Measurements of isotope electromigration in metals

Department of Physics, Chalmers Univ. of Technology, Gothenburg, Sweden., Sweden..

Abstract

The isotope effect of electric current in molten metals (« Haeffner-effect ») has been investigated, with special care taken to avoid the influence of convective mixing. Results are presented for pure Rb. K and In, within wide ranges of temperature. The mass-effect μ of isotope electromigration is of the order 10^-5 and grows approximatively with the cube of absolute temperature. The light isotopes migrate towards anode.

The effect has also been measured in a molten Rb-K alloy at temperatures above and below the melting point of pure K. The mass-effect is for K greater, for Rb smaller than in pure metals. This is thought to be connected with electrolytic de-mixing, K being transported towards anode.

An isotope effect by electromigration has also been found in solid In. At a temperature close to the melting point, the mass-effect is of the order 10^-8, and the light isotope migrates towards cathode, i.e. opposite to the effect in melts. According to theory, the corresponding ion self-transport number U should be of the order 10^-7 This has been confirmmed by a direct measurement of U.