2008 Volume 57 Issue 9 Pages 392-399
This study was conducted in order to clarify the corrosion behavior of galvanized steel pipes which have often been used for building facilities such cooling water systems. We observed corrosion rates, corrosion potentials, and corrosion products of zinc in tap water of Tsukuba city, distilled water and solutions of some salts at 40°C.
The effects of anions on the corrosion of zinc are summarized as follows. HCO3− inhibits the corrosive reaction. The inhibitive nature of HCO3− comes from the formation of Zn4CO3(OH)6·H2O which retards the anodic reaction. On the other hand, SO42−, Cl−, and NO3− promote the corrosion. The order of promotion is determined experimentally as SO42−>Cl−>NO3− in the concentration of various anion range (<1 mmol L−1) included in tap water. SO42− and Cl− promote the corrosion reaction by destructing the protective ability of surface films. NO3− activates the cathodic reaction, due to its oxidizing nature.
Distilled water was more corrosive than tap water of Tsukuba city. This is due to the salts in tap water, which form the protective films on zinc. The corrosivity of tap water could be discussed on the basis of present paper.
