Impurity diffusion measurement in liquid Al based alloys using X-ray Radiography

Abstract

The high accuracy measurements of the impurity diffusion coefficient in liquid metals are indispensable for modeling diffusion theories. The aim of this study is to investigate how the difference in impurity diffusion coefficient in liquid Al is expressed by the hard-sphere model. The impurity diffusion coefficients in liquid Al were measured using the in-situ shear cell method with X-ray radiography technique at 973, 1020, and 1060 K. The concentrations of the two parts of the diffusion couple were chosen to be pure Al and 5 at% Cu, 1 at% Sn, 1 at% Au, 1 at% Ag, and 0.8 at% Bi in Al. The diffusion process was started at connecting each interdiffusion couple after shearing the furnace and concentration profiles were obtained every second. The impurity diffusion coefficients were calculated from the linear fittings to the mean square diffusion distance which is derived from the concentration profiles using Ficks law. The results showed that the excess entropy model using hard sphere reproduced the measured impurity diffusion coefficients in liquid Al better than the hard-sphere model derived from Enskog theory. This excess entropy model reproduces the impurity diffusion coefficients better for other temperatures as well by considering the temperature dependence of the packing density.