The formation of two layers in the internal oxidation of binary alloys by two oxidants in the absence of external scales
- Univ. di Genova (Italy)
An improved treatment of the simultaneous internal oxidation of binary solid-solution alloys by two different oxidants (double internal oxidation) producing two subsequent layers divided by a sharp planar interface in the absence of external scales of the most-noble component has been developed by removing some of the approximations involved in previous theories. The kinetics of internal oxidation are calculated, based on the assumption that all the partial processes follow the parabolic rate law, as expected for diffusion-controlled processes. The overall thickness of internal oxidation for dual oxidants is found to be equal to or smaller than the sum of those produced by the two oxidants taken separately under the same experimental conditions. The ratio between the thickness of the two regions depends critically on the ratio between the diffusion coefficients of the two oxidants, so that under appropriate limiting conditions, one of the two layers becomes negligible. The degree of enrichment of the most-reactive component in the region of internal oxidation by two oxidants is found to be uniform over the whole zone, but lower than what would be produced by each of the oxidants taken singularly. The theoretical predictions would be produced by each of the oxidants taken singularly. The theoretical predictions are then compared to some experimental results. It is finally shown that the external layer will not contain the compound most stable on an absolute scale, but that most stable with respect to the actual composition of the gas phase, while scaling structures different from that assumed here are also possible.
- OSTI ID:
- 335263
- Journal Information:
- Oxidation of Metals, Journal Name: Oxidation of Metals Journal Issue: 1-2 Vol. 51; ISSN OXMEAF; ISSN 0030-770X
- Country of Publication:
- United States
- Language:
- English
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