Abstract
Nickel-copper alloys are widely used as corrosion resistant materials in marine engineering. The corrosion rates of these alloys decrease sharply with increasing nickel content in the alloy. In this study, the corrosion of Monel-400 (70% Ni/30%Cu) in naturally aerated and deaerated Arabian Gulf water (AGW) and 3.5% NaCl solutions was reported. The work has been carried out using cyclic potentiodynamic polarization, chronoamperometric current-time, open-circuit potential, and electrochemical impedance spectroscopy measurements along with scanning electron microscope (SEM) and energy dispersive X-Ray analyzer (EDX) investigations. Polarization data showed that AGW is more corrosive than 3.5% NaCl towards Monel and the deaeration process decreased the corrosion of Monel in both media. Chronoamperometric curves confirmed the results obtained by polarization measurements that the uniform and pitting corrosion of Monel-400 were reduced in the deaerated AGW and 3.5% NaCl solutions. Impedance spectra revealed that the surface and polarization resistances recorded higher values in deaerated solutions. SEM/EDX investigations indicated that the corrosion of Monel-400 proceeds by the selective electrodissolution of nickel, which allows copper enrichment on the surface of the alloy.