Anomalous diffusion coefficients for W(IV) ion diffusion in NaCl-KCl melt at 700-750°C

The electrodepostion of bi-valent iron, zinc and tungsten (IV) on tungsten electrodes in equimolar NaCl-KCl melt at 700-750°C was studied by Cyclic Voltammetry and Chronoamperometry. While iron (II) and zinc (II) ions demonstrate regular values of diffusion coefficients, which are all in the range of 10^-6-10^-5 cm²/sec, tungsten (IV) ions diffuse considerably slower. Plausible process mechanisms were proposed, according to which the tungsten (IV) ions form polynuclear ions and these massive species diffuse at considerably more moderate rates.