An investigation of the growth-mechanism of Cr2O3 on pure chromium in 1 atm oxygen at 950� C

Skeldon, M.; Calvert, J.M.; Lees, D. G.

doi:10.1007/bf00666474

Cited by 36 publications

(15 citation statements)

References 13 publications

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“…If chromium vacancies dominate the growth process in the bulk of the oxide, then k, can be formulated as (4) and consequently diffusion by chromium vacancies gives rise to an easily measurable dependence of k, on the oxygen partial pressure, because Pb, 6 P k 2 .…”

Section: The Oxidation Of Pure Chromiummentioning

confidence: 99%

The reactive element effect; ionic processes of grain-boundary segregation and diffusion in chromium oxide scales

Polman¹,

Fransen²,

Gellings³

1989

J. Phys.: Condens. Matter

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Abstract. The transport processes in chromium oxide reviewed here, are related to the basic ionic processes in oxides. Solid state science has been effective in describing the complicated diffusion-controlled oxide growth of chromium and chromia-forming alloys. Additions of reactive elements to chromia-forming alloys have a remarkably beneficial effect and this effect is also related to ionic transport processes in crystal lattices. Chromia-forming alloys are widely used in coal handling and conversion systems due to their good high-temperature corrosion properties; for industrial applications the requirement is that a good adherent protective oxide with a low diffusion of defects is formed. Recently, improved knowledge has been gained of the identity of the moving species and the values of the corresponding diffusion coefficients in chromia scales. STEM measurements give experimental support for the theory of grain-boundary segregation and blocking of grain-boundary diffusion by reactive elements.In this paper the current ideas on the transport processes in chromia and the role of rare earth additions on the corrosion behaviour are reviewed. In addition calculations on crystal lattices and grain boundaries are discussed. The calculations on chromia have been beneficially influenced by earlier theoretical considerations on nickel oxide. Consequently, results on (doped) nickel oxide as well as chromium oxide are discussed.

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Section: The Oxidation Of Pure Chromiummentioning

confidence: 99%

The reactive element effect; ionic processes of grain-boundary segregation and diffusion in chromium oxide scales

Polman¹,

Fransen²,

Gellings³

1989

J. Phys.: Condens. Matter

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“…Liu et al [19] Figure 4(d) may be an indication that the activity of both silicon and chromium has been increased. Skeldon et al [23] indicated that oxide scale growth on pure chromium took place at the oxide-air interface, which indicated the outward diffusion of chromium was necessary for the growth of the new oxide scale. [23] Although the current set of alloys is far from pure chromium, it may be possible that chromium near the intermediate oxidation interface is responding in a similar fashion.…”

Section: Resultsmentioning

confidence: 98%

“…Skeldon et al [23] indicated that oxide scale growth on pure chromium took place at the oxide-air interface, which indicated the outward diffusion of chromium was necessary for the growth of the new oxide scale. [23] Although the current set of alloys is far from pure chromium, it may be possible that chromium near the intermediate oxidation interface is responding in a similar fashion. Chattopadhyay et al [15] proposed that the substitution of Mo at Nb sites in Nb 2 O 5 resulted in lower anion vacancies that can lead to slower diffusion of oxygen and increased activity of silicon, which can enhance the thermodynamic stability of SiO 2 .…”

Section: Resultsmentioning

confidence: 98%

Oxidation Behavior of Nb-20Mo-15Si-25Cr and Nb-20Mo-15Si-25Cr-5B Alloys

Portillio

Varma

2011

Metall Mater Trans A

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Nb-20Mo-15Si-25Cr (25Cr alloy) and Nb-20Mo-15Si-25Cr-5B (25Cr/5B alloy) alloys have been subjected to oxidation in air for 24 hours from 973 K to 1673 K (700°C to 1400°C). Even though B additions do not improve oxidation resistance at temperatures higher than 1473 K (1200°C), the lower temperature oxidation resistance is superior with B by influencing the microstructure. Porous oxide scale development at lower temperatures has been attributed to the dominant growth of Nb 2 O 5 and the vaporization of MoO 3 . An intermediate oxidation layer is developed between the scale and the metal for the 25Cr/5B alloy at temperatures above 1173 K (900°C). Scale densification at elevated temperatures results in higher stress development as a result of the mismatch of coefficients of thermal expansion, ultimately resulting in oxide spallation.

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“…The oxygen diffuses inward This view is supported by a study of Skeldon et al (11) who used an oxygen isotope as a tracer to understand the mechanism of growth of wavy Cr2O3 scales on pure Cr in pure oxygen.…”

Section: Metallography and Microanalysismentioning

confidence: 83%

Influence of Si or Ti Addition to Fe–23Cr–5Al Alloy on Protectiveness of Preformed Al<SUB>2</SUB>O<SUB>3</SUB> Scale against Sulfidation

Taniguchi

Shibata

1988

Trans. JIM

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An Fe-23Cr-5Al alloy and that containing Si or Ti in 0.2 mass% were oxidized to form a-Al2O3 scales in a flow of pure O2 at 1300K for specified periods up to 400ks and subsequently sulfidized at 1200K in an H2-10% H2S atmosphere without intermittent cooling. The protectiveness of the scale was evaluated by the protection time after which a remarkable mass gain takes place owing to the rapid growth of sulfides. In general, the protection time increases as the scale thickens. The addition of Si, however, decreases the protection time, which does not vary much with the scale thickness. Contrary to this, the addition of Ti increases the protection time, These results were explained in terms of the structural soundness of the scales.

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An investigation of the growth-mechanism of Cr2O3 on pure chromium in 1 atm oxygen at 950� C

Cited by 36 publications

References 13 publications

The reactive element effect; ionic processes of grain-boundary segregation and diffusion in chromium oxide scales

The reactive element effect; ionic processes of grain-boundary segregation and diffusion in chromium oxide scales

Oxidation Behavior of Nb-20Mo-15Si-25Cr and Nb-20Mo-15Si-25Cr-5B Alloys

Influence of Si or Ti Addition to Fe–23Cr–5Al Alloy on Protectiveness of Preformed Al<SUB>2</SUB>O<SUB>3</SUB> Scale against Sulfidation

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An investigation of the growth-mechanism of Cr2O3 on pure chromium in 1 atm oxygen at 950� C

Cited by 36 publications

References 13 publications

The reactive element effect; ionic processes of grain-boundary segregation and diffusion in chromium oxide scales

The reactive element effect; ionic processes of grain-boundary segregation and diffusion in chromium oxide scales

Oxidation Behavior of Nb-20Mo-15Si-25Cr and Nb-20Mo-15Si-25Cr-5B Alloys

Influence of Si or Ti Addition to Fe&ndash;23Cr&ndash;5Al Alloy on Protectiveness of Preformed Al<SUB>2</SUB>O<SUB>3</SUB> Scale against Sulfidation

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Influence of Si or Ti Addition to Fe–23Cr–5Al Alloy on Protectiveness of Preformed Al<SUB>2</SUB>O<SUB>3</SUB> Scale against Sulfidation