Relative Humidity Cycling Effect on Ag and Cu Corrosion

Abstract

In this work, corrosion behavior of Ag and Cu coupons was evaluated during relative humidity (RH) cycling in a mixed flowing gas (MFG) chamber. Three cycling conditions were performed: 52%-35%, 60%-38% and 70%-40%. One cycling period was set at 20 mins and total exposure time in MFG chamber was 2 days, which allowed for 144 cycles in each experiment. RH change rate as high as 180% per hour was achieved in the third condition. Corrosive gas concentrations were set close to field conditions in challenging environments: H2S-50ppb, NO2-200ppb, Cl2-20ppb, SO2-100ppb. Constant RH (maximum and minimum RH within cycling) exposure experiments were also conducted for comparison with RH fluctuation conditions. For all experiments, the corrosion rates of Ag and Cu coupons were found to be determined by the level of the RH, rather than the cycling of the RH. Cathodic reduction and SEM/EDX were also used to understand corrosion products and morphology of Ag and Cu under different RH conditions.