スケール分散剤と防錆剤共存下における銅の孔食に及ぼす硫酸イオンと炭酸水素イオンの影響

抄録

We focused on phosphonic acid (HEDP) as a scale dispersant and benzotriazole (BTA) as a copper corrosion inhibitor to prevent carbon film–dependent pitting corrosion of copper pipes used in air conditioning systems. In the presence of HEDP and BTA, we also found that silicate SiO₄⁴⁻, calcium Ca²⁺, and bicarbonate HCO₃⁻ ions were effective in inhibiting copper corrosion, while chloride Cl⁻ and sulfate SO₄²⁻ ions have been reported to be involved in the promotion of copper corrosion as corrosive anions. Here, we investigated the effects of the corrosive anions SO₄²⁻ and HCO₃⁻, which are effective as corrosion inhibitors, in the presence of HEDP, BTA, SiO₄⁴⁻, Ca²⁺, and Cl⁻ on copper pitting corrosion. Natural electrode potential measurements demonstrated decreases in the potential at stability and the amount of pitting corrosion with increasing SO₄²⁻concentration. When HCO₃⁻ was added to the system, the potential at stability became lower than when only the SO₄²⁻concentration was varied, and the amount of pitting corrosion decreased. In anodic polarization curve measurements, the potential range during a gradual increase in current density was wider when SO₄²⁻ and HCO₃⁻concentrations were varied than when only the SO₄²⁻concentration was varied. In addition, the range of potentials at the time of a gradual increase in the current density was wider, and there was a trend toward a more stable increase in current density value. These results suggested the involvement of SO₄²⁻ in the progression of corrosion of copper in the presence of HEDP and BTA, while HCO₃⁻ had an inhibitory effect.