An extension of the Wagner theory of alloy oxidation and sulfidation

The recent Wagner theory of binary alloy oxidation applies to situations in which an alloy of metals Aand Breacts with nonmetal Xto form a scale consisting of a solid solution of the corresponding compounds, i.e., A(X)and (X).This theory has been modified in two respects. First, the mathematics have been simplified somewhat by establishing an explicit expression for the average equivalent fraction of each compound in the scale. Second, the Wagner analysis has been generalized to allow for transport of nonmetal Xin the alloy. This latter modification involved permitting the dissociation reaction to take place at the scale-alloy interface. The nonmetal thus released into the alloy was assumed to diffuse interstitially inward.