Accelerated Atmospheric Corrosion Testing of Ag

Corrosion behavior of Ag in atmospheres containing humidity and ozone (O-3), with sodium chloride (NaCl) surface contamination and ultraviolet (UV) illumination, has attracted strong interest recently because of the failure of ASTM B117 testing for Ag. This paper further investigates the effects of these parameters on Ag corrosion by laboratory exposure in a home-built environment chamber. Corrosion products were identified by x-ray diffraction (XRD) and quantified by galvanostatic reduction after exposures in different environments. The corrosion rate of Ag decreased as relative humidity (RH) increased in the presence of O-3 and UV. The morphology of exposed Ag was also affected by RH. UV causes both photoreduction of silver chloride (AgCl) back to metallic Ag as well as an increase in the Ag corrosion rate because of O-3 photolysis. Fuzzy analysis indicates that RH is a more significant factor affecting Ag corrosion than O-3 or UV. The corrosion rate of Ag at Daytona Beach, Florida, also was predicted successfully by artificial neural network fitting of lab exposure results.