XPS study on direct detection of passivator Irgamet 39™ on copper surfaces aged in insulating mineral oil

Corrosion of copper conductors in mineral oil insulated power transformers is a well-known problem in electrical power management and distribution worldwide. Recently, some corrosive compounds containing sulfur (e.g. DBDS, dibenzyl disulfide) have been identified to play an important role in this process. A common strategy to limit corrosion, either as precaution or remedy, is the addition of a passivator (Irgamet 39™, I39™) in the oil, with a recommended concentration of 100 ppm to protect the surface of conductors from chemical attack from corrosive oil components. In this study, samples of naturally non-corrosive oil with different concentrations of I39™ are used to treat copper surfaces that are aged under inert atmosphere and analyzed with X-ray Photoelectron (XPS) to assess directly the effective amount of passivator covering the surface of metal and its dependence on the original concentration in oil. The main aim is, therefore, to determine the effect of the concentration of I39™ originally in oil on the effective surface coverage of copper conductors to observe its distribution and to verify the recommended passivator concentration to be used.