Development and evaluation of a low chromate corrosion inhibitor for cooling water systems

The chromate inhibitor held centre stage earlier but is now being phased out because of its toxic and carcinogenic properties. A low chromate inhibitor is hereby developed using Cr-51 and modified radioactive tracer technique. Chromate in solution is replaced systematically from 100 to 5% by berate and the mild steel is still protected at 303 K for at least 6 h. The maximum concentration of Cr in the protective film on the mild steel surface is found to occur in chromate solution containing 40% berate (by weight). The open circuit potential shows the predominance of anodic polarization. The amount of chromate is reduced further from 60% by substituting it with hexametaphosphate. The Cr-containing film increases on the surface displaying the synergistic effect. Optimum composition is thereby found to give the best protective properties. The inhibitor formulation is further modified with the addition of zinc and finally contains only 5% chromate. This inhibitor protects mild steel, copper, brass, solder, Al (3S) even in the presence of 800 ppm Cl- and 200 ppm of SO4- ions. The new inhibitor is more protective, less costly and meets the pollution control requirements. (C) 1998 Canadian Institute of Mining and Metallurgy. Published by Elsevier Science Ltd. All rights reserved.