Abstract: Oleic acid-modified CuS nanoparticles, which can be placed in a long stretch of time without any occurrence of nanoparticle aggregation, were successfully synthesized in-situ in base oil at room temperature. TEM study showed that the average size of the surface-modified nanoparticles prepared by this method was about 30 nm. IR study indicated that the surface of inorganic CuS nanoparticles reacted with carboxyl group of oleic acid via chemical adsorption, which resulted in a layer of organic modification on the surface of CuS nanoparticles and greatly improved their oil-soluble ability. Friction and wear study demonstrated that this kind of lubricant additives could greatly improve the property of antiwear and friction reduction of the base oil. As the increase of additive concentration, both the friction coefficient and wear scar diameter began to dramatically decrease. When the additive concentration was 0.1%(w), both of them reached the lowest points. However, with the further increase of additive concentration both of them began to increase. SEM study proved that the reason was that the oleic acid-modified CuS nanoparticles could help to formfirmlubricating membrane between the surfaces of the friction pairs.

Key words: In-situ synthesis, Copper sulfide, Lubricating, Antiwear and friction reducing