Self-diffusion in liquid metals

Abstract

Self-diffusion in liquid metals is investigated using the hydrodynamic model based Stokes-Einstein equation, and the hard sphere model. Based on a study of sixteen liquid metals over a range of temperatures, it is found that the Stokes-Einstein predictions are satisfactory provided a temperature dependent atomic diameter is used. Attempts to fit the self-diffusivity data to Dμp/T=a constant using the temperature independent Goldschmidt diameter yielded values of p ranging from 0.62 to 1.56 for the sixteen metals studied. Extensive calculations were performed in the case of liquid sodium based on the hard sphere model using three different expressions, based on the Enskog theory and corrections to it, for the diffusion coefficient. The effective hard sphere diameter appearing in these expressions was calculated as per the three well-known prescriptions based on perturbation theory and using two different inter-particle potentials. The hard sphere model, apart from not providing satisfactory numerical accuracy, predicts a much weaker temperature dependence of the self-diffusion coefficient than is observed experimentally.