “Kristallgeister” wird durch Papainbehandlung sehr angegriffen. f) Falls die Schnitte vor dem Einbetten mit EDTA entkalkt werden, können Faserbündel in den Frühzonen der Verkalkung nachgewiesen werden. Diese Ergebnisse bestätigen die organische Natur der “Kristallgeister”. Sie beweisen auch, daß dieselben aus feinen Proteinstäbchen bestehen (verdaulich in Papain) und von Polysacchariden umgeben und vielleicht auch überzogen sind (verdaulich in Hyaluronidase und anfärbbar mit PWS).
    Notes: Abstract The organic/inorganic relationships in calcifying cartilage have been studied in tibialfemoral epiphyses of 5-day-old rats and in costochondral junctions of 1-month-old guinea pigs. The main results are: (a) Apatite crystallites in areas of early cartilage calcification are easily removed from araldite and glycol methacrylate (GMA) sections by 1-hour treatment with 2% formic acid. (b) The decalcified areas have a very low electron density and do not contain recognizable structures. Only after osmium fixation can an amorphous material be found in them. (c) Independently from the fixative and the embedding medium, staining decalcified areas with uranyl acetate and/or lead citrate reveals thin, elongated structures (crystallite ghosts) similar in shape to apatite crystallites. (d) These crystallite ghosts and a dense background are stained by phosphotungstic acid (PTA) in GMA sections, a method which reveals polysaccharides. (e) The dense background is no longer stained by PTA after hyaluronidase digestion and the stainability of the crystallite ghosts is reduced. After uranyl acetate/lead citrate staining there are no recognizable changes due to hyaluronidase. But, on the other hand, the fine structure of the crystallite ghosts is modified by papain digestion. (f) Clusters of fibrillar material are present in the areas of early calcification when EDTA decalcification is carried out before embedding the specimens. These results confirm the organic nature of the crystallite ghosts and suggest that they are formed by thin, rod-like protein/like structures (digested by papain) surrounded, and probably sheathed, by acid polysaccharides (digested by hyaluronidase and stained by PTA in GMA sections).
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    Calcified tissue international 4 (1969), S. 136-146 
    ISSN: 1432-0827
    Keywords: Bone ; Calcification ; Osteoblasts ; Osteoclasts ; Poultry
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Description / Table of Contents: Résumé L'activité des cellules osseuses et la composition du fémur de pondeuses furent examinées pendant sept jours de déficience calcique (diète contenant 0,13% de calcium) et sept jours de réplétion (diète contenant 3,2% de calcium). Du point de vue histologique, seul l'os cortical donnait des signes nets de résorption et d'activité ostéoclastique. Le nombre d'ostéoclastes dans l'os médullaire différait peu des valuers témoin pendant les périodes de déficience et de réplétion subséquente, sauf pour une augmentation significative au premier jour de déplétion. L'effect histologique le plus important dans l'os médullaire était une augmentation marquée en nombre d'ostéoblastes aux troisième, cinquième, et un peu moins au septième jours de déplétion. Le nombre d'ostéoblastes était en corrélation positive avec la teneur de l'os médullaire en ostéoide et négative avec son degré de calcification. L'activité de l'os médullaire en phosphatase alcaline augmentait avec la longueur de la déficience calcique. Un jour après le retour des pondeuses à une diète contenant 3,2% de calcium, la calcification de l'os médullaire avait augmenté de façon significative, le nombre d'ostéoblastes avait diminué au niveau ou au-dessous du niveau de contrôle et l'activité de la phosphatase alcaline avait baissé considérablement. L'importance de ces résultats est discutée par rapport au controle des populations des cellules dan l'os et au rôle de l'os médullaire.
    Abstract: Zusammenfassung Die Zahl der Knochenzellen und die Zusammensetzung des Femurs von Legehennen wurden während einer siebentägigen Calciumentzugsperiode (Calciumgehalt des Futters 0,13%) und einer siebentägigen Ersatzperiode (Calciumgehalt des Futters 3,2%) untersucht. Histologisch zeigte nur die Cortex eindeutige Knochenresorption und osteoklastische Aktivität. Abgesehen von einer signifikanten Zunahme am 1. Tag des Calciumentzuges, variierte die Zahl der Osteoklasten im Markknochen sowohl während der Entzugs- als auch während der nachfolgenden Ersatzperiode wenig. Die wichtigste histologische Änderung im Markknochen bestand in einer starken Zunahme in der Zahl der Osteoblasten am 3., 5. und etwas weniger am 7. Tag der Entzugsperiode. Die Zahl der Osteoblasten zeigte eine positive Korrelation mit dem Osteoidgehalt des Markknochens und eine negative mit dem Grade seiner Verkalkung. Die Aktivität der alkalischen Phosphatase im Markknochen war desto größer je länger den Hennen die calciumarme Ration verfüttert worden war. Die Wiederverabreichung der Ration, welche 3,2% Calcium enthielt, verursachte innerhalb eines Tages eine signifikante Zunahme in der Verkalkung des Markknochens, ein Absinken der Osteoblastzahl auf die Kontrollwerte oder unter sie und eine drastische Verringerung der alkalischen Phosphataseaktivität. Die Bedeutung dieser Ergebnisse in bezug auf die Kontrolle des Knochenzellenbestandes und auf die Funktion des Markknochens wird diskutiert.
    Notes: Abstract Bone cell activity and the composition of the femur of laying hens were studied during 7 days of calcium depletion on a 0.13% calcium diet and 7 days of calcium repletion on a 3.2% calcium diet. Histologically, only cortical bone showed clear signs of bone resorption and osteoclastic activity during the depletion period. The number of osteoclasts in medullary bone varied little from control values throughout both calcium depletion and repletion, except for a significant increase on the first day of depletion. The major histologicalchange in medullary bone was a marked increase in the number of osteoblasts on the third, fifth and, to a lesser extent, seventh, day of depletion. The number of osteoblasts in medullary bone was positively correlated with its osteoid content and negatively correlated with its degree of calcification. Alkaline phosphatase activity of medullary bone increased with the time the hens had been on the calcium-deficient diet. Returning the hens to the 3.2% calcium ration caused, within one day, a significant increase in medullary bone calcification, a decrease of osteoblast numbers to, or below, control levels, and a drastic reduction in alkaline phosphatase activity of medullary bone. The significance of these findings in relation to the control of bone cell populations and the functions of medullary bone is discussed.
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    Calcified tissue international 4 (1969), S. 101-112 
    ISSN: 1432-0827
    Keywords: Calcification ; Ligament ; Mollusc ; Aragonite
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Description / Table of Contents: Une étude de microscopie électronique est réalisée sur la formation et la structure du ligament interne deMytilus edulis etPinctada radiata. Cette partie du ligament est dérivée des cellules isthmiques qui sont de forme cylindrique irrégulière. Elles présentent un ergastoplasme bien développé et un appareil de Golgi, engagé dans l'élaboration de vésicules et granules qui s'incorporent au niveau de la conchioline. Les cristaux se forment au niveau du front de calcification, à la surface interne du ligament. Ils sont entourés par une enveloppe. Ils se présentent comme des monocristaux d'aragonite, allongés et en forme d'aiguilles, dispersés dans le ligament. Bien que les constituants de la carapace et du ligament soient identiques, il existe des différences concernant l'augmentation quantitative de conchioline et une diminution en nombre, forme diverse, groupement et croissance des cristaux. Ces différences sont probablement liées à la fonction spécialisée du ligament.
    Abstract: Zusammenfassung Die Bildung und Struktur des inneren Ligamentes vonMytilus edulis undPinctada radiata wurden am Elektronenmikroskop untersucht. Dieser Teil des Ligamentes stammt von den Isthmuszellen ab, deren Form unregelmäßig säulenartig ist. Sie zeigen ein vorspringendes, rauhes endoplasmatisches Reticulum und einen Golgiapparat, welche sich mit der Bildung von Bläschen und Granula befassen, die schließlich in einem integralen Teil des Conchiolins eingebaut werden. Die Kristalle entstehen an der Calcifikationsgrenze an der inneren Oberfläche des Ligamentes und sind in Hüllen eingeschlossen. Sie bestehen aus langen, nadelförmigen, einzelnen Aragonit-Kristallen, die über das ganze Ligament verteilt sind. Obschon die Bestandteile der Muschel und des Ligamentes gleichartig sind, unterscheiden sich die beiden durch eine erhöhte conchiolinmenge, wie auch durch eine Abnahme der Anzahl der Kristalle, welche verschieden in der Form, in der Anordnung und im Wachstum sind. Dies alles ist vermutlich auf die spezielle Funktion des Ligamentes zurückzuführen.
    Notes: Abstract An electron microscope study was made of the formation and structure of the inner ligament ofMytilus edulis andPinctada radiata. This part of the ligament is derived from the isthmus cells which are irregular columnar in shape. They exhibit a prominent rough endoplasmic reticulum and a Golgi apparatus, which are concerned with the elaboration of vesicles and granules eventually incorporated into an integral part of the conchiolin. The crystals arise at the calcification front at the inner surface of the ligament and are enclosed in envelopes. They consist of long, needle-shaped, single aragonite crystals widely dispersed in the ligament. Although the components of the shell and ligament are similar, differences between them consist of an increased amount of conchiolin, as well as a decrease in the amount, diversity of form, arrangement and growth of the crystals; all probably related to the specialized function of the ligament.
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    Calcified tissue international 4 (1969), S. 359-365 
    ISSN: 1432-0827
    Keywords: Metals ; Ions ; Buffers ; Calcification
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Description / Table of Contents: Résumé L'action de divers ions métalliques polyvalents sur les propriétés métastables d'un tampon calcifiable a été étudiée. A des concentrations de 1 μM ou moins, les ions Pb2+, F2+, Fe3+, Cr3+, Bi3+ et Al3+ déstabilisent le tampon. Il semble que les phosphates insolubles formés par ces ions déclanchent la précipitation de l'apatite. L'importance de ces résultats dans l'étiologie des calcifications pathologiques et la calciphylaxie est décrite.
    Abstract: Zusammenfassung Die Wirkung von verschiedenen polyvalenten Metallionen auf die Metastabilität eines Calcifikationspuffers wurde untersucht. Bei Konzentrationen von 1 μM oder weniger wird der Puffer durch Pb2+, Fe2+, Fe2+, Cr3+, Bi3+ und Al3+ entstabilisiert. Die Resultate lassen vermuten, daß unlösliche Phosphate, die mit diesen Ionen entstehen, eine Fällung von Apatit veranlassen. Die Bedeutung dieser Befunde bei pathologischen Verkalkungen und Calciphylaxis werden besprochen.
    Notes: Abstract The effect was studied of various polyvalent metal ions on the metastability of a calcification buffer. At concentration of 1 μM or less, Pb2+, Fe2+, Fe3+, Cr3+, Bi3+ and Al3+ ions were found to destabilize the buffer. The results suggest that insoluble phosphates formed by these ions initiate the precipitation of calcium apatite. The implications of these findings to pathological calcification and calciphylaxis are discussed.
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    Calcified tissue international 4 (1969), S. 39-47 
    ISSN: 1432-0827
    Keywords: Dehydroepiandrosterone ; Calcification ; Embryo ; Tissue Culture ; Bone
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Description / Table of Contents: Résumé Les modes d'utilisation de glucose, le contenu de calcium et d'hydroxyproline et la densité cellulaire du perioste de les os frontaux d'embryons de poulet de 12 et 13 jours de developpement, cultivés sur coagulum de plasma, se presentant différenment à chaque âge. Cultivés avec sulfate de déhydroèpiandrostérone en concentration 1 mM, les frontaux de 12 jours montrent un synthese augmentée du matrice osseuse, celle de 13 jours se calcifient à une vélocité significativement plus grande que celle des os contôles. Le degré de calcification au quatrième jour de culture measuré par la relation calcium/hydroxyproline, suit un fonction lineáire avec le logarithme des doses de sulfate de dehydroepiandrostérone employées (0.5, 1,0 et 2,0 mM). Les renseignements obtenus indiquent que les frontaux de 13 jours, cultivés “in vitro” constituent modeles experimentaux appropriés pour étudier l'effet des androgénes sur le tissue osseux.
    Abstract: Zusammenfassung Stirnbeine von Hühnerembryonen an ihrem 12. und 13. Entwicklungstag entnommen und in vitro kultiviert zeigen verschiedene Arten der Glucoseverwertung der Periostzellendichte, des Calcium- und Hydroxyprolingehaltes. Wird Dehydroepiandrosteronsulfat dem Medium in einer 1 mM-Konzentration zugegeben, so beteiligen sich die 12tägigen Stirnbeine vorwiegend an der Knochengewebesynthese, während die 13tägigen signifikant stärker verkalken als die Kontrollen. Gemessen an der Calcium/hydroxyprolin Ratio bildet die Verkalkung der 13tägigen Stirnbeine eine lineare Funktion mit den Logarithmen der verwendeten Dosen von Dehydroepiandrosteronsulfat (0,5, 1,0 und 2,0 mM). Das in vitro kultivierte 13tägige Stirnbein schein ein geeignetes Experimentiermodell zur Studie der Dehydroepiandrosteronsulfatwirkung auf das Knochengewebe zu sein, weil es das grundlegende Phänomen (erhöhte Verkalkung) wiedergibt, welches man auch bei mit Androgenen behandelten Menschen und Tieren beobachtet.
    Notes: Abstract Chick embryo frontal bones at 12 and 13 days of development cultivatedin vitro exhibit different patterns of glucose utilization, periosteal cellular density and calcium and hydroxyproline content. When dehydroepiandrosterone sulfate is added to the medium at a concentration 1 mM, 12-day frontals engage primarily in osteoid tissue synthesis while 13-day frontals calcify at a significantly greater rate than controls. Measured with the ratio calcium/hydroxyproline, the calcification of 13-day frontals follows a linear function with the logarithm of the doses of dehydroepiandrosterone sulfate employed (0.5, 1.0 and 2.0 mM). The 13-day frontal bone cultivatedin vitro seems to be an adequate experimental model for the study of the effects of dehydroepiandrosterone sulfate on bone tissue because it reproduces the basic phenomenon (increased calcification) observed in man and animals treated with androgens.
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    Calcified tissue international 56 (1995), S. 140-144 
    ISSN: 1432-0827
    Keywords: Bone sialoprotein ; Collagen ; Hole zone ; Calcification
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Abstract Bone sialoprotein (BSP) has an affinity to collagen fibrils [25]. A role of carbohydrate chains in the affinity was examined by removing sialic acids of BSP. Neuraminidase treatment of the BSP increased the binding to collagen. Binding sites of BSP on collagen were examined by biochemical and electron-microscopic methods. Purified bovine BSP was labeled with biotin. Collagen α chains or CNBr peptides were separated by electrophoresis and transfered to nitrocellulose membranes. The membranes were incubated with the biotin-labeled BSP, and the bound BSP was visualized with avidin conjugated with alkaline phosphatase. The labeled BSP was preferentially bound to the α 2 chain, and peptides derived from α 2 chain. In another experiment, the labeled BSP was incubated with reconstituted native collagen fibrils. The mixture was put on a copper grid, reacted with avidin conjugated with gold particles, and observed with an electron microscope. The gold particles were seen mainly within hole zones of the fibrils. BSP bound to the α 2 chain within the hole zones may regulate the onset of calcification at hole zones and the cell binding to collagen fibrils.
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    Calcified tissue international 2 (1968), S. 1-19 
    ISSN: 1432-0827
    Keywords: Collagen ; Hydroxyapatite ; Keratin ; Enamel ; Calcification
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    Calcified tissue international 2 (1968), S. 60-66 
    ISSN: 1432-0827
    Keywords: Fluorides ; Topical/Pharmacodynamics ; Penicillin/Pharmacodynamics ; Calcification ; Physiologic/Drug Effects ; Rats
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Description / Table of Contents: Résumé L'objet de ce travail était de comparer le phénomène de la maturation postéruptive dans les molaires des rats ordinaires et sans germes à qui on a donné à manger un régime «non-cariogène». On a étudié les effets de l'application topique du fluorure et de la nourriture de la penicilline sur la maturation. Les molaires des rats ordinaires (nourris d'un régime «chow» — aliment mixte pour les animaux préparé d'habitude sous la forme d'une farine ou en boulettes) traités topiquement avec une solution à 1% de NaF et les molaires des rats ordinaires nourris d'un régime «chow» complété avec la penicilline à 1% ont montré un degré de maturation significativement plus grand que les molaires des rats de la même portée nourris de «chow» et traités avec de l'eau. De l'autre côté, les molaires des rats sans germes traités topiquement avec une solution à 1% de NaF n'ont montré aucune différence significative dans le degré de maturation des molaires de rats de contrôle semblables traités topiqument avec l'eau. Ces résultats sont en accord avec l'hypothèse que dans un milieu normal le procédé de minéralisation (maturation) est opposé par un procédé de déminéralisation. Le procédé de déminéralisation est un résultat de la production d'acide par des bactéries qui métabolisent les aliments encastrés dans les «sulci» des molaires. On propose que dans les animaux ordinaires le fluorure et la penicilline peuvent influencer la maturation en empêchant le procédé de déminéralisation. Dans les animaux sans germes le procédé de déminéralisation est absent parce que la microflore orale est absente.
    Abstract: Zusammenfassung Der Zweck dieser Arbeit war ein Vergleich des nach dem Durchbruch auftretenden Reifungsphänomens der Backenzähne von gewöhnlich und von keimfrei gehaltenen Ratten, die mit einer nicht-cariogenen Diät ernährt wurden. Es wurden die Auswirkungen von topisch angewendetem Fluorid, verbunden mit Penicillin-Fütterung auf die Reifung untersucht. Die Backenzähne der gewöhnlich gehaltenen Ratten (mit “Chow”-Diät ernährt), die mit einer 1%igen Na-Fluoridlösung topisch behandelt wurden, und solchen deren “Chow”-Diät zu 1% mit Penicillin versetzt wurde, zeigten einen erheblich größeren Reifungsgrad als die Backenzähne von Tieren des gleichen Wurfes, die nur mit der “Chow”-Diät und Wasser ernährt wurden. Diese Resultate stimmen mit der Hypothese überein, daß in einer normalen Umgebung dem Mineralisationsprozeß (Reifung) ein Demineralisationsprozeß entgegenwirkt. Der Demineralisationsprozeß ist durch eine Säureproduktion von Bakterien bedingt, welche die in die Zahnfurchen eingepreßten Nahrungsbestandteile metabolisieren. Es wird die Annahme vorgeschlagen, daß Fluoride und Penicillin bei den gewöhnlich gehaltenen Tieren die Reifung durch eine Inhibition des Demineralisationsprozesses beeinflussen. Bei keimfrei gehaltenen Tieren findet dagegen kein Demineralisationsprozeß statt, da die orale Mikroflora fehlt.
    Notes: Abstract The purpose of this work was to compare the phenomenon of post-eruptive maturation in molars of conventional and germfree rats fed non-cariogenic diets. The effects of topical application of fluoride and feeding penicillin on maturation were studied. The molars of conventional rats (fed a chow diet) treated topically with a 1% NaF solution and the molars of conventional rats fed a chow diet supplemented with 1% penicillin showed a significantly greater degree of maturation than did the molars of littermate rats fed chow and treated with water. On the other hand, the molars of germfree rats treated topically with a 1% NaF solution showed no significant difference in degree of maturation from the molars of similar control rats topically treated with water. These data are consistent with an hypothesis that in a normal environment the mineralization (maturation) process is opposed by a demineralization process. The demineralization process is a result of production of acid by bacteria metabolizing the diet impacted in the sulci of molars. It is proposed that in conventional animals fluoride and penicillin may influence maturation by inhibiting the demineralization process. In the germfree animals the demineralization process is absent because the oral microflora is absent.
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    Calcified tissue international 2 (1968), S. 361-369 
    ISSN: 1432-0827
    Keywords: Calcification ; Hydroxyapatite ; Keratin ; Hair ; Electron diffraction
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Description / Table of Contents: Résumé Certaines régions du cortex des fibres de kératine contiennent une proportion relativement élevée de matériel non kératinisé. L'orientation microfibrillaire dans ces régions est biaxiale et on y trouve, en outre, des zones de matériel amorphe. Les sels calciques, et en particulier l'hydroxyleapatite, sont étudiés par diffraction électronique qui permet de les localiser et de les identifier. En outre, cette technique permet de déterminer la fréquence de cellules nonkératinisées dans la partie interne du cortex et de les comparer avec les propriétés histochimiques de cette région. Une comparison est effectuée entre la calcification de la kératine et celle intéressant le collagène et l'élastine.
    Abstract: Zusammenfassung Es wird gezeigt, daß Bereiche im Cortex von gewissen Keratinfasern einen relativ hohen Anteil an nichtkeratinösem Material enthalten. Ferner konnte nachgewiesen werden, daß die Orientierung der Mikrofibrillen in diesen Bereichen biaxialer Art ist, und daß Bezirke von amorphem Material vorhanden sind. Die Calciumsalze und insbesondere das Hydroxyapatit konnten mit Hilfe der Elektronendiffraktion lokalisiert und identifiziert werden. Diese Methode hat sich auch als wertvoll erwiesen, um die Wechselbeziehung zwischen dem Vorkommen von einigen nichtkeratinisierten Zellen im Cortexinnern und den histochemischen Eigenschaften dieser Regionen zu zeigen. Ein Vergleich wird gemacht zwischen der Umgebung der Verkalkungsstellen im Keratin mit derjenigen im Kollagen und im Elastin.
    Notes: Abstract Regions in the cortex of some keratin fibres are shown to contain a relatively high proportion of non-keratinous material. The microfibrillar orientation in these regions is shown to be biaxial in nature and, in addition, areas of amorphous material are reported. Calcium salts, in particular hydroxyapatite, have been located and identified using electron diffraction, which has also proved valuable in correlating the incidence of some non-keratinised cells in the inner part of the cortex with the histochemical properties of this region. A comparison is made between the environment of the sites of calcification in keratin with those in collagen and elastin.
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    Calcified tissue international 2 (1968), S. 214-228 
    ISSN: 1432-0827
    Keywords: Calcinosis ; Calcification ; Cartilage ; Collagen ; Mineral metabolism
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Description / Table of Contents: Résumé Les facteurs, influençant la vitesse et l'intensité du phénomène d'association des ions calcium et phosphates avec des fibres contenant du collagène, et préparés à partir du tendon de boeuf par deux méthodes d'extraction différentes, ont été étudiés. Les fibres, obtenues par ces deux méthodes, nécessitent spécifiquement du phosphate pour absorber du calcium et vice versa. L'absorption ionique des deux préparations est inhibée par du Mg++, du pyrophosphate et un peptide acidique, isolé du sérum humain. Alors que les fibres contenant du collagène, préparées selon les deux méthodes, présentent une absorption ionique à des vitesses sensiblement identiques, seule une des méthodes donne une matrice réagissant positivement à la technique de coloration au nitrate d'argent de von Kossa. Etant donné que les deux critères de calcification sont intéressés de façon identique par des conditions de réaction et par des inhibiteurs, il apparait que les deux facteurs sont des manifestations de différents stades de calcification et que des études d'absorption ionique fournissent une base quantitative d'appréciation de la calcification, pouvant être d'importance pour l'étude du mécanisme et de contrôle de la minéralisation tissulaire.
    Abstract: Zusammenfassung Überprüft wurden die Faktoren, welche Geschwindigkeit und Ausmaß der Erscheinung beeinflussen, wobei Calcium- und Phosphationen sich mit den kollagenhaltigen, durch zwei verschiedene Extraktionsmethoden aus Rindersehnen gewonnenen Fasern eng zusammenbinden. Die mit beiden Methoden zubereiteten Fasern benötigen spezifisch Phosphat für die Calciumaufnahme und Calcium für die Phosphataufnahme. Die Ionenaufnahme beider Arten wird durch Mg++, Pyrophosphat und saure, aus dem menschlichen Serum isolierte Peptide gehemmt. Während die nach beiden Methoden präparierten kollagenhaltigen Fasern eine Ionenaufnahme von beinahe gleicher Geschwindigkeit verursachen, ergibt nur eine dieser Methoden eine Matrix, die mit der Silbernitratfärbung nach vonKossa positiv reagiert. Da beide Calcifikationskriterien gleicherweise durch Reaktionsbedingungen und Inhibitoren beeinflußt werden, wird daraus geschlossen, daß beide Erscheinungen verschiedener Stadien des Gesamtcalcifikationsprozesses sind. Untersuchungen über die Ionenaufnahme ergeben eine quantitative Angabe der Verkalkung, welche für die Erforschung des Mechanismus und der Kontrolle der Mineralisation der Gewebe wichtig sein könnte.
    Notes: Abstract Factors that influence the rate and extent of the phenomenon in which calcium and phosphate ions become firmly associated with collagen-containing fibers prepared from beef tendon by two different extraction methods have been investigated. The fibers produced by both methods specifically require phosphate for calcium uptake and calcium is required for phosphate uptake. Ion uptake by both types is inhibited by Mg++, pyrophosphate, and an acidic peptide isolated from human serum. Whereas the collagen-containing fibers prepared by both methods induce ion uptake at nearly identical rates, only one of the methods produced a matrix that gives a positive response to the silver nitrate staining technique of von Kossa. Since both criteria of calcification are similarly influenced by reaction conditions and inhibitors, it is concluded that both are manifestations of different stages of the overall calcification process and that studies of ion uptake provide a quantitative assessment of calcification which could be of importance for investigating the mechanism and control of tissue mineralization.
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  • 64
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    Calcified tissue international 56 (1995), S. 403-407 
    ISSN: 1432-0827
    Keywords: Bone sialoprotein ; Fibronectin ; Type I colfagen ; MC3T3-E1 cells ; Calcification
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Abstract Bone sialoprotein (BSP) containing an Arg-Gly-Asp cell-binding sequence was purified from bovine bone 4 M guanidine-HCl extract after HCl demineralization by a series of chromatographic procedures. When this protein was coated on culture dishes in the presence of type I collagen, it increased both DNA content and alkaline phosphatase (ALP) activity in osteoblast-like MC3T3-E1 cells, and stimulated calcification in the cells, whereas fibronectin, another cell-binding protein, showed a marked increase in the DNA content but had little effect on the ALP activity. These findings suggest that BSP is mitogenic for preosteoblasts and differentiating the cells into osteoblasts, thereby stimulating bone calcification
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  • 65
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    Archives of microbiology 163 (1995), S. 352-356 
    ISSN: 1432-072X
    Keywords: Key wordsThiobacillus ferrooxidans ; Sulfide ; oxidation ; Sulfur colloids ; Bioleaching
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Thiobacillus ferrooxidans was cultivated on 100-nm-thick synthetic pyrite (FeS2) films. The steps of biooxidation were studied with high-resolution transmission electron microscopy. The crystallized sulfide was transformed into colloidal sulfur (4–70 nm, depending on the age of the cell and the degree of substrate oxidation; 70 nm initially and 4 nm after oxidation of the pyrite substrate), which was taken up and distributed over an organic capsule around the bacteria. This colloidal sulfur acted as intermediate energy storage and was transferred by contact to daughter cells not directly attached to the sulfide substrate.
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  • 66
    ISSN: 1432-072X
    Keywords: Key words Fumarase ; Syntrophy ; Propionate ; oxidation ; Fumarate fermentation ; Anaerobic oxidation ; Iron-sulfur cluster
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Fumarase from the syntrophic propionate-oxidizing bacterium strain MPOB was purified 130-fold under anoxic conditions. The native enzyme had an apparent molecular mass of 114 kDa and was composed of two subunits of 60 kDa. The enzyme exhibited maximum activity at pH 8.5 and approximately 54° C. The K m values for fumarate and l-malate were 0.25 mM and 2.38 mM, respectively. Fumarase was inactivated by oxygen, but the activity could be restored by addition of Fe2+ and β-mercaptoethanol under anoxic conditions. EPR spectroscopy of the purified enzyme revealed the presence of a [3Fe-4S] cluster. Under reducing conditions, only a trace amount of a [4Fe-4S] cluster was detected. Addition of fumarate resulted in a significant increase of this [4Fe-4S] signal. The N-terminal amino acid sequence showed similarity to the sequences of fumarase A and B of Escherichia coli (56%) and fumarase A of Salmonella typhimurium (63%).
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  • 67
    ISSN: 1432-072X
    Keywords: Key words Heterologous expression ; Methane ; oxidation ; Methane monooxygenase ; Methanotroph ; Regulation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The methanotrophs Methylococcus capsulatus (Bath) and Methylosinus trichosporium OB3b contain particulate methane monooxygenase (pMMO) and soluble methane monooxygenase (sMMO) genes. Other methanotrophs such as Methylomicrobium album BG8 and Methylocystis parvus OBBP contain only pMMO genes. Although molecular genetic techniques are poorly developed in methanotrophs, sMMO genes were expressed in methanotrophs normally containing only pMMO genes. This was achieved by conjugation using broad-host-range plasmids containing the native promoter and sMMO genes from Mc. capsulatus (Bath) and Ms. trichosporium OB3b. sMMO genes derived from Ms. trichosporium OB3b were expressed in an active form in Mcy. parvus OBBP and in Mm. album BG8. Therefore, all of the genes required for active sMMO synthesis were contained on the broad-host-range plasmids and were expressed in the heterologous hosts. Constitutive synthesis of pMMO was observed in Mm. album BG8 when grown at high and low copper-to-biomass ratios, while transcription of the recombinant sMMO genes was only observed under growth conditions of low copper-to-biomass ratios. Therefore, the regulatory protein(s) for sMMO synthesis was also present on the plasmid used, or the heterologous host contained a regulatory system for sMMO. Expression of sMMO genes in methanotrophs containing only pMMO will assist further investigations on the expression and regulation of MMO genes in methanotrophs.
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  • 68
    ISSN: 1432-072X
    Keywords: Key wordsNitrospira moscoviensis ; Non-marine ; bacteria ; Obligate chemolithoautotroph ; Nitrite ; oxidation ; Nitrate reduction ; 16S rRNA gene sequences
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract A gram-negative, non-motile, non-marine, nitrite-oxidizing bacterium was isolated from an enrichment culture initiated with a sample from a partially corroded area of an iron pipe of a heating system in Moscow, Russia. The cells were 0.9–2.2 μm × 0.2–0.4 μm in size. They were helical- to vibroid-shaped and often formed spirals with up to three turns 0.8–1.0 μm in width. The organism possessed an enlarged periplasmic space and lacked intracytoplasmic membranes and carboxysomes. The cells tended to excrete extracellular polymers, forming aggregates. The bacterium grew optimally at 39°C and pH 7.6– 8.0 in a mineral medium with nitrite as sole energy source and carbon dioxide as sole carbon source. The optimal nitrite concentration was 0.35 mM. Nitrite was oxidized to nitrate stoichiometrically. The doubling time was 12 h in a mineral medium with 7.5 mM nitrite. The cell yield was low; only 0.9 mg protein/l was formed during oxidation of 7.5 mM nitrite. Under anoxic conditions, hydrogen was used as electron donor with nitrate as electron acceptor. Organic matter (yeast extract, meat extract, peptone) supported neither mixotrophic nor heterotrophic growth. At concentrations as low as 0.75 g organic matter/l or higher, growth of nitrite-oxidizing cells was inhibited. The cells contained cytochromes of the b- and c-type. The G+C content of DNA was 56.9 ± 0.4 mol%. The chemolithoautotrophic nitrite-oxidizer differed from the terrestrial members of the genus Nitrobacter with regard to morphology and substrate range and equaled Nitrospira marina in both characteristics. The isolated bacterium is designated as a new species of the genus Nitrospira. Comparative analysis of 16S rRNA gene sequences revealed a moderate phylogenetic relationship to Nitrospira marina, leptospirilla, Thermodesulfovibrio yellowstonii, "Magnetobacterium bavaricum," and the isolate OPI-2. Initial evidence is given that these organisms represent a new phylum of the domain bacteria.
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    Archives of microbiology 167 (1997), S. 106-111 
    ISSN: 1432-072X
    Keywords: Key wordsNitrosomonas ; Anaerobic ammonia ; oxidation ; Anaerobic cell growth ; Nitrogen dioxide ; Nitric oxide ; Nitrous oxide ; Dinitrogen
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Nitrosomonas eutropha, an obligately lithoautotrophic bacterium, was able to nitrify and denitrify simultaneously under anoxic conditions when gaseous nitrogen dioxide (NO2) was supplemented to the atmosphere. In the presence of gaseous NO2, ammonia was oxidized, nitrite and nitric oxide (NO) were formed, and hydroxylamine occurred as an intermediate. Between 40 and 60% of the produced nitrite was denitrified to dinitrogen (N2). Nitrous oxide (N2O) was shown to be an intermediate of denitrification. Under an N2 atmosphere supplemented with 25 ppm NO2 and 300 ppm CO2, the amount of cell protein increased by 0.87 mg protein per mmol ammonia oxidized, and the cell number of N. eutropha increased by 5.8 × 109 cells per mmol ammonia oxidized. In addition, the ATP and NADH content increased by 4.3 μmol ATP (g protein)–1 and 6.3 μmol NADH (g protein)–1 and was about the same in both anaerobically and aerobically grown cells. Without NO2, the ATP content decreased by 0.7 μmol (g protein)–1, and the NADH content decreased by 1.2 μmol (g protein)–1. NO was shown to inhibit anaerobic ammonia oxidation.
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  • 70
    ISSN: 1432-072X
    Keywords: Key words Syntrophy ; Fumarate reduction ; Propionate ; oxidation ; Anaerobic growth ; Electron transport chain
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The growth of the syntrophic propionate-oxidizing bacterium strain MPOB in pure culture by fumarate disproportionation into carbon dioxide and succinate and by fumarate reduction with propionate, formate or hydrogen as electron donor was studied. The highest growth yield, 12.2 g dry cells/mol fumarate, was observed for growth by fumarate disproportionation. In the presence of hydrogen, formate or propionate, the growth yield was more than twice as low: 4.8, 4.6, and 5.2 g dry cells/mol fumarate, respectively. The location of enzymes that are involved in the electron transport chain during fumarate reduction in strain MPOB was analyzed. Fumarate reductase, succinate dehydrogenase, and ATPase were membrane-bound, while formate dehydrogenase and hydrogenase were loosely attached to the periplasmic side of the membrane. The cells contained cytochrome c, cytochrome b, menaquinone-6 and menaquinone-7 as possible electron carriers. Fumarate reduction with hydrogen in membranes of strain MPOB was inhibited by 2-(heptyl)-4-hydroxyquinoline-N-oxide (HOQNO). This inhibition, together with the activity of fumarate reductase with reduced 2,3-dimethyl-1,4-naphtoquinone (DMNH2) and the observation that cytochrome b of strain MPOB was oxidized by fumarate, suggested that menequinone and cytochrome b are involved in the electron transport during fumarate reduction in strain MPOB. The growth yields of fumarate reduction with hydrogen or formate as electron donor were similar to the growth yield of Wolinella succinogenes. Therefore, it can be assumed that strain MPOB gains the same amount of ATP from fumarate reduction as W. succinogenes, i.e. 0.7 mol ATP/mol fumarate. This value supports the hypothesis that syntrophic propionate-oxidizing bacteria have to invest two-thirds of an ATP via reversed electron transport in the succinate oxidation step during the oxidation of propionate. The same electron transport chain that is involved in fumarate reduction may operate in the reversed direction to drive the energetically unfavourable oxidation of succinate during syntrophic propionate oxidation since (1) cytochrome b was reduced by succinate and (2) succinate oxidation was similarly inhibited by HOQNO as fumarate reduction.
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  • 71
    ISSN: 1432-072X
    Keywords: Key wordsParacoccus denitrificans ; Sulfide ; oxidation ; Sulfide-quinone reductase ; Cytochrome ; bc complex ; Flavocytochrome c
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Reduction of exogenous ubiquinone and of cytochromes by sulfide in membranes of the chemotrophic bacterium Paracoccus denitrificans GB17 was studied. For sulfide-ubiquinone reductase activity, K m values of 26 ± 4 and 3.1 ± 0.6 μM were determined from titrations with sulfide and decyl-ubiquinone, respectively. A maximal rate of up to 0.3 μmol decyl-ubiquinone reduced (mg protein)–1 min–1 was estimated. The reaction was sensitive to quinone-analogous inhibitors, but insensitive to cyanide. Reduction of cytochromes by sulfide was monitored with an LED-array spectrophotometer. Under oxic conditions, reduction rates and extents of reduction were lower than those under anoxic conditions. Reoxidation of cytochromes was oxygen-dependent and cyanide-sensitive. The multiphasic behavior of transient reduction of cytochrome b with limiting amounts of sulfide reflects that sulfide, in addition to acting as an electron donor, is a slowly binding inhibitor of cytochrome c oxidase. The initial peak of cytochrome b reduction is dependent on electron flow to an oxidant, either oxygen or ferricyanide, and is stimulated by antimycin A. This oxidant-induced reduction of cytochrome b suggests that electron transport from sulfide in P. denitrificans GB17 employs the cytochrome bc 1 complex via the quinone pool.
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    Journal of thermal analysis and calorimetry 49 (1997), S. 745-753 
    ISSN: 1572-8943
    Keywords: DSC ; kerogen ; oxidation ; pyrolysis ; type determination
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The rate of pyrolysis and oxidation of 8 different samples of oil shale kerogen concentrate (KC) were investigated using DSC analysis. Recently performed thermogravimetric studies (TG and DTG) with the same samples of KC indicated that the activation energy of the pyrolysis of specific KCs increases with increasing paraffinic structure in the KC. An opposite effect, i.e. a decrease of the activation energy with an increase of paraffinic structure was determined in the case of KC oxidation. In this study, using the standard ASTM E-698 method based on the determined temperature at which the maximum heat effect could be observed (exo in the case of oxidation and endo in the case of pyrolysis), an activation energy for the pyrolysis, as well as for the oxidation process was determined and also successfully correlated with the content of paraffinic structure of KC. Thus, the higher content of paraffinic structure in KCs indicates that higher values of the activation energy could be determined either in the case of pyrolysis or oxidation followed by DSC analysis.
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    Journal of thermal analysis and calorimetry 49 (1997), S. 1017-1023 
    ISSN: 1572-8943
    Keywords: degradation ; microcalorimetry ; moisture ; oxidation ; permeability
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The use of isothermal microcalorimetry (MC) as a sensitive monitor for slow reactions is demonstrated in a number of examples. In Example 1 the spontaneous decomposition of a nitrate ester propellant is studied and the absolute degradation rate estimated. Example 2 illustrates how MC can be used for comparing the rate of oxidative ageing at different O2 concentrations. Synergetic effects between oxygen and moisture in accelerated ageing of nitrile rubber are evaluated from a so-called 4-point test in Example 3. The last example shows a simple MC technique for rapid determination of moisture permeability through a polymeric sealant.
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    Journal of thermal analysis and calorimetry 48 (1997), S. 657-664 
    ISSN: 1572-8943
    Keywords: nickel powders ; oxidation ; thermal analysis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Monodispersed fine metal nickel powders of uniform shape and high purity are increasingly required for specific uses in many technological areas, especially in the preparation of electronic materials such as the manufacture of conductive inks and pastes and the formation of catalysts. Metallic nickel powders were prepared in ethylene glycol by the reduction of a nickel solution. Hydrazine was used as a reducing agent. Metal powders were characterized by chemical analysis, scanning electron microscopy (SEM), thermogravimetry (TG), derivative thermogravimetry (DTG) and differential scanning calorimetry (DSC). Particle size distributions were determined using laser light scattering. The reactivity and purity of these fine nickel powders were tested by repeated oxidation and reduction of nickel powders in oxidative and reductive atmospheres.
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    Journal of thermal analysis and calorimetry 49 (1997), S. 1501-1507 
    ISSN: 1572-8943
    Keywords: calcium sulphide ; gypsum ; oxidation ; phosphogypsum ; reduction ; stability ; thermogravimetry
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Using a heating rate of 2°C min−1, CaS reacts with oxygen in air from 700°C to form CaSO4, with a complete conversion at 1100°C. Synthesis of CaS from the reaction between CaSO4 containing compounds and carbon compounds in air would not be possible, as the carbon reacts from 600°C with oxygen in the air to give CO2. Heating stoichiometric amounts of carbon and pure CaSO4, synthetic gypsum or phosphogypsum in a nitrogen atmosphere, results in the formation of CaS from 850°C. Using a heating rate of 10°C min−1, the formation of CaS is completed at 1080°C. Addition of 5% Fe2O3 as a catalyst lowers the starting temperature of the reaction to 750°C. Activation energy values at different fraction reaction values (α) differ between 340 and 400 kJ mol−1. The relationship between the activation energy values and conversion (α) indicates that the reaction proceeds via multiple steps.
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    Journal of thermal analysis and calorimetry 54 (1998), S. 25-34 
    ISSN: 1572-8943
    Keywords: activation energy ; kinetic equation ; oxidation ; vanadium oxides ; Zhuravlev equation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract It has been found that the modified Zhuravlev equation, [(1−α)−1/3−1]2=ktn, which describes the kinetics of oxidation of V2O4 and V6O13 in the temperature range 820–900 K and in the oxygen pressure range 1.0–20 kPa, can be derived via the assumption that the changes in the observed activation energy result from the changing contributions of the two diffusion processes controlling the reaction rate. The values of the observed activation energy are in the range 160–175 kJ mol−1 for V2O4 and 188–201 kJ mol−1 for V6O13 in the scope of the experimental oxygen pressures and temperatures and conversion degrees of 0.1–0.9.
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    Journal of thermal analysis and calorimetry 49 (1997), S. 1161-1170 
    ISSN: 1572-8943
    Keywords: basicity ; dinitramides ; kinetics ; oxidation ; tanδ ; transition temperatures
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The dinitramide salts of ammonia (ADN), hexamethylenetetramine (HDN), potassium (KDN), and sodium (NaDN) showed a linear relationship between the DSC rate of decomposition at the peak maximum and the DEA tanδ value at the low temperature transition peak. As the cation basicity increased in the series ADN〈HDN〈KDN〈NaDN, there was an increase in the low temperature transition peak, the energy barrier for relaxation, and the decomposition peak temperature, and a decrease in the tanδ value at the low temperature transition peak, specific heat capacity, and the rate and enthalpy of decomposition. The more basic salts were more thermally stable (i.e., higher decomposition temperature) and less energetic (i.e., lower enthalpy of decomposition). The more internal free volume (disorder) present in these salts, the higher the rates of relaxation and decomposition. Five aluminum powders of different surface areas were analyzed by DSC in platinum sample pans, and it was found that the enthalpy and rate of oxidation increased as the particle size of Al decreased while the enthalpy of the Al melt decreased. TG showed a two-step weight gain in the oxidation of Al with plateaus in the 650 and 1130°C regions and the percent weight gain increased as the particle size of Al decreased. Variable DSC and TG heating rate studies showed that the activation energies for the first step in the oxidation process increased as the particle size of Al increased.
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    Journal of thermal analysis and calorimetry 54 (1998), S. 211-217 
    ISSN: 1572-8943
    Keywords: DSC ; fatty acids esters ; kinetics ; oxidation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Oxidation of saturated fatty acids ethyl esters: laurate, myristate, palmitate and stearate was investigated by means of DSC techniques under isothermal and non-isothermal conditions. The activation energies of isothermal oxidation were similar to each other (112–123 kJ mol−1) and no influence of carbon length on the rate of oxidative decomposition was observed. Results obtained from non-isothermal experiments were similar only for the first stage of oxidation.
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    Journal of thermal analysis and calorimetry 57 (1999), S. 875-881 
    ISSN: 1572-8943
    Keywords: charge transfer ; Kelvin probe ; oxidation ; work function ; zirconia
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The extent of the surface charge, that develops during oxidation of zirconia, is determined using work function measurements for both bulk specimen and thin films. The bulk specimen of yttria-doped zirconia (10 mol%) exhibits maxima of the surface electrical effect at 373 and 973 K (130 and 280 mV, respectively) that can be considered in terms of oxygen chemisorption and oxygen non-stoichiometry. Thin film of undoped zirconia exhibits a maximum at 473 K (260 eV). Addition of yttria (10 mol%) to the thin film results in a substantial reduction of the maximum, to about 140 eV, that is shifted up to 600 K.
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    Journal of thermal analysis and calorimetry 46 (1996), S. 1657-1669 
    ISSN: 1572-8943
    Keywords: activation energy ; combustion ; differential scanning calorimetry ; kinetics ; lignite ; oxidation ; thermogravimetric analysis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Thermal analysis increasingly being used to obtain kinetic data relating to sample decomposition. This work involves a comparative study of several methods used to analyse DSC and TG/DTG data obtained on the oxidation of Beypazari lignite. A general computer program was developed and the methods are compared with regard to their accuracy and the ease of interpretation of the kinetics of thermal decomposition. For this study, the ratio method was regarded as the preferred method, because it permits the estimation of reaction order, activation energy and Arrhenius constant simultaneously from a single experiment.
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    Journal of thermal analysis and calorimetry 52 (1998), S. 327-340 
    ISSN: 1572-8943
    Keywords: aging ; DTA-TG ; oxidation ; polypropylene
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Several samples of polypropylene were studied by thermal analysis. The photo-oxidation and the aging of polypropylene films showed a mass loss more than 7% in heating from 20 to 220°C (5°C min-1), cooling to 20°C and reheating to 220°C. The authors observed also a decrease of the melting and crystallization temperatures. The non aged samples or these ones with preservatives are thermo-oxidised and presented an exothermic peak at about 200°C in DTA heating. The DTA-TG simultaneous apparatus is very useful in the study of polypropylene oxidation by making comparative trials according to a well definite procedure.
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    Journal of thermal analysis and calorimetry 53 (1998), S. 263-267 
    ISSN: 1572-8943
    Keywords: kinetics ; molybdenum sulphide ; oxidation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract This paper reports on the results attained in the determination of the mechanism of oxidation of molybdenum sulphide under non-isothermal conditions in an air atmosphere. The mechanism of the process was determined by simultaneous DTA-TG-DTG, and the kinetic parameters of the reactions involved were obtained according to the methods of Kissinger and Ozawa.
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  • 83
    ISSN: 1572-8943
    Keywords: DSC ; infrared spectrometry ; oxidation ; polyethylenes ; thermal analysis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The oxidation of pure and recycled polyethylene samples was studied by thermal analysis (DTA-TG-DSC): presence of two exothermic peaks and mass loss. The thermo-oxidation products, containing C-O and C=O links, were identified by IR spectrometry and GC-MS spectrometry. The oxidation is easier from low to high density polyethylene.
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    Journal of thermal analysis and calorimetry 57 (1999), S. 473-486 
    ISSN: 1572-8943
    Keywords: cumene ; oxidation ; polymerization ; quinone-amine inhibitors ; solution microcalorimetry ; styrene
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The application of solution microcalorimetry was demonstrated on two model examples – inhibited oxidation of cumene and radical polymerization of styrene. From the experimental dependences of the rate of heat release on time, the rate constants k 7 of the interaction of an inhibitor with radicals of substrate (RO 2 . or R.) in oxidation or in polymerization were determined for the set of inhibitors of N-aryl N-(2-quinone) amine series. It was shown that these compounds are weak inhibitors of oxidation of cumene and rather efficient inhibitor of polymerization of styrene.
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  • 85
    ISSN: 1572-8986
    Keywords: RF SiCl4 discharge ; mass spectrometry ; kinetics ; decomposition ; oxidation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Technology
    Notes: Abstract Time-resolved mass spectrometry was used for analysis of the plasma reactions in radio frequency (RF) SiCl 4 and SiCl 4 −O 2 discharges as functions of starting partial pressure and electrical power. Molecular concentrations of the reactants and products from SiCl 4 alone and with O 2 were obtained from the mass spectra and used for plotting the kinetic curves. The SiCl 4 and O 2 consumption rates were calculated from the kinetic curves and compared with results of theoretical simulation of the reaction. Direct electron impact decomposition was found to be the main pathway for pure SiCl 4 conversion. On the contrary, the consumption of SiCl 4 in the SiCl 4 +O 2 mixtures was largely chemical. The experimental macrokinetics are in agreement with a model in which oxidation is caused by the atomic oxygen.
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    Plasma chemistry and plasma processing 19 (1999), S. 131-151 
    ISSN: 1572-8986
    Keywords: Styrene ; oxidation ; silent discharge ; plasma ; dielectric barrier
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Technology
    Notes: Abstract A silent discharge plasma reactor has been developed to study the oxidation of styrene vapor in argon/oxygen mixtures. A number of analytical techniques were employed to determine the destruction efficiency and to characterize the intermediate products. The destruction efficiency was measured as a function of initial styrene concentration, temperature, and energy density of the plasma. The formation of solid products was observed in most experiments. At low temperature (100°C), the solid deposit was polymeric in nature, while at high temperature (300°C) the solid appeared to be amorphous carbon. A combination of high temperature and high energy density resulted in high destruction efficiency and minimal production of solid films. The destruction efficiency vs. energy density is shown to be more complex than a simple model predicting exponential behavior. Several reasons for the discrepancy are suggested. The “e-folding” energy density for the destruction of styrene is compared to literature values for other organic compounds, measured using similar types of plasma reactors.
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  • 87
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    Plasma chemistry and plasma processing 19 (1999), S. 383-394 
    ISSN: 1572-8986
    Keywords: Nonthermal plasma ; benzene ; Al2O3 ; BaTiO3 ; oxidation ; absorption ; atmospheric pressure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Technology
    Notes: Abstract The combination of plasma discharge and adsorption was examined for oxidation of dilute benzene in air in a plasma reactor packed with a mixture of BaTiO 3 pellets and porous Al 2 O 3 pellets (i.e., an alumina hybrid reactor). The oxidative decomposition of benzene was enhanced by the benzene concentrating on the Al 2 O 3 pellets. Furthermore, there was a higher selectivity to CO 2 in the products from the hybrid than from a plasma reactor packed with BaTiO 3 pellets alone. The presence of the Al 2 O 3 pellets suppressed the formation of N 2 O.
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  • 88
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    Plasma chemistry and plasma processing 19 (1999), S. 421-443 
    ISSN: 1572-8986
    Keywords: Streamer corona ; NO x removal ; nonthermal plasma ; oxidation ; reduction
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Technology
    Notes: Abstract In this paper, the NO-to-NO 2 conversion in various gaseous mixtures is experimentally investigated. Streamer coronas are produced with a dc-superimposed high-frequency ac power supply (10–60 kHz). According to NO x removal experiments in N 2 +NO x and N 2 +O 2 +NO x gaseous mixtures, it is supposed that the reverse reaction NO 2 +O→NO+O 2 may not only limit NO 2 production in N 2 +NO x mixtures, but also increase the energy cost for NO removal. Oxygen could significantly suppress reduction reactions and enhance oxidation processes. The reduction reactions, such as N+NO→N 2 +O, induce negligible NO removal provided the O 2 concentration is larger than 3.6%. With adding H 2 O into the reactor, the produced NO 2 per unit removed NO can be significantly reduced due to NO 2 oxidation. NH 3 injection could also significantly decrease the produced NO 2 via NH and NH 2 - related reduction reactions. Almost 100% of NO 2 can be removed in gaseous mixtures of N 2 +O 2 +H 2 O+NO 2 with negligible NO production.
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  • 89
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    Journal of sol gel science and technology 12 (1998), S. 35-48 
    ISSN: 1573-4846
    Keywords: yttrium acetate precursor ; particle coating ; oxidation ; corrosion ; Inconel
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract “Sol paint” that yields yttrium-based compounds was prepared by mixing four chemical ingredients, yttrium acetate tetrahydrate precursor, diethanolamine, isopropyl alcohol, and hydrochloric acid, and then applied as oxidation/corrosion resistant coatings for Inconel 625 substrates. Annealing the coatings at 500°C developed a coalescent microstructure of coarse particles consisting of amorphous yttrium carbonate as the major component and crystalline yttrium oxide (Y2O3) as the minor one. At 700°C, the yttrium carbonate was transformed into Y2O3 by decarbonation. Increasing the annealing temperature to 900°C led to the formation of the YCrO3 phase yielded by interaction between Y2O3 and the Cr2O3 which had arisen from the oxidation of the underlying Inconel; the YCrO3 phase created a particle coating with a densified microstructure. There were two key factors in mitigating the degree of oxidation of Inconel at 900°C in air: (1) an uptake of oxygen by Y2O3 in the coatings, and (2) a densified coating layer that suppresses the diffusion and permeation of oxygen through it. Furthermore, inhibiting the rate of NaCl-caused corrosion was not only due to the excellent coverage of particle coatings over the entire surfaces of the substrates, but also may be associated with a good adherence of the coatings to the substrates.
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  • 90
    ISSN: 1573-4889
    Keywords: dilute alloys ; oxidation ; Wagner-Hauffe rule
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Concerning the parabolic oxidation of alloys with a low content of a different valence element, we show that the Wagner-Hauffe valence approach contains some inaccuracies. This paper is devoted to the growth of an oxide MO with metal excess or oxygen deficit. The analytical processing consists in solving the differential equation connecting the point defect flux to the oxygen pressure. This equation has been solved analytically in the case where the foreign-element concentration is very high compared to that of the point defects in the pure oxide. On this assumption with a lower-valence dopant, as long as the oxide conductivity remains essentially electronic, the oxidation is limited only by the transport of ionic defects across the scale under the electric-potential gradient. Moreover, an increase of the dopant concentration may lead to an oxide exhibiting partial ionic conductivity. Consequently, the parabolic constant variations as a function of the dopant concentration is not monotonic, contrary to results published before. With a higher-valence dopant, the conductivity always remains electronic, and this result agrees with predictions based on the Wagner Hauffe approach, though the demonstrations are fundamentally different.
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  • 91
    ISSN: 1573-4889
    Keywords: oxidation ; copper ; Li-doped copper ; Cr-doped copper ; short-circuiting ; Mott's parabola ; Wagner's parabola
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The influence of shorting circuitry attachment between metal-oxide and oxideoxygen interfaces on the oxidation kinetics of copper, lithium-doped copper (Li: 400 ppm), and chromium-doped copper (Cr: 12 ppm) have been studied in dry air $$(P_{O_2 } = 21.27kPa)$$ in the temperature range of 523–1073 K. Oxide film or scale growth under short-circuiting as well as under normal oxidation conditions conforms to the parabolic rate law. The oxidation kinetics under short-circuiting resulted in decreased rates for Cu and Li-doped Cu up to a temperature of 773 K, while Cr-doped Cu exhibited an enhancement in rate compared to its normal oxidation in the same temperature range. However, above 873 K, all three systems under shorting circuitry attachment exhibited enhanced rates compared to their normal oxidation rates in conformity to the existing theoretical model. Use of additional resistances in series in the outer short-circuit Pt path have clearly established that below 773 K Mott's fieldinduced migration plays the most important role, while at elevated temperatures Wagner's electrochemical potential-gradient factor acts as the main driving force in the scale-growth process. The results have been interpreted on the basis of average defect concentration, the electrochemical potential gradient, electrical field gradient, and transport coefficient in the Cu2O layer.
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  • 92
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    Oxidation of metals 46 (1996), S. 109-127 
    ISSN: 1573-4889
    Keywords: oxidation ; Ni3Al base alloy ; chromium ; cobalt ; titanium
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The oxidation behavior of Ni3Al+2.90 wt.% Cr, Ni3Al+3.35 wt% Co, and Ni3Al+2.99 wt.% Ti alloys was studied in 1 atm of air at 1000, 1100, and 1200°C. Isothermal tests revealed parabolic kinetics for all three alloys at all temperatures. Cyclic oxidation for 28 two-hour cycles produced little spallation at 1000°C, but caused partial spallation at 1100°C. Especially, at 1200°C severe spallation in all three alloys was observed. Although additions of Cr, Co, or Ti to Ni3Al alloys slightly increased the isothermal-oxidation resistance, the additions tended to decrease the cyclic-oxidation resistance. The major difference in the oxidation of the three alloys compared with the oxidation of pure Ni3Al alloys was the existence of small α-Al2O3 particles in the middle of the α-Al2O3 scale and the formation of irregularly shaped Kirkendall voids at the alloy-scale interface.
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  • 93
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    Oxidation of metals 47 (1997), S. 381-410 
    ISSN: 1573-4889
    Keywords: Ni-Base superalloys ; Astroloy ; Waspaloy ; Udimet 720 ; oxidation ; chromia
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Several commercially available Ni-base superalloys were exposed isothermally in air at temperatures between 750° and 1000°C and also under cyclic conditions at 1000°C. The kinetics of oxidation were determined and the scales were analyzed by electron microscopy and X-ray diffraction. Thin adherent chromia-rich scales formed on the alloys at 750°C after 1000 hr. Although Waspaloy showed the lowest weight gain in this test, it also showed the deepest internal corrosion due to oxidation of the grain-boundary carbides. At temperatures up to 1000°C the external scales were also chromia-rich but there was greater internal corrosion. Titanium in the alloys oxidized, diffusing through the chromia scale to form faceted rutile (TiO2) grains at the surface as well as forming TiO2 and TiN internally. The amount of rutile at the oxide surface increased with temperature and alloy Ti concentration. Alumina formed as discrete internal oxides below the chromia scale, although Astroloy when oxidized isothermally at 1000°C developed a semicontinuous internal layer of alumina due to its higher Al content. Under cyclic conditions Astroloy formed a thicker, less-protective scale of transition oxides probably due to its lower Cr content.
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  • 94
    ISSN: 1573-4889
    Keywords: oxidation ; Incoloy 909 ; superalloy ; scale ; high temperature ; kinetics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The oxidation of an Fe-38Ni-13Co-4.7Nb-1.5Ti-0.4Si superalloy (Incoloy 909 type alloy), was investigated at temperatures between 1000 K and 1400 K in Ar-(1, 10%)H20 atmosphere using metallographic, electron probe microanalysis, and X-ray diffraction techniques. The oxide scales consist of an external scale and an internal scale which has an intergranular scale (above 1200 K) and an intergranular scale. The oxide phases in each scale are identified asα-Fe2,O3 (below 1200 K) or FeO (above 1300 K) and CoO · Fe2O3 and FeO · Nb2O5, respectively. The morphologies, the oxide phases and the oxidation rates do not depend on the partial pressure of H2O in the range between one and ten percent in Ar gas. The rate constants for the intergranular-scale formation in this alloy are about one-tenth as large as those in Fe-36%Ni alloy reported previously. At all the temperatures the scales grow according to a parabolic rate law and the apparent activation energies for the processes are estimated.
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  • 95
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    Oxidation of metals 47 (1997), S. 445-464 
    ISSN: 1573-4889
    Keywords: oxidation ; Fe-Cr-Al alloy ; water vapor ; ESCA ; RHEED
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Fe-21.5 wt. %Cr-5.6 wt. %Al oxidation, at 1000°C, in dry or wet oxygen shows that steam has an influence on the oxide-scale growth mechanism. Steam modifies the kinetics of early-stage oxidation. In dry oxygen, an initial fast linear regime is observed during one hour. Under wet conditions, weight-gain curves follow the same parabolic regime over the entire oxidation test. The scale structure strongly depends on the presence of steam in the gaseous environment. With dry oxygen, the scale is composed mainly ofα-Al2O3 after the initial formation ofγ-Al2O3 identified by ESCA and RHEED. The kinetics transient stage corresponds to the necessary time for the internal part of the initialγ-Al2O3 scale to transform into a continuousα-Al2O3 diffusion barrier. Under wet oxygen conditions, transient oxides are identified as (Mg, Fe) (Cr, Al)2O4, MgAl2O4 (orthorhombic), Al2O3 (hexagonal), these oxides transform into MgAl2O4 (cubic), Cr3O4, Fe2O3,α-Al2O3, with time. When water vapor does not change drastically oxidation kinetics, the induced presence of iron and chromium in the oxide scale could be responsible for weakening the protectiveness of alumina scales.
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  • 96
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    Oxidation of metals 47 (1997), S. 507-524 
    ISSN: 1573-4889
    Keywords: alloys ; high temperature ; oxidation ; transient state
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The initial transient high-temperature oxidation stage for binary alloys forming the most-stable oxide has been examined by means of a numerical procedure based on the finite-difference method. At variance with previous models, the present treatment takes into account the effect of the rate of the reaction at the scale/gas interface over the corrosion kinetics. The calculations concerning the transient stage are developed either using the general parabolic rate law to represent the overall scaling kinetics or using the rate law of the reaction at the scale/gas interface as a boundary condition without imposing any particular rate law to the overall process. A correct analysis of the oxidation behavior of binary alloys during the transient stage must take into account the kinetics effect of the rate of the surface reaction. The concentration of the most-reactive element at the alloy/scale interface changes regularly with time, decreasing gradually from the initial bulk value to its final steady-state value. The present results are in good agreement with those obtained by means of an approximate analytical model developed previously.
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  • 97
    ISSN: 1573-4889
    Keywords: high temperatures ; oxidation ; transient state
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The transient state in the oxidation of solid solutions of a most-noble componentA in a most-reactive componentB (beta phase) for binaryA-B alloys presenting a limited reciprocal solubility of the two metals has been examined assuming that theirB content is sufficient for the exclusive growth of externalBO scales. Above a criticalB content of the alloy theBO scales may grow directly on the surface of the beta phase, while below this limit they can only form over a layer ofB-depleted solid solution ofB inA (alpha phase), which appears after a critical time. An approximate analytical expression for the profile of concentration ofB in the alloy has been adopted to calculate the flux ofB in the metal. Moreover, the effect of the reaction between the gas and the external oxide surface has been taken into account using a procedure developed by Wagner for the oxidation of pure metals. The corrosion kinetics as well as all the parameters involved, such as the concentration ofB at the alloy-scale interface, have been calculated as functions of the corrosion time. The results show that, as time proceeds, the instantaneous parabolic rate constant increases and the concentration ofB at the alloy-scale interface decreases, both tending gradually to their corresponding steady-state values. It is also predicted that if the rate of transformation of the beta phase in the alpha phase after the alloy reaches the composition of equilibrium at the interface with the oxide is lower than the corresponding rate of displacement of the alloy surface due to scale growth, the corrosion of beta phase alloys may eventually lead to the formation of two phase mixtures of alpha phase andBO which are expected to grow at much larger rates than in the presence of a uniform continuous alpha layer.
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  • 98
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    Oxidation of metals 48 (1997), S. 1-39 
    ISSN: 1573-4889
    Keywords: Ni-base ODS superalloys ; oxidation ; initial stages of oxidation ; alumina ; chromia
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Mechanically-alloyed Ni-base ODS superalloys currently receive attention for application in future gas turbines because they exhibit outstanding mechanical properties at high temperatures. They also protect themselves against oxidation by forming chromia and/or alumina scales. However, little attention has been given so far to the initial stages of oxidation of Ni-base ODS superalloys, containing Cr as well as Al in considerable amounts. In the current work, oxidation at 1150°C was studied for different holding times up to 200 hr for the commercial materials MA6000 and PM3030 which contain. Al in increasing amounts. MA 754, a chromia former, was investigated as a reference. It was shown that for the potential alumina formers MA6000 and PM3030 the continuity and therefore protectiveness of the secondary Al2O3 at later stages is indeed determined by the initial stages of oxidation.
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  • 99
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    Oxidation of metals 48 (1997), S. 129-141 
    ISSN: 1573-4889
    Keywords: decarburization ; nickel ; oxidation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract A commercial-grade nickel containing small amounts of carbon, manganese, and silicon was exposed to air for periods up to 288 hr at 1050°C to study the effect of oxidation on the formation of oxides of these impurity elements. Exposure of nickel to air led to decarburization. The maximum amount of decarburization occurred during the initial period of air exposure and the loss in carbon was more in the metal with a smaller section size. Decarburization in the metal produced voids in the oxide scale due to the formation of CO2 gas. It has been shown further that CO and/or CO2 gas bubbles, which form in high purity nickel on grain boundaries during exposure to air at elevated temperatures, cannot exist in commercial-grade nickel where manganese is present as an impurity. Instead, oxides of manganese form in the grain boundaries as well as in the matrix. This is because manganese oxide is more stable than CO or CO2 gas.
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  • 100
    ISSN: 1573-4889
    Keywords: oxidation ; kinetics ; iron ; iron-nitride
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The oxidation of α-Fe and ɛ-Fe2N1−z at 573 K and 673 K in O2 at 1 atm was investigated by thermogravimetrical analysis, X-ray diffraction, light-optical microscopy, scanning electron microscopy and electron probe X-ray microanalysis. Upon oxidation at 573 K and 673 K, on α-Fe initially α-Fe2O3 develops, whereas on ɛ-Fe2N1−z initially Fe3O4 develops. In an early stage of oxidation the oxidation rate of ɛ-Fe2N1−z appears to be much larger than of α-Fe. This can be attributed largely to an effective surface area available for oxygen uptake, which is much larger for ɛ-Fe2N1−z than for α-Fe due to the porous structure of ɛ-Fe2N1−z as prepared by gaseous nitriding of iron. The development of a magnetite layer in-between the hematite layer and the α-Fe substrate, at a later stage of oxidation, enhances layer-growth kinetics. After 100 min oxidation at 673 K the (parabolic) oxidation rates for α-Fe and ɛ-Fe2N1−z become about equal, indicating that on both substrates the oxide growth is controlled by the same rate limiting step which is attributed to short-circuit diffusion of iron cations. Oxidizing ɛ-Fe2N1−z increases the nitrogen concentration in the remaining ɛ-iron nitride, because the outward flux of iron cations, necessary for oxide growth, leads to an accumulation of nitrogen atoms left behind.
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