Application of Wagner's Theory to the Parabolic Growth of Oxides Containing Different Kinds of Defects: II . Doped Oxides

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Abstract
The theory of parabolic oxidation of metals forming oxides with a complex defect structure developed in a previous paper is applied here to the oxidation of dilute alloys with incorporation of aliovalent impurities in the scale. The treatment is limited, however, to the simple case of a uniform distribution of the dopant. First, the effect of the dopant on the oxidation rate is examined quantitatively for oxides containing a single kind of defect, obtaining simple analytical expressions for the relevant parameters for limiting situations. Then the growth of on dilute cobalt alloys at 1000°C is analyzed by means of numerical calculations both in the case of the presence and of the absence of metal interstitials, allowing for the presence of metal vacancies of different electric charge. This case is examined as an example of the oxidation behavior of metals forming oxides with a complex defect structure in the presence of dopants. The treatment shows that in some cases even minority defects may change deeply the effect of impurities on the oxidation rate of the pure metal, even reversing the behavior predicted on the basis of a simpler defect model.

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