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

Potential-pH diagrams for the Cu-NH3-H2O and Zn-NH3-H2O systems have been constructed for 15 M ammonia solutions commonly used for studying SCC of alpha-brass. Equilibria and pH calculations were based on activities of NH3 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 alpha-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. (C) 1997 Elsevier Science Ltd.