Inhibition of copper corrosion by orthophosphate: A mechanistic study

Abstract

The behavior and mechanism of orthophosphate as corrosion inhibitor on copper in drinking water system was investigated under different immersion time, pH value and dosages. Electrochemical impedance and polarization methods were employed to study the electrochemical process under experiment conditions. SEM and XPS provided supplementary information on the surface scale composition and morphology. The diffusion process control the entire reaction based on the EIS simulation results. Rct, Rfilm and Zfilm increased with extended immersion time; the change tendency became slow after 15 days of immersion at pH of 8.0, 1.0 mg P/L was dosed. The inhibition efficient under pH of 7.2 is about 90%, higher than the 40% under pH of 8.4. The high dosage of orthophosphate promoted the anodic passivtion. A simple mechanism model was proposed and experiments were conducted to prove this hypothesis.