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Atmospheric silver corrosion was examined by galvanostatic reduction, as part of a larger study attempting to model corrosion damage on various metals based on exposure location, time, and conditions. Silver coupons were exposed for a specific amount of time (3-18 months) in different beachfront locations in Florida. These coupons were brought back and the resulting corrosion films were characterized with regards to their chemical composition. The presence of a specific chemical compound (e.g. silver chloride) on the silver coupon is determined through an electrochemical reduction of the coupon. The reduction is the result of the application of a constant current applied to the silver coupon, resulting in a measured voltage that is specific for each chemical compound on the coupon surface. A three-electrode cell was used for the reduction process, with the silver coupon as the working electrode, a platinum mesh as the counter electrode, and a mercurous sulfate electrode (MSE) as the reference, all immersed in a sodium sulfate electrolyte. Using a computer controlled potentiostat, a graphical plot of voltage vs. time was generated. The amount of time that the potential remains at a constant value indicates the reduction of a single chemical species on the surface. This time is then converted to film thickness and is analyzed across the different exposure times and locations. Increasing exposure times of the coupons in the field locations showed increasing chloride film thickness, and exposure at different field sites showed different silver chloride film growth rates. Additionally, seasonal exposure condition changes at each site were observed to result in changes in the chloride film growth rate. These findings will assist in the development of accelerated exposure testing and corrosion modeling for other metals.
Douglas C. Hansen, Ron A. Zeszut
Primary Advisor's Department
Chemical and Materials Engineering
Stander Symposium project, School of Engineering
"Silver Beachfront Exposure: Chloride Film Growth as Corrosion Indicator" (2021). Stander Symposium Projects. 2361.