Performance and anti-wear mechanism of CaCO3 nanoparticles as a green additive in poly-alpha-olefin

This paper reports the tribological behavior of CaCO3 nanoparticles as a green additive in poly-alpha-olefin (PAO) base oil under variable applied load, sliding speed, sliding duration, and temperature. The tribological properties and the electrical contact resistance between the tribo-pairs lubricated with PAO alone, and PAO containing CaCO3 nanoparticles, were determined using an Optimol-SRV 4 oscillating friction and wear tester (SRV). The morphology and wear volume of the worn scar were measured simultaneously using a surface profilometer. The results showed that CaCO3 nanoparticles can dramatically improve the load-carrying capacity, as well as the anti-wear and friction-reduction properties of a PAO base oil. In addition, higher applied load, moderate frequency, longer duration time, and lower temperatures are beneficial to the deposition of CaCO3 nanoparticles accumulating on rubbing surfaces. X-ray photoelectron spectroscopy (XPS) reveals a boundary film composed of CaCO3, CaO, iron oxide, and some organic compounds on the worn surfaces.