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  • Artikel  (45.390)
  • Chemistry  (45.059)
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  • 1
    Digitale Medien
    Digitale Medien
    Amsterdam : Elsevier
    The @Journal of Supercritical Fluids 3 (1990), S. 240-248 
    ISSN: 0896-8446
    Schlagwort(e): kinetics ; oxidation ; phenol ; reaction product ; supercritical water
    Quelle: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Thema: Maschinenbau , Physik , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Materialart: Digitale Medien
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  • 2
    Digitale Medien
    Digitale Medien
    Amsterdam : Elsevier
    The @Journal of Supercritical Fluids 5 (1992), S. 72-78 
    ISSN: 0896-8446
    Schlagwort(e): NO"x ; nitrogen ; oxidation ; supercritical ; water
    Quelle: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Thema: Maschinenbau , Physik , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Materialart: Digitale Medien
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  • 3
    Digitale Medien
    Digitale Medien
    Amsterdam : Elsevier
    The @Journal of Supercritical Fluids 5 (1992), S. 262-268 
    ISSN: 0896-8446
    Schlagwort(e): Raman spectroscopy ; flames ; ignition ; oxidation ; supercritical water
    Quelle: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Thema: Maschinenbau , Physik , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Materialart: Digitale Medien
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  • 4
    ISSN: 1572-8862
    Schlagwort(e): Palladium ; carbene ; oxidation ; phosphonate ; carboxylate
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau , Physik
    Notizen: Abstract Thermolysis of tetranuclear palladium clusters Pd4(μ-Q)4 Pd4(μ-Q)4(μ-O2CR)4 (Q=CPh2 or CO;R=Me, CMe3, Ph, CH2Cl or CF3) has been found to involve innersphere oxidation of carbene or carbonyl ligands during which an oxygen atom transfer occurs from the carboxylate group to the carbene or carbonyl ligand. The thermolysis of the carbonyl clusters gives rise to the products of CO2 insertion into the C–H bond of benzene or toluene used as solvents forming benzoic acid from benzene and a mixture of phenylacetic and toluic acids from toluene. The reaction of [Pd(OAc)2(PPh3)]2 with HCO2H includes the transfer of an O atom from formate ligand to the P atom and cleavage of the P-Ph bond accompanied by transfer of the Ph group from PPh3 ligand to the palladium atom. The structure of the complex formed, [Pd(μ-O2PPh2)(C6H5)(PPh3)]2, has been resolved by X-ray analysis.
    Materialart: Digitale Medien
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  • 5
    Digitale Medien
    Digitale Medien
    Springer
    Journal of polymers and the environment 1 (1993), S. 275-279 
    ISSN: 1572-8900
    Schlagwort(e): Chemiluminescence ; oxidation ; stability ; acrylonitrile-butadiene-styrene (ABS) ; ABS/polycarbonate blend
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie , Energietechnik , Maschinenbau
    Notizen: Abstract The thermal oxidative stability of various ABS/PC compounds was studied by means of the chemiluminescence technique. Similarly to pure ABS, Irganox 1076 and Irganox MD 1024 perform as moderate antioxidants in ABS/PC and (ABS/PC + lubricant) blends. Neither Tinuvin 144, Irgaphos 168, nor their mixture affects the durability of the ABS/PC blend. At the same time, (Irgaphos 168 + Tinuvin 144) in combination with Irganoxes was found to provide a noticeable enhancement in durability to the (ABS/PC + lubricant) system. Titanium dioxide pigments by themselves have only a slight influence on the oxidative stability of the ABS/PC blend. Durability of the (ABS/PC + pigment) and (ABS/PC + lubricant) systems was found to be the same and the overall protective effect of Irganox 1076 was similar in both the (ABS/PC + lubricant) and the (ABS/PC + lubricant + pigment) systems. Certain modifiers significantly improve the durability of the ABS/PC compounds, although their function may differ in the systems with and without pigments.
    Materialart: Digitale Medien
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  • 6
    ISSN: 1572-8900
    Schlagwort(e): Chemiluminescence ; oxidation ; stability ; acrylonitrile-butadiene-styrene (ABS)
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie , Energietechnik , Maschinenbau
    Notizen: Abstract The influence of lubricants, UV stabilizers, antioxidants, and metal deactivators on the resistance of ABS to thermal oxidation was studied by means of the chemiluminescence technique. Neither of the additives seems to affect significantly the induction period of oxidation. At the same time, the influence of various additives on the oxidation rate constant is remarkably different: the introduction of lubricants and UV stabilizers increases its value, while antioxidants and metal deactivators have the opposite effect. For the particular systems studied durability is decreased in samples containing the lubricant and UV stabilizers and increased in samples stabilized with the antioxidant and metal deactivator.
    Materialart: Digitale Medien
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  • 7
    Digitale Medien
    Digitale Medien
    Springer
    Journal of polymers and the environment 3 (1995), S. 199-203 
    ISSN: 1572-8900
    Schlagwort(e): Chemiluminescence ; oxidation ; stability ; acrylonitrile-butadiene-styrene
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie , Energietechnik , Maschinenbau
    Notizen: 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.
    Materialart: Digitale Medien
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  • 8
    ISSN: 1572-8765
    Schlagwort(e): carbonado ; diamond ; oxidation
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: 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.
    Materialart: Digitale Medien
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  • 9
    Digitale Medien
    Digitale Medien
    Springer
    Plasma chemistry and plasma processing 1 (1981), S. 217-232 
    ISSN: 1572-8986
    Schlagwort(e): Anodization ; oxidation ; plasma
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Technik allgemein
    Notizen: Abstract The physical processes occurring at the surface and in the bulk of an oxide during plasma oxidation or anodization are discussed. It is shown that (i) the majority of oxygen ions used in the growth are formed by electron-assisted surface processes, (ii) the nature of the oxide surface and especially the presence of electrode contamination can have a determinant role in the oxygen exchange between the plasma and the oxide, and (iii) ion space charge can control the anodization kinetics. Two applications (formation of the insulating barrier of Josephson junctions, and GaAs MOSFET devices) are presented.
    Materialart: Digitale Medien
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  • 10
    Digitale Medien
    Digitale Medien
    Springer
    Plasma chemistry and plasma processing 6 (1986), S. 27-38 
    ISSN: 1572-8986
    Schlagwort(e): AC discharge ; discharge chemistry ; hydrogen cyanide ; cyanogen ; chemiluminescence ; oxidation
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Technik allgemein
    Notizen: Abstract The AC high-voltage discharge-induced decomposition chemistry of trace levels of hydrogen cyanide in helium has been studied. In the absence of oxygen only low levels of molecular nitrogen were evolved. With oxygen added, the principal products were CO, CO2, and N2. No significant concentrations of NO or N2O were observed. The response of a commercial NOx analyzer to HCN and C2N2, in the NOx mode, was determined to be linear through three decades in concentration. The oxidation chemistry of HCN and C2N2 in the stainless steel converter of the analyzer was studied as a function of the amount of added oxygen.
    Materialart: Digitale Medien
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  • 11
    ISSN: 1572-8986
    Schlagwort(e): RF SiCl4 discharge ; mass spectrometry ; kinetics ; decomposition ; oxidation
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Technik allgemein
    Notizen: 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.
    Materialart: Digitale Medien
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  • 12
    Digitale Medien
    Digitale Medien
    Springer
    Plasma chemistry and plasma processing 19 (1999), S. 131-151 
    ISSN: 1572-8986
    Schlagwort(e): Styrene ; oxidation ; silent discharge ; plasma ; dielectric barrier
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Technik allgemein
    Notizen: 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.
    Materialart: Digitale Medien
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  • 13
    Digitale Medien
    Digitale Medien
    Springer
    Plasma chemistry and plasma processing 19 (1999), S. 383-394 
    ISSN: 1572-8986
    Schlagwort(e): Nonthermal plasma ; benzene ; Al2O3 ; BaTiO3 ; oxidation ; absorption ; atmospheric pressure
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Technik allgemein
    Notizen: 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.
    Materialart: Digitale Medien
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  • 14
    Digitale Medien
    Digitale Medien
    Springer
    Plasma chemistry and plasma processing 19 (1999), S. 421-443 
    ISSN: 1572-8986
    Schlagwort(e): Streamer corona ; NO x removal ; nonthermal plasma ; oxidation ; reduction
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Technik allgemein
    Notizen: 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.
    Materialart: Digitale Medien
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  • 15
    Digitale Medien
    Digitale Medien
    Springer
    Oxidation of metals 28 (1987), S. 195-211 
    ISSN: 1573-4889
    Schlagwort(e): Uranium ; corrosion ; oxidation ; liquid metal
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: Abstract The reactions of water vapor and oxygen with liquid uranium were studied by modulated molecular-beam mass spectrometric methods. Equivalent pressures of the reactant fluxes on the surface ranged from 6×10 −6 to 2×10−4 torr. Temperatures up to 1570 K were investigated. The metal surface was kept clean during reaction by mechanical removal of the oxide formed with a tungsten needle. For the clean liquid uranium surface, a water reaction probability of ∼0.4 was deduced both from measurement of the reaction-product hydrogen signal and by the temperature dependence of the scattered reactant signal. Based solely on the latter measure, a reaction probability of 0.6 was estimated for oxygen. The reaction probabilities on the clean surface were temperatureindependent. They decreased as the coverage of the surface by islands of oxide increased and, for water, appeared to approach a value of 0.08 for a surface completely covered with an oxide estimated to be 500 Å thick. Bombardment of the surface during reaction with argon ions produced an increase in the reactivity on solid uranium but had a negligible effect on the reaction probability for the liquid.
    Materialart: Digitale Medien
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  • 16
    Digitale Medien
    Digitale Medien
    Springer
    Oxidation of metals 28 (1987), S. 353-389 
    ISSN: 1573-4889
    Schlagwort(e): Grain growth ; nickel oxide ; high temperature ; oxidation ; nickel
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: Abstract In systems such as the oxidation of nickel, in which grain-boundary diffusion in the oxide can control the rate of oxidation, understanding of the factors governing the grain structure is of importance. High-purity mechanically polished polycrystalline nickel was oxidized at 700°C, 800°C, and 1000°C for times up to 20 hr in 1 atm O2. The scale microstructures were examined by parallel and transverse cross section transmission electron microscopy (TEM) and scanning electron microscopy (SEM). Texture coefficients were found by X-ray diffraction (XRD). Each grain in the transverse section grain boundary networks was systematically analyzed for width parallel to the Ni-NiO interface and perpendicular length, for boundary radius of curvature and for number of sides. The variation of these parameters with depth in the scale was examined. In particular, grains were increasingly columnar (i.e., with ratio of grain length to width 〉1) at higher temperatures and longer times. Columnar grain boundaries tended to be fairly static; the columnar grain width was less than the rate controlling grain size predicted from the oxidation rate. The mean boundary curvature per grain provided a guide to the tendency for grain growth, except in the region of the Ni-NiO interface, where the boundaries were thought to be pinned.
    Materialart: Digitale Medien
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  • 17
    Digitale Medien
    Digitale Medien
    Springer
    Oxidation of metals 10 (1976), S. 347-359 
    ISSN: 1573-4889
    Schlagwort(e): oxidation ; nickel-chromium alloys ; Group III–V elements ; reactive minor additions
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: Abstract The corrosion of a number of experimental ternary Ni-15 wt. % Cr-0.5wt. %X alloys (where X= Y, La, Ce, Sm, Th, U, Zr, or V) has been assessed in pure oxygen at 900° C for periods of exposure up to 450 hr, and compared with the behavior of an Ni-15% Cr control alloy. It has been established that while all of the alloys oxidize in accordance with a protective, approximately parabolic regime, considerable differences in oxidation rates are exhibited. In particular, additions of La, Ce, and Th bring about progressively enhanced rates of oxidation relative to the binary alloy, whereas Y, Sm, V, U, and Zr effect increasingly reduced rates of oxidation in the order given. The rate constant for the Th-bearing alloy is about two orders of magnitude larger than that for the alloy containing Zr. Such differences in behavior seem to be associated with subtle variations in the morphology/composition of the corrosion products from alloy to alloy. The observations are considered in the light of earlier published literature concerning the effects of rare-earth and other reactive elements on the oxidation behavior of Ni/Cr alloys.
    Materialart: Digitale Medien
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  • 18
    Digitale Medien
    Digitale Medien
    Springer
    Oxidation of metals 10 (1976), S. 189-223 
    ISSN: 1573-4889
    Schlagwort(e): oxidation ; platinum ; platinum-aluminum alloys ; alumina (Al2O3) ; oxide-scale adhesion
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: Abstract The development, growth, and adhesion of α-Al2O3 scales on platinum-aluminum alloys containing between 0.5 and 6 wt.% aluminum have been studied at temperatures in the interval between 1000 and 1450° C. The morphologies and microstructures of the α-Al2O3 scales were found to be influenced by the temperature, oxygen pressure, and the microstructures of the alloys. The oxidation rates of the alloys appeared to be controlled by transport of oxygen along grain boundaries in the α-Al2O3 scales. The α-Al2O3 scales adhered to the platinum-aluminum substrates even after extensive periods of cyclic oxidation. The good adhesion of the α-Al2O3 may result from mechanical keying of the oxide to the alloys due to the development of irregular oxide-alloy interfaces.
    Materialart: Digitale Medien
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  • 19
    Digitale Medien
    Digitale Medien
    Springer
    Oxidation of metals 10 (1976), S. 277-289 
    ISSN: 1573-4889
    Schlagwort(e): alloy ; iron ; aluminum ; silicon ; oxidation
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: Abstract Silicon or chromium can be used as an oxygen getter in iron-aluminum alloys to prevent the internal oxidation of aluminum. This suppresses the formation of the iron oxide nodules that tend to destroy binary iron-aluminum alloys during high-temperature oxidation. Alloys of iron containing aluminum and silicon in varying proportions were heated in flowing air for 50 hr at 1093°C. Of the alloys tested, one containing 6% aluminum and 1 % silicon was the most resistant to oxidation.
    Materialart: Digitale Medien
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  • 20
    Digitale Medien
    Digitale Medien
    Springer
    Oxidation of metals 10 (1976), S. 311-327 
    ISSN: 1573-4889
    Schlagwort(e): defect structure ; CoO ; oxidation
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: Abstract The total concentration of point defects and deviation from stoichiometry in Co1-yO have been determined experimentally as functions of temperature and equilibrium oxygen pressure in the temperature range 1000–1250°C and oxygen pressure range 10−3-1 atm. This total concentration of defects has also been calculated from known values of the coefficients of chemical diffusion and tracer self-diffusion of cobalt. The results of the two methods agree well. It has been found in the investigated range of temperature and oxygen pressure that the defect structure of cobaltous oxide is composed not only of defects due to deviation from stoichiometry, singly ionized cation vacancies, and an equivalent amount of electron holes, but also of intrinsic defects, probably of the Frenkel type.
    Materialart: Digitale Medien
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  • 21
    Digitale Medien
    Digitale Medien
    Springer
    Oxidation of metals 10 (1976), S. 341-345 
    ISSN: 1573-4889
    Schlagwort(e): α-Al2O3 ; platinum ; oxidation ; adhesion
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: Abstract The influence of externally located platinum on the isothermal stability of α-Al2O3 scales formed at high temperatures has been examined. It has been observed that a nickel-base alloy forms an external scale of α-Al2O3 during oxidation at 1200°C, but this scale breaks down isothermally, enabling a faster-growing Cr2O3-rich scale to develop. However, in the presence of platinum metal alongside the specimen in the furnace hot zone, the breakdown of the α-Al2O3 scale is postponed for a substantial period of time. It appears that platinum, as the volatile species PtO2, is incorporated into the growing α-Al2O3 scale where it either influences the stress relief mechanism at temperature or reduces oxidation growth stress generation and thus significantly enhances the isothermal stability of the scale.
    Materialart: Digitale Medien
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  • 22
    Digitale Medien
    Digitale Medien
    Springer
    Oxidation of metals 10 (1976), S. 377-401 
    ISSN: 1573-4889
    Schlagwort(e): oxidation ; iron ; Mössbauer ; electron re-emission ; ERM spectroscopy
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: Abstract The results of an electron re-emission Mössbauer (ERM) spectroscopy study of the oxidation of metallic Fe at temperatures from 150 to 500°C in pure oxygen ( $${\text{p}}_{{\text{O}}_{\text{2}} } \approx {\text{ }}10$$ Torr) are presented. The oxidized samples were prepared from a metallic Fe sample enriched to 70% in the Mössbauer isotope Fe57 and the oxidation kinetics were determined volumetrically. Scanning electron microscopy was employed to characterize the morphology of the oxide films. The hematite, magnetite, and total-oxide thicknesses were determined from the ERM spectra using a theory recently developed in this laboratory, and the results were found to agree well with the measured oxygen content of the oxide films. For Fe and Fe-base alloys it is shown that the ERM technique is most useful in the oxide-thickness range of approximately 20–3000 Å within that range, oxide-phase identifications and thickness determinations are perhaps more readily determined by ERM spectroscopy than by any competing technique. In particular, the ERM measurement is nondestructive, and no supplementary measurements (such as surface-roughness determinations) or special sample preparations (such as oxide-film stripping) are required
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  • 23
    Digitale Medien
    Digitale Medien
    Springer
    Oxidation of metals 11 (1977), S. 57-62 
    ISSN: 1573-4889
    Schlagwort(e): oxidation ; scale growth
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: Abstract Equations are presented to modify the classical theoretical expressions for the parabolic rate constant for the case in which the scale has a large composition range and a large variation in molar volume. The modifications appear as simple averages, together with a factor f.Evaluation of f for some hypothetical cases shows that it is near unity unless the composition gradient has an extreme deviation from linearity.
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  • 24
    Digitale Medien
    Digitale Medien
    Springer
    Oxidation of metals 11 (1977), S. 193-198 
    ISSN: 1573-4889
    Schlagwort(e): oxidation ; scaling ; wustite ; magnetite ; iron
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: Abstract The theory of the growth of two oxide layers by Yurek et al. has been applied to the oxidation of iron at 1100° C. The theoretical parabolic rate constants for the simultaneous growth of the two oxide layers were calculated from radioactive tracer diffusion coefficients for wustite and magnetite. Good agreement was found between the theoretical and experimental values of the ratio of scale thicknesses.
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  • 25
    Digitale Medien
    Digitale Medien
    Springer
    Oxidation of metals 12 (1978), S. 227-245 
    ISSN: 1573-4889
    Schlagwort(e): oxidation ; sulfidation ; iron-chromium-nickel alloy ; thermochemical diagram ; parabolic rate constant
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: Abstract Oxidation-sulfidation studies of Fe-Cr-8Ni alloys with 4, 12, and 22 wt. % Cr were conducted at 750 and 875°C in multicomponent gas mixtures that contained CO, CO2, CH4, H2, and H2S. The reaction processes resulted in parabolic kinetics. A chromium concentration in the range 0–12 wt. % in the alloy had a negligible effect on the parabolic rate constant; however, the rate constant for the alloy with 22 wt. % Cr was significantly lower. For a given sulfur partial pressure, the oxygen partial pressures required for the formation of a continuous oxide layer in an Fe-22Cr-8Ni alloy were ∼102 to 103 times those calculated for Cr-Cr2O3 equilibrium at temperatures of 875 and 750° C, respectively.
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  • 26
    Digitale Medien
    Digitale Medien
    Springer
    Oxidation of metals 12 (1978), S. 451-471 
    ISSN: 1573-4889
    Schlagwort(e): HCl gas ; H2O vapor ; Ni-Cr-Al alloy ; oxidation ; hot corrosion
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: Abstract Moist air containing HCl gas caused the oxide formed on a Ni-Cr-Al alloy at 850°C to crack during the early stages of growth, and extensive blistering and spalling occurred on cooling. In dry air containing HCl gas no oxide cracking was observed at temperature although the oxide blistered and spalled on cooling. In dry or moist air free from HCl an adherent protective oxide formed which did not spall on cooling. The oxide cracking at temperature has been attributed to the production of hydrogen by reaction of Cr and Al in the alloy with water vapor and the removal of NiO as NiCl2 by reaction with HCl gas. Hydrogen produced by reaction of water vapor or HCl with Cr or Al dissolved in the alloy at temperature, but on cooling the hydrogen was released, causing the oxide to blister and spall. Preoxidation of the alloy in HCl-free atmospheres eliminated these effects of HCl gas in short-term isothermal tests.
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  • 27
    ISSN: 1573-4889
    Schlagwort(e): ion implantation ; oxidation ; thermal ; stainless steel ; ion-beam analysis ; aluminum
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: Abstract AISI-321 steel samples were implanted with Al ions (implantation-energy:40 keV; dose: 2×1017 ions/cm2). Thermal oxidationof the samples was performed at 450, 550, 600, and 650°C for periodsvarying from 1 to 6 days in air and in a corrosive CO2-containingenvironment. Nuclear Reaction Analysis (NRA) and Rutherford BackscatteringSpectrometry (RBS) were used to investigate the oxidized samples. Asignificant improvement of the oxidation resistance of the implantedmaterial in comparison to the nonimplanted material was observed. Thisespecially applies for samples oxidized at high temperatures. The aluminumdepth distribution determined by NRA [using the resonance at 992 keV of the27Al(p, γ )28Si nuclear reaction] and RBS,indicated no variation of the Al profile in the temperature region450–600°C, whereas at 650°C a slight Al diffusion wasobserved. Scanning electron microscopy (SEM–EDS) was applied to studythe surface morphology and the constitution of the oxide scale formed, aswell as to explain the influence of Al implantation on the oxidation behaviorof AISI-321 austenitic stainless steel.
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  • 28
    Digitale Medien
    Digitale Medien
    Springer
    Oxidation of metals 53 (2000), S. 467-479 
    ISSN: 1573-4889
    Schlagwort(e): Ni–5Cr–5Al ; oxidation ; magnetron sputtering ; nanocrystalline coating
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: Abstract A NiO-forming Ni–5Cr–5Al (at.%) alloy has been developed anddeposited as a sputtered nanocrystalline coating. The oxide formation andoxidation behavior of this coating have been studied at 1000°C inair. The oxidation rate markedly decreased with time and the oxidationkinetics obeyed the fourth power law. Complex oxide scales, consisting ofNiO, NiAl2O4 and α-Al2O3,were formed during 200 hr oxidation. The outer oxide layer consisted of NiOand NiAl2O4 and an inner oxide layer ofα-Al2O3. The sputtered Ni–5Cr–5Alnanocrystalline coating showed good oxidation resistance due to theformation of an α-Al2O3 inner layer andexcellent adhesion of the complex oxide scales.
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  • 29
    Digitale Medien
    Digitale Medien
    Springer
    Oxidation of metals 53 (2000), S. 529-537 
    ISSN: 1573-4889
    Schlagwort(e): ion plating ; steel ; TiAlN coating ; oxidation
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: Abstract To improve the high-temperature oxidation resistance of STD61 steels used ashot dies or cutting tools, Ti0.3Al0.2N0.5films were deposited on STD61 steel substrates by arc-ion plating. Thedeposited film consisted of Ti3Al2N2 andTi2N phases. The oxidation characteristics were studied attemperatures ranging from 700 to 900°C in air. The deposited STD61steels displayed excellent oxidation resistance up to 800°C, butexhibited large weight gains and breakaway oxidation at 900°C. Theoxidation products were primarily Fe2O3, TiO, TiO2,and α-Al2O3, the relative amount of each oxidebeing dependent on the oxidation condition. Among various oxides, TiO2and α-Al2O3 were the major oxides at 800°Cfor at least up to 16 hr. However, at a higher temperature or a longeroxidation period, the significant outward diffusion of iron from thesubstrate resulted in the formation of iron oxides, together with otheroxides of Ti and Al.
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  • 30
    Digitale Medien
    Digitale Medien
    Springer
    Oxidation of metals 54 (2000), S. 155-162 
    ISSN: 1573-4889
    Schlagwort(e): Ni–8Cr–3.5Al ; nanocrystallization ; oxidation
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: Abstract Magnetron-sputter deposition was used to produce a Ni–8Cr–3.5Al(wt.%) nanocrystalline coating on substrates of the same alloy. Theoxidation behavior of the cast Ni–8Cr–3.5Al alloy and itssputtered coating were investigated at 1000°C in air. Complex,layered-oxide scales composed of Cr2O3 outer layer,mixed spinel NiAl2O4 and NiCr2O4middle layer, and α-Al2O3 inner layer were formedon the Ni–8Cr–3.5Al nanocrystalline coating during 200-hroxidation, whereas Cr2O3, with some NiCr2O4external layer with internal Al2O3, formed on the castalloy. Because of the formation of this α-Al2O3inner layer on the coating, the sputtered Ni–8Cr–3.5Al coatingshowed better oxidation resistance than the cast alloy. The effect ofnanocrystallization on oxide formation is discussed. It was indicated thatthe formation of this α-Al2O3 inner layer was closely related to therapid diffusion of Al through grain boundaries in the nanocrystallinecoating and the relatively high Cr content in Ni–8Cr–3.5Al.
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  • 31
    Digitale Medien
    Digitale Medien
    Springer
    Oxidation of metals 54 (2000), S. 189-209 
    ISSN: 1573-4889
    Schlagwort(e): oxidation ; β-FeAlCr ; coatings ; magnetron sputter-deposition ; ridge-type oxide ; Al2O3 phase transformation
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: Abstract β-FeAl coatings containing various Cr contents of 6.5–45 wt.%were produced with a closed-field, unbalanced magnetron sputter (CFUMS)deposition technique. Cyclic oxidation tests at 1100°C in air for100 1-hr cycles and isothermal exposures at 1000°C in pure O2 for100 hr were carried out with the coatings and an as-cast FeAlspecimen. All of the coatings showed good scale-spallation resistanceduring cyclic oxidation and the coating with 6.5 wt.% Cr exhibited thelowest oxidation rates in both cyclic and isothermal oxidationexposures. After oxidation, fine-grain ridge-type oxide scales formed onthe coatings, while the oxide scale formed on the cast FeAl showed alarge quantity of θ-Al2O3 blades and large interfacial voids on thebase–alloy surface. The transformation from θ to α-Al2O3was accelerated due to the presence of Cr in the coatings. The fasttransformation considerably reduced oxidation rates, suppressed fastoutward Al diffusion for the growth of a θ-Al2O3 scale, and preventedthe formation of interfacial voids that played a major role in causing thescale spallation.
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  • 32
    Digitale Medien
    Digitale Medien
    Springer
    Oxidation of metals 54 (2000), S. 549-558 
    ISSN: 1573-4889
    Schlagwort(e): plasma spraying ; chromium steel ; oxidation ; Fe–Cr spinel oxide
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: Abstract During plasma spraying of metals in air, rapid-oxidation reactions occur, inmost cases. In oxidation products of Cr-rich steels, Fe–Cr spineloxide is often found as a dominant oxide phase. A thermodynamic analysisof a system composed of Fe–13%Cr alloy and water vapor or air showedthat the oxidation product in a wide range of high temperatures isFe3-wCrwO4 (w〉2). This tetragonallydistorted spinel oxide is not stable at room temperature. Water vapor andair were considered as limits of the gaseous-phase composition inatmospheric spraying by a water-stabilized plasma gun, where the compositionof the plasma plume is modified by air entrainment. The equilibriumcalculations enabled determination of the effects of temperature andgas-to-solid ratio on w. To show the existence of chromium-rich,tetragonally distorted spinel oxide experimentally, a typical productresulting from oxidation of 13%Cr–steel particles during their flightin the plasma plume was studied after rapid solidific ation. This was madepossible by trapping and quenching the flying particles in liquid nitrogenat a distance from the plasma-gun nozzle corresponding to thenozzle–substrate distance in conventional plasma spraying. The resultsobtained by X-ray diffraction, Mössbauer spectroscopy, and X-rayfluorescence analysis showed that this oxide, in which w≈2.4, constitutedthe dominant phase in the oxidation product.
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  • 33
    Digitale Medien
    Digitale Medien
    Springer
    Oxidation of metals 8 (1974), S. 393-407 
    ISSN: 1573-4889
    Schlagwort(e): cobalt alloys ; oxidation ; manganese
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: Abstract Earlier studies have suggested that manganese might be attractive as an alternative fcc stabilizer to nickel in cobalt base alloys because of its beneficial effect on the sulfidation resistance. Because it has relatively high oxygen affinity, it seemed possible that it might modify the ability of the alloys to form a protective Cr 2O3 scale. Thus, a range of alloys having compositions close to the critical Co-20 Cr value have been investigated in the temperature range 900–1150° C for times up to 240 hr in air and oxygen. Similar, but less extensive studies, have been conducted on alloys containing iron or nickel. None of these elements has a significant effect on the oxidation behavior, or on the ability of the alloys to develop a protective Cr 2O3 layer. However, manganese has a significant adverse effect on the scale spallation, apparently because of its increasing the brittleness of the oxide, particularly the CoO.
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  • 34
    Digitale Medien
    Digitale Medien
    Springer
    Oxidation of metals 9 (1975), S. 45-67 
    ISSN: 1573-4889
    Schlagwort(e): oxidation ; hot corrosion ; nickel alloys ; composites
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: Abstract The oxidation and hot corrosion behavior of a tungsten-fiber, reinforced Ni~ 20Cr alloy has been examined under the following exposure conditions: (a) pure oxygen at 1 atm pressure; (b) sulfidation in H2–10 %H2S; (c) presulfidation in H2–10 %H2S followed by oxidation in oxygen; and (d) oxidation in 1 atm oxygen after precoating with approximately 1 mg/cm2 of Na2SO4. Rapid oxidation of the tungsten fibers causes considerable distortion of the matrix and catastrophic degradation of the matrix follows. Inter diffusion between the matrix and the fibers is also important. During sulfidation, only the matrix forms sulfides, the fibers remaining unaffected. Consequently, presulfidation, although having a dramatic effect on the oxidation of the matrix does not have a damaging effect on the fibres. Equally, the presence of sodium sulfate is not critical, although severe oxidation of the exposed tungsten fibers is still observed.
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  • 35
    ISSN: 1573-4889
    Schlagwort(e): dilute alloys ; oxidation ; Wagner-Hauffe rule
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: 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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  • 36
    Digitale Medien
    Digitale Medien
    Springer
    Oxidation of metals 9 (1975), S. 275-305 
    ISSN: 1573-4889
    Schlagwort(e): oxidation ; Ni-Cr alloys ; rare-earth oxide dispersion ; dispersion-strengthened alloys
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: Abstract The oxidation behavior of Ni-20%Cr alloys containing approximately 3 vol.% Y2O3, ThO2, and A12O3 as dispersed particles has been examined in the temperature range 900 to 1200° C in slowly flowing oxygen at 100 Torr. The results show that the oxidation behavior of the Y2O3-, ThO2-, Al2O3-, and Ce02-containing alloys is very similar and that some anomalies in the behavior of the ThO2-containing alloy might be explained by the slower rate of chromium diffusion in this coarse-grained alloy. Two Al2O3-containing alloys were studied. One with a relatively coarse dispersoid size behaved in a manner analogous to a dispersion-free Ni-30% Cr alloy at 1100°C. The other alloy contained a dispersion of fine Al2O3 particles and behaved exactly like the Y2O3-containing alloy at 1000 and 1100°C, but at 1200° C oxidized at a faster rate. It has been shown that the adherent scales on dispersion-containing alloys have a stabilized fine grain size, whereas the nonadherent scales on dispersion-free alloys undergo grain growth.
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  • 37
    ISSN: 1573-4889
    Schlagwort(e): oxidation ; copper ; Li-doped copper ; Cr-doped copper ; short-circuiting ; Mott's parabola ; Wagner's parabola
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: 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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  • 38
    Digitale Medien
    Digitale Medien
    Springer
    Oxidation of metals 46 (1996), S. 109-127 
    ISSN: 1573-4889
    Schlagwort(e): oxidation ; Ni3Al base alloy ; chromium ; cobalt ; titanium
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: 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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  • 39
    Digitale Medien
    Digitale Medien
    Springer
    Oxidation of metals 47 (1997), S. 381-410 
    ISSN: 1573-4889
    Schlagwort(e): Ni-Base superalloys ; Astroloy ; Waspaloy ; Udimet 720 ; oxidation ; chromia
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: 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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  • 40
    ISSN: 1573-4889
    Schlagwort(e): oxidation ; Incoloy 909 ; superalloy ; scale ; high temperature ; kinetics
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: 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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  • 41
    Digitale Medien
    Digitale Medien
    Springer
    Oxidation of metals 47 (1997), S. 445-464 
    ISSN: 1573-4889
    Schlagwort(e): oxidation ; Fe-Cr-Al alloy ; water vapor ; ESCA ; RHEED
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: 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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  • 42
    Digitale Medien
    Digitale Medien
    Springer
    Oxidation of metals 47 (1997), S. 507-524 
    ISSN: 1573-4889
    Schlagwort(e): alloys ; high temperature ; oxidation ; transient state
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: 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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  • 43
    ISSN: 1573-4889
    Schlagwort(e): high temperatures ; oxidation ; transient state
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: Abstract The transient state in the oxidation of solid solutions of a most-noble componentA in a most-reactive componentB (beta phase) for binaryA-B alloys presenting a limited reciprocal solubility of the two metals has been examined assuming that theirB content is sufficient for the exclusive growth of externalBO scales. Above a criticalB content of the alloy theBO scales may grow directly on the surface of the beta phase, while below this limit they can only form over a layer ofB-depleted solid solution ofB inA (alpha phase), which appears after a critical time. An approximate analytical expression for the profile of concentration ofB in the alloy has been adopted to calculate the flux ofB in the metal. Moreover, the effect of the reaction between the gas and the external oxide surface has been taken into account using a procedure developed by Wagner for the oxidation of pure metals. The corrosion kinetics as well as all the parameters involved, such as the concentration ofB at the alloy-scale interface, have been calculated as functions of the corrosion time. The results show that, as time proceeds, the instantaneous parabolic rate constant increases and the concentration ofB at the alloy-scale interface decreases, both tending gradually to their corresponding steady-state values. It is also predicted that if the rate of transformation of the beta phase in the alpha phase after the alloy reaches the composition of equilibrium at the interface with the oxide is lower than the corresponding rate of displacement of the alloy surface due to scale growth, the corrosion of beta phase alloys may eventually lead to the formation of two phase mixtures of alpha phase andBO which are expected to grow at much larger rates than in the presence of a uniform continuous alpha layer.
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  • 44
    Digitale Medien
    Digitale Medien
    Springer
    Oxidation of metals 48 (1997), S. 1-39 
    ISSN: 1573-4889
    Schlagwort(e): Ni-base ODS superalloys ; oxidation ; initial stages of oxidation ; alumina ; chromia
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: Abstract Mechanically-alloyed Ni-base ODS superalloys currently receive attention for application in future gas turbines because they exhibit outstanding mechanical properties at high temperatures. They also protect themselves against oxidation by forming chromia and/or alumina scales. However, little attention has been given so far to the initial stages of oxidation of Ni-base ODS superalloys, containing Cr as well as Al in considerable amounts. In the current work, oxidation at 1150°C was studied for different holding times up to 200 hr for the commercial materials MA6000 and PM3030 which contain. Al in increasing amounts. MA 754, a chromia former, was investigated as a reference. It was shown that for the potential alumina formers MA6000 and PM3030 the continuity and therefore protectiveness of the secondary Al2O3 at later stages is indeed determined by the initial stages of oxidation.
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  • 45
    Digitale Medien
    Digitale Medien
    Springer
    Oxidation of metals 48 (1997), S. 129-141 
    ISSN: 1573-4889
    Schlagwort(e): decarburization ; nickel ; oxidation
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: Abstract A commercial-grade nickel containing small amounts of carbon, manganese, and silicon was exposed to air for periods up to 288 hr at 1050°C to study the effect of oxidation on the formation of oxides of these impurity elements. Exposure of nickel to air led to decarburization. The maximum amount of decarburization occurred during the initial period of air exposure and the loss in carbon was more in the metal with a smaller section size. Decarburization in the metal produced voids in the oxide scale due to the formation of CO2 gas. It has been shown further that CO and/or CO2 gas bubbles, which form in high purity nickel on grain boundaries during exposure to air at elevated temperatures, cannot exist in commercial-grade nickel where manganese is present as an impurity. Instead, oxides of manganese form in the grain boundaries as well as in the matrix. This is because manganese oxide is more stable than CO or CO2 gas.
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  • 46
    ISSN: 1573-4889
    Schlagwort(e): oxidation ; kinetics ; iron ; iron-nitride
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: Abstract The oxidation of α-Fe and ɛ-Fe2N1−z at 573 K and 673 K in O2 at 1 atm was investigated by thermogravimetrical analysis, X-ray diffraction, light-optical microscopy, scanning electron microscopy and electron probe X-ray microanalysis. Upon oxidation at 573 K and 673 K, on α-Fe initially α-Fe2O3 develops, whereas on ɛ-Fe2N1−z initially Fe3O4 develops. In an early stage of oxidation the oxidation rate of ɛ-Fe2N1−z appears to be much larger than of α-Fe. This can be attributed largely to an effective surface area available for oxygen uptake, which is much larger for ɛ-Fe2N1−z than for α-Fe due to the porous structure of ɛ-Fe2N1−z as prepared by gaseous nitriding of iron. The development of a magnetite layer in-between the hematite layer and the α-Fe substrate, at a later stage of oxidation, enhances layer-growth kinetics. After 100 min oxidation at 673 K the (parabolic) oxidation rates for α-Fe and ɛ-Fe2N1−z become about equal, indicating that on both substrates the oxide growth is controlled by the same rate limiting step which is attributed to short-circuit diffusion of iron cations. Oxidizing ɛ-Fe2N1−z increases the nitrogen concentration in the remaining ɛ-iron nitride, because the outward flux of iron cations, necessary for oxide growth, leads to an accumulation of nitrogen atoms left behind.
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  • 47
    Digitale Medien
    Digitale Medien
    Springer
    Oxidation of metals 48 (1997), S. 201-214 
    ISSN: 1573-4889
    Schlagwort(e): titanium-aluminum alloys ; niobium ; intermetallics ; oxidation
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: Abstract In a recent study, CO2 has been reported to enhance the oxidation rate of binary titanium-aluminum alloys. The detrimental effect of CO2 was not, however, observed in a ternary alloy containing niobium. In this paper, possible explanations for these observations are examined. First, results from the literature regarding the effects of niobium in improving the resistance of titanium-aluminum alloys are briefly reviewed. Second, a thermodynamic analysis which offers a possible explanation for the beneficial effect of niobium in eliminating the CO2-enhanced oxidation of titanium-aluminum alloys is presented.
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  • 48
    Digitale Medien
    Digitale Medien
    Springer
    Oxidation of metals 48 (1997), S. 215-224 
    ISSN: 1573-4889
    Schlagwort(e): nanocrystallization ; oxidation ; mechanism
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: Abstract Many mechanisms for the effect of reactive elements on the selective oxidation and scale adhesion of alloys have been proposed. However, nanocrystallization (or microcrystallization) has recently been found to have almost the same effect as that of reactive elements. This note reviews the effect of nanocrystallization on the selective oxidation and adhesion of Al2O3 scale with particular reference to the author's own results.
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  • 49
    Digitale Medien
    Digitale Medien
    Springer
    Oxidation of metals 48 (1997), S. 289-302 
    ISSN: 1573-4889
    Schlagwort(e): oxidation ; titanium ; rutile ; scale ; high temperature ; kinetics
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: Abstract The oxidation behavior of pure titanium has been investigated in the temperature range of 1000 K to 1300 K in CO2 or Ar-10%CO2. Optical microscopy, electron probe microanalyses, and X-ray measurements on the oxide scales formed during oxidation indicate that their structures are nearly independent of temperature and the corrosion atmosphere. The scales consisted of two layers, an external one and an internal one, having a rutile (TiO2) structure. The parabolic rate law was confirmed for growth of the external scale and the permeation depth of oxygen in titanium with apparent activation energies of 266 and 226 kJ/mol, respectively. The rate-determining diffusion species in the oxidation processes are discussed.
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  • 50
    Digitale Medien
    Digitale Medien
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    Oxidation of metals 48 (1997), S. 329-345 
    ISSN: 1573-4889
    Schlagwort(e): zirconium ; X-ray diffraction ; oxidation ; phase analysis ; texture
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: Abstract The oxidation of zirconium at high temperature (T〉 400°C) leads to reaction products of two allotropic oxide (ZrO2 monoclinic and ZrO2 tetragonal). The distribution and proportion of these two phases were studied as a function of time and space by X-ray diffraction techniques. Quantitative analyses are possible after some corrections, and we demonstrate the presence of a phase gradient in the oxide scale. The interest of this nondestructive method is then discussed.
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  • 51
    Digitale Medien
    Digitale Medien
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    Oxidation of metals 48 (1997), S. 357-380 
    ISSN: 1573-4889
    Schlagwort(e): chromium ; copper ; binary alloys ; two-phase alloys ; oxidation ; high temperatures
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: Abstract The oxidation in air of three two phase Cu-Cr alloys with nominal Cr contents of 25, 50, and 75 wt. % was studied at 700–900°C. The alloys corroded nearly parabolically, except at 900°C, when the corrosion rates decreased with time more rapidly than predicted by the parabolic rate law. The corrosion rate decreased for higher Cr contents in the alloy under constant temperature and generally increased with temperature for the same alloy composition. The scales were complex and consisted in most cases of an outermost copper oxide layer free from chromium and an inner layer composed of a matrix of copper oxide or of the double oxide Cu2Cr2O4, often containing particles of chromium metal surrounded by chromia and then by the double oxide. Metallic copper was also frequently mixed with chromia. Cr-rich regions tended to form continuous chromia layers at the base of the scale, especially at the highest temperature. No chromium depletion was observed in the alloy.
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  • 52
    ISSN: 1573-4889
    Schlagwort(e): iron ; oxidation ; CeO2 coating ; in situ ; growth stress ; residual stress ; texture ; X ray diffraction
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: Abstract In situ XRD stress determinations have been performed during oxidation of pure iron (p(O2=2 × 10−3 Pa,T=800°C)). The compressive stress, initially present in the substrate due to surface preparation, is completely released at 400°C. Under the test conditions, the in situ compressive-stress level determined in the FeO scale during oxidation is not strongly dependent upon the presence of a ceria coating. On blank and coated specimens, the compressive stress varies from −400 ± 80 MPa to −150 ± 100 MPa during 30 hr oxidation. The decrease is quicker at the beginning of the test performed on blank specimens. Epitaxial relationships between the wüstite scale and iron (under low-pressure starting conditions) caused thein situ compressive stress in the oxide scale to be two times greater compared to the usual test conditions. This indicates that epitaxial relationships can be a source of stress in an oxide scale that ceria coatings may lower compressive stresses.
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  • 53
    Digitale Medien
    Digitale Medien
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    Oxidation of metals 48 (1997), S. 527-551 
    ISSN: 1573-4889
    Schlagwort(e): chloridation ; oxidation ; Fe-Cr alloys ; Ni-Cr alloys
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: Abstract The chloridation-oxidation behavior of Fe-Cr (0–25 wt. %Cr) and Ni-Cr (0–20 wt.%Cr) alloys was studied at 800°C in three different H2-HCl-H2O(ν) environments. In a low-HCI and low-H2O(ν) environment, where Cr2O3 is thermodynamically stable, the corrosion resistance of the Fe-Cr alloys increased with increasing Cr content in the alloys. In a high-HCl and high-H2O(ν) environment, where FeCr2O4 is stable and CrCl2 is metastable, the corrosion resistance of the Fe-Cr alloys depended similarly on the Cr content. Low-Cr-Fe-Cr alloys exhibited large weight losses, while Fe-Cr alloys with higher than 19 wt. %Cr showed good corrosion resistance. In an environment of high-HCl in the absence of H2O(ν), the evaporative corrosion rate was fast and limited by gas phase diffusion, and independent of the Cr content in the Fe-Cr alloys. Ni and Ni-Cr alloys generally showed good corrosion resistance in the environments of high H2O(ν) because of the low NiCl2 vapor pressure and formation of a protective Cr2O3 scale. However, in the environment of high HCl in the absence of H2O(ν), selective formation and evaporation of CrCl2 occur, which results in Cr depletion and networks of voids for even a high-Cr Ni-Cr alloy.
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  • 54
    Digitale Medien
    Digitale Medien
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    Oxidation of metals 48 (1997), S. 553-596 
    ISSN: 1573-4889
    Schlagwort(e): chloridation ; oxidation ; HCl ; high-temperature alloys ; high-temperature corrosion
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: Abstract Chloridation-oxidation studies of nine commercial high-temperature alloys were carried out at 800°C in three different H2-HCl-H2O(ν) environments: (A) both low HCl and H2O(ν) partial pressures, where either Cr2O3 or FeCr2O4 is stable, (B) both high HCl and H2O(ν) partial pressures, where FeCrO4 is stable and CrCl2 is metastable, and (C) high HCl partial pressure in the absence of H2O(ν), where either CrCl2 or Cr2O3 is stable. Although alloy 600 has the lowest Cr content of these nine alloys, it showed excellent corrosion resistance in all three environments because of its high Ni content. Alloy 304, with the lowest Ni content of the nine alloys, exhibited poor corrosion resistance in the environment C, fair resistance in the environment B and good resistance in the environment A. Alloy 800 showed very good resistance in Environment A, and fair corrosion resistance in Environment B; however, it suffered linear weight-loss kinetics when exposed to Environment C The alloys 617, 214, HR-160, X, 230 and 86 have good corrosion resistance in Environments A and B because of their relatively high contents of oxide-scale-forming elements Cr and/or Al. In Environment C, chlorine dramatically decreased the adhesion of the scale on the surface, and aluminum in alloys 617 and 214 hardly showed its usual beneficial effect in combating corrosion, nor does silicon in alloy HR-160. Different corrosion mechanisms are proposed for the alloys in the different environments.
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  • 55
    Digitale Medien
    Digitale Medien
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    Oxidation of metals 9 (1975), S. 415-425 
    ISSN: 1573-4889
    Schlagwort(e): vanadium carbide ; vanadium oxycarbide ; oxidation ; parabolic rate law ; cubic rate law ; chemisorption
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: Abstract The oxidation of an oxycarbide of vanadium, VO0.6C0.7, and of a vanadium carbide, VC0.98, was studied athermally up to temperatures of 800° C and isothermally between 400 and 580° C at oxygen pressures ranging from 10−2 to 1 atm. The oxycarbide followed the parabolic rate law below 450° C with V2O5 forming as the only reaction product. The activation energy was 49 kcal/mole. VC0.98 did not form an oxide in this temperature range, but rather dissolved oxygen, the activation energy being 26.6 kcal/mole. No oxygen pressure dependence on the kinetics was found for either sample in this temperature range. Both samples followed the cubic rate law during oxidation in the range of 500–580° C during which V2O5 formed. There was a P1/3 dependence and the activation energy was the same for both materials, 51 kcal/mole. The cubic rate law and the positive pressure dependency (rather than an anticipated negative dependency) were attributed to an electric field associated with oxygen ions chemisorbed on a thin layer of V2O5.
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  • 56
    Digitale Medien
    Digitale Medien
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    Oxidation of metals 9 (1975), S. 459-472 
    ISSN: 1573-4889
    Schlagwort(e): Cr ; oxidation ; kinetics ; Cr2O3 grain size ; short-circuit diffusion ; surface ; preparation ; Fe-Cr
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: Abstract Cr was oxidized in 1 aim O2 at 980, 1090, and 1200°C. ElectropolishedCr and some orientations of etched Cr oxidize rapidly and develop compressive stress in the growing Cr2O3; other orientations oxidize slowly, apparently free of stress. SEM examination of fracture sections shows that the thick oxide is polycrystalline whereas the thin oxide on etched Cr is monocrystalline. It is deduced that the monocrystalline oxide grows by lattice diffusion of cations outward, and the polycrystalline layer by the two-way transport of cation diffusion outward and anion diffusion inward along oxide grain boundaries. The consequent formation of oxide within the body of the polycrystalline layer generates compressive stress and leads to wrinkling by plastic deformation. The activation energy for oxidation of Cr by cation lattice transport is 58 kcal/mole. Polycrystalline Cr2O3 forms on Fe-26Cr alloy, whether electropolished or etched; oxidation is accordingly rapid and accompanied by compressive stress.
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  • 57
    Digitale Medien
    Digitale Medien
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    Journal of materials synthesis and processing 8 (2000), S. 359-363 
    ISSN: 1573-4870
    Schlagwort(e): Mechanical activation ; brown coal ; electrophoretic mobility ; oxidation ; humic acids
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: Abstract This paper presents a study of the influence of mechanochemical activation of coal on the process of formation and degradation of humic acids. The increasing period of mechanical activation of coal causes an increase in hydrophility, electrophoretic mobility, and of electrokinetic potential of surface layers as a result of acidic carboxyl and phenolic OH groups. The effective activation requires a short period of grinding. The increased time of activation causes the secondary processes of grain agglomeration and degradation of humic acids.
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  • 58
    Digitale Medien
    Digitale Medien
    Springer
    Oxidation of metals 10 (1976), S. 85-95 
    ISSN: 1573-4889
    Schlagwort(e): boron carbide ; oxidation ; kinetics ; chromatography method
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: Abstract Thermogravimetry and gas-adsorption chromatography were used to study the kinetics of formation of solid and gaseous products during the hightemperature oxidation of compact boron carbide in oxygen at 740 Torr. Oxidation resistance was observed at temperatures up to 1200°C. The main oxidation products were B2O3 and CO2. Oxidation was paralinear; the carbon consumption exceeded the consumption of boron as compared to the ratio of these elements in the compound B4C. This difference resulted in carbon depletion of the carbide layer in the substrate near the scale〉.
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  • 59
    Digitale Medien
    Digitale Medien
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    Oxidation of metals 10 (1976), S. 255-276 
    ISSN: 1573-4889
    Schlagwort(e): Zircaloy-4 ; zirconium ; alloy ; oxidation ; microstructure
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: Abstract The ZrO 2 scales formed on Zircaloy-4 PWR tubes during corrosion in steam in the temperature range of 1000–1300°C have been found to contain a metallic phase that is relatively rich in Sn. The precise composition of the metallic phase has not been determined. Most of the metallic phase is located in a line of metallic particles, which is oriented parallel to the alloy-scale interface and located near the center of the scale. The exact morphology of the scale on either side of the particle line has not been identified. The oxide between the metallic particles and the scale-steam interface contains very little Sn, except for a narrow zone adjacent to the scale-steam interface, which was formed in the beginning of the reaction. It appears that the scale between the metallic particles and the alloy-scale interface consists of thin columnar grains of ZrO 2 with a very fine metallic phase probably located at the ZrO 2 grain boundaries. The experimental evidence presently available indicates that the metallic phase exists in the scales at the reaction temperature. If the metallic particles were rich enough in Sn, then a liquid metallic phase would exist in the oxide during the reaction. Kinetic studies demonstrate that these particles move with respect to the scale-steam interface toward the center of the alloy during the course of the oxidation reaction. It appears that the presence of the line of metallic particles could, under certain conditions, markedly influence the mechanical properties of the oxide scales formed on Zircaloy-4.
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  • 60
    Digitale Medien
    Digitale Medien
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    Oxidation of metals 11 (1977), S. 23-56 
    ISSN: 1573-4889
    Schlagwort(e): oxidation ; carburization ; carbonaceous gases ; superalloys ; stainless steels ; film formation ; structure of oxide scales ; preoxidation ; metal dusting
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: Abstract Formation and deterioration of oxide films on several contemporary high-temperature alloys was studied in various carbonaceous gas atmospheres. Scanning electron microscopy and metallographic examination were applied to films on Fe-Cr-Ni and Ni-Cr-Al type alloy compositions exposed in CH 4/H2 and CO/CO2 atmospheres at temperatures up to 900° C and pressures up to 900 psi (6.2 × 106 N/m2). The effects of various preoxidation treatments were evaluated. Reduction of certain oxide phases is observed to promote catalytic gas decomposition. Al2O3 components in the films are observed to be stable under the reducing conditions experienced. Carbon uptake by various alloys is found to be quite sensitive to surface finish, with an observed increase in penetration with surface roughness.
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  • 61
    Digitale Medien
    Digitale Medien
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    Oxidation of metals 11 (1977), S. 225-239 
    ISSN: 1573-4889
    Schlagwort(e): tantalum ; oxidation ; high temperature ; kinetics
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: Abstract The oxidation of tantalum in oxygen-nitrogen and oxygen-inert gas mixtures at925°C has been studied. The oxygen pressure was close to 0.5 atm in all experiments, and partial pressures of the second component of from 0 to 180 Torr were employed. Spherical specimens were used to provide quantitatively significant kinetic data. A model has been proposed which suggests that the oxygen pressure at the reaction interface close to the metal surface is lower than the external pressure because of the finite permeability of the porous outer oxide layer, and that the inert gas effectively reduces the permeability. The model gives good quantitative agreement with the experimental results.
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  • 62
    Digitale Medien
    Digitale Medien
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    Oxidation of metals 12 (1978), S. 1-22 
    ISSN: 1573-4889
    Schlagwort(e): NaCl vapor ; Ni-Cr-Al alloy ; oxidation ; hot-salt corrosion
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: Abstract A thin protective oxide formed on a Ni-19.7 Cr-2.4 Al alloy in air at 850°C. Microstructural examination of stripped films showed that the oxide was duplex with an inner chromium-rich layer of NiCr2O4 + Cr2O3 with probably some NiAl2O4 + Al2O3, and an outer nickel-rich layer, principally NiO. The oxide grew faster in the presence of NaCl and it differed significantly in microstructure and composition from a very early stage. The thicker regions of the oxide assumed regular polyhedral shapes in air + NaCl, rather than the irregular nodular shape exhibited in clean air, as well as becoming richer in chromium. The results suggest that chloride vapor increases cationic mobility in the oxide. It is proposed that Cl− ions are incorporated in the oxygen close-packed lattice, thereby increasing ionic mobility in Cr2O3.
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  • 63
    Digitale Medien
    Digitale Medien
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    Oxidation of metals 12 (1978), S. 83-110 
    ISSN: 1573-4889
    Schlagwort(e): oxidation ; iron ; chromium ; Fe-9% Cr alloy ; Auger electron spectroscopy
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: Abstract The oxidation or general corrosion behavior of metals at pressures of 1 atm or more is usually investigated by oxidizing samples under prescribed conditions and then subsequently characterizing the surface produced using one or more of the experimental methods available. This article describes a method which obviates the necessity of transferring samples from the oxidizing environment to the instrument for analysis, is nondestructive, and monitors the oxidizing surface in situ. The oxidation of iron, chromium, and a 9% chromium-iron alloy in carbon dioxide at atmospheric pressure and at 773°K is described. The surfaces of these materials were analyzed by Auger electron spectroscopy during exposure to the gas. Spectra and diagrams illustrating the variation in surface composition as oxidation proceeded are shown and possible mechanisms for the oxidation reactions are briefly discussed. The formation of the surface oxide on iron and on the 9% Cr-Fe alloy appears to follow very similar paths under the conditions of oxidation used. In all the materials studied trace impurities such as sulfur participated in the oxidation reactions.
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  • 64
    Digitale Medien
    Digitale Medien
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    Oxidation of metals 13 (1979), S. 181-195 
    ISSN: 1573-4889
    Schlagwort(e): copper-manganese alloys ; oxidation ; scale composition
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: Abstract The oxidation behavior of copper-manganese alloys (2–35 wt. % Mn) in pure oxygen at 760 Torr was investigated at 100° intervals between 550 and 850°C. Gravimetric measurements of the oxidation kinetics have been combined with microstructural studies of the reacted samples in order to evaluate the reaction mechanisms. The scales formed on Cu-2Mn, Cu-5Mn, Cu-10Mn are always composed of three different layers; in any case manganese is present only in the inner layer. The scales formed on Cu-20Mn and Cu-35Mn are composed of two layers, both containing manganese, with a more Cu-rich outer layer. In all the samples internal oxidation in combination with external scale formation is observed.
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  • 65
    ISSN: 1573-4889
    Schlagwort(e): Cu-Si alloys ; oxidation ; kinetics ; silica
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: Abstract The oxidation of Cu-Si alloys (containing up to 4.75 wt. % Si) in $${\text{p}}_{O_2 } $$ =0.01 atm from 800 to 1000°C has been investigated using thermogravimetry and other techniques. A 0.04% Si alloy followed a parabolic oxidation law with a rate similar to that of pure Cu. As the Si concentration increased the rate decreased and became irregular owing to SiO2 particles or flakes at the alloy-scale interface. It is considered that sintering of SiO2 particles and rupture of the sinter because of contraction during sintering are responsible for the irregular kinetics. A SiO2 layer forms directly on the 4.75% Si alloy which oxidizes uniformly. The SiO2 was always amorphous. In pure CO2 a similar pattern of amorphous SiO2 particles, flakes, and layers occurs.
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  • 66
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    Digitale Medien
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    Oxidation of metals 13 (1979), S. 283-298 
    ISSN: 1573-4889
    Schlagwort(e): oxidation ; surface alloys ; Fe-Cr alloys ; iron ; kinetics
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: Abstract The oxidation behavior of several surface and bulk Fe-Cr alloys and iron at 300°C and 4×10−6 Torr oxygen was studied. The surface alloys were fabricated by implantation of 25 keV Cr ions into the outermost 300Å of polycrystalline iron samples. The oxide thickness as a function of oxygen exposure was obtained using proton-excited X-ray analysis, and composition profiles of oxide films were obtained using Auger electron spectroscopy and ion sputtering. The addition of Cr to Fe by surface and bulk alloying caused the oxidation rate to decrease and changed the oxidation kinetics from parabolic (for Fe) to logarithmic (for Cr concentrations ≥4.7at.%). Interpretation of the data in terms of simple oxidation theories indicates that the Cr additions may reduce the oxidation rate by altering the electronic properties of the metal-oxide interface.
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  • 67
    Digitale Medien
    Digitale Medien
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    Oxidation of metals 13 (1979), S. 311-330 
    ISSN: 1573-4889
    Schlagwort(e): oxidation ; oxide maps ; alloying additives ; Fe-Ni-Al alloys
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: Abstract The oxidation behavior of iron-nickel-aluminum alloys containing 0–40 wt.% nickel and 0–30 wt.% aluminum has been investigated at 600 and 800° C. Through the construction of “oxide maps” it can be shown that three possible oxide morphologies may exist: Alloys containing less than approximately 5 wt.% aluminum form scales consisting of predominantly Fe2O3 and spinel; alloys with between 5 and 10 wt.% aluminum form Al2O3 scales interspersed by Fe2O3 nodules, and alloys with greater than 10 wt.% aluminum form predominantly γ-Al2O3 scales.
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  • 68
    Digitale Medien
    Digitale Medien
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    Oxidation of metals 14 (1980), S. 31-45 
    ISSN: 1573-4889
    Schlagwort(e): oxidation ; directionally solidified eutectic alloy
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: Abstract The isothermal oxidation behavior of a directionally solidified Ni-Al-Cr3C2 eutectic alloy in flowing air at 1100° C has been studied using various physical techniques. Initially, the alloy oxidizes relatively slowly as a protective α- Al2O3 layer develops on its surface. However, this layer breaks down mechanically at temperature, enabling a more rapidly growing Cr2O3 -rich scale to develop, the carbide fibers supplying chromium for the oxidation process. The extent of oxidation is further increased by the development of substantial amounts of internal oxide in the alloy beneath this scale, with some preferential oxidation down the alloy-carbide fiber interfaces. The influence of carbide fiber orientation on the oxidation behavior is considered and discussed in relation to proposed oxidation mechanisms.
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  • 69
    Digitale Medien
    Digitale Medien
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    Oxidation of metals 13 (1979), S. 223-236 
    ISSN: 1573-4889
    Schlagwort(e): nickel ; oxidation ; surface reactions ; X-ray photoelectron spectroscopy
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: Abstract X-ray photoelectron spectroscopy has been used to study the oxidation of polycrystalline nickel metal. The results indicate that the oxidation process takes place in three stages; associative adsorption of molecular oxygen, followed by the combination of oxygen atoms with surface nickel atoms and, ultimately, the formation of bulk oxide. At room temperature only the first two stages can be detected. For exposures below 1 L the O 1s photoelectron spectrum is considered to be characteristic of an associatively adsorbed oxygen species, but for exposures above this value evidence for the formation of a monolayer of “NiO” is suggested by the development of an O 1s peak at 529.9 eV. Incorporation of oxygen into the nickel lattice is observed at temperatures 〉500°K. The activation energy for this place-exchange process was estimated at 1.80±0.06 eV.
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  • 70
    Digitale Medien
    Digitale Medien
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    Oxidation of metals 13 (1979), S. 255-272 
    ISSN: 1573-4889
    Schlagwort(e): oxidation ; Fe-C ; graphite deposition ; nonadherent oxide ; kinetics
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: Abstract The oxidation of Fe-C alloys containing 0.5 and 1.0% C was studied in 1 atm O2 at 700° C. The oxidation rate is considerably slower than for pure Fe. The oxide scale formed is detached, multilayered, and overoxidized, containing little or no FeO. A thin film of graphite was identified at the metal-oxide interface by electron diffraction. It is proposed that the slow oxidation and abnormal scale are caused by a residue of graphite left at the metal surface from the oxidation of Fe3C. This inhibition of the oxidation of Fe by carbon at 700°C is in contrast to the stimulation observed at 500°C.
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  • 71
    Digitale Medien
    Digitale Medien
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    Oxidation of metals 14 (1980), S. 263-277 
    ISSN: 1573-4889
    Schlagwort(e): oxidation ; Ni-Cr alloys ; two-phase alloys
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: Abstract Oxidation of the relatively simple, two-phase alloy Ni-70 wt.%Cr in oxygen between 1073 and 1473°K results in the formation of a Cr2O3 scale containing less than O.5 wt.% Ni in solid solution. The oxidation kinetics are irreproducible for an initial period, which is brief at 1073 and 1273°K but much more pronounced at 1473°K, both in duration and degree. This behavior is associated with the failure of the protective Cr2O3 scale. However, after longer periods a compact layer of Cr2O3 becomes established under isothermal conditions and results in a change to more reproducible kinetics, especially at 1073 and 1273°K. Oxidation causes chromium depletion and the formation of a single-phase zone which separates the scale and the two-phase bulk alloy. The depth of Cr2O3 internal oxide coincides with this zone. The oxidation behavior is compared with that of more Ni-rich, single-phase Ni-Cr alloys, with particular reference to the effects of the constitution of the underlying alloy and the integrity of the protective oxide.
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  • 72
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    Digitale Medien
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    Oxidation of metals 15 (1981), S. 251-276 
    ISSN: 1573-4889
    Schlagwort(e): oxide dispersion strengthening ; oxidation ; hot corrosion ; powder metallurgy ; porosity
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: Abstract Cyclic hot corrosion and oxidation testing of an experimental oxide dispersion strengthened (ODS) superalloy MA-755E were conducted in a hot gas stream at Mach 0.3. The response of the ODS alloy, bare or with protective coatings, was similar to that of a conventional cast alloy, IN-792, in hot corrosion at 900°C. However, during oxidation at 1100 and 1150°C the ODS alloy differed from the cast alloy by developing a greater amount of subsurface porosity. Compared with a diffused aluminide coating, an electron beam vapor deposited NiCrAlY coating offered superior oxidation protection and decreased porosity formation. In additional testing, the tendency to form porosity was associated with the large grains of recrystallized powder metallurgy alloys but was independent of the presence of an oxide dispersion.
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  • 73
    ISSN: 1573-4889
    Schlagwort(e): oxidation ; iron ; Mössbauer ; conversion electron ; ERM Spectroscopy
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: Abstract A reanalysis of earlier electron reemission Mössbauer (ERM) data obtained from iron oxidized in pure oxygen at 150 to 500°C is presented. The new data analysis utilized the same theoretical method used previously, but with significantly altered values for the electron attenuation coefficients determined from recent experimental work by Graham, Mitchell, and Channing. The recalculated oxide-thickness values were found to be in much better agreement with the volumetrically measured oxygen uptake.
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  • 74
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    Digitale Medien
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    Oxidation of metals 14 (1980), S. 549-566 
    ISSN: 1573-4889
    Schlagwort(e): oxidation ; microhardness data ; sintering experiments ; electron microprobe analyses.
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: Abstract Oxidation kinetics in either air or oxygen of prenitrided Ti-4.32 wt.% Nb alloy are investigated in the temperature range of 900–1200°C. Based on X-ray and electron microprobe analyses, thermogravimetric measurements, microhardness data, and sintering experiments, a quantitative oxidation model is developed to explain the gas-metal reactions. Temperature cycling experiments, in the temperature range of 900–1200°C and for a 12-hr duration, are performed in an attempt to reduce the oxidation rates of the alloy in air or oxygen. The oxidation resistance of nitrogen pretreated alloy is comparable to that in air and it is considerably higher than in oxygen alone.
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  • 75
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    Oxidation of metals 15 (1981), S. 287-295 
    ISSN: 1573-4889
    Schlagwort(e): oxidation ; dispersoids ; scale adherence ; ferritic alloys
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: Abstract The present investigation examines the high-temperature oxidation behavior of Fe-Cr ferritic alloys containing 1.0% Hf which has been convened into an oxide dispersion. The oxide dispersions were produced by an internal oxidation treatment using a 50-50 Cr-Cr2O3 powder mixture in a sealed quartz capsule at 1100°C: the samples were not in direct contact with the powders. The effect of the dispersed oxide was spectacular under isothermal oxidation conditions, but it had almost no effect during thermal cycling conditions. Unlike the TiO2-containing Fe-Cr ferritic alloys, virtually no particle coarsening was observed. The absence of the coarse particles caused poor thermal cycling behavior, whereas in TiO2-containing ferritic alloys, coarse particles acted as oxide pegs giving a keying-on effect.
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  • 76
    Digitale Medien
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    Oxidation of metals 15 (1981), S. 355-373 
    ISSN: 1573-4889
    Schlagwort(e): Fe-Cr-Al alloy ; oxidation ; α-Al2O3
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: Abstract Oxidation kinetics of a parent Fe-5Cr-4Al alloy subjected to two types of anneals were investigated at temperatures ranging from 1000°C to 1320°C. The alloy annealed at 850°C exhibited a rapid transient oxidation stage associated with growth of nodules containing iron oxides and internal precipitation of α-Al2O3 in the alloy beneath these nodules. The nodules nucleated and grew from sites located in the regions of the alloy grain boundaries during the period of rapid alloy grain growth. Nodular growth virtually ceased when a continuous α-Al2O3 film formed at the nodule-alloy interface. The alloy subjected to anneal at 1000°C and at the reaction temperature to stabilize the alloy grain size tended upon oxidation to form a protective α-Al2O3, layer by parabolic kinetics at temperatures to 1250°C. If this alloy was oxidized in stages at 1000°C, a protective α-Al2O3 scale was formed up to 1320°C. The temperature coefficient of the parabolic oxidation kinetics was consistent with diffusion processes at boundaries of the α-Al2O3 grains playing an essential role during growth of this protective oxide layer.
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  • 77
    Digitale Medien
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    Oxidation of metals 16 (1981), S. 339-353 
    ISSN: 1573-4889
    Schlagwort(e): Iron-carbon ; oxidation ; decarburization
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: Abstract The oxidation behavior of Fe-C alloys in the temperature range 600–850°C has been studied. CO 2 evolved during oxidation was measured using an infrared gas analyzer. The presence of C lowers the oxidation rate relative to that of pure Fe and this has been related to the rejection of carbon at the alloy-scale interface causing poor contact between scale and alloy. As a result, the scale contains a higher proportion of magnetite, which reduces its overall growth rate. Very little carbon is lost to the atmosphere. The ease with which the rejected carbon is incorporated into the alloy depends on the alloy structure.
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  • 78
    Digitale Medien
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    Oxidation of metals 17 (1982), S. 157-176 
    ISSN: 1573-4889
    Schlagwort(e): reflectance spectroscopy ; chromium ; oxidation
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: Abstract Infrared reflectance spectra of oxidized chromium are presented as the first of a series of investigations of the reflectance spectra of oxidized materials. The spectra agree well with the behavior predicted in an earlier note, and confirm that simultaneous identification and thickness measurements of corrosion films are possible using this technique. The most prominent features for identification purposes are absorption bands at 610, 540, and 440 cm −1 for films ⪝1.5-μ thick, and at 610 and 300 cm−1 for thicker films. These bands are discernable despite the complicated effects introduced by interference fringes in the low-energy spectral region.
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  • 79
    Digitale Medien
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    Oxidation of metals 18 (1982), S. 295-314 
    ISSN: 1573-4889
    Schlagwort(e): Nickel-manganese alloys ; oxidation ; solid solution scales ; internal oxidation
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: Abstract Ni-Mn alloys containing up to 38% Mn have been oxidized in pure oxygen between 873 and 1273 K and the parabolic rate constants measured. The scale morphologies and oxide compositions are interpreted in terms of modifications to the scale on pure Mn caused by the presence of Ni. The scales are composed predominantly of two layers at all temperatures, giving the sequences of phases alloy/cubic monoxide (Ni, Mn)O/ternary spinel, with the cubic (Ni, Mn)O layer always having the greater thickness. There is limited evidence for a third, very thin, outer layer in the scales on all alloys at 873 K and for Ni-38%Mn at 1073 K, which is tentatively considered to be Mn2O3, giving layers in the order alloy/cubic monoxide/ternary spinel/Mn2O3, by analogy with the scale formed on pure Mn. The distribution of the alloy components in the scale is discussed in relation to the Ni-Mn-O phase diagram and in terms of recent theoretical treatments of solid solution scale formation on binary alloys, as far as the available diffusion data allow. The occurrence of internal and intergranular oxidation and the formation of a Mn-depleted zone coincident with the band of uniform internal oxide are considered briefly.
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  • 80
    Digitale Medien
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    Oxidation of metals 19 (1983), S. 53-76 
    ISSN: 1573-4889
    Schlagwort(e): Two-phase alloy ; cobalt-copper ; oxidation
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: Abstract The oxidation in 1 atm of pure oxygen of a binary two-phase Co-Cu alloy has been studied as a simple example of the oxidation behavior of a multiphase alloy. The two-phase alloy oxidizes according to a parabolic rate law to a good approximation throughout the entire exposure period over the temperature range 700–1000°C with an oxidation rate constant greater than that for pure cobalt in the whole temperature range, and greater than that for pure copper at 900–1000°C, but lower below 900°C. The scale presents essentially the same type of layered structure at all the temperatures investigated, with an outer region composed of copper oxides, while cobalt is preferentially accumulated in the inner region of the scale, mainly in the form of CoO. A subscale formed by internal oxidation of the particles of the Co-rich phase is also present. The observed increase of the oxidation rate of the alloy in comparison with pure cobalt is attributed mainly to the presence of a high concentration of copper dissolved in CoO in the form of monovalent ions, which produces a significant modification of the concentration of defects of cobalt oxide with a consequent increase of the oxidation rate constant of the alloy if a suitable model for the defect structure of pure CoO is considered, which takes into account also the presence of a small concentration of interstitial metal ions.
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  • 81
    Digitale Medien
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    Oxidation of metals 18 (1982), S. 285-294 
    ISSN: 1573-4889
    Schlagwort(e): Iron-manganese-aluminum ; oxidation
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: Abstract A series of austenitic Fe-Mn-Al alloys containing C, Si, and Zr was tested for oxidation resistance in air at 850 and 1000°C. The resultant oxide scales were examined for morphology and elemental distribution. Some alloys, particularly Fe, 32Mn, 7.5Al, 2Si, and 0.6C, had good oxidation resistance at 850°C but none was adequate at 1000°C. Poor oxidation resistance was associated with the internal oxidation of Al and formation of voluminous (Fe, Mn)O scale nodules. The results are discussed in terms of possible mechanisms for formation of a protective alumina layer.
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  • 82
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    Oxidation of metals 17 (1982), S. 391-405 
    ISSN: 1573-4889
    Schlagwort(e): Aluminide coating ; steel ; diffusion ; oxidation
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: Abstract Aluminide coatings are known to protect steels from oxidation and corrosion in hydrocarbon and sulfur-bearing atmospheres. Pack cementation is ideally suited for forming these coatings on small intricate components, wherein a diffused layer is formed which is well bonded to the substrate. Even though pack aluminide coated steels are being commercially used, there has not been any systematic investigation of the factors that control the coating formation. The present investigation has been carried out to define the boundary conditions under which diffusion in the solid phase determine the coating kinetics. The effect of pack activity and temperature on the structure and kinetics of aluminde layer formation on EN-3 steel has been investigated. The coating characteristics were evaluated by metallography, EPMA, X-ray diffraction, and scanning electron microscope (SEM). Oxidation resistance of the coated samples were compared to that of 304 stainless steel after heating in air at 900°C for 72 h. The surface aluminum composition was found to be about 20% by weight which remained constant with time in the temperature range of 750°C–900°C. Weight gains and layer thicknesses obeyed parabolic relationship with time at all temperatures. Under these conditions, the system constitutes a vapor-solid diffusion couple. Interdiffusion coefficient $$(\tilde D)$$ values in the Fe-Al system have been determined, and the activation energy has been calculated to be 57 Kcals/mole, which agrees well with the literature values.
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  • 83
    Digitale Medien
    Digitale Medien
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    Oxidation of metals 18 (1982), S. 115-126 
    ISSN: 1573-4889
    Schlagwort(e): Iron-silicon ; oxidation ; creep ; scale morphology
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: Abstract Studies of the simultaneous creep and oxidation of Fe-1Si and Fe-4Si alloys at a constant tensile stress of 16 N· mm−2 at 973–1073 K have shown that scales formed at oxygen partial pressures of 20–1013 mbar were thicker by a factor of 2 than those formed on uncrept specimens. Scales on uncrept alloys comprised alternate layers of wustite and fayalite, whereas scales on crept alloys exhibited an additional external layer of magnetite. Only intergranular oxidation (fayalite) was observed in uncrept alloys, but crept alloys showed both intra- and intergranular oxidation (silica). Uniquely nodular scales were formed only on the Fe-4Si alloy on crept and uncrept specimens. Oxidized, uncrept Fe-1Si showed a fine-grained ferrite substrate which was absent in the crept alloy. It is believed that oxide growth stresses stimulated a recrystallization process.
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  • 84
    Digitale Medien
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    Oxidation of metals 21 (1984), S. 205-231 
    ISSN: 1573-4889
    Schlagwort(e): oxidation ; titanium ; chromium ; adherence
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: Abstract The oxidation behavior of Ti-Cr alloys (1, 4, 11, and 19% chromium by weight) was investigated, between 550 and 700°C, in air and in oxygen, for a maximum duration of about 800 hr. The kinetics results revealed a significant influence of the chromium content with a maximum, in the unfavorable sense, around 4%. Moreover, the analysis of kinetics curves showed that stable rate constants could be obtained only if the duration of oxidation was sufficiently long. The oxide layers were duplex with a much higher chromium content in the inner layer. The morphological investigations performed on cross-sections of the oxidized specimens showed that the chromium modifies the crystallization of the oxide layers. The adherence of the oxide layers evolves nonmonotonically as a function of chromium content for the same degree of progression of the reaction and as a function of the oxidation rate, which is itself dependent on chromium content.
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  • 85
    Digitale Medien
    Digitale Medien
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    Oxidation of metals 21 (1984), S. 285-297 
    ISSN: 1573-4889
    Schlagwort(e): Galvalume ; elevated temperature ; intermetallic formation ; Al13Fe4 ; oxidation ; vaporization
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: Abstract Galvalume (trademark of Bethlehem Steel Corp.) sheet steel samples were heated in pure oxygen and 97% O2/3% H2O atmospheres at temperatures ranging from 300 to 670°C. Time at a particular temperature was varied but did not exceed 48 hr. Above 480°C, the Galvalume coating became rapidly alloyed with iron to form Al13Fe4, and zinc was lost by vaporization. The Zn content dropped to about 15 wt%. The time required to fully alloy the overlay at 490°C was less than 4 hr. Below 480°C, only minor microstructural changes occurred, and coating integrity was maintained. No differences in behavior were observed by the addition of 3% water vapor to the gas stream.
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  • 86
    Digitale Medien
    Digitale Medien
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    Oxidation of metals 20 (1983), S. 67-73 
    ISSN: 1573-4889
    Schlagwort(e): Thermal barrier coating ; plasma spraying ; oxidation ; hot corrosion
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: Abstract Various zirconate coatings were prepared on bare Nimonic-75 and on CoCrAlY bond coat by plasma spraying. The cyclic oxidation and hotcorrosion resistance of these coatings have been evluated. The wide difference in the properties of these coatings has been rationalized in terms of the thermal expansion mismatch between the coating and the substrate. On continued thermal cycling and in presence of molten salt, the life-limiting factor has been identified to be oxidation of the bond coat. The interconnected porosity in the ceramic coating is mainly responsible for such oxidation, and controlling this porosity would lead to life improvement.
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  • 87
    Digitale Medien
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    Oxidation of metals 24 (1985), S. 133-148 
    ISSN: 1573-4889
    Schlagwort(e): oxidation ; nickel ; yttrium
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: Abstract The oxidation of Ni, Ni-0.1 wt.% Y, and Ni-0.3 wt.% Y alloys was carried out in the temperature range 500–900°C at pO 2= 1 atm.
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  • 88
    Digitale Medien
    Digitale Medien
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    Oxidation of metals 24 (1985), S. 177-197 
    ISSN: 1573-4889
    Schlagwort(e): oxidation ; short-circuit diffusion ; nickel ; chromium ; binary Ni-Cr alloys
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: Abstract The evidence for short-circuit diffusion during the oxidation of nickel, chromium, and nickel-chromium alloys is reviewed. On the basis of experimental evidence for the Ni/NiO and Cr/Cr2O3 systems, inferences are made about the role of short-circuit diffusion through the oxide scales forming on the binary nickel-chromium alloys. The review highlights the importance of scale microstructure in governing oxidation rates.
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  • 89
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    Digitale Medien
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    Oxidation of metals 26 (1986), S. 139-155 
    ISSN: 1573-4889
    Schlagwort(e): oxidation ; Co-Cr-Ti alloys ; kinetics ; scale morphology
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: Abstract Cobalt-based alloys containing 3,5,10,15, and 20% Cr with 1 and 3% Ti were oxidized at 1000°C in slowly flowing oxygen gas. In general, titanium additions decreased the oxidation rate with the most pronounced effect being observed at the 10% Cr level. Titanium accelerated the formation of Cr2O3 layers at the metal-oxide interface. Faceted CrxTiyOz spinel particles were found at the metal-oxide interface which varied in composition according to microprobe results. There was no evidence of spalling on the Co-Cr-Ti alloys studied in contrast to the severe spalling normally encountered in Ni-Cr-Ti alloys. Distinct morphological differences existed on the outer CoO layer of the 1% Ti alloys in comparison to the O and 3% Ti alloys.
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  • 90
    Digitale Medien
    Digitale Medien
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    Oxidation of metals 26 (1986), S. 305-314 
    ISSN: 1573-4889
    Schlagwort(e): oxidation ; metals ; high temperatures ; oxidation theory ; oxidation kinetics
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: Abstract A theoretical study on the high-temperature oxidation of thick oxide films grown under a time-dependent gas partial pressure is reported. The diffusion across the film is assumed to be the rate-limiting step of the overall reaction, and Wagner's hypotheses were used as the starting point for our reasoning. A general formulation for the oxidation under no time constant gas pressure, in terms of a time-dependent answer function is given. The effect of an external electric field on the reaction rate is also reported when a constant current density,J, is applied to the oxide scale. If the oxide is a good electronic conductor atJ=0 andt ≫ τ, we found that the reaction rate assumes formally the well-known Wagner's expression of the rate constant but with a gas partial pressure at oxide/gas interface which is a time function. If the oxide is a good ionic or electronic conductor, the effect due to an external electric field,J ≠ 0, on the reaction rate is the same as predicted by the Wagner's theory.
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  • 91
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    Oxidation of metals 26 (1986), S. 201-212 
    ISSN: 1573-4889
    Schlagwort(e): chromium ; NaCl ; chloride ; oxidation ; hot corrosion
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: Abstract This paper describes new phenomena about chloride-induced accelerated oxidation of chromium. Thermal analysis was adopted to examine the oxidation, which was studied particularly in the case of NaCl. The presence of NaCl remarkably accelerates the oxidation of chromium. The process occurs below the melting point of NaCl, and the main reaction product is Cr2O3. In the accelerated oxidation NaCl plays a catalytic role because it is not consumed significantly in the process. DTA analysis reveals that the heat of reaction also accelerates the rate of oxidation, especially at an early stage of the reaction. The accelerated oxidation takes place similarly under the presence of chlorides other than NaCl, but the oxidation rate depends on the kind of salt. Therefore the Cl− anion plays an important role in the process, while the nature of the cation affects the rate of acceleration.
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  • 92
    Digitale Medien
    Digitale Medien
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    Oxidation of metals 26 (1986), S. 231-252 
    ISSN: 1573-4889
    Schlagwort(e): oxidation ; titanium ; thermogravimetry ; microhardness ; modeling
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: Abstract The oxidation kinetics of commercial purity Ti-A55 exposed to laboratory air in the 593–760°C temperature range were continuously monitored by thermogravimetric analysis. The oxide thickness was measured by microscopy and the substrate contamination was estimated from microhardness measurements. The microhardness depth profiles were converted to oxygen composition profiles using calibration data. The oxygen diffusion coefficient in alpha-Ti appears to be approximately concentration independent in the 1–10 at. % oxygen range. The combination of an “effective diffusion coefficient” and an “effective solubility” at the oxide-metal interface usefully describes the diffusion process over the entire composition range. A model for the total parabolic oxidation kinetics, accounting for the two individual components, oxide growth and solid solution formation, has been proposed. Diffusion coefficient for oxygen in TiO2 has been estimated as a function of temperature and is found to be about 50 times the value in alpha-Ti. The metallographically prepared cross-sections of the oxidized specimens revealed a “moving boundary” in the substrate, parallel to the oxide-metal interface. This boundary was associated with a specific oxygen level of 5.0±0.5 at.%. It occurred at a distance from the oxide-metal interface which was correlatable with temperature and time of exposure. The diffusion coefficient corresponding to the composition of this moving boundary is in excellent agreement with the effective diffusion coefficient for the substrate contamination.
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  • 93
    ISSN: 1573-4889
    Schlagwort(e): Raman microscopy ; Fe-Cr alloys ; oxidation
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: Abstract Raman microscopy has been used to study the nature and distribution of corrosion products formed on iron and iron-chromium alloys in air at high temperatures. Fe and Fe-Cr alloys containing 2, 5, 14, and 18% Cr were oxidized at 400, 600, and 850°C for 2 hr, in addition samples of each alloy were oxidized for 24 hr at 400°C to obtain thicker scales at this temperature. The corroded samples showed varying distributions of the oxides Fe2O3, Fe3O4, Cr2O3, and FeCr2O4. Fe2O3 and Fe3O4 were formed exclusively on the pure iron and the 2 and 5% chromium alloys at all temperatures and on the 14% chromium alloy at 400°C. The 14 and 18% Cr alloys formed scales containing Cr2O3 and FeCr2O4 at the higher temperatures (600 and 850°C). Examples of small regions of Fe2O3 being formed within Cr2O3-FeCr2O4 scales are suggested as possible indications of breakaway corrosion initiation sites.
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  • 94
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    Oxidation of metals 27 (1987), S. 83-93 
    ISSN: 1573-4889
    Schlagwort(e): silicon carbide ; oxidation ; constructional ceramics
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: Abstract The process of high temperature oxidation of two silicon carbide based materials differing by methods of their production and properties has been studied up to 1500°C in air. The oxidation was performed under the isothermal conditions and at the programmed heat rate of 10° per minute. It was found that the oxidation resistance of the material was the function of the presence of extrinsic metals having close affinity for oxygen. It was also found that under heating up to 1500°C in air phase transitions occurred in the SiC surface layer.
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  • 95
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    Oxidation of metals 26 (1986), S. 385-396 
    ISSN: 1573-4889
    Schlagwort(e): coatings ; oxidation ; rare earth addition ; dispersed oxides ; scale adhesion
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: Abstract Oxidation studies were conducted on plasma sprayed coatings of Ni-20Cr-12.5Al containing one of the following: 1% MgO, 1% La2O3, 1% Y2O3, and 0.8% Y. The alloy powders containing dispersed oxides were prepared by a variety of processes employing attrition and ball milling. The TEM characterization of the plasma sprayed deposits of Ni-20Cr-12.5Al-1Y2O3 indicated that the oxide particles ranged from almost pure aluminum oxide to various compounds of aluminum and yttrium oxide. In cyclic tests conducted at 1150 and 1225°C, the coating containing 1% Y2O3 appeared to provide the best oxidation resistance. The oxidation resistance appeared to be influenced by the size and distribution of the oxide particles.
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  • 96
    ISSN: 1573-4889
    Schlagwort(e): oxidation ; adhesion ; growth-mechanisms ; impurities ; sulfur
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: Abstract The “sulfur effect” theory proposes that elements such as sulfur segregate to the scale-metal interface, where they have a deleterious effect on scale-metal adhesion, and that reactive elements and dispersions of their oxides are beneficial because they prevent this segregation. Evidence in favor of this theory has been obtained by showing that the adhesion of the scale formed on chromium in 0.1 atm. oxygen at 950°C. is greatly improved if the chromium is annealed beforehand in hydrogen instead of in vacuo. It is shown that the theory can explain not only all the experimental observations regarding the beneficial effects of reactive elements and their oxides on scale-metal adhesion, but also their effects on scale growth-mechanisms.
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  • 97
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    Oxidation of metals 26 (1986), S. 105-124 
    ISSN: 1573-4889
    Schlagwort(e): oxidation ; titanium ; thermogravimetry ; microhardness ; modeling ; mechanical properties ; space shuttle reentry
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: Abstract Ti-6Al-2Sn-4Zr-2Mo titanium alloy is a candidate material for multiwall thermal protection system concepts for advanced space transportation system vehicles. The total oxidation kinetics for this alloy, exposed to laboratory air in the 593–760°C range, were monitored by thermogravimetric analysis. The oxide thickness was measured by microscopy and the substrate contamination was estimated from microhardness measurements. Tensile elongation was determined for selected foil specimens after exposure to simulated space shuttle reentry conditions. The variation of total weight gain with time was found to have two distinct parabolic stages separated by a transient region. This transient was due to a process which involved an increase in the parabolic growth rate constant for the oxide and a simultaneous increase in oxygen solubility at the oxide metal interface. The time dependent increase in oxygen solubility at the interface was from about 7 at. % in stage 1 to about 18 at. % in stage 2. The diffusion coefficient for oxygen in the alloy was determined as a function of temperature using the difference between the total weight gain in stage 1 and the corresponding weight gain due to oxide growth. A model for the total oxidation kinetics, accounting for the two individual components namely oxide growth and solid solution formation, is proposed. The activation energy for the diffusion of oxygen in the alpha-solid solution is shown to be roughly equal to the activation energy for the degradation of tensile elongation for the alloy in the foil gage condition.
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  • 98
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    Oxidation of metals 26 (1986), S. 315-332 
    ISSN: 1573-4889
    Schlagwort(e): oxidation ; multilayer oxides ; oxidation kinetics theory ; diffusion mechanisms ; iron
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: Abstract A quantitative theory for the growth of three-layered oxide scales on pure metals that form MevO, MeδO, and MeɛO has been developed. The theoretical parabolic rate constants,K p (MevO),K p (MeδO), andK p (MeɛO), for the simultaneous growth of each oxide on metals are related to oxidation data of the overall rate constant,K p , and the oxide thickness ratios. These theoretical parabolic rate constants can also be calculated from diffusion data in each oxide, and the oxide thickness ratios can therefore be predicted. To verify the validity of the theory, it was applied to the oxidation of iron in air at temperatures of 800 to 1200° C. Good agreement was found between the theoretical parabolic rate constants calculated from oxidation data and from diffusion data for wustite and magnetite. However, to match with the rate constant calculated from oxidation data, additional information about short-circuit diffusion in hematite is required.
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  • 99
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    Oxidation of metals 27 (1987), S. 21-36 
    ISSN: 1573-4889
    Schlagwort(e): oxidation ; steam ; Ni-base superalloy ; Al oxides ; Ti oxides
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: Abstract The role of aluminum and titanium on the oxidation process of a nickel-base superalloy containing 18.89%Cr, 2.13%Al, and 2.41%Ti was investigated in steam at 800°C. A Cr2O3-rich scale was formed on the alloy surface. Aluminum formed only internal oxides below the Cr2O3-rich scale. On the other hand, titanium formed not only internal oxides but also oxides in the scale and the granular particles of TiO2 outside the scale. Agglomeration of the TiO2 particles also occurred. The oxidation behavior of aluminum and titanium was discussed from thermodynamic and kinetics aspects.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 100
    Digitale Medien
    Digitale Medien
    Springer
    Oxidation of metals 27 (1987), S. 37-55 
    ISSN: 1573-4889
    Schlagwort(e): laser treatment ; chromia scales ; oxidation ; nickel-chromium alloys ; laser glazing
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: Abstract The influence of laser surface treatment on the isothermal oxidation of Ni-10%Cr and Ni-15%Cr at 1025°C in oxygen at 1 atm pressure has been studied. Particular emphasis has been placed on the progressive establishment of a Cr2O3 healing layer, which is facilitated by rapid-diffusion paths for chromium to the surface from the bulk alloy. For nonlaser treated alloys, such paths are alloy grain boundaries. A partial Cr2O3 layer forms initially in localized sites at, and immediately adjacent to, these boundaries and progresses into the alloy grains in a stepwise manner following lateral diffusion of chromium from the grain boundaries, thereby developing a contoured configuration. For Ni-15%Cr, there is sufficient chromium in the bulk alloy grains to sustain the eventual development of a self-healing layer parallel to the surface. For Ni-10%Cr, this is not the case and complete development of the healing layer results entirely from the stepwise progression from the grain boundaries. Establishment of the healing layer on laser-glazed surfaces is facilitated by additional rapid-diffusion paths, particularly retained alloy grain boundaries, retained alloy twins, a laser-induced microstructure and solidification artifacts (such as ripples). The relative importance of these features is discussed in relation to the oxidation behavior.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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