Study on the selectivity of calcium carbonate nanoparticles under the boundary lubrication condition

In this study, three kinds of calcite calcium carbonate nanoparticles (CCNP) with different average diameters as eco-friendly grease additives were successfully fabricated via the carbonation method. The morphologies and phase compositions of the CCNP were determined via XRD, FTIR and TEM. The effects of the concentration and size of synthesized products on the tribological properties of grease have been investigated via an Optimol-SRV IV oscillating friction and wear tester (SRV) and MicroXAM 3D non-contact surface mapping profiler. The results show that the tribological properties of grease can be improved significantly by addition of CCNP. There exists an optimum CCNP concentration, where the grease can exhibit simultaneously optimal anti-wear and friction-reducing properties. Meanwhile, the final tribological performances of the grease not only depend on the mechanical properties of tribofilm formed with CCNP, but also lie on the perfection of grease fiber structure. More importantly, it is interesting to observe a selectivity of nanoparticles with different size for the test conditions. That is, the larger CCNP exhibits optimal performance under higher frequency, while for the smaller CCNP, it happens under higher load and lower frequency.