A Diffusion Model for Oxidation of Nickel-Iron Alloys at 1000°C

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Abstract
A generalized diffusion model involving ternary oxides is used to formulate the oxidation mechanism of Ni‐Fe alloys containing 2 and 4 weight per cent Fe. A defect structure, adopted for the inner nickel oxide layer containing iron, yields the variation of its cation diffusion coefficients which, when substituted in the diffusion equations, yield the cation concentration and the oxygen activity profiles in the oxide and the oxidation constants for the respective alloy. Thermodynamic considerations are used in deriving the oxygen activity profile in the outer two‐phase nickel oxide‐spinel layer of an external scale. A solution to the diffusion problem in the alloy is considered. The experimentally derived composition path in an alloy and the scale is superimposed on the Fe‐Ni‐O phase diagram. This path is shown to be consistent with the structural observations and composition determinations, and it is also consistent with thermodynamic and kinetic considerations.

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