Preparation And Tribological Behavior Of Cu Nanoparticles

In this dissertation, surface-modified Cu nanoparticles were synthesized by different methods. The tribological behaviors were studied to explore the anti-wear and friction reducing mechanism of the Cu nanoparticles.(1) Polyelectrolyte multilayers (PEMs) fabricated by spin-assisted layer-by-layer assembly technique were used as "nanoreactors" for in situ synthesis of Cu nanoparticles, initiated by a series of reaction cycles in which Cu2+was absorbed into the polymer-coated silicon substrate and reduced in NaBH4solution, allowing generation of Cu nanoparticles polyelectrolyte multilayers. The as-prepared Cu nanoparticles were small with a size distribution ranging from3-20nm. Futhermore, the size and the density of Cu nanoparticles in PEMs increased with the number of reaction cycle increasing. And the tribological behaviors of Cu nanoparticles PEMs were also affected by the reaction cycles. PEMs reinforced with appropriate density and size of Cu nanoparticles possess considerably good tribological behavior, allowing nanoparticles therein to maintain strength and robustness while keeping soft and fluid-like exposed surface of the polymer chain at the optimum amount of Cu nanoparticles in the PEMs.Then the surface of Cu-nanoparticles PEMs was modified by fluoroalkylsilane (FAS-17) with low surface energy, generating hydrophobic Cu nanoparticles PEMs. The tribological behavior and wettability of the hydrophobic Cu nanoparticles PEMs were affected by the number of reaction cycles and the number of bilayer of PEMs. And the tribological behaviors of hydrophobic Cu nanoparticles PEMs were also studied under water lubrication than under dry-sliding. The result show that the more hydrophobic the surfaces are, the longer the antiwear life is.SiO2nanoparticles capped with y-aminopropyltrimethoxysilane were doped into polyelectrolyte multilayer films via spin-assisted layer-by-layer self-assembly. The resulting nano-SiO2-doped different composite films (SiO2/PAA)9and (PAH/PAA)3(SiO2/PAA)3(PAH/PAA)3. The amide bond (-CONH-) was formed between not only PAH and PAA but also SiO2and PAA after heating at a proper temperature to transform the adhesion from static electricity to covalent bond. The tribological behavior of the multilayer films was evaluated on a micro-tribometer. It was found that the "sandwich-like" structure (PAH/PAA)3(Si02/PAA)3(PAH/PAA)3was beneficial to contributed to increasing the wear resistance of multilayer film. Namely, the outermost strata of (PAH/PAA)3in composite multilayer film were able to eliminate defects associated with the middle strata, allowing the nanoparticles therein to maintain strength and robustness while keeping soft and fluid-like exposed surface and hence decreasing shearing stress during sliding. And the inner strata of (PAH/PAA)3well anchored to Si substrate acted as an initial "bed" for SiO2nanoparticles to be inhabited, resulting in better antiwear ability associated with good load-carrying capacity and "miniature ball bearings" effect as well of SiO2nanoparticles.(2) Cu nanoparticles surface-modified by dioctylamine dithiocarbamate, alkanethiolate and tetradecyl hydroxamic acid were synthesized with hydrazine hydrate as a reductant using a two-phase extraction route. The size, morphology and structure of resultant surface-capped Cu nanoparticles were analyzed by means of infrared spectrometry, X-ray diffraction and transmission electron microscopy. And the different modifier bond to Cu nanoparticles with different structure chemical bonds. The tribological behavior of surface-modified Cu nanoparticles as an additive in liquid paraffin was evaluated with a four-bail machine. Results show that as-synthesized surface-modified Cu nanoparticles as additive in liquid paraffin have excellent antiwear ability, This is because surface-capped Cu nanoparticles with a low melting point are able to deposit on sliding steel surface to form a good protective film thereon; also because surface-capped Cu nanoparticles can fill up micro-pits on the rubbing steel surface and exert self-repairing function.(3) From the point view of molecular design, two kinds of straight-chain and heterocyclic S-and P-free borate esters as environmental friendly lubricant additive were synthesized. The tribological properties of the borate esters as additive in liquid paraffin were investigated on a four-ball tester. The morphologies and the chemical components of the worn scars were analyzed by means of scanning electron microscopy and X-ray photoelectron spectroscopy or energy dispersive spectrometer. The results showed that the load-carrying capacity and the antiwear performance of the liquid paraffin with the additive added were improved, and wear scar diameter was decrease in comparison with the base oil. This may be closely related to the protective film consisting of boron oxide, Fe2O3, N-containing compounds and other inorganic salts formed during the friction process. And the tribochemical reaction films and physisorption films formd during the friction process play a certain role in reducing wear.