Role of solution chemistry on corrosion of copper in synthetic solutions: effect of bicarbonate ion concentration on uniform and localised attack

摘要

Pitting of copper pipes was simulated in the laboratory in synthetic tap waters with various water chemistries under stagnant conditions at room temperature. The primary interest was the effect of bicarbonate ion concentration on uniform and localised attack. Long term experiments were conducted by immersion tests (weight loss) of 8 months duration. Short term tests were conducted using electrochemical tests. It was found that increasing the bicarbonate concentration in tap waters results in a decrease in the corrosion rate due to uniform attack and increases the tendency to pit. This is irrespective of the (HCO_3~-)/(SO_4~(2-)) concentration ratio. Pitting of copper can be enhanced if the solution contains an oxidising agent such as ferric ions which are recognised to be a common constituent in water supply' systems. A mechanism is presented that predicts the observed relationship between bicarbonate ion concentration and corrosion rate and is supported by experimental data.