Tribological interaction of plasma functionalized CaCO3 nanoparticles with zinc and ashless dithiophosphate additives

Abstract Surface-modified CaCO3 nanoparticles, synthesized through plasma-enhanced chemical vapor deposition (PECVD), were employed to improve lubricant additive technology for internal combustion engines via reduction and/or replacement of additives, such as zinc dialkyl dithiophosphate (ZDDP), in engine oil. Various oil formulations were prepared with functionalized CaCO3 nanoparticles, in combination with ashless dialkyl dithiophosphate (DDP) and ZDDP at low concentrations of phosphorus. Tribological test results indicate synergistic interaction of functionalized CaCO3 nanoparticles with ZDDP and DDP, providing enhanced friction and wear performance under boundary lubrication. A comparative study of the tribo-surfaces morphology and chemistry was assessed via atomic force microscopy and X-ray absorption near-edge spectroscopy. Improved wear protection by functionalized CaCO3BM (borate and methacrylate coated) nanoparticles under boundary lubrication was attributed to the formation of calcium and boron-rich 50–80 nm thick tribofilms on the worn surfaces. XANES results revealed that plasma functionalized CaCO3 nanoparticles interact with ZDDP and DDP and participate in tribofilm formation through tribo-chemical reactions and metal cation supply to form stable and wear-resistant tribofilms. These results provide strong support for the potential application of plasma functionalized CaCO3 nano-additives to reduce the concentration of harmful P-based additives in automotive lubricants.