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 potentiodyna mic polarisation tests, cyclic voltammetry and complex impedance spectrosco py. It was found that UV illumination exerted a slight activating effect on the passive behaviour in the alkaline pH 13.0 solution, with slightly high er passive current densities being recorded under conditions of illuminatio n. A more pronounced UV illumination effect was observed in the pH 9.2 solu tion. This was characterised by a 4-fold increase in the passive current de nsity, 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 doubl e 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 Zn O phase occurs leading to a modification of the passive layer rendering it more susceptible to pitting attack in the chloride environments. (C) 2000 E lsevier Science Ltd. All rights reserved.