Surface Chemical Factors in the Stress-Corrosion Cracking off Alpha Brass

Abstract

Abstract Stress corrosion cracking of alpha brass in ammonia solutions containing copper-ammonia complexes is most rapid in the pH range 6 to 7, where weight loss corrosion is insignificant, Linear relationships were found for (a) log 1/tc (tc = cracking time) vS log Cu++ (initial copper concentration) and (b) l/tc vs 1/T (T = absolute temperature). Oxygen appears necessary for general corrosion and cracking at pH values above 8. Rapid cracking is interpreted in terms of a drastic surface free energy decrease caused by the adsorption of an intermediate copper-zinc- ammonia complex (not yet identified) which is catalytically formed at the brass/solution interface and is surface active. It is suggested also that linear relationships like (a) and (b) above may be distinguishing features of stress corrosion cracking mechanisms which involve surface energy lowering.