Isothermal diffusion of strontium and cobalt ions in pure NaCl crystals and reconsideration of the Soret effect

Abstract

The tracer diffusion coefficients of Sr²⁺ and Co²⁺ ions were measured simultaneously in pure NaCl in the temperature range 600–750°C. The results for Sr²⁺ differ from previous measurements Used in conjunction with previous Soret measurements they lead to the conclusion that the heat of transport of a Sr²+ vacancy complex is approximately twice the magnitude expected if the heat of transport for each jump were equal to the enthalpy of activation for the jump. The Co²⁺ diffusion profiles are qualitatively different from those of Sr²⁺ and exhibit an unexplained region of slow diffusion in the first 65 µ below the surface.