ISSN:
1573-4889
Keywords:
Cr2O3-formers
;
CO−CO2−N2 mixtures
;
inner corrosion
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 Fe−28Cr, Ni−28Cr, Co−28Cr, and pure chromium in a number of gas atmospheres made up of CO−CO2(−N2) was studied at 900°C. In addition, chromium was reacted with H2−H2O−N2, and Fe−28Cr was reacted with pure oxygen at 1 atm. Exposure of pure chromium to H2−H2O−N2 produced a single-phase of Cr2O3. In a CO−CO2 mixture, a sublayer consisting of Cr2O3 and Cr7C3 was formed underneath an external Cr2O3 layer. Adding nitrogen to the CO−CO2 mixture resulted in the formation of an additional single-phase layer of Cr2N next to the metal substrate. Oxidizing the binary alloys in CO−CO2−N2 resulted in a single Cr2O3 scale on Fe−28Cr and Ni−28Cr, while oxide precipitation occurred below the outer-oxide scale on Co−28Cr, which is ascribed to the slow alloy interdiffusion and possibily high oxygen solubility of Co−Cr alloys. Oxide growth followed the parabolic law, and the rate constant was virtually independent of oxygen partial pressure for Fe−28Cr, but varied between the different materials, decreasing in the order chromium 〉Fe−28Cr〉Ni(Co)−28Cr. The formation of an inner corrosion zone on chromium caused a reduction in external-oxide growth rate. Permeation of carbon and nitrogen through Cr2O3 is thought to be due to molecular diffusion, and it is concluded that the nature of the atmosphere affects the permeability of the oxide.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF01052021
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