The electrochemical behaviour of tungsten—II. The dissolution of tungsten in NaOH solutions

Abstract The anodic dissolution of W in NaOH solutions of pH 13–14 has been studied. The open-circuit potential becomes more noble with time up to a period of about 15 h; thereafter it remains constant. The Tafel slope of the current/potential curves is the same regardless of pre-treatment of the electrode, but the Tafel lines coincide only after polarization for longer than 15 min. The value of α z (transfer coefficient × valency change) was 0·74, and the order of the dissolution reaction, with respect to OH − , was 1. From these two values the variation of the steady-state open-circuit potential with pH could be calculated, assuming that the cathodic reaction is due to oxygen reduction and that it is diffusion-controlled. The valency of the dissolved W was 6·0. The dissolution of WO 3 in NaOH was also studied. The rate-determining step for W dissolution considered the most likely is WO 2 + OH − → WO 3 + H + + 2 e − .