ON THERMODYNAMIC FACTORS IN THE THEORY OF DIFFUSION IN ALLOYS

In a recent paper on a model A-B alloy containing a high concentration of vacancies, Qin and Murch (1995, Phil. Mag. A, 71, 323) obtained 't hermodynamic factors' for diffusion of the two components. These diffe red from one another, whereas the usual treatment of chemical diffusio n leads one to expect them to be equal. In this letter the reasons for the difference are analysed from two points of view, one purely therm odynamic, and the other statistical (in the sense that it recognizes t he presence of vacancies in the system). Within the statistical framew ork (used also by Qin and Murch), a relation between the thermodynamic factors for A and B is derived. In the special case of the symmetrica l model used by Qin and Murch, this relation shows the reciprocity vis ible in their numerical results.