ANTIOXIDATION SYNERGISM BETWEEN ALKALI-METAL SALTS AND ARYLAMINE COMPOUNDS IN SYNTHETIC LUBRICANTS

Differential scanning calorimetry (DSC) was employed to evaluate the p erformance of an ester lubricant containing alkali metal salts. In the isothermal DSC oxidation lest, the alkali metal salts of perfluorobut yric acid are effective synergists for arylamine antioxidants such as p,p'-dioctyldiphenylamine (DODPA). Among the salts, the order of syner gistic effectiveness is K > Na > Li. When used in combination with ary lamine antioxidants, the Na and K salts can also effectively reduce th e increases in viscosity and acid number of the ester oil in oxidation -corrosion tests. The electron paramagnetic resonance (EPR) results in dicated that the alkali metal salts can reduce the free radical conten ts in the oxidized oil with arylamine antioxidants present.