Nitrogen-Phosphorus Codoped Carbon Nanospheres as Lubricant Additives for Antiwear and Friction Reduction

Nitrogen and phosphorus doping have been proven to be effective strategies for improving the tribological properties of carbon-based materials when used as lubricating oil additives. Herein, an efficient strategy is demonstrated for the preparation of nitrogen and phosphorus codoped organic carbon nanospheres (denote as N, P@CN) via a template-free interfacial copolymerization combined with ammonium hypophosphite-assisted carbonization. The N and P are found to be homogeneously distributed through the entire carbon shell. The tribological properties of as-prepared materials as base oil additives under different test conditions were evaluated. The as-prepared N, P@CNs exhibit good dispersibility and stability in base oil due to the presence of many organic functional groups. Moreover, they are considered to be thermal stable at elevated temperatures, and the existing robust structure makes them favorable as lubricant additives. The experiment results show that the friction reduction and wear resistance abilities of N, P@CNs were superior to that of pure base oil, because N, P@CNs can induce tribo-chemical reactions to form a protective film on the interfaces due to the combined effect of nitrogen and phosphorus. The obtained N, P@CNs could increase the load carrying capacity of base oil from 250 N to 1050 N. The coefficient of friction can be reduced to 0.08, and the corresponding wear volume loss can be decreased by 90%. These findings open up a possibility to prepare environmentally friendly lubricant additives, such as carbon nanospheres doped with other elements, to achieve excellent antiwear and friction-reducing characteristics.