The influence of ultraviolet illumination on the passive behavior of zinc

The passive behavior of zinc in alkaline pH 13.0, 10.3, and 9.2 solutions, under dark and illumination conditions, has been studied using de polarizat ion and ac impedance techniques. It was found that illumination with polych romatic light caused dissolution of anodically formed passive layers on zin c, with this photoinduced dissolution effect bring more pronounced in the m ore alkaline pH 13.0 solution. Photoinduced dissolution in the pH 10.3 and 9.2 solutions is explained in terms of the photodecomposition of ZnO throug h reaction with photogenerated holes. The more intense dissolution in the p H 13.0 solution is explained in terms of the photodecomposition of ZnO and the additional electrochemical dissolution in this alkaline solution which occurs as a result of the photodecomposition of the passive layer. Although the electrodes repassivated once the light source was removed, it was foun d that prior illumination led to a decrease in the donor densities and thus a modification of the defect structure of the passive layers. (C) 2000 The Electrochemical Society. S0013-4651(99)08-104-5. All rights reserved.