Effect of static charge on the tarnishing behaviour of silver in iodine atmosphere at low temperatures

Abstract

The kinetics of Agl film growth on silver under the action of applied static charge of both the polarities, as well as under normal iodination conditions in the temperature range of 294 to 338 K and in the iodine partial pressure range of 0.03 to 0.22kPa, conform to parabolic rate law. Compared to normal iodination, an enhancement in rate under both positive and negative surface charge conditions at the Ag/Agl interface and a decrease in rate under either surface charge condition at the Agl/l₂ interface have been observed. The increased rate with negative charge at the Ag/Agl interface and the decreased rate with same kind of charge at the Agl/l₂ interface, compared to normal iodination, can be explained on the basis of positive hole transport, while the observed effects with positive charge at either of the interfaces receive reasonable support from cation migration as the rate limiting factor during the film growth process.