Limiting currents of electrochemical dissolution of metals under pulse conditions

Limiting pulse currents ii, for anodic dissolution of tungsten in alkaline solution and of zinc in ZnSO4 solution were measured with a rotating disc electrode and under conditions of free convection. In the first case, i(lp) is reached, when the surface concentration of hydroxyl ions involved in the reaction of electrochemical dissolution of metals becomes zero; in the second case, i(lp) is reached when the surface concentration of the salt increases to the concentration of saturation. The it, for dissolution of a tungsten rotating disc electrode was calculated by the equations of Chin, Cheh, and Ibl; i(lp) for zinc dissolution was calculated by a numerical method. Experimental and calculated results were compared. It was shown that existing methods are applicable for calculating i(lp) of tungsten dissolution for various parameters of the pulse current and of zinc dissolution in the limited ranges of parameters. Zinc dissolution is complicated by the fact that not only removal of dissolved salt from the electrode, but also dissolution of the salt, which has precipitated at the electrode, is required during a pulse-off time. (C) 1997 Elsevier Science Ltd.