Effect of pressure on the diffusion coefficient of silver ions in molten alkali metal nitrates

Abstract

The interdiffusion coefficient of silver ions (D_Ag⁺) in molten NaNO₃, KNO₃, RbNO₃ and CsNO₃ has been measured at temperatures in the range 623–723 K and at pressures up to 1 kbar (1 bar = 10⁵ N m^–2), using the chronopotentiometric method. The volume ΔV_D=–RT(∂ ln D_Ag⁺/∂p)_T was evaluated for each system, at several temperatures. For a given solvent, ΔV_D was independent of temperature within experimental error; at a given temperature, ΔV_D increases as the size of the solvent cation increases. In each case, the activation energies for interdiffusion were derived, at constant pressure and also at constant volume. The results are compared with the corresponding volume and energy terms for electrical conductivity in the molten alkali metal nitrates.