Preparation and tribological performance of core-shell structured rare-earth nanocomposites as lubricating additives

<p indent="0mm">In this paper, ZIF-67@CeO₂ core-shell structured nanocomposites were synthesized using 2-methylimidazole and cobalt nitrate as raw materials. The synthesis was carried out via a layer-by-layer self-assembly method, coordinating on the surface of cerium oxide (CeO₂) nanoparticles. This process significantly improved the dispersion stability of CeO₂ nanoparticles in 500SN base oil. Tribological test results showed that adding 1 wt% ZIF-67@CeO₂ to 500SN base oil resulted in optimal performance. The coefficient of friction (COF) was reduced by 41.54%, and the wear rate decreased by 81.76% compared to pure 500SN base oil. Additionally, the enhanced lubricating properties were maintained even under conditions of high load, high temperature, and high frequency. The morphology and chemical composition of the wear scar was analyzed using a non-contact 3-dimensional surface profile, scanning electron microscope (SEM) equipped with an energy dispersive X-ray spectrometer (EDS), and X-ray photoelectron spectroscopy (XPS) to explore the lubrication mechanism. The results indicated that the ZIF-67 structure was disrupted during friction, releasing CeO₂ particles. This transition transformed sliding friction into rolling friction. Simultaneously, tribochemical reactions occurred among the ZIF-67@CeO₂ nano additives, the 500SN base oil, and the steel substrate. These reactions formed a protective film containing metal oxides, carbon-based materials, and nitrogen-based materials, reducing friction and wear.