Role of traces of cupric copper on nitrate induced corrosion.

Corrosion trials on tinplate strips were conducted using media containing 2% ivy gourd alcohol-insoluble solids (AIS) + 100 p.p.m. nitrate in succinate/malate/citrate buffer at pH 4.0, 4.5, 5.0 and 5.5. AIS enhanced corrosion activity of nitrate, by a factor of 4 at pH 4.0-4.5, by a factor of 2 at pH 5.0-5.5. This effect was mainly due to protein present in AIS; effects of the pectin and crude fibre fractions were negligible. Studies on effects of Cu-2-+ (at concn. O10 p.p.m.) on corrosion by 100 p.p.m. nitrate at pH 4.5 or 5.0 showed Cu-2-+ to enhance the corrosive action of nitrate. In the absence of nitrate, Cu-2-+ exerted negligible corrosion activity. Possible mechanisms of the synergistic effects of Cu-2-+ and nitrate are briefly considered. [See preceding abstr. for part I.]