Evaluation of Organic molybdenum Complex as a Synergist for Arylamine Antioxidant in Synthetic Lubricants

An oil-soluble additive molybdenum complex (MoCP) compound was synthesized. The antioxidation properties of a formulation including polyalphaolefin synthetic lubricant (PAO), the complex of p, p'-dioctyldiphenylamine (DODPA) and MoCP, were evaluated by a differential scanning calorimetry (DSC) test and oxidation-corrosion tests. The former measures the incipient oxidation temperature (IOT) and oxidation induction time (OIT) of the lubricant at high temperature. The latter measures the oxidation stability of the oil including viscosity and total acid number increase. In the first test, the IOT and OIT of the PAO containing DODPA were improved respectively after combining with MoCP compound. In the oxidation-corrosion test, in comparison to the base fluid, the additive hardly exhibited antioxidation properties, but the combination of MoCP with DODPA showed a reduction in viscosity Increase of about 32.4%. The Total acid number increase was 25.4% less than those of the lubricants containing DODPA. These results indicate that the additive shows good oxidative synergisms with DODPA antioxidant. In addition, the changes occurring to DODPA in the oxidation of the PAO with and without MoCP were followed by gas chromatography mass spectrometer (GC/MS) measurements. The proposed mechanism of the inhibition involves a synergy between MoCP and DODPA.