Preparation Of Carbon Nanomaterials And Their Application In Composite

Recently, carbon nanotubes, diamond films and diamond like carbon (DLC) films have attracted tremendous attention due to their remarkable properties. So far, although rapid advances with their application in various fields have been achieved, three critical problems conrresponding to the three kinds of carbon nanomaterials respectively are still needed to be solved properly. They are bad dispersion of carbon nanotubes within nanocomposites, especially in metal matrix, large thermal stress between the diamond film and substrate, and considerable residual stress inside the DLC film which leads to a limited theckness. Therefore, in this paper, carbon nanotubes reinforced nanocomposite particles and bulks were seriously designed to study the dispersion of the carbon nanotubes within the matrix. Diamond and DLC nanocompsite films instead of single-layer films were farbricated to decrease the large thermal stress and residual stress respectively. The research is novel and pioneering, and is of great significance on application potential.1. Preparation of carbon nanotubes, diamond films and DLC films.Multi-walled carbon nanotubes (MWCNTs) were synthesized by thermal chemical vapor deposition (CVD), hot filament CVD (HFCVD) and microwave CVD (MWCVD) using Ni-Mg-Mo-O alloy oxides as catalyst. The resultant CNTs were characterized by transmission electron microscope (TEM) and Raman spectroscope. The results reveal that the MWCNTS synthesized by different methods have different characteristics, probably attributing to different atomic hydrogen concentrations produced by different methods. High temperature plasma produces high concentration of atomic hydrogen to etch the amorphous carbon or defected CNTs formed during the processing, thus increasing the degree of graphitization and reducing the diameter of the resultant CNTs. In addition, MWCNTs were synthesized successfully at low temperatures (550oC or below) using MWCVD due to the enhancement of plasma in decomposition of methane and production of high concentration of atomic hydrogen at low temperatures.In addition, micro-diamond films were synthesized with 99vol% concentration of hydrogen and 1vol% concentration of methane by both HFCVD and MWCVD, while nano-diamond films were synthesized with the 95vol% concentration of hydrogen and 5vol% concentration of methane in both of the systems. Moreover, hydrogenated DLC films with high hardness (28.39GPa) and elastic modulus (131.84GPa) were deposited in dual ion beam sputtering system using low energy ion source. The deposition beam energy is 100eV, and the beam current density is 0.3mA/cm2.2. Nanocmpostie particlesFirst, wealth of superfine single-crystal hollow cuprous oxide spheres with nanoholes have been prepared for the first time with glucose as the reducing agent and gelatin as a soft template. Then, carbon nanotube-implanted cuprous oxide spheres were fabricated. This kind of morphology makes MWCNTs'locked'inside various spheres and aviod moving freely to form large aggregates. Moreover, many technical processes have been investgated. An important feature is that much more uniform distribution and dispersion of carbon nanotubes within the cuprous oxide spheres were achieved using the gelatin-coated carbon nanotubes as the addives in stead of addition of pure carbon nanotubes to the reducing solution. At last, differential scanning calorimetry (DSC) results show that the decomposition temperature of ammonium perchlorate (AP) is decreased a lot when carbon nanotube/cuprous oxide nanocomposite spheres act as the catalyst.3. Nanocomposite bulk materialsThree methods named co-deposition method; nanocomposite-sphere method and carbon- nanotube -foam-frame method respectively have been developed to assist dispersion of carbon nanotubes within the carbon nanotube/copper composite precursors. Then, several kinds of pressing forming methods were used to fabricate the carbon nanotube/copper bulk, which are cold pressing and sintering, vacuum forming and sintering, hot rolling and sintering after vacuum forming and infiltration at high temperature. The results show that the composite that is hot rolled after vacuum forming, has relatively high density and can avoid being oxidized effectively. The composite prepared by nanocomposite-sphere method displays the best dispersion of carbon nanotubes within the copper matrix. Futhermore, the microhardness of the nanocomposites are twice higher than that of pure copper, which is ascribed to the good dispersion of the MWCNTs in matrix. Another important feature is that carbon nanotubes has dominate decreasing the thermal expansion coefficient with the temperature between 100℃and 150℃, which is decreased to 5.76*10-6/K, far less than the 19.03*10-6/K for the pure copper. Furthermore, the thermal conductivity of the composite can keep more than 100 W/mK, which makes this kind of nanocomposite an ideal candidate for electronic packaging materials. In addition, the thermal expansion coefficient of carbon nanotube/copper nanocomposite foam frame is six times as low as the pure copper. Due to the simple technical process and high concentration of the carbon nanotubes, this kind composite has a great potential application in various fields.4. Nanocomposite filmsFor the first time, High orientation c-axis AlN and a-axis AlN films were deposited on different substrates with the controllable technical processes without epitaxial growth. The possible mechanism explained that the preferential orientation changes from the c-axis to the a-axis with changing in the growth unit from atoms to Al-N dimmers. In addition, two kinds of AlN/DLC multilayer films, named DA structure (the out layer is AlN film) and AD structure (the out layer is DLC film) respectively, were deposited on the silicon wafers. The DA structures exhibit enhanced hardness and improved orientation, and the AD structures keep their good mechanical properties with increasing their thickness. Furthermore, in order to enhance the nucleation and adhesion of diamond on copper plates, interlayers of AlN on copper plates were investigated by dual ion beam deposition. Highly orientated w-AlN thin films with (002) plane parallel to the substrate surface have been achieved on copper when a thin Al layer was deposited on copper before AlN deposition. The resulted Al/AlN thin films were used as an interlayer to synthesize diamond thin films on copper. The results of the diamond deposition show that the AlN interlayer significantly increases the nucleation density and the growth rate of diamond thin films as compared with diamond deposition directly on silicon plates. Consequently, continuous adhesive diamond thin films were fabricated on the Al/AlN coated copper plates within 1 h deposition by both hot filament and microwave chemical vapor deposition. These multi-layered thin films are expected to exhibit very high thermal conductivity and very low thermal expansion coefficient and would be excellent candidates for electronic package applications.