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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Entomologia experimentalis et applicata 91 (1999), S. 403-412 
    ISSN: 1570-7458
    Keywords: aphid ; Diuraphis noxia ; Triticum aestivum ; endosymbiont ; insect-plant interactions ; phloem ; amino acids
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The feeding behavior of Diuraphis noxia Mordvilko (Homoptera: Aphididae) on susceptible hosts causes both ultrastructural and tissue level damage which may affect phloem composition. Genetic evidence suggests that endosymbiotic bacteria in most aphids overproduce limiting amino acids to benefit hosts but that D. noxia depends less on endosymbionts for these nutrients, possibly due to an enriched diet. To determine whether D. noxia feeding damage results in higher concentrations of essential amino acids, stylet exudates were analyzed from wheat (Triticum aestivum) damaged to different degrees. Comparison of samples from undamaged and damaged susceptible wheat revealed changes in amino acid composition and an increase in levels of essential amino acids, indicating a nutritionally enhanced ingesta. The changes in stylet exudates paralleled changes in leaf exudates, indicating that the effects are systemic. Feeding damage is not observed on a resistant wheat host, var. Halt, and leaf exudates from infested Halt did not show changes in amino acid composition. Mean relative growth of nymphs was significantly lower on Halt than on susceptible Arapahoe, indicating that Halt is a less suitable host. Both varieties show similar amino acid levels in non-infested samples, suggesting that D. noxia infestation does not enhance the phloem environment in Halt. This study provides evidence that aphid feeding can generate a nutritionally enhanced phloem diet.
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  • 2
    ISSN: 1570-7458
    Keywords: sieve element ; salivation ; aphid ; plant resistance ; wheat ; Sitobion fragariae ; Triticum aestivum
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Extended sieve element salivation (E1 waveform in the electrical penetration graph) is a characteristic activity during early sieve element punctures, particularly in resistant plants. In order to explore a chemically-mediated mechanism of resistance associated with sieve element salivation, we compared the pattern of feeding behaviour of the aphid, Sitobion fragariae (Walker), on two cultivars of the wheat Triticum aestivum L., with different concentrations of hydroxamic acids (Hx). During 24 h of electronic monitoring, aphids dedicated over 50% of the total time to phloem ingestion from the sieve elements. Total time allocated to E1 in the experiment, time to first E1 within the experiment, time allocated to E1 before a sustained phloem ingestion (E2) and the contribution of sieve element salivation to the phloem phase (E1/[E1+E2]) were significantly higher in the high-Hx cultivar. The increased salivation in plants with higher contents of Hx suggests the existence, at least in this system, of a chemically-mediated sieve element constraint.
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  • 3
    Electronic Resource
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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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  • 4
    Electronic Resource
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    Springer
    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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  • 5
    Electronic Resource
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    Springer
    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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  • 6
    Electronic Resource
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    Springer
    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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  • 7
    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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  • 8
    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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  • 9
    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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  • 10
    Electronic Resource
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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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  • 11
    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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  • 12
    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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  • 13
    Electronic Resource
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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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  • 14
    Electronic Resource
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    Springer
    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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  • 15
    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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  • 16
    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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  • 17
    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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  • 18
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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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  • 19
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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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  • 20
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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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  • 21
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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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  • 22
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    Cellular and molecular life sciences 51 (1995), S. 768-774 
    ISSN: 1420-9071
    Keywords: Cortisol ; stress ; heat ; Antarctic ; fish
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract Radioimmunoassay was used to determine levels of the stress-inducible glucocorticoid, cortisol, circulating in the plasma of the extremely stenothermal Antarctic fishPagothenia borchgrevinki at rest and after heat stress. Fish sampled immediately after capture (−1.9°C) had low cortisol levels (10.4±1.4 ng ml−1, mean±SEM) as did fish which were laboratory rested for 3 days. Sudden exposure to 5°C (48h) resulted in a peak cortisol value after 3 h (69.9±6.8 ng ml−1) whereas exposure to 8°C (6h) resulted in a peak value after 1 h (73.5±8.0 ng ml−1). At both temperatures levels remained significantly elevated (p〈0.05) for the entire period of exposure. Increased temperature also resulted in a significant change in haemoglobin, haematocrit and mean cell haemoglobin concentration (MCHC) (p〈0.05). Plasma lactate was significantly elevated only after exposure to 8°C (p〈0.05). Plasma cortisol levels fromP. borchgrevinki are reported here for the first time and show this cryopelagic Antarctic species to have an unusual hormonal stress profile.
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  • 23
    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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  • 24
    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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  • 25
    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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  • 26
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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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  • 27
    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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  • 28
    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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    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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  • 30
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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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  • 31
    ISSN: 1572-879X
    Keywords: synergistic effect ; carbon monoxide ; oxidation ; mixed oxides ; iron oxide ; tin oxide ; manganese oxide
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    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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  • 32
    ISSN: 1572-879X
    Keywords: non-uniform surface ; kinetics ; ethanol ; oxidation ; molybdenum oxide
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    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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  • 33
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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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  • 34
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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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  • 35
    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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  • 36
    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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  • 37
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    Catalysis letters 56 (1998), S. 199-202 
    ISSN: 1572-879X
    Keywords: cerium ; gas carbonic ; propane ; oxidation
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    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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  • 38
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    Catalysis surveys from Japan 3 (1999), S. 27-35 
    ISSN: 1572-8803
    Keywords: oxidation ; oxygen ; alkane ; N‐hydroxyphthalimide ; radical catalyst
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    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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  • 39
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    Cellulose 2 (1995), S. 265-272 
    ISSN: 1572-882X
    Keywords: Hydrogen peroxide ; oxycellulose ; bleaching ; oxidation
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    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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  • 40
    ISSN: 1432-1890
    Keywords: Key words Glomus mosseae ; Hydroponics ; Nitrate uptake ; Root respiration ; Triticum aestivum
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract  Oxygen and CO2 fluxes were measured in hydroponically grown mycorrhizal and non-mycorrhizal Triticum aestivum L. cv. Hano roots. The NO3 – uptake of the plants was used to estimate the amount of root respiration attributable to ion uptake. Plants were grown at 4 mM N and 10 μM P, where a total and viable mycorrhizal root colonisation of 48% and 18%, respectively, by Glomus mosseae (Nicol. and Gerd.) Gerd. and Trappe (BEG 107) was observed. The O2 consumption and NO3 – uptake rates were similar and the CO2 release was higher in mycorrhizal than in non-mycorrhizal wheat. This resulted in a significantly higher respiratory quotient (RQ, mol CO2 mol–1 O2) in mycorrhizal (1.27±0.13) than in non-mycorrhizal (0.79±0.05) wheat. As the biomass and N and P concentrations in mycorrhizal and non-mycorrhizal wheat were the same, the higher RQ resulted from the mycorrhizal colonisation and not differences in nutrition per se.
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  • 41
    ISSN: 1432-0789
    Keywords: 15N-labelled fertilizer ; Added N interaction Fertilizer N uptake ; Soil N uptake ; Wheat ; Triticum aestivum
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract The effects of 15N-labelled ammonium nitrate, urea and ammonium sulphate on yield and uptake of labelled and unlabelled N by wheat (Triticum aestivum L. cv. Mexi-Pak-65) were studied in a field experiment. The dry matter and N yields were significantly increased with fertilizer N application compared to those from unfertilized soil. The wheat crop used 64.0–74.8%, 61.5–64.7% and 61.7–63.4% of the N from ammonium nitrate, urea and ammonium sulphate, respectively. The fertilizer N uptake showed that ammonium nitrate was a more available source of N for wheat than urea and ammonium sulphate. The effective use of fertilizer N (ratio of fertilizer N in grain to fertilizer N in whole plant) was statistically similar for the three N fertilizers. The application of fertilizer N increased the uptake of unlabelled soil N by wheat, a result attributed to a positive added N interaction, which varied with the method of application of fertilizer N. Ammonium nitrate, urea and ammonium sulphate gave 59.3%, 42.8% and 26.3% more added N interaction, respectively, when applied by the broadcast/worked-in method than with band placement. A highly significant correlation between soil N and grain yield, dry matter and added N interaction showed that soil N was more important than fertilizer N in wheat production. A values were not significantly correlated with added N interaction (r=0.719). The observed added N interaction may have been the result of pool substitution, whereby added labelled fertilizer N stood proxy for unlabelled soil N.
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  • 42
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    Biology and fertility of soils 23 (1996), S. 327-331 
    ISSN: 1432-0789
    Keywords: CO2 emission ; Field method ; Soil respiration ; Triticum aestivum ; Soil moisture ; Carbon reservoirs ; Greenhouse effect ; Grey forest soil ; Mineralization
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract The dynamics of the rate of CO2 evolution from soil in fallow and croplant under spring wheat (Triticum aestivum L.) was studied in a crop rotation in grey forest soil of the Baikal forest-steppe during the growing season and in different years. It was shown that the regional characteristics of soils and hydrothermal conditions in different years affect the rate of CO2 evolution in agroecosystems. The seasonal dynamics of CO2 is characterized by insignificant changes in the autumn to spring period and enhanced emission in hot and dry summers. CO2 evolution is assumed to increase due to enhanced mineralization and partial diffusion from the carbonate horizon at the depth of the seasonal frost. During the growing season the dynamics of CO2 evolution depends on the soil moisture regime. There was a strong correlation between the rate of CO2 emission and soil moisture in the particularly dry year of 1993 (η=0.86) and a moderate correlation in the other years (η=0.38–0.54). The effect of the previous crop and fertilizer application on the rate of CO2 emission was insignificant. In a continuous fallow the total carbon release into the atmosphere varied throughout the years studied from 558 to 1880 kg ha-1. Humus losses varied from 0.9% to 3.1%.
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  • 43
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    Biology and fertility of soils 23 (1996), S. 327-331 
    ISSN: 1432-0789
    Keywords: Key words CO2 emission ; Field method ; Soil respiration ; Triticum aestivum ; Soil moisture ; Carbon reservoirs ; Greenhouse effect ; Grey forest soil ; Mineralization
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract The dynamics of the rate of CO2 evolution from soil in fallow and cropland under spring wheat (Triticum aestivum L.) was studied in a crop rotation in grey forest soil of the Baikal forest-steppe during the growing season and in different years. It was shown that the regional characteristics of soils and hydrothermal conditions in different years affect the rate of CO2 evolution in agroecosystems. The seasonal dynamics of CO2 is characterized by insignificant changes in the autumn to spring period and enhanced emission in hot and dry summers. CO2 evolution is assumed to increase due to enhanced mineralization and partial diffusion from the carbonate horizon at the depth of the seasonal frost. During the growing season the dynamics of CO2 evolution depends on the soil moisture regime. There was a strong correlation between the rate of CO2 emission and soil moisture in the particularly dry year of 1993 (η=0.86) and a moderate correlation in the other years (η=0.38–0.54). The effect of the previous crop and fertilizer application on the rate of CO2 emission was insignificant. In a continuous fallow the total carbon release into the atmosphere varied throughout the years studied from 558 to 1880 kg ha–1. Humus losses varied from 0.9% to 3.1%.
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  • 44
    ISSN: 1432-0789
    Keywords: Key words Phosphate-solubilizing microorganisms ; Mussoorie rock phosphate ; Vesicular-arbuscular mycorrhizae ; Triticum aestivum ; Nutrient-deficient soils
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract  The effect of inoculating wheat (Triticum aestivum L.) with the PO4 3–-solubilizing microorganisms (PSM) Bacillus circulans and Cladosporium herbarum and the vesicular-arbuscular mycorrhizal (VAM) fungus Glomus sp. 88 with or without Mussoorie rock phosphate (MRP) amendment in a nutrient-deficient natural sandy soil was studied. In the sandy soil of low fertility root colonization by VAM fungi was low. Inoculation with Glomus sp. 88 improved root colonization. At maturity, grain and straw yields as well as N and P uptake improved significantly following inoculation with PSM or the VAM fungus. These increases were higher on combined inoculation of PSM and the VAM fungus with MRP amendment. In general, a larger population of PSM was maintained in the rhizosphere of wheat in treatments with VAM fungal inoculation and MRP amendment. The results suggest that combined inoculation with PSM and a VAM fungus along with MRP amendment can improve crop yields in nutrient-deficient soils.
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  • 45
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    Biology and fertility of soils 23 (1996), S. 273-281 
    ISSN: 1432-0789
    Keywords: Wheat ; Triticum aestivum ; Rhizosphere ; Soil microflora ; Gram-negative bacteria ; API 20 NE ; Flavobacterium spp ; Cytophaga
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract We identified 161 Gram-negative bacterial strains isolated from the root surface of wheat grown under different soil conditions. The strains were divided into seven groups based on major morphological and physiological properties. Taxonomic allocation of the groups was verified by guanine+cytosine contents of DNA. Except for one group, which may be assumed to include bacteria belonging to the genera Flavobacterium and Cytophaga, the various groups were taxonomically united. The distribution of the groups changed with soil improvement. Pseudomonads predominated in unimproved soil, but Flavobacterium and Cytophaga spp. were predominant in the most improved soil. As all the strains were non-fermentative by Hugh and Leifson's test, API 20NE identification was applied. However, many strains were misidentified by this system, especially in the Flavobacterium and Cytophaga spp. group. For ecological studies, the strains were classified to species level by the API 20 NE system and by the results of a combination of guanine+cytosine (mol%) and isoprenoid quinone data. The pattern of distribution of the bacteria on the root surface of wheat varied at species level within one genus depending on soil conditions.
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  • 46
    ISSN: 1432-0975
    Keywords: Key words Dispersal ; coral reefs ; fish ; swimming ; Larvae ; Juveniles
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences
    Notes: Abstract  Characteristics of the pelagic stages of reef fishes have generally been investigated at the family level, which may mask important differences among species. Here the variation in sustained swimming ability of the late pelagic stages is examined among species, within two families (Pomacentridae and Chaetodontidae). The pomacentrids displayed a 7.5-fold difference in sustained swimming ability across 24 species, while the chaetodontids displayed a 2-fold difference across 10 species. The variation within the Pomacentridae was not related to pelagic larval duration, post-settlement habitat or taxonomy. There was, however, a significant correlation between sustained swimming ability and total length (TL) of individuals (r=0.435, P〈0.0001). Differences in the mean distance swum by pomacentrid species, however, was most strongly related to differences in mean wet weight (r=0.814, P〈0.0001). When the mean distance swum by species was scaled with respect to mean TL there was still a strong correlation with mean wet weight (r=0.644, P〈0.005). Among chaetodontid individuals TL and sustained swimming ability were not correlated (r=−0.004, P=0.978). Furthermore, sustained swimming ability was not significantly related to the trans-oceanic distribution of species in either family. The variation in sustained swimming ability, however, may contribute to explanations of the observed levels of gene flow within populations.
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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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  • 48
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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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  • 49
    ISSN: 1436-5073
    Keywords: mercury ; fish ; collaborative study ; atomic absorption spectrometry
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract One of the major analytical problem in the analysis of fish tissues for total mercury is the dissolution of the sample. This paper compares two different methods of wet digestion (microwave and closed pressurized vessel), followed by FIAAS as final determination and a Zeeman-solid-sample-AAS determination method without previous mineralization. Six fish samples were selected for this study. The top, the central and the bottom portions of the fish were analyzed separately. The mercury contents in the bottom portions determined by Zeeman-solid-sample-AAS were significantly higher than those obtained by the other two systems. A good correlation was observed among the results of the different techniques.
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  • 50
    ISSN: 1436-5073
    Keywords: microwave digestion ; fish ; mercury ; CVAAS
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    Topics: Chemistry and Pharmacology
    Notes: Abstract Food samples digestion, in view to quantify total mercury, is the first step to perform before measuring mercury by cold vapour atomic absorption spectrometry (CVAAS). We have compared two microwave digestion systems, one working at atmospheric pressure (open system) and the other one under pressure (closed system). Results obtained for fish muscle samples by the two methods are in good agreement. However, fat is not digested in the open system, whereas in the closed system no more fat remains in the final solution. During the quantification step, applying the CVAAS technique, we have noticed that the choice and the concentration of the reductant solution is very important to obtain good results. Elaborated methods have been validated using certified reference materials.
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  • 51
    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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  • 52
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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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  • 53
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    Nutrient cycling in agroecosystems 53 (1999), S. 157-175 
    ISSN: 1573-0867
    Keywords: Brassica napus ; Cicer arietinum ; current P ; Lens culinaris ; Lupinus albus ; Lupinus angustifolius ; P concentration response ; P content response ; Pisum sativum ; previous P ; sigmoid response ; single superphosphate ; Triticum aestivum ; Vicia faba ; yield response
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Phosphorus (P) is a major deficiency of soils of south-western Australia (WA). The fertilizer P requirements are not known for grain legumes being evaluated for neutral to alkaline, fine textured soils in WA. To rectify this, glasshouse and field experiments were undertaken to compare the responses of several grain legume species, wheat and canola to applications of single superphosphate and the results are reported in this paper. The glasshouse experiments measured responses of dried tops, harvested at 26 to 42 days after sowing, to P that was freshly-applied (current P) and previously-applied (previous P). Responses in the glasshouse were measured using yield, P concentration and P content (P concentration multiplied by yield) of oven dried tops of the following: wheat (Triticum aestivum), canola (Brassica napus), faba bean (Vicia faba), chickpea (Cicer arietinum), lentil (Lens culinaris), field pea (Pisum sativum), albus lupin (Lupinus albus) and narrow leaf lupin (Lupinus angustifolius). Field experiments in 1994 and 1995 compared seed (grain) yield responses of faba bean, chickpea, lentil, albus lupin and wheat to applications of current P. The P was banded (drilled) with the seed while sowing at 5 cm depth. Canola and wheat produced very large yield responses to increasing applications of current P. Responses were much smaller for albus lupin, faba bean and chickpea. Responses for lentil, narrow leaf lupin and field pea, fell in between responses of the small and large seeded species. Similar trends for responses were obtained as measured using yield, P concentration, or P content. For soils treated with previous P, similar trends were observed as for current P, but differences in yield responses between species were much less marked and the response curves tended to become more sigmoid. In the field experiments, grain yield responses to current P of albus lupin and chickpea were less than that for wheat. Relative to wheat, faba bean was the most responsive grain legume to applications of current P, with lentil producing similar responses to wheat in one experiment at a newly cleared, P deficient site.
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  • 54
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    Nutrient cycling in agroecosystems 44 (1995), S. 205-215 
    ISSN: 1573-0867
    Keywords: Incubation of phosphorus in soil ; relative effectiveness ; superphosphate ; ×Triticosecale ; Triticum aestivum
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Single superphosphate was incubated for six months at 25°C in soil which had been subject to one of three moisture treatments. These were: dried in a glasshouse, dried at a constant temperature of 25°C, or moist soil. Phosphorus (P) effectiveness was then compared with effectiveness of P from freshly-applied superphosphate using yields of wheat (Triticum aestivum) and triticale (×Triticosecale) tops in pot experiments. Incubation in soil which had been dried at 25°C did not decrease the effectiveness of the P. Incubation in moist soil decreased it to about 20% of the effectiveness of freshly-applied P in one case and to about 50% in the other case. Incubation in soil which had been dried in a glasshouse also decreased its effectiveness. The decrease varied with conditions, but in two cases the P was 70% as effective as freshly-applied P, and in one case only 45% as effective. Presumably sufficient moisture was present in the soil dried in the glasshouse to enable water-soluble P present in the fertilizer to react with the soil.
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  • 55
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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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  • 56
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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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  • 57
    ISSN: 1572-9508
    Keywords: X-ray ; calibration ; filters ; interference ; oxidation
    Source: Springer Online Journal Archives 1860-2000
    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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  • 58
    ISSN: 1572-977X
    Keywords: culverts ; culvert trap ; mosquito impoundment ; seine ; fish
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Fish population dynamics in a 24.3 ha mangrove-dominated mosquito impoundment in east-central Florida were examined by seining and culvert traps before and after installation of culverts that established estuarine connection for the first time in 39 years. In a 27-day period following the culvert opening, fish species increased from 9 to 21, while total number of fish in the impoundment decreased. Movement of fishes through culverts in both directions commenced immediately following culvert opening. Recruitment of transient species into the impoundment appeared to key on a single wind-driven high tide event. Such short-term events may be important cues for fish movement into and out of impounded salt marshes.
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  • 59
    ISSN: 1420-9055
    Keywords: Phoxinus phoxinus ; fish ; Diplostomum phoxini ; Macrolecithus papilliger ; parasitism
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The influence of parasites on the breeding biology of the European minnow (Phoxinus phoxinus) was studied by examining 268 adult and 59 young-of-the-year minnows from an artificial Swiss Alpine lake for parasites during the breeding seasons in 1990 and 1991. Two trematode parasites;Diplostomum phoxini, in their brains, andMacrolecithus papilliger, in their guts, were found. The prevalence ofD. phoxini was 100% in both years. The mean abundance was 231 in 1990 and 448 in 1991; the difference was significant. Prevalence (and abundance) ofM. papilliger was 37.5% (1.04±0.39) in 1990 and 59.5% (2.68±0.55) in 1991; also significantly higher in 1991 than in 1990. No differences in prevalence or abundance between males and females were found. Numbers of both parasites were significantly correlated with fish length. There was seasonal variation in the abundance ofD. phoxini metacercariae, with a peak in June/July in both years. The prevalence ofM. papiller decreased after July in both years. Distribution of the two trematodes was overdispersed as indicated by the variance to mean (abundance) ratio. The observed seasonal variation inD. phoxini abundance also suggests that sublethal parasites could influence the population dynamics of their hosts.
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  • 60
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    Aquatic sciences 57 (1995), S. 106-118 
    ISSN: 1420-9055
    Keywords: Benthos ; fish ; vertical distribution ; predation risk ; selective fishing ; Lake Constance
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract To compare the vertical distributions of benthos and fish species of Upper Lake Constance (Bodensee), 552 benthos samples were taken with an Auerbach grab at four transects (10–250 m). An additional 54 samples (1–10 m) were collected elsewhere. Complementary data was taken from the literature. In winter, most fish feed on benthos, mainly chironomids, but in summer less than 5% do so. Formerly the bottom gill-netting aimed mainly at catchingCoregonus pidschian, but it now aims atPerca fluviatilis. Contrary to expectation, in winter the greatest abundance ofP. fluviatilis is much deeper (55 m) than that of its preferred food, i.e. chironomids (〈20 m). Comparably,C. pidschian also stayed deeper than its main food source (chironomids and mollusks).Lota lota, Salvelinus profundus andS. alpinus — unlike the unwanted cyprinids — also stay or stayed deeper than the attractive chironomids. It is argued that the fish reduce their “predation risk”, i.e. the risk of being gillnetted in the upper 50 m, by “selecting” the deeper less dangerous, but also less food-abundant habitat. Balancing predation risk against food abundance may have led to “survival of the deepest”.
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  • 61
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    Sexual plant reproduction 8 (1995), S. 266-272 
    ISSN: 1432-2145
    Keywords: Triticum aestivum ; Alloplasmic lines ; Apomixis ; Parthenogenesis ; Protein patterns ; 2-D gel electrophoresis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract An in vivo model system to study the initiation of embryo development is presented. From the so-called Salmon system of wheat (alloplasmic lines with a 1BL-1RS chromosome translocation), three completely isogenic and homozygous lines were produced by selection for uniformity in about 20 selfing/backcross generations as well as between sublines of doubled haploids. The line (aestivum)-Salmon is male fertile and sexual. The lines (caudata)-Salmon and (kotschyi)-Salmon are male sterile and have a parthenogenetic capacity of about 90%. The expression of nuclear-cytoplasmic male sterility is different for the two parthenogenetic lines. The initiation of autonomous embryo development at defined developmental stages of the ovaries and the maximum degree of parthenogenesis are identical in both parthenogenetic lines as proved by the auxin test and progeny analyses. The protein patterns from ovary extracts of the three isogenic lines were identical for more than 200 spots of 2-D polyacrylamide gels, confirming their homogeneity. However, one protein (P 115.1) was found 3 days before and during anthesis only in ovaries of the parthenogenetic lines. It seems to be involved in the initiation of parthenogenesis.
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  • 62
    ISSN: 1432-2145
    Keywords: Key words Male sterility ; Starch ; Triticum aestivum ; Water stress ; Anther ; Pollen
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract  Water deficit during meiosis in microspore mother cells of wheat (Triticum aestivum L.) induces male sterility, which reduces grain yield. In plants stressed during meiosis and then re-watered, division of microspore mother cells seems to proceed normally, but subsequent pollen development is arrested. Stress-affected anthers generally lack starch. We employed light microscopy in conjunction with histochemistry to compare the developmental anatomy of water-stress-affected and normal anthers. The earliest effects of stress, detectable between meiosis and young microspore stages, were the degeneration of meiocytes, loss of orientation of the reproductive cells, and abnormal vacuolization of tapetal cells. Other effects observed during subsequent developmental stages were deposition of starch in the connective tissue where it is normally not present, hypertrophy of the middle layer or endothecial cells, and deposition of sporopollenin-like substances in the anther loculus. The resulting pollen grains lacked both starch and intine. These results suggest that abnormal degeneration of the tapetum in water-stressed anthers coupled with a loss of orientation of the reproductive cells could be part of early events leading to abortion of microspores.
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  • 63
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    Plant cell reports 16 (1997), S. 663-667 
    ISSN: 1432-203X
    Keywords: Key words Embryogenesis ; Ovule culture ; Triticum aestivum ; Zygote
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Ovules of the wheat breeding line Veery #5 were excised and transferred to culture within 24 h after pollination. When ovules were cultured on Phytagel-solidified medium, and the pericarp removed exclusively at the micropylar tip and the abaxial side, zygotes from up to 79.2% of the ovules underwent embryogenesis with the same developmental pattern as found in planta. Embryos from more than 50% of the cultured ovules germinated when transferred to regeneration medium. More than 100 plantlets were randomly chosen for transfer to soil, all of which developed to phenotypically normal and fertile plants. With this system, the entire process of zygotic embryogenesis can be studied using living material. Furthermore, the method could be used as an embryo rescue technique for plant breeding purposes.
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  • 64
    ISSN: 1432-203X
    Keywords: Key words Abscisic acid ; Anther culture ; Light ; Metallothionein ; Pollen embryogenesis ; Triticum aestivum
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract A cloned cDNA to the wheat (Triticum aestivum) early cysteine-labeled metallothionein has many characteristics of a molecular marker for pollen embryogenesis in this plant. This transcript was not detected in uninucleate microspores at the time of culture or in pollen at any stage during normal ontogeny; its mRNA did begin to increase in embryogenic microspores within 6 h of culture, peaked at around 24 h, declined, then leveled off through the 21-day-old embryoid stage. Additionally, the accumulation of the embryoid-abundant EcMt gene transcript showed a direct and positive correlation with an increase of ABA in embryogenic microspores and developing pollen embryoids. Irradiating cultures with high intensity white light or with far-red, or blue light, suppressed EcMt transcript accumulation and the ability of microspores to form embryoids; however, light did not affect ABA concentrations during the early stages of culture. These results suggest that although a promoter of pollen embryogenesis in bread wheat, ABA alone cannot maintain the sporophytic differentiation of microspores subjected to inhibitory regimes of light in vitro. Whether or not light acts directly or indirectly in suppressing EcMt gene expression and pollen embryogenesis remains unknown.
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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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  • 69
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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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  • 74
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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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  • 75
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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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  • 76
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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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  • 77
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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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  • 78
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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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  • 79
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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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  • 82
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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
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    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. 283-291 
    ISSN: 1572-8943
    Keywords: DSC ; fish ; general proteolytic activity ; pyloric caeca ; ripening ; salted herring product
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The thermoanalytical behaviour of pyloric caeca during salting and ripening was investigated using a Perkin Elmer DSC 7. Not only the thermal stability of the muscle proteins was influenced by salting but also that of pyloric caeca. It was recognised that the salting itself leads to a remarkable increase of the transition temperature compared with raw herring. An influence of the salt:fish ratio could be observed. The higher the salt content the higher the increase of the denaturation temperature. During ripening the transition temperature remained on a high level or showed only a slight decrease during the investigation period. The dependency from the salt content remained evident. The increase of the transition temperature was accompanied by a decrease of the transition enthalpy. The increase of thermal stability is connected with a decrease of the general proteolytic activity in pyloric caeca. Possibly, the enzymes are diffusing from the pyloric caeca into the muscle and cause there an increase of enzymatic activity observable in North Sea herring accompanied by a decrease of activity in pyloric caeca itself. Simultaneous the thermal stability of pyloric caeca is lowered. The reason for the differences in ripening could be seen in some enzyme-inhibiting factors unknown until now.
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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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  • 86
    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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    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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    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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    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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    Water, air & soil pollution 85 (1995), S. 303-308 
    ISSN: 1573-2932
    Keywords: Acidification ; fish ; forestry ; water-chemistry ; management ; calcium ; aluminium ; TOC
    Source: Springer Online Journal Archives 1860-2000
    Topics: Energy, Environment Protection, Nuclear Power Engineering
    Notes: Abstract The soils and waters in the Galloway hills of south-west Scotland have undergone considerable acidification during the present century. The aims of this study were to examine the extent to which afforestation can influence water chemistry, and the occurrence of fish stocks within an individual catchment in this area. Studies were carried out at 45 sites in the Bladnoch catchment during 1994. River water samples were collected at all sites and determinations made of pH, total organic carbon, calcium and monomeric aluminium concentrations. In order to quantify the size and abundance of fish populations, electrofishing was carried out at 21 of the sites. Estimates of afforestation were made by a combination of field surveys and the use of 1∶:10 000 scale ordnance survey maps. The presence of coniferous trees had a substantial affect on water chemistry. In areas where the whole catchment was afforested, the water pH was 0.7 units lower than in unafforested areas (p〈0.001). Afforestation was also correlated with low concentrations of calcium, and increases in the concentrations of monomeric aluminium and total organic carbon. There was a clear relationship between fish populations and water chemistry. Numbers of trout were positively correlated with pH (r 2=0.69; p〈0.001), and with concentrations of calcium (r 2=0.55; p〈0.001). The study has shown that salmonid fish populations are sensitive to acidity and the associated changes in river water chemistry; these problems were exacerbated by afforestation.
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  • 92
    ISSN: 1573-2932
    Keywords: Na+ flux ; Cl− regulation ; chloride cells ; anal papillae ; acid-sensitivity ; crustaceans ; insect larvae ; fish
    Source: Springer Online Journal Archives 1860-2000
    Topics: Energy, Environment Protection, Nuclear Power Engineering
    Notes: Abstract Fishes, Zooplankton, insect larvae, and benthic invertebrates differ in their sensitivity to acidic waters. Some species are able to survive and complete their life-cycle below pH 3.5 while others are eliminated once the pH drops below 5.5. Generally, acid-sensitive fauna are highly water permeable and have difficulty regulating osmotically essential ions, such as sodium and chloride, at low pH. Increased permeability during certain stages of a life-cycle (post-molt crayfish, for example) are often associated with increased acid-sensitivity. Special adaptations, including enlarged anal papillae in Chironomids and the number and morphology of chloride cells in such diverse organisms as crustaceans, insect larvae, and fishes, may enhance acid-tolerance. To test the hypothesis that Na+ regulation can be used to predict relative acid-sensitivity of aquatic fauna we will need a mechanism for standardizing Na+ regulatory capability.
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    Water, air & soil pollution 85 (1995), S. 889-894 
    ISSN: 1573-2932
    Keywords: acidification ; acid neutralizing capacity ; calcite ; fish ; liming ; mitigation ; ecosystems
    Source: Springer Online Journal Archives 1860-2000
    Topics: Energy, Environment Protection, Nuclear Power Engineering
    Notes: Abstract The Experimental Watershed Liming Study (EWLS) evaluated the application of CaCO3, to a forested watershed to mitigate the acidification of surface water. During October 1989, 6.9 Mg CaCC3/ha was applied by helicopter to two subcatchments of about 50% (102.5 ha) of the Woods Lake watershed area. The EWLS team investigated the response to treatment of soils (chemistry and microbial processes), vegetation, wetland, stream and lake waters, and phytoplankton and fish, and applied the Integrated Lake Watershed Acidification (ILWAS) model in predicting a watershed treatment duration of up to 50 years. Observations showed a gradual change in pH, acid neutralizing capacity (ANC) and Ca2+ in the water column; direct lake additions of CaCO3 (three different times) were characterized by abrupt changes following base addition and subsequent rapid reacidification. Moreover, the watershed treatment eliminated the snowmelt acidification of the near-shore region of the lake observed during direct lake treatments. Positive ANC water in the tributary and near-shore area improved conditions for fish reproduction and for a viable fish population. Budgets for 12-month periods before and after the watershed treatment showed that the lake shifted from a source of ANC to a sink due to retention of elevated inputs of Ca2+ from the watershed CaCO3 application.
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  • 94
    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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  • 95
    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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    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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    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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  • 98
    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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  • 99
    Electronic Resource
    Electronic Resource
    Springer
    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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  • 100
    Electronic Resource
    Electronic Resource
    Springer
    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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