Influence of copper on iron corrosion in weakly alkaline environment containing chloride ions

The influence of copper content on the corrosion of iron has been investigated to make possible the use of scrap as a source material for reinforcing steel in concrete structures. An AC impedance technique was used to monitor the corrosion of iron, Fe-0.4 mass%Cu and Fe-3 mass%Cu undergoing cyclic wet-dry conditions with a I hour immersion in a pH10 solution of Ca(OH)(2) containing 0.01 M NaCl followed by a 3 hour drying at 298 K and 50% RH. The corrosion rate of iron is greatly accelerated by wet-dry cycles. This is because active FeOOH species produced by the oxidation of Fe(11,111)oxide in air during drying act as very strong oxidants that promote corrosion in the wet condition. In each cycle, shortly before the surface dried out, a large increase in the corrosion rate was observed. This can be explained by the acceleration of oxygen transport through the thin electrolyte layer. Fe-0.4 mass%Cu showed a similar trend to iron. On the other hand, Fe-3 mass%Cu showed much lower corrosion rates and the corrosion was not accelerated by wet-dry cycling. Monitoring showed that the addition of 0.4 mass%Cu does not diminish the corrosion resistance of iron and the addition of 3 mass%Cu improves it under these wet-dry conditions. Energy Dispersive Analysis of X-ray (EDX) results indicated enrichment of copper in an inner rust layer after exposure to 56 wet-dry cycles.