INHIBITION BY HETEROCYCLIC-COMPOUNDS OF CORROSION OF COPPER

The corrosion behaviour of copper in 30% ethylene glycol solution containing 100 ppm SO2-4, 100 ppm Cl- and 100 ppm HCO-3 at pH values of 7.0 and 8.5 and at temperatures of 60 and 70°C were studied in the presence of different concentrations of two heterocyclic compounds: 3-phenyl-1,2,4-triazol-5-thione (PTH) and 2-amino-4,6-dimethyl-pyrimidine(ADP). The electrochemical polarization studies and the weight loss results showed that the presence of 5 ppm of (PTH) or 50 ppm of (ADP) gave better corrosion protection for copper than other concentrations. The chemical nature of the protective layer(s) formed on the copper surface was determined by X-ray photo-electron spectroscopy. The results show that in the presence of 5 ppm PTH, a Cu(I) complex was formed at pH 8.5 and at a temperature of 60°C. However, a Cu(II) complex was formed when the temperature was raised to 70°C or at a pH of 7.0 at temperatures of 60 and 70°C. ADP shows a very weak Cu(II) state covered with a considerable amount of the ADP compound at all the different experimental conditions. © 1990.