An Improved Treatment of the Kinetics of Coupled I

Authors: S Wang F Gesmundo Y Niu

Publish Date: 2009/07/04

Volume: 72, Issue: 5-6, Pages: 279-

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Abstract

An improved treatment of the kinetics of coupled internal oxidation of the two mostreactive components of ternary alloys by a single oxidant involving the presence of two different fronts of internal oxidation as well as of the critical contents of these two components needed to avoid this oxidation mode is developed both for the case of the absence and of the presence of external scales of the oxide of the mostnoble component These analyses are compared with the approximate solutions presented earlier based on the assumption of a simultaneous precipitation of the two oxides at the same front of internal oxidation The mostimportant parameter to establish the magnitude of deviation of the doublefront solution from that calculated under the assumption of a single front is the solubility product of the oxide of intermediate thermodynamic stability Only when this parameter is relatively large the kinetics for the doublefront solution differ significantly from the simpler case of single front In the presence of external scales another important factor is the magnitude of the respective parabolic rate constant An increase of this constant tends to reduce the differences between the single and doublefront solutions under the same values of all the remaining relevant parameters The same approach is adopted to calculate the critical contents of the two most reactive components required to avoid this form of internal oxidation In this case the assumption of the existence of a single front of internal oxidation represents an even better approximation than for the calculation of the kinetic parameters of internal oxidation

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