Preparation And Performance Of High Thermal Conductivity C/SiC Composites

Not only did C/SiC composites have low density,low thermal expansion coefficient,high strength,high thermal conductivity,but also have high temperature oxidation resistance.It has a wide range of applications in the hypersonic aircraft,missile head cone,satellite thermal protection system,rocket motor nozzle and other thermal management fields.With the rapid development of aerospace technology,more and more high thermal conductivitve materials is required in these areas.In this paper,a new type of high thermal conductivity carbon material named graphite film,is the first time to be used as a thermal conductive material to prepare high thermal conductivity C/SiC composites to meet the requirement.In this paper,high thermal conductivity C/SiC composite was prepared by the precursor infiltration pyrolysis with high thermal conductivity graphite film,mesophase pitch based carbon fibers,polycarbosilane and so on.The impregnation,hot pressure molding formation and pyrolytic process of high thermal conductivity C/SiC composites was determined by the study of structure and the changes in the pyrolytic process of the polycarbosilane.The density of composites are measured by Archimedes method.The flexural strength of the composites was tested by using three point bending method.The composition and microstructure of the composites are characterized and analyzed by XRD and SEM.The resistivity and thermal conductivity of composites are measured by the four probe resistivity tester and the laser thermal conductivity testing instrument.Meanwhile,the effects of impregnating-pyrolyzing times,pyrolysis temperature and fiber content on the properties of high thermal conductivity C/SiC composites were also investigated.The results of the study show that:1)With increasing the impregnating-pyrolyzing times,the pores and micro cracks are gradually reduced in the composites.The density and flexture strength of the composites are increased.It increased rapidly in the early impregnating-pyrolyzing times stage,and the later stage growth is slower.2)Raising the pyrolysis temperature can make the amorphous matrix SiC gradually disappear,thus improving the degree of crystallization of SiC,optimizing the interface of SiC with carbon materials and improving the interface contact points of the composites.That will improving the density and flexture strength of the C/SiC composites and reducing the resistivity.3)The introduction of fibers increases the area of bonding with the matrix and improves the structure and interface state of the composites.The density and flexural strength of the composite are increased,and the resistivity is reduced.The density,flexture strength and resistivity of adding 20wt%MPCF of the composite are 1.72 g/cm3,20.95MPa 23mQ·cm respectively after 7 impregnating-pyrolyzing times at 1200℃.4)With increasing the impregnating-pyrolyzing times,the densification of composites is increasing.The phonon would have higher propagation speed through this compact and almost no apparent defects interface,which makes the thermal conductivity of the composite increase.Raising pyrolysis temperature improves the degree of crystallization of SiC and weakens the interface between the carbon materials and SiC.SiC is evenly distributed around carbon materials,thus increasing the average free range of the phonons and increasing the thermal conductivity of the composite.Introducing MPCF can improve the internal structure of the material.Compared with the graphite membrane,the precursor solution is more easily impregnated into the fiber,and the SiC is more easily distributed bewteen the fibers.The micro crack around the fiber is less,the phonon’s propagation distance in the composite will be much farther,and the thermal conductivity of the composite is higher.The adding 20wt%MPCF C/SiC composites is 183 W·m-1·K-1 after 7 impregnating-pyrolyzing times at 1200℃.In this paper,a new high thermal conductivity carbon material named high thermal conductivity graphite film was used to prepare high thermal conductivity C/SiC composites,which has widened the application field of C/SiC composites.