銅管の腐食に及ぼすホスホン酸溶液中のCa^2＋, SiO₄^4– 濃度およびカーボン皮膜の影響

抄録

Water leakage from copper tubes for air conditioners was a problem due to carbon film dependent pitting corrosion, which was caused by the carbon film formed on the inner surface during copper tube production and the quality of the water flowing inside the tube. In the presence of phosphonic acid (HEDP), which was used as a scale inhibitor, silicate ion (SiO₄^4–) and calcium ion (Ca²⁺), which were considered to be corrosion inhibitors, act on the copper plate surface, which was polished and acid washed to remove carbon film as a measure against pitting corrosion. In this study, copper tubes with carbon coating were used to simulate the real environment, and the corrosion inhibition effect of copper in the presence of HEDP, SiO₄^4–, and Ca²⁺ was investigated electrochemically. The anodic polarization curves showed that the current density of the copper tube was lower than that of the copper plate as the Ca²⁺ concentration increased, and that the copper was less likely to dissolve as ions due to the decrease in the current flowing on the copper surface. The above results suggest that the copper tube with carbon film was more effective than the copper plate in inhibiting copper corrosion due to the increase in Ca²⁺ concentration in the presence of SiO₄^4–.