Anodic dissolution of cemented carbides of the type [(WC, M); M Co, Ni OR Fe] in sulphuric acid solution. Electrochemical impedance spectroscopy

Abstract Stationary electrodes prepared from the sinterd tungsten carbide (WC, M) containing 10 vol% of M  Co, Ni or Fe binder, with Vickers hardness > 1200 kg mm −2 , have been investigated in 0.5 M H 2 SO 4 using the Scanning Electron Microscopy (SEM) and the Electrochemical Impedance Spectroscopy (EIS) methods. The EIS were carried out at the polished electrode surfaces at the E ss , E p and E pas polarization potentials. The investigated electrode materials undergo a selective anodic dissolution in which the grains of the carbides play the role of microcathodes in relation to anodic parts of the iron group metal binders. On the basis of the obtained results the respective simulated equivalent circuits (EQC) have been calculated. The presence of Warburg impedance suggests the ions migration in/through the porous oxide layer.