A thin plate of isotropic solid with a constant surface molal fraction was considered. The regular solution could be described by a factor () such that, when  was positive, the attraction between unlike atoms was greater than the attraction between like atoms. It was noted that the depths of penetration, and the average molal fraction for a given period, increased with increasing . The separation of 2 curves for given  value increased with increasing molal fraction. It was found that the diffusion coefficient was positive only if  was greater than -1/X(1-X), where X was the molal fraction.

J.L.Chu, S.Lee: Journal of Materials Research, 1995, 10[6], 1354-7