Tribological enhancement of potential electric vehicle lubricants using coated TiO2 nanoparticles as additives

Abstract

This work presents the antifriction and antiwear properties of TiO2 nanoparticles coated with oleic acid, TiO2-OA, as additives of a low viscosity polyalphaolefin base oil, PAO8. To find the optimal concentration of nanoadditives that minimize friction and wear, four PAO8 based nanodispersions were formulated: PAO8 + 0.10 wt% TiO2-OA, PAO8 + 0.25 wt% TiO2-OA, PAO8 + 0.35 wt% TiO2-OA and PAO8 + 0.50 wt% TiO2-OA. Tribological experiments were performed under pure sliding and rolling-sliding conditions at 120 °C, with the four formulated nanolubricants and with PAO8 base oil. All the nanolubricants showed lower friction coefficients than that obtained with the PAO8 base oil, reaching maximum reductions for the 0.35 wt% TiO2-OA nanolubricant, for both types of test conditions. The tribological specimens tested under pure sliding conditions with the nanolubricants showed fewer wear than those tested with PAO8, finding the highest wear decreases also with the PAO8 + 0.35 wt% TiO2-OA nanolubricant, being 26 %, 65 % and 73 %, in wear track width, depth and area, in that order. Through Raman microscopy and roughness study of the worn samples, it can be inferred that tribofilm, mending and polishing mechanisms occur. Moreover, the thermal conductivity of the optimal nanolubricant (0.35 wt%) was measured at 20, 30, 40 and 50 °C.