Lubricating properties of Cyanex 302-modified MoS2 microspheres in base oil 500SN

The lubricating properties of molybdenum disulphide (MoS2) microspheres modified by Cyanex 302 (bis(2,4,4-trimethylpentyl) monothiophosphinic acid) in base oil 500SN were investigated and compared with those of commercial colloidal MoS2 on a four-ball tester and an Optimol SRV oscillating friction and wear tester in a ball-on-disc contact configuration. The worn surfaces of the flat disc lubricated with the additive-containing base oil were analysed by means of X-ray photoelectron spectroscope and scanning electron microscopy. The MoS2 microspheres showed much better extreme pressure properties and anti-wear and friction-reduction properties in 500SN than commercial colloidal MoS2. The effective chemical adsorption and protection film formed by the active elements (S and P) and long chain alkyls in Cyanex 302 and boundary-lubricating transfer film of thin sheets containing the solid lubricant particles (tribochemical products) of the additives could account for the boundary lubrication mechanism. Copyright © 2006 John Wiley & Sons, Ltd.