Impurity diffusion measurements of Bi in liquid Sn using stable density layering and the shear cell technique

Abstract

To obtain reliable diffusion data on earth, impurity diffusion experiments of Bi in liquid Sn were performed using a stable density layering and the shear cell technique with a reservoir system to provide pressure on the liquid. The experiment type was diffusion of Bi from a SnBi3at.% (5wt%) thick layer into Sn. The diffusion temperatures (diffusion times) were 300°C (8h), 500°C (4.5h) and 800°C (2.5h). At each temperature four parallel experiments were performed simultaneously in one shear cell cartridge. After the diffusion experiments, the Bi concentration profiles were measured by atom absorption spectroscopy. The diffusion coefficients were determined by fitting with the thick layer solution considering the correction method of the shear convection and the averaging effect. As a result, the concentration profiles had only small deviations and the diffusion coefficients agreed well among the four parallel experiments. The mean diffusion coefficient at 300°C agreed well with data from the 1g-diffusion experiments in a magnetic field and with μg-data. It was also shown that this method can be applied also to interdiffusion experiments, in which the influence of Marangoni convection can be investigated by the variation of the pressure inside the capillary and artificial free surfaces on the liquid sample. The temperature dependence of the diffusion coefficient was empirically described as the nth power law (n≈1.8) of T.