XXXVIII. Diffusion of the chloride ion in NaCl

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Abstract
The rate of diffusion of 24Na in NaCl has been measured (Mapother, Crooks and Maurer 1950) by evaporating a film of 24NaCl on to the surface of a crystal of NaCl and subsequently determining the concentration of 24Na as a function of the distance from the surface. Two diffusion processes have been found-diffusion by vacancies created thermally at higher temperatures (intrinsic range) and by vacancies produced by positive divalent impurities at lower temperatures (structure sensitive range). Some problems of interpretation raised by the experiments have been discussed by the above authors and by Seitz (1954). The study of the diffusion of the chloride ion using the same technique with the isotope 36Cl (Chemla 1952) has been limited to temperatures exceeding 650°c by the low mobility of the chloride ion. The present note describes a different tracer method which allows diffusion of the chloride ion to be studied at much lower temperatures. Preliminary results for the diffusion coefficient and activation energy of chloride ion diffusion at 510°c and below are compared with data from the above mentioned papers.