Measurement of Impurity Diffusion Coefficient of Sn in Al

The objective of this study is to identify the conditions for accurate diffusion coefficient measurements with suppression of error factors. The impurity diffusion coefficient of Sn in liquid Al ( D SnAl ) was measured using the shear cell technique. An experiment to confirm concentration dependence (Ex-Conc.) was conducted with varying c 0 , and experiments to confirm reproducibility (Ex-Rep.) were conducted with constant c 0 . D SnAl = (6.27 +/- 0.04) x 10-9-9 m 2 s-1 was obtained in Ex-Rep. In Ex-Conc., the measured diffusion coefficient of Sn in Al ( D SnAl_meas ) increased as initial concentration of Sn c 0 decreased. The following two effects were investigated as the reason for the increase in D SnAl at small c 0 value. First, the effect of convection caused by slight temperature differences during the experiment was clarified by computational fluid dynamics calculations. The apparent diffusion coefficient D app obtained from the calculation was within +/- 10% of the experimental results. Therefore, the effect of convection was sufficiently small. Second, the effect of a small amount of Sn in pure Al (background c bg ) was examined. The background c bg was negligible compared with the concentration change through diffusion and reliable D SnAl_meas was obtained