ON THE EFFECTS OF COMMON POLLUTANTS ON THE CORROSION OF COPPER-NICKEL-ALLOYS IN SULFIDE POLLUTED SEAWATER

Various pollutants are often introduced in seawater by wet and dry deposition and by improper dumping of municipal wastewater. These pollutants often affect the corrosivity of seawater on copper-based alloys which might be thought to be resistant in this environment and do not receive sufficient research efforts. In the present investigation the effect was determined of some common pollutants such as urea, sodium sulfite, sodium nitrate, sodium phosphate, copper sulfate, lead acetate, ammonium sulfate, and ammonium chloride at a level of 10 ppm and of chlorine at 1 ppm concentration on the corrosion characteristics of the 90Cu-10Ni and the 70Cu-30Ni alloys in seawater, both in the presence and in the absence of 10 ppm sulfide. Both small amplitude cyclic voltammetry (SACV) and the Tafel extrapolation technique were employed as test procedures. All pollutants under investigation have led to an increase in corrosion rate and their effect was more pronounced when sulfide was also present. The effects of pollutants were more intense on 90Cu-10Ni as compared to 70Cu-30Ni alloys. In unpolluted seawater, the worst pollutant for 90Cu-10Ni alloy is sulfide followed by urea add chlorine, while for the 70Cu-30Ni alloy, the worst pollutant was ammonium chloride followed-by sulfide and sodium phosphate. In unpolluted seawater, the introduction of pollutants led to a corrosion reaction which was under cathodic control except for sulfide where the reaction was under anodic control and resulted in a sharp negative shift in the corrosion potential. In sulfide polluted seawater, the worst pollutant for 90Cu-10Ni alloy was ammonium sulfate followed by urea while for 70Cu-30Ni alloy, the worst pollutant was urea followed by ammonium chloride, ammonium sulfate, and sulfite ions.