TiO2 Nanoparticles Coated with Nitrogen-Doped Amorphous Carbon as Lubricant Additives in Engine Oil

Nanoparticle-dispersed lubricants reduce friction and wear of tribo-pairs by providing nanoscale polishing and asperity filling mechanisms. But these particles also have an adverse effect on the lubrication due to the agglomeration and poor interaction with the tribo-interface. Herein, we explore the effect of surface modification of TiO2 nanoparticles on the tribological properties of commercial engine oil. Surface modifications of TiO2 nanoparticles are done by coating layers of amorphous carbon and nitrogen-doped amorphous carbon. Investigations of the tribological properties of surface-modified TiO2 nanoparticle-dispersed oils show improved performance due to high dispersibility in engine oil. There is a decrease in the coefficient of friction by similar to 35% and the wear scar diameter by similar to 27% when compared to the base oil. Both a surface roughness reduction of similar to 85% and a wear depth profile reduction of similar to 88% are due to the nanoscale polishing mechanism at the tribo-interface by nanoparticles. To gain insights of the effects of oil concentration and ball types on the wear scar diameter, a statistical approach is employed. The analysis of variance test yields that the different oil concentrations have a significant effect on the wear scar diameter. The trends obtained from this statistical test are consistent with the experimental results. This novel approach opens up exploring advanced methods of statistical analysis for tribological applications.