SUB-MICROMETER ORDER CORROSION OF SILVER BY SULFUR VAPOR IN AIR STUDIED BY MEANS OF QUARTZ CRYSTAL MICROBALANCE

摘要

The purpose of this study is to clarify the effect of temperature (T = 30-75)°C, relative humidity (RH = 10-100%) and distance between sulfur source and silver surface (l = 1-12 cm) on sub-micron order corrosion of silver during exposure to sulfur vapor. Quartz Crystal Microbalance (QCM) technique was employed to continuously and reproducibly detect extremely small mass changes during corrosion of silver by sulfur vapor. Corrosion progressed linearly with time during all the tests. No significant dependence on RH was observed. The corrosion rate increased as temperature rose. This corresponds to the temperature dependence of sulfur vapor pressure. The corrosion rate decreased markedly with increasing distance of up to 6 ～ 8 cm, and beyond that the corrosion rate reached a constant value. The results were in good agreement with the calculated profile of the amount of the arrived sulfur vapor from the solid sulfur source using Jost's cylindrical diffusion model. This suggests that the diffusion of sulfur vapor to the silver controls initial sulfide formation of silver.