Analysis of Ag Corrosion Products

The corrosion behavior of Ag in outdoor environments and in a salt spray chamber was investigated. The coulometric reduction technique was applied to identify various silver corrosion products including Ag 2 SO 4 and AgO. These corrosion products were observed on samples exposed in certain field environments. A plateau in the coulometric reduction curve associated with metastable hydrogen evolution was observed under conditions in which a considerable amount of Ag 2 S was formed and reduced. Soluble silver chloride complexes were the dominant corrosion product, instead of insoluble AgCl, when the chloride deposition rate was high enough. Under those conditions, the corrosion rate measured by coulometric reduction is lower than the actual corrosion rate. Ag particles formed on the surface during exposure to different environments. During exposure in a marine environment, photodecomposition of AgCl corrosion product resulted in the formation of Ag nanoparticles embedded in AgCl. Isolated Ag particles of a few micrometers in size formed during exposure in a salt spray chamber due to the high exchange current density for the Ag/Ag + reaction.