GRAIN-BOUNDARY SEGREGATION AND DIFFUSION IN AG-S SOLID-SOLUTION

A study is presented of grain boundary equilibrium segregation and diffusion of sulphur in high purity silver, using the 35S radiotracer. At 550°C the segregation coefficient α = Cgb Cb does not depend on the bulk concentration Cb for very low concentrations; it depends only on temperature; the energy for sulphur grain boundary interaction is ΔH = -15,000cal-mole-1. For higher Cb, α decreases while the segregated sulphur varies slightly. The simultaneous study of both equilibrium segregation and diffusion brings out the close relationship between these two phenomena. At a given temperature, the complex variations of αDgb are explained by the increase of Dgb for very low bulk concentrations and by a decrease of α for higher ones. For Cb constant, the grain boundary diffusion energy Qgb (33,500 cal-mole-1) is derived from the measured activation energy (Qgb + ΔH = 18,500 cal-mole-1). © 1979.