Marine corrosion

Abstract

The accelerating effect of nitrates on the dissolution of tin sometimes observed in tinplate cans of acid products has been investigated by measurements of cathodic polarisation and by direct measurements of corrosion rate in oxygen-free solutions of sulphates and organic acids. The rate of reduction of nitrate, and hence the corrosion rate, increased as the corrosion potential of tin became more positive, possibly as a result of potential dependence of nitrate adsorption on tin. This finding may explain the known influences of pH, of dissolved tin and of the nature of the organic acids present, on the stimulation of corrosion produced by nitrate. The addition of anionic surface active agents created a negative shift of potential and inhibited corrosion but cationic agents caused a positive shift and stimulated corrosion. Sodium lauryl sulphate had a strong inhibitive effect at a concentration of 5 ppm and at 30 ppm almost completely suppressed the effect of nitrate.