Wirtz’s equation and the phenomenological equation for C diffusion in a temperature gradient were combined. It was recalled that Shewmon had proposed the relationship, Q = -Em, where Q and E were the heat of transfer and the migration enthalpy for C in α-Fe. It was pointed out here that the vector spaces in which Wirtz’s equation and the phenomenological diffusion equation were defined were not the same. Therefore, it was not theoretically permissible to combine the 2 equations directly in order to obtain the Shewmon relationship. A corrected equation was derived, to be combined with Wirtz’s equation and thus give the correct expression for solute atom diffusion in a temperature gradient. This involved replacing the migration enthalpy above by the partial molar enthalpy of the solute.

Diffusion Equation for Solute Atoms under a Temperature Gradient. R.Habu: Materials Transactions, 1999, 40[12], 1355-60