The Fabrication, Structure And Properties Of Mesophase Pitch-based Carbon Foam Modificated By Fiber

Mesophase pitch-based carbon foam possessed excellent properties such as low density, high thermal conductivity, excellent thermal stability, corrosion resistance, low coefficient of thermal expansion. It was a kind of promising carbon material. However, the strength of carbon foam is low, which limited its application. To enhance the strength without decreasing its high thermal conductivity was our aim. In this work carbon foam was fabricated by foaming at high temperature. Mesophase pitch was used as precursor. Investigations were carried out to determine the effects of constant autoclave pressure and preoxidation of pitch on the structure and properties of carbon foam. PAN-based carbon fiber, PAN-based preoxidized fiber and carbon nanotubes were respectively added into mesophase pitch. The influence of kinds of fiber, fiber length, mass ration between mesophase pitch and fiber, different graphite temperature on microstructure, strength properties and thermal conductivities was discussed. The results were summarized as follows.1.Carbon foam had high open porosity under low foaming pressure. The open porosity was decreased when the foaming pressure was increased. Both of the compressive strength of carbon foam and graphite foam was improved. The thermal conductivity and specific conductivity tend to decrease while they were increased at first. When the pressure was7MPa, the thermal conductivity and specific thermal conductivity reached61.0W/m K and93.1W/m K respecitvely. The specific thermal conductivity was higher than conventional radiater (copper and aluminum foam).2.The bulk density and compressive strength of carbon foam and graphite foam was increased with the extension of oxidation time. The maximal values reacehd1.07g/cm3,1.23g/cm3,12.07MPa and9.06MPa when the oxidation time was6h.3.The addition of carbon fiber powder could improve the compressive strength and thermal conductivity. While the addition of short carbon fiber had less effects in improving these properties.The stress-introduced graphitization between fiber and carbon matrix can improve the graphitization in micro-aera. The microcrystalline value was increased. The thermal conductivity was also improved. When the carbon fiber powder content was6wt%, the maximal value of compressive strength of graphite foam was6.7MPa. The thermal conductivity of graphite foam reached83W/m K, which was a times of that of graphite foam. The microcrystalline value was further increased with the increasing of temperature(2000℃～2500℃). The thermal conductvity was improved, while the compressive strength was decreased.4.The addition of PAN-based preoxidized fiber powder could improve the compressive strength and thermal conductivity. While the addition of short carbon fiber had less effects in improving these properties. The stress-introduced graphitization between fiber and carbon matrix can improve the graphitization degree and thermal conductivity.When the preoxidized fiber powder content was2wt%, the microcrystalline value was further increased with the increasing of temperature(2000℃～2500℃), and the compressive strength was decreased. Both of the bulk density and thermal conductivity were increased. The thermal conductivity reached71.8W/m K at2500℃5.Moderate amount of CNTs could be dispersed uniformly in carbon matrix. CNTs could form good interfaces with carbon matrix, and improve the mechanical properties.The compressive strength of carbon foam reached11.5MPa when the CNTs content was2wt%. CNTs could promote the increasing of microcrystalline of graphite, which inproved the thermal conductivity. La and Lc values were increased obviously when the graphite foam contain lwt%CNTs was heat treated at2500℃. The thermal conductivity reached78.2W/m K, while the compressive strength decreased.