Tribological Characteristics and Synergistic Lubrication Mechanisms of a Novel Additive Based on TiO ₂ Supported by Coal-to-Oil Soot Nanoparticles

This study successfully prepared oleic-acid-modified nitrated soot-loaded TiO 2 composite material (CS/TiO 2 ) using the hydrothermal method, aiming to explore the tribological performance and lubrication mechanism of the synergistic effect between CS and TiO 2 . This composite material significantly improves its dispersion stability in lubricating oil by growing TiO 2 nanoparticles in situ on the CS surface and grafting them onto the oleic acid surface. Through the four-ball friction and wear test, it was found that when the concentration of CS/TiO 2 added to liquid paraffin (LP) was 0.4 wt %, it exhibited the best antifriction and antiwear performance. Compared with the LP, the average friction coefficient and average wear scar diameter were reduced by 36.6 and 14.3%, respectively. XPS and SEM analysis of the worn surface showed that CS/TiO 2 formed a lubricating protective film rich in C, O, and Fe on the surface of the steel ball through frictional chemical reactions during the friction process. Mechanism studies have shown that TiO 2 nanoparticles have the polishing effect of “micro bearings”, while CS constructs a hard carbon-based lubricating film, and the two mechanisms work together to reduce direct contact on the friction surface. Density functional theory (DFT) and molecular dynamics (MD) simulations further reveal at the atomic scale that the long-chain molecular steric hindrance effect of CS effectively suppresses the aggregation of TiO 2, increases the adsorption energy of the composite material at the metal interface, and forms a stable and continuous friction film, endowing the composite material with excellent long-term effectiveness and high load lubrication potential. This study provides a new paradigm for developing efficient carbon-based lubricant additives.