Friction-Reducing and Anti-Wear Mechanism of BP/Nano-Fe3O4 Nanocomposite as a Lubricant Additive in Soybean Oil

As an emerging two-dimensional material, black phosphorus (BP) has excellent tribological properties, but the poor dispersion of BP in oil inhibits its application in friction to some extent. Surface modification is one of the effective methods to solve the dispersibility of BP, and the use of nano-Fe₃O₄ dotted on the surface of BP improves the dispersion stability of BP in soybean from 3 days to about 15 days. Compared with pure soybean oil, friction coefficient and wear rate of the addition of 0.12 wt% BP/Fe₃O₄ are reduced 65% and 78%, respectively. To elucidate the excellent tribological mechanisms of BP/Fe₃O₄ as additives in soybean oil, the compositional and structural characterisation of the abrasion mark surface was studied accordingly. On the one hand, soybean oil reacts with BP/Fe₃O₄ to form a composite tribo-film during the scraping process. This tribo-film composed of amorphous carbon, iron oxide and phosphorus oxide nitrides prevents direct contact between the sliding interfaces. On the other hand, BP and Fe₃O₄ nanoparticles form a mechanical rollerball structure, which can further reduce interfacial friction and wear through synergistic lubrication. The results provide new insights into the design of additives in biomass lubricating oils and propose new application prospects for BP in the field of lubricating additives.