Inhibition of copper corrosion in a simulated cooling water by pyrophthalone compounds

The inhibiting action of some alpha and gamma pyrophthalone compounds on the corrosion of copper has been studied in a simulated cooling water (SCW) with a low pH. Corrosion tests and polarisation measurements were carried out at 20, 40, 60 degrees C. The pyrophthalones retard active copper dissolution and formation of Cu2O on a surface as well as oxygen reduction. Gamma derivatives show a higher degree of protection in comparison with alpha derivatives. The alpha derivatives form a film of insoluble complexes on the surface but with poor protective properties. It has been demonstrated that gamma pyrodiphenone is a highly effective inhibitor for general and pitting corrosion up to 60 degrees C in SCW and provides protection comparable to that of mercaptobenzothiazole. X-ray photoelectron spectroscopy and SEM studies suggest formation of a film of polymeric structure by coordination of gamma pyrodiphenone with Cu2O on the surface. (C) 1996 The Institute of Materials.