The electrochemical behaviour of CuZn under conditions of illumination

The influence of UV illumination on the passive behaviour of Cu372n in pH 9.2 and 13.0 chloride-containing electrolytes was studied using potentiodynamic polarisation tests, cyclic voltammetry and complex impedance spectroscopy. It was found that UV illumination exerted a slight activating effect on the passive behaviour in the alkaline pH 13.0 solution, with slightly higher passive current densities being recorded under conditions of illumination. A more pronounced UV illumination effect was observed in the pH 9.2 solution. This was characterised by a 4-fold increase in the passive current density, a shift in the breakdown potential by 250 mV in the active direction, a decrease in the charge transfer resistance and an increase in the double layer capacitance. These results are explained in terms of the nature of the passive film on CuZn, which consists of a complex layer involving ZnO . xH(2)O and Cu2O/CuO, On illumination, photo-decomposition of the n-type ZnO phase occurs leading to a modification of the passive layer rendering it more susceptible to pitting attack in the chloride environments. (C) 2000 Elsevier Science Ltd. All rights reserved.