Grain boundary segregation and diffusion in Ag-S solid solution

Abstract

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 = C gb C b does not depend on the bulk concentration C b for very low concentrations; it depends only on temperature; the energy for sulphur grain boundary interaction is ΔH = −15,000 cal- mole −1. For higher C b , 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 αD gb are explained by the increase of D gb for very low bulk concentrations and by a decrease of α for higher ones. For C b constant, the grain boundary diffusion energy Q gb (33,500 cal-mole −1) is derived from the measured activation energy ( Q gb + ΔH = 18,500 cal- mole −1).