Synergistic effects of copper corrosion inhibitors for copper and copper alloy archaeological artefacts

Benzotriazole (BTA) is one of the most widespread treatments used at present for the stabilisation of bronze disease. Unfortunately, BTA does not always work effectively when applied to heavily corroded copper and copper alloy archaeological artefacts. Combinations of corrosion inhibitors are extensively used in industry to retard copper corrosion. When two or more corrosion inhibitors are used, the inhibition efficiency of the mixture may be improved. This paper presents data that indicate the mixture of BTA with other inhibitors for chloride-containing corrosion products improve corrosion prevention under accelerated testing conditions. The six selected compounds. 5-Amino-2 Mercapto-1, 3, 4-Thiadiazole (AMT), Benzylamine (BZA), Ethanolamine (ETH), 1-Phenyl-5-Mercapto-Tetrazole (PMT), Potassium Ethyl Xanthate (KEX) and Potassium Iodide (KI) were tested individually and in combination with BTA. Factors such as concentration of the solution, time of immersion and solvent (de-ionised water, and ethanol) were examined. The inhibitors were applied initially on artificially corroded copper coupons and accelerated corrosion tests were assessed. The treated coupons were analysed using Scanning Electron Microscope (SEM-EDS) to examine the effects of such combinations. The results indicate that the combination of BTA with AMT improves the inhibitive efficiency at lower concentrations with ethanol or deionised water as a solvent. Finally, the combinations of BTA with AMT and BTA with PMT were applied on archaeological objects from the excavations of Kaman Kalehoyuk in Turkey and Mochlos in Crete, Greece. Treated objects have been monitored on an annual basis to investigate their long-term performance.