Abstract: MnZnFe2O4 nano-magnetic particles have both magnetic properties and nano-size which will have a significant impact on the resulting film properties and forming mechanism as lubricant additives. MnZnFe2O4 magnetic nanoparticlesare are prepared by the coprecipitation method. Their size distribution and magnetic properties are tested. MnZnFe2O4 magnetic nanoparticles can be directly added into base oil to obtain lubricant oil. Viscosity of lubricating oil is detected. At the same time, the effects of different mass fraction on the thin film lubrication performance are studied with nano-film thickness measuring instrument. Studies show that lubricant viscosity is affected by different mass fraction differently. Under the different entrainment speeds, film thickness, center thickness patterns, liquidity and viscosity are affected by mass fraction directly, but has nothing to do with its viscosity. Then it is pointed out: when distance between MnZnFe2O4 magnetic particles is smaller to some value, weak magnetic-moment will be formed among magnetic particles, magnetic particles and the metal surface. It makes part of the adjacent magnetic particles form a dynamic aggregation, some magnetic particles are adsorbed on the metal surface, which contribute to form a higher strength, more stable and thicker physical adsorbed film.

Key words: Magnetic nanoparticles, Thin film lubrication, Viscosity