Preparation and Tribological Properties of Monodispersed Nano-SiO2 Particles as Additive in Lubricating Oil

Monodispersed SiO_2 spherical particles were prepared by the hydrolysis of tetraethoxy silane (TEOS) in the presence of ammonia as a catalyst. The chemical and phase structures of the resulting SiO_2 nano-particulates were characterized using a Fourier transformation infrared spectrometer, and their morphology was observed using a transmittance electron microscope. A four-ball friction and wear tester was performed to investigate the tribological properties of the nano-SiO_2 particles as additive in 500SN base oil. The worn surfaces of the steel balls lubricated with different lubricant systems were observed using a scanning electron microscope, while the elemental compositions of the wear scars were determined by means of energy dispersive spectrometry. It was found that the target nano-SiO_2 particles were spherical-shaped and had a diameter about 60 nm and amorphism structure. At the same time, many hydroxyls were exposed on the surfaces of the nano-SiO_2 particles, which made it possible for them to adsorb and form lubricating and protective layer on the worn steel surface. This accounted for the effectiveness of the nano-SiO_2 particles as the additive in improving the tribological properties of the base stock. Moreover, the 500SN oil doped with 2.0% nano-SiO_2 particles showed the best tribological properties among the tested oil samples.