Preparation And Tribological Behavior Of Environment-friendly Cu Nanoparticles As Additive

Oil-soluble Cu nanoparticles without phosphorus and sulphur elements were prepared using in-situsurface-modification technique with hydrazine hydrate as a reductant and various organic compounds assurface-modifiers. The phase composition, morphology and chemical structure of as-synthesized Cunanoparticles were analyzed by means of X-ray diffraction, transmission electron microscopy and Fouriertransform infrared spectrometry. The antiwear ability of surface-modified Cu as an additive in base oil wasexamined using a four-ball machine, and the morphology and elemental composition of worn steel ballswere examined using a scanning electron microscope, an energy dispersive spectrometer and an X-rayphotoelectron spectroscope. Furthermore, the anti-wear and friction reducing mechanism of surface-cappedCu nanoparticles was explored. The main contents and research results of this thesis are as follows:(1) Oil-soluble Cu nanoparticles were prepared using in-situ surface-modification technique withtetradecyl hydroxamic acid (THA) as a modifier. The antiwear ability of as-synthesized Cu nanoparticles(coded as THA-capped Cu or THA-capped nano-Cu) as an additive in liquid paraffin was examined using afour-ball machine. It has been found that THA-capped Cu nanoparticles can be well dispersed in someorganic solvents. As-synthesized Cu as an environmentally friendly additive in liquid paraffin showsexcellent antiwear ability for steel-steel contact. This is attributed to the coordinative actions between thetribochemical reaction film of the organic modifying agent with active O and N elements and the depositedfilm of Cu nanoparticles on steel sliding surfaces. Namely, at a low applied load, the tribochemical reactionfilm formed by the organic modifying agent mainly contributes to improve the tribological properties. At ahigh enough load (e.g.,1000N), Cu nanocore of THA-capped nano-Cu particulates is able to deposit onworn steel surface to form a protective film, leading to greatly improved antiwear ability and load-carryingcapacity. Thanks to the cooperative actions of both the tribochemical reaction film of the surface-modifierand the deposition film of Cu nanocore, the friction-reducing and antiwear ability as well as load-carryingcapacity of the base stock are significantly increased.(2) Stearyl hydroxamic acid-modified copper nanoparticles were prepared. As-prepared Cunanoparticle was used as a lubricant additive in liquid paraffin, and its dispersion stability and tribologicalproperties were examined. It has been found that stearyl hydroxamic acid-modified copper nanoparticle hassimilar dispersion stability as THA-Cu, but the former possesses better tribological properties than the latteras an additive in liquid paraffin. This means that the tribological properties of the surface-capped Cunanoparticles tend to improve with increasing carbon chain length of the surface-modifiers, but theirdispersion stability keeps almost unchanged therewith.(3)5-nonyl salicylaldoxime-capped Cu (denoted as N902-capped Cu) nanoparticles were prepared.The tribological properties of N902-capped Cu as an additive in poly-alpha olefin (denoted as PAO6) baseoil were evaluated using a ring-on-block friction and wear tester and a four-ball friction and wear tester;and its dispersion stability was also examined. It has been found that N902-capped Cu nanoparticles haveexcellent dispersion stability. As to the ring-on-block frictional pair with a line contact mode (ring-on-block test rig), N902-capped Cu nanoparticles can significantly enhance the friction-reducing and antiwear abilityof the base stock, showing a negative weight gain. In terms of the steel-steel pair with a point-contact mode(four-ball test rig with a relatively higher contact load), N902-capped Cu nanoparticles are able to depositon steel sliding surfaces and fill up micro-pits and grooves thereon, thereby greatly reducing wear of thesteel-steel pair by way of self-repairing worn steel surfaces. In one word, N902-Cu nanoparticle as a kindof environmentally acceptable lubricant additive has potential application in engineering.