Effect of phosphate ions on electrochemical behaviour of copper in sulphate solutions

The effect of phosphate ions on the corrosion behaviour of copper in sulphate solutions was investigated at different temperatures (293, 313, 333, and 353 K) and at different pH values (pH = 2.1, 7.2, and 12.3). A three electrode electrochemical technique was used for the measurements, using a saturated colonel electrode (SCE) for reference purposes. Both anodic and cathodic polarisation curves were established, from which the anodic and cathodic Tafel constants were determined. Corrosion potentials were determined by extrapolation of the anodic and cathodic Tafel lines to the point of zero current density. The results showed that for a pH value of 2.1, the corrosion rate of copper showed a marked tendency to increase with increasing temperature in solutions containing either sulphate alone or sulphate plus phosphate. However, at pH values of 7.2 and 12.3, this tendency became less pronounced in solutions containing sulphate alone and in solutions containing sulphate plus phosphate together, maximum corrosion rates were greatly reduced and showed less tendency to increase with increasing temperature. Anodic and cathodic reaction mechanisms are proposed to explain the observations for the corrosion of copper