Preparation Of Metal, Alloy, Oxide And Sulfide Nanomaterials By Solution Dispersion And Its Tribological Properties

In this paper, various metal, alloy and organic molecule surface-modified metal nanoparticles were prepared by solution dispersion or organic compounds-assisted solution dispersion methods, with low melt metals as starting materials, and the mechanism for formation of metal nanoparticles was also examined. The size and morphology of the resulting products could be controlled by adjusting reaction conditions, and dendritic alloy nanocrystals, oxide and sulfide nanoparticles were also obtained. Meanwhile, the tribological properties and wear mechanism of these particles as lubricating additives were investigated. Based on the above results, the following main conclusions are reached:1. During the dispersing process, metal droplets can form oxide shell through reaction with oxygen, which can reduce total surface energy of the system and prevent smaller droplets from coagulating; the oxide layer seems to adsorb solvent molecules, which might improve the stability of droplets in solvent. With the presence of the oxide layer and adsorbing molecules, metal droplets can be gradually dispersed into nanosized ones, which can be converted into nanoparticles when the temperature is reduced.2. In organic compounds-assisted dispersion, organic compounds can react with droplets and form organic layer at the droplet surface, which should suppress the possibility of aggregation, and make the system bearing emulsion-like property. In addition, the organic layer can control the oxidation of metal droplet, and improve the stability of droplets at room temperature.3. In the dispersion of melt alloy, the active element atoms at the droplet surfaces reacts with oxygen in medium, and form oxide shell that is propitious to prevent the aggregation of droplet. As the surface oxidation, more active metal atoms inner the droplet should diffuse to the surface, which directly influences the relative content of equilibrium phases of alloy droplets. In addition, weak shear effect could lead to one-dimensional nanomaterials with special morphology.4. The low-melt metal nanoparticles as lubricating additives can remarkably improve the antiwear properties of base oil, and the antiwear mechanism might be rolling effect. In addition, the alloy nanoparticles show better antiwear properties than the corresponding monometallic nanoparticles, which might be attributed to the alloy structure.5. In air, tin or indium oxide nanoparticles can be produced by dispersing melt tin or indium in a suitable solvent. The particles seem to adsorb solvent molecules to keep droplets isolated in solvent. In addition, the oxide nanoparticles show a strong luminescence emission, which is mainly attributed to the existence of oxygen vacancies and defects.6. In a sulfur-dissolved solvent, dispersing melt tin or indium can give tin sulfide or indium sulfide nanoparticles. In this process, metal droplets react with sulfur and form sulfide shell to suppress the possibility of aggregation of droplets, and finally develop into sulfide nanoparticles. The sulfide nanoparticles as lubricating additives can improve the antiwear properties of base oil by forming lubrication film between rubbing surfaces.