防錆剤を含む水溶液中における銅の孔食に及ぼすスケール分散剤と塩化物イオンの影響

抄録

Water leakage has been reported to occur in copper tubes used in air conditioners due to carbon film–dependent pitting corrosion caused by the carbon film on the inner surface of copper tubes and water quality. Addition of the scale dispersant phosphonic acid (1–hydroxyethylidene–1,1–diphosphonic acid, HEDP) and copper corrosion inhibitor benzotriazole (BTA) to water has been reported to have preventive effects on corrosion. We investigated the effects of silicate ions (SiO₄^4–) and calcium ions (Ca²⁺), which are thought to contribute to scale formation and corrosion inhibition, and chloride ions (Cl^–), which are corrosive anions, in the presence of HEDP and BTA. In this study, the effective concentration of HEDP for pitting corrosion resistance was investigated by varying the concentration of the corrosive anion Cl^– in systems containing HEDP, BTA, SiO₄^4–, and Ca²⁺. Anodic polarization curve measurements showed that there was no significant difference in breakdown potential at HEDP concentrations of 2 mg L^–1 and 10 mg L^–1 at Cl^– concentrations of 0–100 mg L^–1, but breakdown potential at a Cl^– concentration of 500 mg L^–1 was higher at a HEDP concentration of 2 mg L^–1 than that at 10 mg L^–1. These results suggested that similar corrosion inhibition effects were obtained at HEDP concentrations of 2 mg L^–1 and 10 mg L^–1 at Cl^– concentrations of 0–100 mg L^–1, while the corrosion inhibition effect was greater at a HEDP concentration of 2 mg L^–1 than 10 mg L^–1 in the presence of Cl^– at a concentration of 500 mg L^–1.