Preparation Of Surface Modification Copper Nanoparticles And Their Tribological Performances

In recent years, the copper nano-particles have played an important role because of their properties different from bulk material. As a vital industrial raw material, copper nanoparticles are more economic when they take the place of the noble metal nanoparticles. Therefore, the researches on copper nanoparticles have attracted extensive attention in the world.In this dissertation, the electrochemical performances of reductants were detected by cyclic voltammetry. Sodium hypophosphite is chosen as reductant due to their price and environmentally friendly. Various morphologies of copper nanoparticles were prepared via a two-step reduction method, and their growth mechanisms were reviewed. The tribology performances of copper nanoparticles when they used as lubricant additive were also studied. The main contents are the following:1. The electrochemical performances of various reductants were studied by the Zennium electrochemical workstation. The relationships between electrochemical performances of reductants and the pH value of the system, electrolyte concentration and photodynamic scanning rate were studied by the cyclic voltammetric curves which obtained from different experiment conditions. The optimum conditions of reductibility in liquild system can be obtained.2. The influences of various reaction conditions on particles'morphology, size and dispersibility were studied. Copper nanoparticles with well dispersibility and uniform morphology were finally obtained. The products were characteristic by XRD, FTIR, SEM and TEM, and the growth mechanisms of spherical nanoparticles were discussed.3. The growth mechanisms of various morphology copper nanoparticles were studied in liquid system by changing the experiment conditions. The results showed that 1) the combined action of steric effects of oleic acid and Ostwald ripening process were the reasons of the formation of spherical copper nanoparticles; 2) the structure-directing effect of oleic acid and ageing time were the main reasons of the formation of dentritic nano-copper crystals. As a structure-director, oleic acid could guide crystal nucles grow successively along some orientations direction in the growth process. With the extension of ageing time, Ostwald ripening process took place continuously which caused small nuclei constantly dissolved, deposited and grew in the surface of big nuclei, finally dentritic copper nanoparticles obtained; 3) the growth mechanism of hollow spherical copper nanoparticles was studied in liquid system. In the formation process of hollow spherical copper nanoparticles, oleic acid was used as a soft template. The molecules of oleic acid could form to globularmicelles which were availed to the formation of hollow structure. Ostwald ripening process caused small nuclei constantly dissolved, which further promoted the formation of hollow structure; 4) Ostwald ripening and the structure directing effect of oleic acid were the main reasons of rodlike copper nanoparticles. Firstly, the structure directing effect of oleic acid could make the growth rate of various crystal faces are different. Crystals grew successively towards to some orientations. Secondly, Ostwald ripening was in favour of the formation of one-dimensional rodlike crystals from primary nanoparticles; 5) the formation of flowerlike copper nanoparticles could be considered as the results of the Ostwald ripening and screw dislocation growth process. Due to ripening process continuously, the products underwent a proess from fine particles to flake. With the increasing concentration of nanoflakes, they layer-grew around screw dislocation, and then flowerlike copper nanoparticles obtained. And since the temperature of system had some influence on the formation of nanoflakes, it could also affect the formation of flowerlike crystals.4. The friction coefficient and wear scar width were studied if copper nanoparticles were used as lubricant additive, when the concentration of copper nanoparticles, fiction time, load and rotational speed were changed. In the friction process, copper nanoparticles combined with the wear surface, evenly and smooth lubrication film formed. Thus the friction coefficient and the amount of wear reduced. At the same time, copper nanoparticles filled the grinding mark on the wear surfaces, the anti-wear ability and carrying capacity of 15 ON base oil were improved significantly. Negative wear and the deposition of copper nanoparticles on wear surface proved that a self-repairing mechanism existed on the wear surface when spherical and hollow spherical copper nanoparticles used as lubricant additives. When dentritic, rodlike and flowerlike copper nanoparticles were used as lubricant additives, the irregular morphology would make the wear surface further wearing, so they are not good at improving the anti-wear properties of base oil. In addition, the viscosity of lubricant was also made the tribological performance of lubrication less favorable.