Formation and Breakdown of Surface Films on Copper in Sodium Hydrogen Carbonate and Sodium Chloride Solutions: II. Effects of temperature and pH

The anodic behaviour of copper in air-saturated solutions at 25°, 60° and 90°c has been determined by stepwise potentiortatic polarisation. In 0·01 M NaHCO₃, the critical breakdown potential of the protective oxide layer is displaced to considerably more positive potentials as the temperature increases. In 0·01 M NaHCO₃ containing 0·01 M NaCl, the critical breakdown potential is displiiced tornore negative values with increasing temperature, but the corrosion potential–breakdown potential difference undergoes little change. In 0·01 M NaCl, the surface film on copper is essentially non-protective, and linear Tafelplots are observed. A change in the pH of 0·01 M NaHCO₃, with or without 0·01 M NaCl, from 8·6 to 7·3 has little effect on the valuesof the breakdown potentials. The significance of the results in relation to the initiation of pitting corrosion of copper in natural waters is discussed.