The Preparation And Properties Of Carbon Foam And Its Composite

Mesophase pitch-based carbon foam as a new class of structural and functional material has attracted attention owing to their peculiar properties such as high open porosity, light weight, high temperature tolerance, adjustable thermal conductivity, low coefficient of thermal expansion, corrosion resisting, and good electrical conductivity. The graphite foam is obtained after graphitizing of carbon foam at the high temperature. The specific thermal conductivity of the graphite foam is up to 209 (W/(m·K))/(g·cm-3), which is 5 times of that of copper,4 times of that of aluminum. It is one of the promising candidate materials for applications as radiators, heat exchangers, sandwich materials, evaporimeters.Considering the situation of polymer composites, the graphite foam/polymer with thermal conductivity was prepared. The thermal conductivity was enhanced by using three-dimensional network of carbon foam ligaments to form a continuous hot-channel structure. Scanning electron microscopy was performed to observe the microstructure. Bulk density and porosity were measured by the solid densitometer and the equation. Soxhletextractor was used to determine the component. Compressive strength was measured by using a universal testing machine. Thermal diffusivity was measured at room temperature by the laser flash technique.Firstly, the carbon foam was prepared at low temperature and pressure. The pore diameter is up to 800μm, and the open cell ratio is higher than 90%. As a good matrix, the resulting carbon foam was used in impregnated steps of preparations of composites. Then the effect of foaming process and mesophase pitch on the structure and properties of graphite foam were studied. The experimental results showed that the compressive strength of non-oxidation carbon foam was 12% lower than that of pre-oxidation carbon foam. The higher the foaming temperature is, the more round the pore of the graphite foam is. The lower the foaming temperature is,the less uniform the pore size is. The depth of pore wall increased with increasing pressure, and the open cell ratio decreased with decreasing pressure.The graphite foams were prepared by two kinds of mesophase pitches. The softening points of the pitches were 285℃and 250℃, respectively. The basic properties of two kinds of mesophase pitches were analyzed. The discrepancy of structure and porosity of graphite foams made by two kinds of mesophase pitches were studied. The porosity and open cell ratio were found to be increased with the decreasing of softening point and the increasing of weight loss.Oxidation had little effect on the property of carbon foam, the non-oxidation foam was therefore selected as the matrix of composite. The graphite foam/epoxy resin was prepared through vacuum impregnation. The thermal diffusivity of the composites increased up to 6.541 mm2/s, nearly 47 times of that of pure epoxy resin. The compression strength of graphite foam/epoxy resin composite reached a maximum of 106.76 MPa, which was 55% higher than that of pure epoxy resin. Both the microstructure of graphite foam and the mass fraction of epoxy resin effected the properties of graphite foam/epoxy resin composite. The smaller the pore size of graphite foams is, the lower the mass fraction of epoxy resin is, the higher thermal diffusivity would be. The smaller the pore size of graphite foams is, the higher the mass fraction of epoxy resin is, the higher the compression strength of the graphite foam/epoxy resin composites is.