| Silicon carbide ceramic materials have many excellent properties,such as high strength,high hardness,high temperature oxidation resistance,wear resistance and corrosion resistance.As high-temperature structural materials,they play an important role in aerospace,automotive,and chemical energy fields.Silicon carbide ceramics prepared by precursor conversion method has gradually become the most widely used,and the cross-linking curing of precursors is an indispensable part of this method.Traditional thermal cross-linking and radiation cross-linking methods require high temperature,long time and high cost,which limits the application of precursors in SiC ceramic materials.Therefore,in this paper,the initiator cross-linking method was used to realize the low-temperature rapid cross-linking curing of the precursor,and its application in porous silicon carbide ceramic materials was discussed.In this paper,tert-butyl peroxybenzoate(TBPB)was used as an initiator.1 wt%of TBPB was added to liquid hyperbranched polycarbosilane(LHBPCS),and it was cured at 80°C for 2 h.Combining FTIR,~1H NMR,DSC,rheological properties test,TG,XRD,elemental analysis,SEM and other analytical methods,the crosslinking mechanism of LHBPCS by adding initiator was studied,and the ceramic yield,crystallization behavior and elemental composition of ceramic products were investigated.It was found that during the heating process,inititor TBPB decomposed and produced the free radicals,allyl polymerization on side chains of LHBPCS was initiated by these free radicals,and the molecular chains increased continuously to achieve curing of LHBPCS.The cross-linking and solidiafication of LHBPCS effectively inhibited the volatilization of low-molecular-weight LHBPCS during the pyrolysis process.As a result,the ceramic yield was 79.0%at 1000°C in an inert gas atmosphere,which was 12.6%higher than that of conventional heat-cured LHBPCS,and the ceramic yield was significantly improved.The pyrolysis products were a near-stoichiometric ratio of SiC ceramics with a very low oxygen content and dense structure.Porous SiC ceramics were successfully prepared using PAN-PMMA expanded microspheres as pore forming agent.The microstructure,density,porosity and thermal conductivity of porous SiC ceramics were studied by FTIR,TG,XRD,elemental analysis,SEM and thermal conductivity test.It was found that the optimum expansion temperature of PAN-PMMA expandable microspheres mixed with LHBPCS was 120°C,the expansion radio was~10 times,and the optimum content of TBPB was 0.2 wt%.The prepared porous SiC ceramics had a homogenous pore distribution and pore diameters of 20±10μm,high porosity and low density.As the content of microspheres increased,the density of porous ceramics decreased and the porosity increased gradually.The prepared porous ceramics had a low thermal conductivity of 0.053 W/(m·K)at room temperature,and increased slightly with temperature. |
