Atmospheric Corrosion of Silver

Date of Award

2022

Degree Name

M.S. in Chemical Engineering

Department

Department of Chemical and Materials Engineering

Advisor/Chair

Ronald Zeszut

Abstract

Atmospheric corrosion of silver was investigated to be used as an indicator metal for corrosion of steel and aluminum. Silver coupons were exposed for 3-18 months in three beachfront locations in Florida: Key West (NRL-KW), Kennedy Space Center (KSC), and Daytona Beach. A galvanic reduction technique was used to characterize the silver corrosion film on both the front and backs of each coupon. Spread of electrolyte outside the standard reduction area was observed during testing. It was determined that the rough and porous corrosion film allows this over-wetting phenomenon to occur, which can result in silver corrosion product electrochemically reducing outside the experimental area. Proper data interpretation and improvement in experimental parameters to mitigate the over-wetting effect are presented. Each exposure site showed different silver corrosion product growth. Daytona Beach had the highest AgCl growth rate on the fronts of the coupons, whereas KSC had the highest on the backs of the coupons. Other than AgCl, Ag2S was the only other silver corrosion product observed at any site, although it was not observed at Daytona Beach. With the difference in growth rates, it was hypothesized that environment differences were the cause. Five different weather parameters were analyzed: temperature, relative humidity (RH), solar light irradiation, ozone concentration, and wind. Wind showed the highest correlations within and between sites. The backs of the coupons were also analyzed to determine if specific weather parameters affected the fronts and backs differently. It was found that relative humidity had the strongest trend difference between the fronts and backs, not solar light irradiance. Additionally, environmentally deposited ions were analyzed using a wet candle. The deposition of the chloride ion had a strong correlation to AgCl film thickness at NRL-KW but not at KSC or Daytona Beach.

Keywords

Chemical Engineering, Beachfront Silver Corrosion, Atmospheric Silver Corrosion, Silver Reduction Techniques, Coulometric Reduction, Silver Chloride, Environmental and Climatic Factors

Rights Statement

Copyright © 2022, author

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