Synthesize Novel Nano-carbon Materials And Study Their Thermal Performance

The paper has three parts. Part one is about multi-walled carbon nanotubes (MWCNTs) synthesis. In order to accelerate catalyst producing, a novel method was present by plating iron on nickel foams substrate for synthesizing MWCNTs with chemical vapor deposition. The MWCNTs were characterized by scanning electron microscope, transmission electron microscope, resonance Raman spectroscopy and thermogravimetric analysis. Results show the diameters of MWCNTs are well-distributed and the purity is higher than90%. For exploring the potential of this method, various growth conditions were investigated. Some original conclusions were obtained. First, when hydrogen gas was introduced on growth, as-grown materials transforms from solid to hollow. Second, if the flow rate of acetylene was dropped to25sccm on growing, a new kind of the needle-like nano-material comes with MWCNTs. Third, output of MWCNTs which laying the substrate parallel to the axis of the flow tube is more than perpendicular. Fourth, the minimum growth temperature of MWCNTs is550℃which is much less than the decomposition temperature of precursor acetylene. Finally, it was found that the MWCNTs grown on nickel foam substrate exhibit higher value of thermal conductivity than the substrate itself. It suggests a feasible way to develop ultra-high thermal conductivity material, namely, by transplanting the orientated MWCNTs onto a substrate with high thermal conductivity such as silver and copper.The new structure nano-materials is significant for developing extraordinary products. In part two, the iron was plated on nickel foam to prepare the catalyst and synthesis the carbon nano-material with plasma-enhanced chemical vapor deposition. Then transmission electron microscope was used to characterize them and found these materials are incline to bunch. Meanwhile, it was found that they have grass-like shape and each single one has much hollow area.We believe these unique structure nano-materials have impressive prospects in electron field emission and hydrogen storage. The research deepens the comprehension of film deposition on the rough surface. Meanwhile, it was found that introducing of voltage changes the geometry of carbon material. It also increases the aspect ratio. From the study of synthesis techniques, we found the carbon material is sensitive to the flow rate of methane. They need to fluctuate on a narrow space. Oppositely, for growth temperature, they don’t have demanding requirements. Even at300℃, it still can grow,In Part three, a novel composite material of nano-carbon with the highest value of thermal conductivity2.6W (m K)-1was present by dispersing graphite powders (GP) and MWCNTs in a polymer matrix of epoxy resin and the curing agent. Furthermore, this composite has been prepared as the heat dissipation system of high-brightness light emitting diodes (HB-LEDs), using a sandwich structured thermal interface material with metal for the inner layer and two composites for outer layers. The optimal for thermal conductivity of this thermal interface material is4.9W (m K)-1,58%higher than that of commercial products. This promising material can increase the cooling rate and lower the energy consumption of HB-LEDs.At the same time, there is a max value for MWCNTs dispersion in the polymer was found. It decreases with the increment of the load of hybrid filler. Analysis and experiment indicate the relation semi-quantitatively between the load of MWCNTs and thermal conductivity of the composite. The best ratio between MWCNTs and GP was found. It gives the direction to improve the thermal conductivity value of composites.