The Preparation Of Mesophase Pitch And Carbon Foam

Carbon foam is a novel thermal management material which is produced from mesophase pitch, and possesses high thermal conductivity after carbonization and graphitization. The new material has exceptional high thermal conductivity and low density (whose thermal conductivity equivalent to that of aluminum alloys while its density is only 1/5th of aluminium). The typical carbon foam prepared by thermosetting polymer which can't be graphitized, usually used as heat insulation material. A new method that utilizes coal-tar pitch based mesopitch and simplified production of carbon foam are introduced in this paper. Thermal conductivity of carbon foam in this study can up to 110W/m.K, combined with excellent mechanics and lower cost. In addition, carbon foam has a wide application in thermal protection systems, light weight antennas, joiner bulkheads, brake disk, engine components, energy absorbing crash barriers, structural insulation panels, fire doors and blocks, etc. In recent years, carbon foam with these advanced properties has become an ideal material in aerospace field, which is considered as one of the most potential materials of future aerospace field.We have studied the process and properties of both mesophase pitch and carbon foam on following aspects in this paper.First, Coal-tar pitch which is abundance and cheap is used in producing the required mesophase pitch by a simple heat treatment. The mesophase pitch which is adapted to producing carbon foam should has the appropriate light fraction, appropriate softening temperature (300~350°C), appropriate viscosity and high content of mesophase pitch. The mesophase pitch is prepared by the pyrolysis of crude coal tar pitch, and is characterized by the SEM, X-Ray, IR ,softening point, mesophase content,, carbon yield. Then, the influences of different heating time, heating temperature, the process on the mesophase pitch are also studied. In this study, the coal tar pitch can be transformed into mesophase pitch with softening point 320°C and higher than 70% of mesopahse content after pyrolyzing for 4 hours, which is suitable for the preparation of carbon foam.Secondly, Carbon foam is produced by the obtained mesophase pitch at a temperature of 400~500°C and pressure of <10MPa. Effect of foaming temperature, foaming pressure and the rising/falling rate of temperature on the morphology and properties of carbon foam are studied. In this study, the thermal conductivity of carbon foam obtained at 500°C, 8Mpa soaking for 2 hours can reach 110 W/m.K, while its density is only 0.8g/cm3 ,porosity is 55% and diameters ranging from 200 to 400um. SEM, X-Ray, polarized micrography are used in the characterization of carbon foam. The modification of morphology and properties of carbon foam after high temperature heat-treatment are also studied.Finally, the foaming mechanisms, the influence factors on foaming and structure of the foam, the variation of the thermal conductivity with the process are studied. We also try to improve the mechanics of the foam in this paper.The results prove that the carbon foam produced by the method in this paper have excellent thermal management properties, lightweight andexcellent mechanical properties, has a great potential application infuture.