Ultra-low friction with SiO2 nanoparticles bonded sorbitan monostearate oleogel as green lubricant additives

SiO 2 nanoparticles bonded sorbitan monostearate oleogel (SiO 2 -SMS gel) was prepared by water bath heating. The green oleogel additive in the mineral base oil reduced both the friction coefficient and the wear depth by over 50 % for the DLC and cast iron tribopairs. It achieved an ultra-low friction coefficient of 0.0411. The excellent tribological properties are attributed to the formation of a 300 nm bilayer tribofilm on the cast iron surface. The tribofilm effectively prevents plastic deformation and abrasive wear of the tribopairs. Hydroxyl bonding in the SMS molecules and the embedding of SiO 2 NPs ensure strong adhesion of the tribofilm to the substrate. The findings offer valuable insights for the development of high-performance lubricant additives.