Copper and zinc equilibria in concentrated ammonia solutions: Relevance to stress corrosion cracking of alpha-brass

Potential-pH diagrams for the CuNH 3H 2O and ZnNH 3H 2O systems have been constructed for 15 M ammonia solutions commonly used for studying SCC of α-brass. Equilibria and pH calculations were based on activities of NH 3, and water that were 37.4 and 0.68, respectively. The equilibrium diagrams are in agreement with the reported behaviour of brass in copper-containing 15 M ammonia, and with the active behaviour of zinc. They are the most useful diagrams to date for studies relating to SCC of α-brass in tarnishing and non-tarnishing 15 M ammonia solutions. Anodic polarisation tests indicated that formation of the zinc-tetrammine complex in 15 M ammonia may involve transient zincate ions.