Physical origin of surface segregation in binary alloys

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Abstract
Mills's theory of surface effects on a magnetic system is applied to the surface segregation phenomenon in binary alloys. The effect of lattice strain energy is not considered. It is shown that there are two driving forces for the surface segregation: (1) the difference in the surface energy of the composing elements, and (2) a collective effect depending on the relative concentration only. The former force predicts that the element with lower surface energy is enriched on the surface, while the latter force predicts an enrichment of the minority element on the surface. The above results are restricted to the alloys with positive heat of mixing and at a temperature higher than the bulk critical temperature.