The Chemistry of Copper Corrosion

Corrosion Chemistry: Copper corrosion is the loss of solid copper metal, Cu + o2 (copper oxidation), to solution. This occurs when electrons, e-, are lost by the base metal and the solid phase is transformed to soluble, dissolved cuprous, Cu+ , and/or cupric, Cu++, ions. The loss of electrons from the solid metal (electron donor) is called oxidation. Anodic Reaction: Cu + o2 ^ Cu++ (aqueous) + 2eIn metal corrosion, chemical oxidation occurs at sites called anodes where electrons are released (lost). Alternately, chemical reduction (the gain of the electrons) occurs at the cathode. The electron acceptors are called oxidizing agents.

Cathodic Reaction: Cl2 o2 + 2e- ^ 2Cl in pitting corrosion, the anodes are small, fixed points at which copper metal is lost. The remainder of the entire pipe surface serves as the cathode. The electron acceptors are called oxidizing agents. Cathodic Reaction: Cl2 o2 + 2e- ^ 2ClIn pitting corrosion, the anodes are small, fixed points at which copper metal is lost. The remainder of the entire pipe surface serves as the cathode. Since the electron acceptors are chlorine (the disinfectant residual) and oxygen, the rate of corrosion is sensitive to the concentrations of both of these oxidizing agents. The rates of virtually all corrosion reactions in water are strongly influenced by temperature and pH. High temperatures markedly accelerate reaction rates whereas higher pH reactions normally decelerate them.