Fabrication And Structural Transformation Of New Carbon Nanoparticles

At present, the sintering of the polycrystalline diamond (PCD) is needed to add additives. On one hand the additives are easy to form the residue in the PCD; on the other hand the additives are easy to form the carbide. The physical and mechanical properties of them are much lower than that of the diamond leading to the existence of weak phase in the PCD. Additive-free sintering of the PCD is a fundamental way to solve the problem. The emergences of the nanodiamond and the onion-like carbon (OLC) make this study possible. The fabrication, the microstructure and the properties of these nanoparticles determine the sintering process of the PCD. Therefore, the work was carried out focusing on the flowing several aspects.Characterization of the nanodiamond microstructures and properties. The microstructures, the morphologies, the thermal stability, and the surface states of the nanodiamond were investigated by an X-ray diffractometer (XRD), an energy diffraction spectrometer (EDS), a transmission electron microscope (TEM), a Fourier transform infrared spectrometer (FTIR), a Raman spectrometer (Raman), and a total thermal analyzer (DSC/DTA). The results showed that the nanodiamond was cubic structure. Its shapes were spherical or elliptical. Its average size was approximately 5 nm. The start oxidization temperature was about 520℃in the air. The graphitization temperature in Ar and in vacuum was approximate 1305℃and 1146℃, respectively. There were many functional groups absorbed on the surfaces of the nanodiamond particles including -OH, -CH3, -CH2, CO2, -C=O, -COOH and amido.Post-processing of the nanodiamond removing the functional groups from its surface. The nanodiamond was treated using a potassium permanganate solution, in the air, in vacuum, in hydrogen, and in inert gas. The results suggested that the functional groups could be removed better treated in hydrogen. Moreover, this method could solve the problem of second absorption. However, other approaches had their own disadvantages.Fabrication and characterization of the OLC microstructures and properties. The OLC was fabricated by annealing the nanodiamond in 1 Pa vacuum and at the temperatures from 500℃to 1400℃. The results indicated that when the annealing temperatures were lower than 900℃, there was no OLC fabricated. At the temperature of 900℃, the OLC particle began appearing. However, the average particle size of the OLC was smaller than 5 nm. When the annealing temperatures were increased from 1000℃to 1100℃, the OLC particles were fabricated with particle size larger than 5 nm. Nevertheless, there was untransformed nanodiamond existing in the center of the OLC particle. At the temperature of 1400℃, all the nanodiamond particles were transformed into the OLC. The shape and the average particle size of the OLC were similar to that of the nanodiamond. The layers of the OLC particle were varied from several to 12. The transformation of the OLC from the nanodiamond by annealing including the following stages: formation of graphite fragment, the connection and curve of graphite layer in the (111) crystal plane in the edge of the nanodiamond particle, closure of graphite layer, formation of the OLC complete particle.Fabrication and characterization of the carbon nanoparticle and the carbon nanorod microstructures and properties. The carbon nanoparticle and the carbon nanorod were fabricated using the atmospheric pressure CH4 microplasma generated in a scanning electron microscope (SEM). When the deposition time was less than 2 s, there was carbon nanoparticles generated within the deposition area. With the deposition time prolonged, the carbon nanoparticles gradually grew into the carbon nanorods. When the deposition time was 5 s, the diameter and the length of the carbon nanorod were approximate 20 nm and 800 nm respectively. When the deposition time was more than 6 s, the deposition area was melt. However, the carbons nanorods melt were generated. When the deposition time was more than 9 s, the carbon nanorods melt were generated in the vicinity of sedimentary area melt. When the deposition time was more than 10 s, there were no carbon nanomaterials generated. In conclusion, 10μm gap, 100 kPa pressure and 5 s deposition were the optimum conditions. The carbon nanoparticles were the OLC with hollow structure. However, the carbon nanorod had typical nanorod structure.Fabrication and characterization of the polycrystalline sinter microstructures and properties. The polycrystalline sinter was fabricated using the nanodiamond and the OLC. The results revealed that the nanodiamond was graphited without additives after being sintered in 1200℃, 55 Gpa and 500 s conditions. The additive of Si could help to prevent the nanodiamond from graphitization. However, the OLC was transformed into the PCD after being sintered under these conditions without any additives. The additive of the nanodiamond into the polycrystalline cubic boron nitride (PcBN) binder system could improve the density and the microhardness of the PcBN.