Copper Corrosion in Simulated Acid Rain

Abstract

Copper corrosion in a simulated acid rain has been investigated by the electrochemical impedance analysis, the galvanostatic catholic-polarization, FT-IR and ICP-AES. Effects of pH and the Cl^- concentration on the rate and the mechanism of the corrosion were studied adding H₂SO₄ (or NaOH) and NaCl to the simulated acid rain respectively. The corrosion rate increased with decreasing pH, and with increasing Cl^- concentration. Warburg impedance resulting from a diffusion process for dissolved oxygen was observed at pH below about 3. The rate determining step of corrosion was found to be a film formation/dissolution process at pH≥3.5, and to be a diffusion process for dissolved oxygen at pH≤2.9. The film thickness increased with Cl^- addition to the simulated acid rain, but the film formed at the Cl^- concentration of 1000mg·dm^-3 was thinner than that of 100mg·dm^-3. This decrease in the film thickness at the Cl^- concentration of 1000mg·dm^-3 may result from the formation of CuCl whose solubility is much greater than that of Cu₂O which is one of the major components of the film at low Cl^- concentrations. The corrosion rate is thought to be controlled by CuCl₂^- diffusion when the Cl^- concentration is high.