Effect of Applied Potential on Pit Propagation in Copper as Function of Water Chemistry

Abstract

The effect of potential on pit propagation as a function of water chemistry was investigated using artificial pit electrodes. In both 0.01 M HCO3− + 0.01 M SO42− and 0.01 M HCO3− + 0.01 M Cl− solutions, pits grew faster at higher applied potentials. However the magnitude of the pitting rate depends on the solution chemistry. A higher pitting rate was observed during pit growth in 0.01 M HCO3− + 0.01 M SO42− solution compared to 0.01 M HCO3− + 0.01 M Cl− solution. The chemistry of the water determined the morphology and the molecular identity of corrosion products deposited inside and outside of the pits. Thick and porous layers of malachite and brochantite/posnjakite covered pits in 0.01 M HCO3− + 0.01 M SO42− solution. In contrast, thin and compact layers of malachite, cuprite and atacamite/nantokite/eriochantite covered pits in 0.01 M HCO3− + 0.01 M Cl− solution. Modeling successfully predicted these corrosion products. Applied potential determined the amount, the structure and the distribution of corrosion products in both experiment and model. However, the effect of potential was more pronounced in 0.01 M HCO3− + 0.01 M SO42− solution in comparison to 0.01 M HCO3− + 0.01 M Cl− solution.