Laboratory study: Mitigation of sulphidation attacks on copper by use of a Benzo-Tri-Azole derivative

Irgamet 39 and other BTA derivatives have been launched as being remedial treatment against the sulphidation attacks which under certain conditions may arise due to the wide spread use of DBDS as antioxidant, firstly in non oxidation-inhibited insulating oils and later on, as a combination additive with BHT to create superior oxidation stability behaviour in the type of testing prescribed by e.g. IEC. The purpose of the laboratory study was test if BTA-derivatives did have the potential to function as a remedy against induced copper sulphidation. Metal deactivators like BTA (Benzo-TriAzole) and Irgamet 39, which is a BTA derivative that has been modified to provide better oil solubility, compete with the antioxidant DBDS because the DBDS antioxidant function is to passivate the copper surface so the two chemical species compete for the available sites on the surface. De-activation is a weaker form of decreasing metal surface catalytic activity because it involves only the adsorption of protective molecules on the metal surface while passivation involves the chemical reaction between the metal surface and e.g an oxygen or sulphur-donating compound. This provides a permanent deactivation, which is called passivation. This type of reaction is well known in metallurgy and catalyst industries. For catalysts the passivation is a problem and is therefore called catalyst poisoning. A logical assumption for the outcome of a correctly designed laboratory experiment is that BTA-derivatives will never outperform the true passivators like DBDS. An additional negative consequence is that BTA decomposes rapidly if subjected to only mildly elevated transformer temperature. The decomposition takes place on the metal surface and obey the Arrhenius equation. Consequently the degradation rate for BTA is of interest to evaluate.