Corrosion Products Formed on Silver After a One-Month Exposure to Urban Atmospheres

Abstract

Silver plates were exposed to an urban atmosphere for one month to investigate the corrosion products formed in the early stages. After the exposure experiments, the corrosion products on the silver plates were characterized using x-ray techniques, including x-ray diffraction (XRD) and x-ray fluorescence analysis (XRF). The XRD patterns of the corrosion products on silver revealed that both silver chloride (AgCl) and silver sulfide (Ag2S) formed. The diffraction peaks originating from AgCl were much stronger than those of Ag2S; therefore, AgCl was predominant in the corrosion products observed on the outdoor-exposed silver. The chlorine that formed the AgCl originated primarily from sea-salt aerosols. The seasonal differences in the AgCl intensities in the XRD pattern could be observed. However, there was almost no difference in the Ag2S intensities. This was due to the low sea-salt concentrations and relative humidity during winter. Only Ag2S formed on the indoor-exposed silver. The absence of AgCl peaks in the XRD patterns indicated that the sea-salt concentrations were quite low in the indoor exposure site. Silver was found to be sensitive to the chloride in sea-salt aerosol and reduced sulfurous gases.