Rapid synthesis of onion-like nitrogen-doped carbon nanospheres with microwave and study of its tribological behavior

In this study, a simple and rapid method for the preparation of Nitrogen-doped carbon nanospheres (N–CNOs) was proposed. N–CNOs were successfully prepared by microwave heating the mixture of naphthalene, melamine, and carbon fibers for 2 min, which showed a nearly spherical morphology with a multi-layer onion-like structure, and the average diameter was 197 nm. Compared with CNOs, the coefficient of friction (COF) of N–CNOs decreased from 0.36 to 0.31 and the wear rate decreased from 1.03 × 10 −5 to 0.83 × 10 −5  mm³/(N·m), which decreased by 14 % and 19 %, respectively. When the N–CNOs concentration increased from 4.0 wt% to 16.0 wt%, the COF and wear rate of N–CNOs reached the minimum (0.22 and 0.53 × 10 −5 mm 3 /(N·m)), respectively. The excellent tribological properties of N–CNOs were attributed to the increase of interlayer spacing (0.07 nm) and the atomic scale lattice mismatch, both of which weakened interlayer interactions, thereby improving lubrication performance and reducing friction. This study not only proposed a new preparation method for N–CNOs, but also revealed the lubrication mechanism at the atomic scale, providing a technical support for their application in the field of lubrication.