Abstract: Three kinds of modification methods were used to modify the active functional groups of five graphenes with different thicknesses and different oxidation degrees to improve their dispersion stability in hydraulic oil. The dispersion of modified graphenes was investigated through long standing test and centrifugal test. The effect of modified graphenes on the friction and wear performance and anti-oxidation performance of hydraulic oil was investigated by four-ball machine friction test and oxidation stability test. The results showed that after modified by KH570, MMA, oleylamine and oleic acid, the few or multi-layer graphenes with low oxidation degree, had poor dispersion stability when added into hydraulic oil. And the high-oxidation graphenes modified by oleamine or oleic acid, when the added amount was 0.01%, the hydraulic oil obtained good oil solubility with stable dispersion for more than one year. At the same time, anti-wear, anti-friction and extreme pressure performance of hydraulic oil was significantly improved.

Key words: graphene, hydraulic oil, modification, dispersion stability, anti-wear and anti-friction