Influence of the atmosphere on the reaction of dibenzyl disulfide with copper in mineral insulation oil

A mineral insulation oil containing 500 mg/l dibenzyl disulfide (DBDS) was aged under different thermal (105 °C to 165 °C) and atmospheric (nitrogen and air) conditions to further understand the reaction mechanism of corrosive sulfur with copper. The DBDS concentration of each oil sample was measured using high-performance liquid chromatography (HPLC), and the change in the color of each oil and copper specimen was subsequently observed. The following conclusions were drawn: copper sulfide (Cu₂S), which is the decomposition product of the DBDS-Cu complex, can be formed under both nitrogen and air environments but is highly prone to deposition on the copper surface under nitrogen. However, the DBDS-Cu complex tends to peel off the copper surface in air, which leads to significantly higher concentration of dissolved copper in oil or to the deposition on the wrapped insulation paper surface. DBDS simultaneously reacts with oxygen and copper when the oil contains oxygen. In addition, the activation energy of the reaction of DBDS with copper was determined as approximately 98.61 kJ/mol by using the Arrhenius equation.