2018 Volume 35 Issue 4 Pages 350402-
Impurity diffusion coefficients D of five kinds of solute elements in liquid Sn were measured using the Foton shear cell with stable density layering on the ground. This experiment involved diffusion from a thin alloy layer of 3-mm thickness into pure Sn. The Sn alloys contained Ag, Bi, In, Pb, or Sb at 5at%. The diffusion couple was set vertically so that the side with higher density was on the bottom, which is called stable density layering. Four identical parallel experiments were performed simultaneously for each condition. The diffusion temperature was 573 K, and the diffusion time was 8 h. Each obtained profile agreed well with the theoretical equation for the thick layer solution of the diffusion equation (coefficient of determination r2>0.999). The reproducibility of the diffusion coefficients among the four parallel experiments was very good with a standard deviation less than 2.5%. The obtained diffusion coefficients DBi and DIn agreed well with μg-reference data. Therefore, the buoyancy convection was assumed to be suppressed by the stable density layering during the diffusion experiments in this study, including the experiments of SnPb, SnAg, and SnSb with high density gradient. The impurity diffusion coefficients in liquid Sn at 573 K can be expressed as a proportional relationship to the product of the ratio of atomic radii rs/ri of the two substances and thermodynamic factor Φ is, with a gradient equivalent to the value of the self-diffusion coefficient of Sn.
