Effect of silica and chloride ion on initial film of copper formed in water

摘要

A part of copper surface changes from metallic luster to brown at an early stage of immersion under water. We term this brown film" initial film" and investigate the effect of silica and chloride ion in water on the formation of the initial film. An expansion of initial film after prolonged immersion depends on the water composition. A high concentration of chloride ion in water increases the area of initial film, whereas a high concentration of silica inhibits formation of the initial film. Cathodic reductions for copper tubes with an initial film revealed that the chloride ion acted as an accelerator of an initial film formation. The initial film of copper formed in the water containing silica and chloride ion was ascertained to consist of cuprous oxide and silicate containing siloxane bonds by FT-IR analysis.