Tribological Properties Of Copper And Silver Sulfide Nanomaterials As Lubricant Additives

In this dissertation, copper and silver sulfide nanoparticles were synthesized by different methods. Thetribological properties of silver sulfide and copper nanomaterials as lubricant additive were studied toexplore the anti-wear and friction reducing mechanism.（1） Cu/SiO₂nanocomposite was synthesized by sol–gel method. The size, morphology and phasestructure of as-prepared Cu/SiO₂nanomaterials were analyzed by means of XRD, TEM and UV-vis wasmeasured in relation to surface Plasmon excitation of Cu particles. The tribological properties ofas-synthesized Cu/SiO₂nanocomposite as an additive in distilled water were investigated with a four-ballmachine, and the morphology and elemental composition of worn steel surfaces were examined. Resultsshow that as-synthesized Cu/SiO₂nanocomposite as a lubricant additive is able to significantly improve thetribological properties of distilled water. A protective and lubricious film composed of Cu and a smallamount of FeS, FeSO₄and SiO₂is formed on steel sliding surfaces lubricated by distilled water containingCu/SiO₂nanocomposite. During friction process Cu nanoparticles can be released from Cu/SiO₂nanocomposite to fill up micro-pits and grooves of steel sliding surfaces, resulting in greatly reducedfriction and wear of steel frictional pair via self-repairing. The state and thickness of the film formed on theworn surface is closely related to applied load; and Cu/SiO₂nanocomposite might be a promisingwater-based lubricant additive for steel-steel contact subjected to moderate load.（2） Cu nanoparticle surface-capped by methoxylpolyethyleneglycol xanthate was synthesized usingin-situ surface-modification technique. The tribological properties of as-synthesized Cu nanoparticle as anadditive in distilled water were investigated with a four-ball machine, and the morphology and elementalcomposition of worn steel surfaces were examined using XPS and SEM. Results show that as-synthesizedCu nanoparticle as a water-based lubricant additive is able to significantly improve the tribologicalproperties of distilled water, which is ascribed to the deposition of Cu nanoparticles on steel slidingsurfaces giving rise to a protective and lubricious Cu layer thereon. The tribological properties and antiwearmechanism of as-prepared surface-capped Cu nanoparticle as an additive in distilled water were discussed.The surface-capped Cu nanoparticles as additive in distilled water （mass fraction5%） can increase the PB values from88N of distilled water to696N.（3） Wate-soluble Cu nanoparticle surface-capped by po1yoxyethylene octylphenol ether xanthate wassynthesized using in-situ surface-modification technique. The tribological properties of as-synthesized Cunanoparticle as an additive in distilled water were investigated with a four-ball machine. We investigatedtribological properties of copper nanoparticles as water-based additive with the additive concentration,rolling speed and load. The results show that po1yoxyethylene octylphenol ether xanthate modified coppernanoparticles as distilled water additives can significantly improve the carrying capacity and anti-wear ofdistilled water. The surface-capped Cu nanoparticles as additive in distilled water （mass fraction0.3%） canincrease the tribological properties of distilled water when rolling speed are400rpm,800rpm,1200rpm,1450rpm.（4） We prepared Cu nanoparticles by thermolysis of copper oleate precursor in oil amine under240℃.The tribological properties of as-prepared Cu nanoparticles as lubricating additive in PAO6wereinvestigated using a four-ball friction and wear tester. Results show that as-synthesized Cu nanoparticles asa lubricant additive is able to significantly improve the tribological properties of PAO6. A protective andlubricious film composed of Cu is formed on steel sliding surfaces lubricated by PAO6containing Cunanoparticles. During friction process Cu nanoparticles can fill up micro-pits and grooves of steel slidingsurfaces, resulting in greatly reduced friction and wear of steel frictional pair via self-repairing.（5） Ag₂S nanoparticles with different diameters were prepared by solventless thermolysis of silveroctyl xanthate, silver hexadecyl xanthate and silver carnaubyl xanthate as single-source precursors.As-prepared Ag₂S nanoparticles were characterized by transmission electron microscopy, x-ray diffraction,and Fourier transform infrared spectrometry. Possible growth mechanism of Ag₂S nanoparticles wasspeculated. In the meantime, the tribological properties of as-prepared Ag₂S nanoparticles as additives inliquid paraffin were evaluated using a four-ball friction and wear tester. It was found that Ag₂Snanoparticles prepared from silver carnaubyl xanthate had the smallest mean diameter of10nm, while thesame products obtained from silver octyl xanthate and silver hexadecyl xanthate had a larger meandiameter of50nm and20nm. The three types of as-prepared Ag₂S nanoparticles as additives were all ableto improve the friction-reducing and antiwear properties of liquid paraffin, and as-prepared Ag₂Snanoparticles of the smallest average size possessed the best tribological properties for steel-steel pair. This could be because Ag₂S nanoparticles with a smaller mean diameter are easier to be deposited on slidingsurfaces and exert self-repairing function more efficiently.