Abstract: Using stearic acid as modifier, layered sodium silicate (LSS) was modified by ultrasonic treatment to serve as additive of lubricating oil. Modified layered sodium silicate (MLSS) was characterized by sedimentation volume analysis, optical microscope, FT-IR and XRD. The tribological properties of LSS and MLSS as additive in 500SN base oil were investigated with friction and wear testers. The morphologies of worn steel surfaces lubricated with various lubricant systems were observed by a scanning electron microscope. The mechanism of friction reduction and anti-wear function of MLSS additive were also discussed. Dispersion test results showed that MLSS well dispersed in 500SN base oil stably. FT-IR spectra observed that organic functional groups existed on MLSS surface. XRD results indicated that the crystal structure of MLSS was the same as prior to modification. As compared with LSS additive, oil sample having a MLSS dosage of 0.6% exhibited the best anti-wear property, the wear scar diameter decreased by 11.5％; oil sample having a MLSS dosage of 0.8% possessed the best friction reducing performance, the friction coefficient decreased by 29.7％.

Key words: layered sodium silicate, stearic acid, modification, coefficient of friction