Combination of diketone and PAO to achieve macroscale oil-based superlubricity at relative high contact pressures

1-(4-ethylphenyl)-nonane-1,3-dione (0206) is an oil-soluble liquid molecule with rod-like structure. In this study, the chelate (0206-Fe) with octahedral structure was prepared by the reaction of ferric chloride and 1,3-diketone. The experimental results show that when using 0206 and a mixed solution containing 60% 0206-Fe and 40% 0206 (0206-Fe(60%)) as lubricants of the steel friction pairs, superlubricity can be achieved (0.007, 0.006). But their wear scar diameters (WSD) were very large (532 μm, 370 μm), which resulted in the pressure of only 44.3 and 61.8 MPa in the contact areas of the friction pairs. When 0206-Fe(60%) was mixed with PAO6, it was found that the friction coefficient (COF) decreased with increase of 0206-Fe(60%) in the solution. When the ratio of 0206-Fe(60%) to PAO6 was 8:2 (PAO6(20%)), it exhibited better comprehensive tribological properties (232.3 MPa). Subsequent studies have shown that reducing the viscosity of the base oil in the mixed solution helped to reduce COF and increased WSD. Considering the COF, contact pressure, and running-in time, it was found that the mixed lubricant (Oil3(20%)) prepared by the base oil with a viscosity of 19.7 mPa∙s (Oil3) and 0206-Fe(60%) exhibited the best tribological properties ( 0.007, 161.4 MPa, 3,100 s).