SULFIDING CORROSION OF COPPER-NICKEL ALLOY IN SYNTHETIC SEAWATER

Abstract

90% Cu and 10% Ni wafers were corroded abiotically in synthetic seawater solutions containing various concentrations of H+, dissolved O2, and dissolved sulfide. The samples were not disturbed during the corrosion process by stirring or monitoring of the solution chemistry. The Eh, pH and the concentrations of dissolved O2, and sulfide in the initial and final solutions were measured. Upon removal, the corroded wafers were analyzed by SEM, EDX, XPS and electron microprobe. These analyses revealed the presence of chalcocite, paratacamite, cuprite, aragonite, and possibly djurleite and digenite on the surfaces of the wafers. Adherence of the corrosion films varied with solution chemistry from those that were non-adherent to those showing good adherence. Significant movement of Ni from the wafer was observed. The data suggests a model for an abiotic corrosion process that involves rapid scavenging of dissolved sulfide by copper to form an amorphous or crypto-crystalline Cu-S phase which later recrystallizes into large, well-formed Cu-S minerals. The Cu-S minerals initially formed under reducing conditions persisted even after the solutions became quite oxidizing.