Fabrication,Structure And Properties Of Precursor-derived Graphene/Silicon Carbide Composites

Fabrication of silicon carbide(SiC)ceramics via precursor route has been developed for decades.Polycarbosilane-derived SiC ceramics possess excellent mechanical properties and high temperature resistance.Compared with traditional techniques to fabricate SiC,polymer pyrolysis route owns unparalleled advantages including higher flexibilities in precursor design,lower temperature requirements during consolidation and free of sintering additives.Although polymer-derived SiC ceramics show prominent advantages in fibers,films and coatings products,it is difficult to fabricate monolithic SiC ceramics via the pyrolysis of polycarbosilane(PCS).There will be a large amount of gas escape during the pyrolysis process of precursors,which may destroy the integrity of the bulk ceramics.In order to expand the application of precursor route,it is necessary to develop new technologies for the fabrication of monolithic SiC ceramics and their composites.As a consequence,in this thesis,monolithic graphene/SiC composites were prepared via precursor route and their structures and properties were emphatically studied.The main works are as follows:First of all,PCS and graphene oxide(GO)were grafted via vinyltriethoxysilane(VTES)to obtain a PCS-VTES-GO precursor.After molding,PCS-VTES-GO was heated to 1100 ?,1200 ?,1300 ?,1400 ? and 1500 ? under argon atmosphere to obtain SiC(rGO)nanocomposites.All the sintered samples possess good integrity,smooth surface,higher ceramic yield and hardness,enabling them to have a promise application prospect.Secondly,to develop their characteristic of structural and functional integration,PCS-VTES-GO was mixed with different content of graphene powders.After fully mixing and molding,PCS-VTES-GO/graphene was sintered to 1400 ? and maintained for 30 min under an argon atmosphere to obtain SiC(rGO,Graphene)composites.It is found that the electrical conductivity and thermal diffusion coefficient of composites increase with the increase of graphene.The electrical conductivity and thermal diffusion coefficient of SiC(rGO,G20%)are 20.83 S/cm and 3.745 mm2/s respectively.To explore the heat dissipation performance of the samples,high-power LED devices were packaged on SiC(rGO,Graphene)composite heat-dissipating substrates by COB(Chip on Board)technology,and their junction temperature and thermal resistance were further tested.The results show that the thermal resistance and junction temperature of high power LED devices decrease with the increase of graphene amounts.The junction temperatures of all samples are lower than 120?,which meets the application requirements.The thermal resistance and junction temperature of SiC(rGO,G20%)are 38.05 K/W and 41.55 ?,respectively.Finally,to expand the application of precursors in preparing porous materials,spherical polystyrene(PS)pore formers with different diameters and proportions were added into PCS-VTES-GO.After mixing and molding,the mixtures were sintered to 800? to obtain porous materials with different pore sizes.The results show that the prepared porous materials have good integrity and smooth surface without cracking deformation.It is expected to explore their application in adsorption purification,biopharmaceutical carrier,transpiration cooling and other fields through the evaluation of mechanical properties and the regulation of pore size regulation in the future.