Inhibitive effect of benzotriazole on atmospheric corrosion of copper in presence of hydrogen sulphide

Abstract

The effectiveness of benzotriazole (BTA) vapour as an inhibitor for copper in sulphidising atmospheres (N₂−O₂+H₂S+H₂O) containing 0·1 vol.-ppm H₂S has been investigated. The corrosion products formed were analysed by a coulometric method and by infrared spectroscopy. Pretreatment in either alcoholic BT A solution or BT A vapour before exposure was necessary to ensure effective protection owing to the rapid attack of the unprotected copper oxide layer by the atmosphere. It is shown that BT A produces a protective layer by forming a complex with copper oxide rather than with metallic copper. On exposure to the atmosphere, oxidation from Cur (I)–BT A to a Cur (II)–BTA complex occurs. The presence of oxygen was found to promote formation of Cu₂S on unprotected copper, whereas water vapour acted as a retardant: the sulphidation rate was slower at 75% relative humidity than in the absence of water vapour. However, following pretreatment in BTA the humid atmosphere was more aggressive. In the absence of oxygen, a thin layer of Cu₂S was formed on the specimen surface. It is concluded that this method of protection will be of practical use for copper or copper alloy devices exposed to tarnishing sulphide pollutants.