Diffusion Coefficients of Silver Ion in LiNO₃–CsNO₃ and KNO₃–CsNO₃ Mixtures

Abstract

The diffusion coefficients of silver ion in molten lithium nitrate-cesium nitrate and potassium nitrate-cesium nitrate mixtures have been determined by chronopotentiometry in the temperature range from 260 to 380°C.
The diffusion coefficient of silver ion in lithium nitrate-cesium nitrate mixture increases with the increase of concentration of cesium nitrate from 0 to 20 mol% and decreases with the increase of concentration of cesium nitrate from 20 to 100 mol%, indicating a maximum value at 20 mol% of cesium nitrate. The diffusion coefficient of silver ion in the potassium nitrate-cesium nitrate mixture decreases monotonously with the increase of the concentration of cesium nitrate.
The activation energy for diffusion of silver ion has a minimum value at about 20 mol% of cesium nitrate in the lithium nitrate-cesium nitrate mixture and increases monotonously with the increase of concentration of cesium nitrate in the potassium nitrate-cesium nitrate mixture.
By comparing the determined diffusion coefficients of silver ion in alkali nitrate mixtures with those in pure alkali nitrates, it is found that the circumstances around the silver ion diffused at the concentration of about 20 mol% of cesium nitrate in the lithium nitrate-cesium nitrate mixture approach that in pure sodium nitrate. Such a finding may explain the above concentration dependence of the activation energy for diffusion of silver ion in the lithium nitrate-cesium nitrate and potassium nitrate-cesium nitrate mixtures.