Golfomitsou, S.; (2006) Synergistic effects of additives to benzotriazole solutions applied as corrosion inhibitors to archaeological copper and copper alloy artefacts. Doctoral thesis , University of London.

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Abstract

Benzotriazole (BTA) is a corrosion inhibitor extensively used for the stabilisation of active corrosion of archaeological copper and copper alloys. However, BTA often fails to effectively retard corrosion when applied on heavily corroded artefacts. Although there are numerous studies about its mode of action on clean copper, there is no comprehensive understanding about the way it is bonded to corroded copper. This thesis aimed to understand and compare BTA and its mode of action on clean and corroded copper by examining possible factors that could affect efficiency including concentration, solvent, period of immersion and pH. BTA efficiency could be improved by making use not only of these results but also of the synergism that is observed between BTA and other inhibitive compounds. The combination of inhibitors and the use of the synergistic effect between compounds is common in industry but has never been tested before for use in conservation. The synergistic effect could be beneficial for use on corroded copper alloys suffering with active corrosion. The six compounds selected were 5-Amino-2-Mercapto-l, 3, 4- Thiadiazole (AMT), Benzylamine (BZA), Ethanolamine (ET), l-Phenyl-5-Mercapto- Tetrazole (PMT), Potassium Ethyl Xanthate (KEX) and Potassium Iodide (KJ). These were tested on their own and in combination with BTA. Accelerated corrosion tests were carried out on artificially corroded copper coupons. Analysis using SEM-EDS, XPS, and FT-IR allowed a better understanding of the way different factors affect the formation of the copper-BTA complex formed and subsequently the BTA efficiency. The addition of other compounds into the BTA solutions significantly affected the complex formed and the film properties. Copper(I)-inhibitor complexes were proven to be more protective than copper(II) complexes. The results also showed that there is a synergistic effect between BTA and AMT which results in improved inhibitive efficiency of both inhibitors. The composition of the film formed was mainly dependent on the concentration of the solution, however, it was found to be effective in very low concentrations as well as aqueous solutions. Finally, field trials of some of the more effective solutions of compounds were performed on archaeological objects from Turkey and Greece and these results confirmed those of the laboratory experiments. All of the experiments and fields trials were designed and analysed statistically.

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