Effect of High Electronic Current Density on the Motion ofAu195andSb125in Gold

The effect of high electronic current density on the motion of the ${\mathrm{Au}}^{195}$ and ${\mathrm{Sb}}^{125}$ ions in gold was studied by means of a novel lathe-sectioning technique that permitted the assay of radioactive sections from a specimen only 3 mm in diameter. The mobility $\frac{v}{j}$ of the ${\mathrm{Au}}^{195}$ ion in gold was investigated in the temperature range 874 to 1016°C, with a corresponding variation in mobility of from 9.6×${10}^{-13\mathrm{}}$ to 7.3×${10}^{-12\mathrm{}}$ ${\mathrm{cm}}^3$/A sec, and was found, within experimental uncertainty, to obey the Nernst-Einstein relation, $\frac{v}{j}=\frac{e^{*}\rho D}{\mathrm{kT}}$. The effective charge $e^{*}$ was determined to be independent of temperature, with the value $(9\mathrm{}\pm 1)e$, indicating that momentum exchange with the conduction electrons dominates the force arising from the direct interaction between the external electric field and the positively charged ion. The specific resistivity of the gold ion-vacancy complex was calculated to be (1.2±0.3) μΩcm/(% defect). The electromigration of the ${\mathrm{Sb}}^{125}$ ion in gold was studied at a temperature of 853°C, for which the mobility was 9.24×${10}^{-11\mathrm{}}$ ${\mathrm{cm}}^3$/A sec, and at 1009°C, corresponding to a mobility of 4.54×${10}^{-10\mathrm{}}$ ${\mathrm{cm}}^3$/A sec. The effective charge and specific resistivity of the activated complex are $(140\mathrm{}\pm 40)e$ and (18±6) μΩ cm/(% defect), respectively. As the shift of the ${\mathrm{Sb}}^{125}$ tracer was some 50% greater than the mean-square diffusional penetration distance of the antimony, and the mobility of the antimony ion some one to two orders of magnitude greater than that of the solvent gold atoms, it appears that electromigration techniques could be adapted as a practical method for purifying metals, as an addition to, or substitute for, zone refinement.