Surface tension, wettability and tribological properties of a low viscosity oil using CaCO3 and CeF3 nanoparticles as additives

The rise of the electric vehicles as a more sustainable transport alternative makes it necessary to study new transmission fluids that adapt to their needs and improve their efficiency. The thermophysical properties (contact angle, surface tension and rheology) and tribological properties (friction and wear) of potential PAO8 transmission nanofluids using CaCO3 and CeF3 nanoparticles as additives are evaluated at mass concentrations of 0.05, 0.10, 0.15 and 0.20 wt%. Low contact angle and surface tension values are obtained, indicating good wettability. When the nanoparticles are used as PAO8 additives, small reductions in surface tension are achieved, but no differences in contact angle are observed. All nanolubricants and base oil exhibit Newtonian behavior. Concerning the tribological behavior, reductions in the friction coefficient are achieved for both types of nanoparticles, with the largest reductions comparing to PAO8 base oil being 13 % and 10 % for nanolubricants containing 0.05 wt% CaCO3 and 0.10 wt% CeF3 nanoparticles (NPs), respectively. In terms of antiwear performance, maximum reductions are obtained for the CaCO3 nanolubricant of 28 % (0.15 wt%), 41 % (0.10 wt%) and 59 % (0.15 wt%) and for the CeF3 nanolubricant of 19 % (0.20 wt%), 53 % (0.10 wt%) and 58 % (0.20 wt%) for the parameters of diameter, depth, and area of the worn track, respectively. Through Raman microscopy, the tribological mechanisms of tribofilm formation, repairing, and rolling can be proposed. A discontinuous tribofilm formed by the CaCO3 and CeF3 nanoparticles reduces the contact area between the two surfaces protecting them.