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.
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