Analysis of Aluminum-Brass Corrosion Products in Sea Water and in Chloride Solutions

Abstract

Abstract A separation and chemical analysis method has been developed of corrosion products forming on aluminum brass surfaces immersed in sodium sulfate solutions at pH= 7.25 (simulating river water) and in sea water at pH= 8.2. This method is based upon a selective solubilization of various oxidation compounds with the aid of proper solvents (i.e. dissolving the metal matrix only to a negligible extent). These analyses can be performed on oxidation films of more than 100 Å thickness. The following solvents were used: 1) Methanol for solubilization of Na+, Cu++ and Zn++ chlorides and sulfates; 2) Glycine to solubilize bivalent metal compounds:Cu and Zn oxydes oxysulfates, oxycarbonates, oxychlorides of Cu and Zn; 3) NH4 OH to solubilize Cu++ and aluminum compounds. A fair agreement was observed between the formulae derived by stoichiometric calculation applied to chemical analyses and the values obtained by X-ray analysis. Agreement was satisfactory for all compounds, except aluminum, determined by chemical analysis and identified by X-rays only in very thick oxidation films (≥ 103 Å). The role of chemical analysis is therefore determinant to finalize the formation mechanism of aluminum brass passivation films.