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  • 1
    Electronic Resource
    Electronic Resource
    Influence of the solubility product on the concentration profiles of internal oxidation (1989)
    Springer
    Oxidation of metals 32 (1989), S. 111-123 
    Details
    ISSN: 1573-4889
    Keywords: internal oxidation ; carburization ; computer simulation ; finite-difference technique
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract A computer-based method is used to simulate the process of penetration of a foreign element (e.g., oxygen) into an alloy connected with internal precipitation of a compound of this element with a solute in the alloy. The method employed is based on the solution of the differential equations corresponding to this high-temperature corrosion phenomenon with the help of the finite-difference technique. To demonstrate the possibilities of the calculation method, various cases were treated which differ especially regarding the thermodynamic stability of the internal precipitates. The calculated concentration profiles and penetration depths obtained are reported and discussed. In the case of internal precipitates of high stability, the results are compared with the approaches derived in the literature for internal oxidation and are used to determine the parameter ranges in which the analytical equations apply. The results obtained for the case of a less-stable compound is used to illustrate the influence of the solubility product on the concentration profiles.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00665271
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  • 2
    Electronic Resource
    Electronic Resource
    The oxidation of Co−Nb alloys under low oxygen pressures at 600–800°C (1995)
    Springer
    Oxidation of metals 43 (1995), S. 527-542 
    Details
    ISSN: 1573-4889
    Keywords: Co−Nb alloys ; high temperature ; oxidation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The oxidation of two Co−Nb alloys containing 15 and 30 wt.% Nb has been studied at 600–800° C in H2−CO2 mixtures providing an oxygen pressure of 10−24 atm at 600°C and 10−20 atm at 700 and 800°C, below the dissociation pressure of cobalt oxide. At 600 and 700°C both alloys showed only a region of internal oxidation composed, of a mixture of alpha cobalt and of niobium oxides (NbO2 and Nb2O5) and at 700°C also the double oxide CoNb2O6, which formed from the Nb-rich Co3Nb phase. No Nb-depleted layer formed in the alloy at the interface with the region of internal oxidation at these temperatures. Upon oxidation at 800°C a transition between internal and external oxidation of niobium was observed, especially for Co−30Nb. This corrosion mode is associated with the development of a single-phase, Nb-depleted region at the surface of the alloy. The corrosion mechanism of these alloys is examined with special reference to the effect of the low solubility of niobium in cobalt and to the relation between the microstructures of the alloys and of the scales.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01046897
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  • 3
    Electronic Resource
    Electronic Resource
    The oxidation of two Fe−Nb alloys under low oxygen pressures at 600–800°C (1995)
    Springer
    Oxidation of metals 43 (1995), S. 561-579 
    Details
    ISSN: 1573-4889
    Keywords: Fe−Nb alloys ; high temperature ; corrosion ; low oxygen pressure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The oxidation of two Fe−Nb alloys containing 15 and 30 wt.% Nb has been studied at 600–800°C under low oxygen pressures, similar to those prevailing in environments of the coal-gasification type. The reaction produced only an internal oxidation of niobium to form two niobium oxides (NbO2 and Nb2O5) and in some cases a double Fe−Nb oxide. The kinetics of this reaction were very slow at 600°C but rather fast at 700 and 800°C. A peculiar feature of the internal oxidation of these alloys is that the distribution of the internal oxides follows closely that of the Nb-rich phase in the original two-phase alloys. This behavior, as well as the lack of formation of external scales of niobium oxides, is mainly a result of the limited solubility of niobium in iron and of the consequent presence of two metal phases in the alloys.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01046899
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  • 4
    Electronic Resource
    Electronic Resource
    The oxidation of Ni-Nb alloys at low-oxygen pressures at 600–800°C (1995)
    Springer
    Oxidation of metals 44 (1995), S. 399-415 
    Details
    ISSN: 1573-4889
    Keywords: Ni−Nb alloys ; high temperature ; oxidation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The oxidation of two Ni−Nb alloys containing 15 and 30 wt.% Nb has been studied at 600–800° C in H2−CO2 mixtures providing an oxygen pressure of 10−24 atm at 600° C and 10−20 atm O2 at 700 and 800° C, these pressures being less than the dissociation pressure of nickel oxide. The scales formed on both alloys at 600 and 700° C show only a region of internal oxidation composed of a mixture of alpha nickel and niobium oxides (Nb2O5 or/and NbO2), which formed from both the metal phases present, i.e., Ni8Nb and Ni3Nb. Only small, or even no, Nb depletion was observed in the alloys close to the interface with the zone of internal oxidation at these temperatures. On the contrary, samples of both alloys corroded at 800° C produced a continuous external scale of niobium oxides without internal oxidation. The corrosion mechanism of these alloys is examined with special reference to the effect of the low solubility of niobium in nickel.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01058244
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  • 5
    Electronic Resource
    Electronic Resource
    Effect of Ion Plating TiN on the Oxidation of Sputtered NiCrAlY-Coated Ti3Al-Nb in Air at 850-950°C (1998)
    Springer
    Oxidation of metals 50 (1998), S. 71-88 
    Details
    ISSN: 1573-4889
    Keywords: OXIDATION ; Ti3Al-Nb ; COATINGS ; SPUTTERED NiCrAlY ; ION-PLATED TIN
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract A single sputtered NiCrAlY coating and a complexcoating of inner ion-plated TiN and outer sputteredNiCrAlY were prepared on the intermetallic compoundTi3Al-Nb. Their oxidation behavior wasexamined at 850, 900, and 950°C in air by thermalgravimetry combined with XRD, SEM, and EDAX. The resultsshowed that Ti3Al-Nb followed approximatelyparabolic oxi dation, forming an outer thinAl2O3-rich scale and an inner TiO2-rich layer doped withNb at the three temperatures. The TiO2-richlayer doped with Nb dominated the oxidation reaction.The single NiCrAlY coating did not follow parabolicoxidation exactly at 850 and 950°C, but oxidizedapproximately in a parabolic manner, because theinstantaneous parabolic constants changed slightly withtime. Besides the Al2O3 scale,TiO2 formed from the coating surface at the coating-substrate interface. Thedeterioration of the coating accelerated with increasingtemperature. The NiCrAlY-TiN coating showed two-stageparabolic oxidation at 850 and 900°C, and anapproximate parabolic oxidation at 950°C. The TiN layerwas effective as a barrier to inhibit coating-alloyinterdiffusion.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1018823901649
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  • 6
    Electronic Resource
    Electronic Resource
    An analysis of the internal oxidation of binary M-Nb alloys under low oxygen pressures at 600–800°C (1996)
    Springer
    Oxidation of metals 46 (1996), S. 441-463 
    Details
    ISSN: 1573-4889
    Keywords: niobium alloys ; oxidation ; high temperatures
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The corrosion of M−Nb alloys based on iron, cobalt, and nickel and containing 15 and 30 wt% Nb has been studied at 600–800°C under low oxygen pressures (10−24 atm at 600°C and 10−20 atm at 700–800°C). Except for the Co−Nb and Ni−Nb alloys corroded at 800°C, which formed external scales of niobium oxides, corrosion under low O2 pressures produced an internal oxidation of niobium. This attack was much faster than expected on the basis of the classical theory. Furthermore, the distribution of the internal oxide in the alloys containing two metal phases was very close to that of the Nb-rich phase in the original alloys. These kinetic, microstructural, and thermodynamic aspects are examined by taking into account the effects of the limited solubility of niobium in the various base metals and of the two-phase nature of the alloys.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01048640
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  • 7
    Electronic Resource
    Electronic Resource
    The Oxidation of Fe-2 and 5 at.% Y Alloys at 600-800°C in Air (1999)
    Springer
    Oxidation of metals 51 (1999), S. 495-506 
    Details
    ISSN: 1573-4889
    Keywords: PURE FE ; Fe-Y ALLOYS ; OXIDATION
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The oxidation of Fe-Y alloys containing 2 and 5at.% Y and pure iron has been studied at 600-800°Cin air. The oxidation of pure iron follows the parabolicrate law at all temperatures. The oxidation of Fe-Y alloys at 600°C approximatelyfollows the parabolic rate law, but not at 700 and800°C, where the oxidation goes through severalstages with quite different rates. The oxide scales on Fe-2Y and Fe-5Y at 700 and 800°C arecomposed of external pure Fe oxides containingFe2O3,Fe3O4, and FeO, with FeO being themain oxide and an inner mixture of FeO andYFeO3. The scales on Fe-2Y and Fe-5Y at 600°C consist ofFe2O3,Fe3O4, andY2O3, with a minor amount of FeO.Significant internal oxidation in both Fe-Y alloysoccurred at all temperatures. The Y-containing oxidesfollow the distribution of the original intermetalliccompound phase in the alloys. The effects of Y on theoxidation of pure Fe are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1018843327998
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  • 8
    Electronic Resource
    Electronic Resource
    The oxidation of Fe—Nb alloys in 1 atm of pure oxygen at 600-800°CDedicated to Professor Dr. H. J. Grabke on the occasion of his 60th birthday (1995)
    Weinheim [u.a.] : Wiley-Blackwell
    Materials and Corrosion/Werkstoffe und Korrosion 46 (1995), S. 223-231 
    Details
    ISSN: 0947-5117
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Description / Table of Contents: Die Oxidation von Fe—Nb—Legierungen in 1 atm reinen Sauerstoffs bei 600-800°CDie Korrosion von zwei Fe-Nb-Legierungen mit 15 bzw. 30 Gewichts-% Nb ist bei 600-800 °C unter 1 atm reinen Sauerstoffs untersucht worden. Die Reaktion folgte im wesentlichen dem parabolischen Geschwindigkeitsgesetz mit Geschwindigkeitskonstanten, die erheblich niedriger lagen als für die Oxidation von reinem Eisen. Interne Oxidation und eine Verringerung an Niob in der Legierung sind in keinem Fall beobachtet worden. Der externe Zunder besteht aus einer Matrix aus Fe2O3, die eine Dispersion aus zweifachem Fe-Nb-Oxid enthält, während FeO und Fe3O4 nicht gefunden wurden. Das Oxidationsverhalten dieser Legierungen wird interpretiert in Bezug auf ein angepaßtes Phasendiagramm für das ternäre System Fe—Nb—O, wobei die Effekte der geringen Löslichkeit des Niobs im Grundmetall und die Anwesenheit von zwei Metallphasen in der Legierung berücksichtigt werden.
    Notes: The corrosion of two Fe-Nb alloys containing 15 and 30 wt% Nb has been studied at 600-800°C under 1 atm of pure oxygen. The reaction followed the parabolic rate law to a reasonable approximation with rate constants much lower than for the oxidation of pure iron under the same conditions. Internal oxidation and depletion of niobium in the alloy have never been observed. The external scales were composed of a matrix of Fe2O3 containing a dispersion of double Fe-Nb oxide, while FeO and Fe3O4 were not observed. The oxidation behavior of these alloys is interpreted with reference to an approximate phase diagram of the ternary system Fe—Nb—O, taking into account the effects of the low solubility of niobium in the base metals and of the presence of two metal phases in the alloy.
    Additional Material: 11 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/maco.19950460406
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