Materials Transactions Online

Transactions of the Japan Institute of Metals, Vol. 21 No. 2 (1980) pp.104-114
© 1980 The Japan Institute of Metals

Impurity Diffusion of Silver Ion in Molten Alkali Metal Chlorides*

Tatsuhiko Ejima**, Tsutomu Yamamura**
and Michio Kawashima***

In order to clarify the relative importance of various factors for solute diffusion of impurity cation, the inter-diffusion coefficients of the silver ion in molten alkali chlorides were determined by use of the capillary reservoir method at the temperatures ranging from the melting points of solvent salts to 200 K.
The results obtained can be summarized as follows:
(1) The temperature dependence of the inter-diffusion coefficient of the Ag+ ion was well represented by an equation of the Arrhenius type. Pre-exponential term and the apparent activation energy for diffusion were determined by use of the least squares method.
(2) The applicability of the Stokes-Einstein equation was examined. The diffusion coefficient of Ag+ ions increases linearly with increasing value of kT/η r, where η is the viscosity of solvent salt. The radius of the silver ion in molten chlorides was considered to be nearly equal to that of the sodium ion.
(3) A linear relation was found between the molar volume of solvent salts and the value of D/(T/M)1/2 in the temperature range wherein the diffusion coefficients were measured. The diffusive movement of solute cation was considered to be correlated with that of solvent cations.
(4) The polarization energy of anion as well as the energy for hole formation is an important factor controlling the diffusive movement of the solute cation in molten alkali metal chlorides.

(Received October 18, 1979)

*This article was originally published in Japanese in J. Japan Inst. Metals, 43 (1979), 425.
**Department of Metallurgy, Faculty of Engineering, Tohoku University, Sendai 980, Japan.
***Graduate School, Tohoku University, Sendai 980, Japan. Present address: Osaka Titanium Co., Ltd., Amagasaki 660, Japan.

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