THE EFFECT OF TEMPERATURE ON THE CORROSION BEHAVIOR OF A 70/30 CU-NI COMMERCIAL ALLOY IN SEAWATER

A series of experiments was carried out in seawater at different temperatures in order to investigate the correlation between the modification of the composition of the passive layer linked to temperature change and the resistance of the alloy against generalized or localized corrosion. Free corrosion and electrochemical tests (polarization curves, impedance measurements) were carried out at 20, 40, 60, 80-degrees-C in quiescent seawater at pH 8.2 with dissolved oxygen (D.O.) contents ranging from 6.5 ppm (at 20-degrees-C) to 3.0 ppm (at 80-degrees-C). The corrosion products adherent to the metallic surface were analysed with chemical and XPS methods. It was found that by increasing the temperature: (a) the corrosion rate of the alloy increases; (b) selective copper dissolution takes place; and (c) the nickel amount in the corrosion products increases owing to the formation of a copper-nickel oxide, with a nickel content higher than in the alloy.