Morphology-Controlled Preparation Of Nano-Copper, Nano-Nickel And Their Tribological Properties

Nanomatedals,often referred as research forward field of materials science,have widely potential applications because of their special physicochemical properties. Nanostructured metals have recently attracted increasing interests because of their novel properties and potential applications.The research has been a new subject of material science and chemical engineering,and attracted considerable interests in the fields such as materials,physics,chemistry,and industry.A number of methods have been developed to prepare nanostructured metals up to date.Chemical reduction synthesis method was most extensively used and researched because of its simple apparatus,mild reaction condition and easy to production in a large scale.Nano-copper and nano-nickel are extensively concerned functional materials because of their applications span over catalysis,solid lubricantion,and so on. To obtain mature and stable size- and shape-controlled preparation technology of nano-Cu and nano-Ni,more works must be done on researching the effects of operation parameters such as reaction system,precursor,reductant,reaction time and temperature, and so on.The disciplinarian and the effects of different modifiers on the product sizes and morphologies are emphasized researches as being due to that selecting an appropriate modifier is crucial to preparation of size- and shape-controlled nanostructured metal.Size- and morphology-controlled preparations of nano-Cu and nano-Ni have been carded out at low temperature and atmospheric pressure starting from copper sulfate pentahydrate,nickel sulfate pentahydrate or nickel acetate tetrahydrate with ascorbic acid,hydrazine hydrate or 1,2 -propanediol as a reductant in the presence of modifiers such as eco-friendly polyoxyethylene sorbitan monooils (Tweens),polyethylene glycols(PEGs),sodium dodecyl benzene sulfonate(SDBS),and sodium dodecyl sulfate(SDS).The morphologies,size distributions,average particle sizes,and crystalline structures of the as-prepared nano-Cu and nano-Ni samples were characterized by powder X-ray diffraction(XRD),X-ray photoelectron spectrometry (XPS),transmission electron microscopy(TEM),selected area electron diffraction (SAED).The modifying and stabilizing effects of modifiers on the samples were analyzed by thermogravimetric analysis differential scanning calorimetry(TG-DSC), and Fourier transform infraredspectroscopy(FTIR).In order to investigate the promoting effects of nanostructured metals on oil tribological property,the as-prepared nano-Cu and nano-Ni samples were added into different kinds of oils.The experiments were carried out on a UNT-â…¡friction-abrasion tester and a M-2000 ring-piece friction-abrasion tester to investigate the effects of the nanostructured metal size and shape on the anti-wear and friction reducing performances as well as the repair-self mechanism of tribopairs.Some significant results are summarized as follows:1)In water system,among the single modifiers,PEG-2000 was beneficial to fabricating smaller sized nano-Cu spheres with an average particle size of 2.5 nm and a size distribution ranging from 0.5 to 3 nm,PEG-6000 beneficial to preparing bigger sized nano-Cu spheres with an average particle size of 17.0 nm and a size distribution ranging from 5 to 25 nm.Among the mixtures of two modifiers,the co-presence of SDBS and PEG-2000 was beneficial to fabricating abundant monocrystal nano-Cu strips.The co-presence of SDS and PEG-6000 favored the formation of big-sized irregular nano-Cu with an average particle size of 21.8 um and a size distribution in a range of 5-35 nm.2)In water system,single modifier was beneficial to fabricating sphere or sphere-like nano-Ni crystals,composite modifiers were in favor of forming snowflake-like and needle-like Ni crystals.Tween-80 was beneficial to fabricating small sphere or sphere-like nano-Ni with an average particle size of 36 nm and a size distribution in a range of 25-52 nm,as well as PEG-2000 did with an average particle size of 53 nm and a size distribution in a range of 24-106 nm.PEG-6000 was beneficial to fabricating bigger sphere or sphere-like Ni crystals with an average particle size of 167 nm and a size distribution between 76 and 310 nm.The co-presence of SDS and PEG-600 were beneficial to decreasing the sizes of nano-Ni with an average particle size of 33 nm and a size distribution 16-78 nm.However,the coexisting of SDS and Tween-80 was in favor of increasing the sizes of nano-Ni with an average particle size of 230 nm and size distribution in arrange of 120-480 um.By analyzing the size and shape of nano-Cu and nano-Ni,it can be concluded that the modifiers,Tweens,PEGs, SDBS,and SDS have the same modification effect on crystal growth during the preparation of nanostructured metals with chemical reduction synthesis method in the water system.3)Needle-like Ni nanocrystals with different lengths and diameters were formed under microwave irradiation in water system using nickel acetate tetrahydrate as a precursor,hydrazine hydrate as a reductant,and sodium hydroxide as a pH adjusting reagent.4)In 1,2-propanediol system,SDS was beneficial to fabricating irregular snowflake-like and dodecahedra Ni crystals with a small average particle size;PEG-200 and PEG-600 beneficial to forming bigger or smaller irregular snowflake-like Ni crystals;PEG-2000 beneficial to fabricating dodecahedra Ni crystals;PEG-6000 beneficial to fabricating triangular Ni crystals;Tween-20 beneficial to forming regular crystals such as dodecahedra and triangular crystals with small particle sizes;Tween-80 beneficial to obtaining irregular snowflake-like Ni crystals with a big average particle size.The co-presence of SDS and PEG-600 was beneficial to forming bigger irregular snowflake-like Ni crystals,as well as coexisting of SDS and PEG-6000 did.The co-presence of SDS and Tween-40 was beneficial to obtaining dodecahedra and octahedral Ni crystals with a bigger average particle size.By analyzing the size and shape of nano-Ni in water or 1,2-propanediol system,it can be concluded that the modifiers Tweens and PEGs have the contrast modification effects on crystal growth during the preparation of nanostructured Ni with chemical reduction synthesis method in water or 1,2-propanediol system.5)The disciplinarian and the modification mechanism of modifiers on the samples were analyzed by TG-DSC,and FTIR.It was found that there were chemical bonds between oxygen atoms present in modifiers and the surface of the as-prepared nanocrystals.Space block and electrostatic effects efficiently reduced grain aggregation and avoided the sample oxidation,in which the former is the priority factor and the latter assisted.6)The effects of the sizes and shapes of nanostructured metals on the anti-wear and friction reducing performances as well as repairing-self mechanism on tribopairs was investigated.It was found that the size and shape of nanostructured metals affected oil tribological property.