Electrochemical oxidation of WC in acidic sulphate solution

The electrochemical oxidation of WC in aqueous solutions is critical for the functional stability of hardmetals in aggressive environments. The oxidation of WC and the nature of the oxides formed in 0.1 M sulphuric acid under electrochemical polarisation have been studied by electrochemical methods (cyclic voltammetry, chronoamperometry). The structure and composition of the electrochemically treated surfaces has been analysed by X-ray diffraction, surface Raman spectroscopy and energy dispersive analysis of characteristic X-rays. The morphology of the attacked surfaces was investigated by scanning electron microscopy. Anodic attack gives rise to hydrous WO3 forming a continuous film which tends to develop pits. Alternated anodic and cathodic polarisation yields a very similar composition, but with a lower degree of hydration. The morphology is characterised by micrometric loose grains forming by disruption of the larger grains of the pristine sintered WC surface. The electrochemical conditions giving rise to the inception of WO3 formation by WC oxidation could be accurately identified by monitoring the inception of the development of the cathodic loop corresponding to the electrochemical behaviour of the electrochromic material. (C) 2003 Elsevier Ltd. All rights reserved.