Anodic reaction characteristics of tungsten in basic phosphate solutions

DC polarization and electrochemical impedance spectroscopy techniques were used to investigate the pH dependent anodic behaviour of tungsten in basic solutions. Anodic currents of W were pH independent between pH 8 and 11. Above pH 12 as pH increased the anodic currents of W also increased. The diffusion control in pH independent regime was observed to arise from slow diffusion of the solubilized species. At higher pH levels, however, OH− ion diffusion from bulk of solution was observed to control the anodic process. Hydrate layer formation, which was observed with low frequency capacitive loop formation, accelerated with increase in pH.