Preparation, Characterization And Formation Mechanism Of Nano Diamond Composite Particles

Diamonds have high hardness and chemical stability, excellent heat conductivity, broad band gap, high electron and hole transmission rate, which makes them in great value of mechanics, optics, acoustics, thermology, electricity, etc. They become’gems’in modern industry and science technology. Nanodiamonds (NDs) not only inherit the outstanding performance of macroscopic diamonds, but also exhibit unique characteristics of nano materials, that is to say, the great specific surface area and high surface activity, thus they have wide application prospects in the potential fields of composite, biomedicine, electrochemical degradation of pollutants. So far, to find a perfect synthetic method is still a baffling question for the industrialized production of NDs. Traditional technics cannot meet the demands of NDs because the they always have the deficiencies such as the cost, low productivity, difficult synthesis condition, hard to choose dopants, etc. These problems must be solved for the mass production and promotion of NDs.In this work, nanoparticles have first been achieved by DC-arc discharge plasma method using binary-component Si-C. Ni-C and Ni-Si as raw materials. All the samples were characterized by XRD, Raman and TEM (HRTEM). The condition of the nucleation and growth of nanodiamond in nonequilibrium state was predicted according to the analysis results. Based on this, diamond-contained nanopowders were synthesized under relative low pressure using ternary-component Ni-Si-C as raw materials. The influence of graphite content (10wt.%,15wt.%,20wt.%) and hydrogen pressure (0.01MPa,0.06MPa) was investigated. Considering the existence of metal and non-diamond carbon impurities in raw nanopowders, a purification process with acid treatment was designed, and the samples before and after purification were characterized. The results suggested that the raw nanopowders were composed of composite particles with structure of Ni/SiC/diamond, the diamond crystals grown had intact cubic lattice, with grain size of10-30nm. The raw nanopowders synthesized under different condition had distinct compositions and microstructures:the content of diamond increased with the increasing of graphite, and diamond could only form under high hydro gen pressure, otherwise carbon onion would exist except diamond phase.Furthermore, the formation mechanism of diamond nanoparticles in nonequelibrium state was studied based on the principle of physical vapor deposition. It was confirmed that Ni played the role of catalyst for providing the growth rate of carbon atoms and SiC induced the process of the nucleation of diamond. This method is conductive to the preparation of electrodes with large scale, high stability and activity, which would also be the basic of synthesis of conductive diamond nanoparticles and realize industrialization in the future.