2002 Volume 51 Issue 6 Pages 240-249
Copper tube is generally used in water supplying systems, however the copper tube rarely suffers from a type I pitting-corrosion. To begin with, the effect of components dissolved in tap water on copper-corrosion rate was investigated in this paper.
Copper specimens were immersed in 20 samples of tap water. After 48 hours immersion tests, electrochemical impedance spectroscopy (EIS) measurements were carried out. The copper-corrosion rate was estimated by the result of the EIS measurement. A relationship between the copper-corrosion rate and components dissolved in the tap water was calculated from a multiple regression analysis. This analysis shows that the copper corrosion-rate increases with concentration of a free carbon dioxide.
Polarization curves of the copper specimens were also measured in the tap water samples. Cathodic polarization curves in 20 waters have various profiles in the range of 0 to -0.4V vs. SSE. The slope (ΔV/mV decade-1) of the cathodic polarization curve at -0.25V vs. SSE decreased as the copper corrosion-rate decreased. The profile of the cathodic polarization curve might depend on a state of the oxide film on the surface of copper. It is considered that protective oxide film prevents reduction of dissolved oxygen and that copper corrosion-rate decreases with inhibition of the reduction reaction.
