Action mechanism of oil‐soluble potassium‐containing antioxidant synergists: evidence for micellar inhibition

One of the most promising synergistic compositions for use in high‐temperature lubricants comprises aromatic amine and an oil‐soluble alkali metal compound although action mechanism of this synergism is still questionable. The greatest efficiency of this additive pair is demonstrated for PEE based compositions using thin‐layer oxidation test at 250°C. Addition of potassium‐containing additive to aromatic amine antioxidant results in decreasing of formation of strongly‐oxidized substances. Determination of electrophysical parameters (dielectric constant and specific conductivity) for tested samples indicates formation of reversed micelles at the potassium content of about 0.6⋅10^‐2 mol/l, and the latter corresponds to the potassium content that provides the highest antioxidant efficiency. A novel method of inhibiting oxidation is proposed: micellar inhibition that suggests novel possibilities for protection of lubricants against oxidative degradation.