Preparation And Thermal Properties Of Multi-component SiZrBC Ultra-high Temperature Ceramic

With the development of aerospace spacecraft and atmospheric reentry systems,extreme environments with extreme temperatures,aggressive environments,and a combination of rapid heating/cooling are beyond the capabilities of current engineered ceramics.Ultra-high temperature ceramics(UHTCs)are materials that can work at extremely high temperatures(T>>2000℃)and for short periods of time(usually minutes,sometimes hours)due to their excellent thermodynamic properties such as high melting point,stability and strength.These precursors are heated to a high enough temperature to prepare components that can be converted into ceramic components to produce multifunctional inorganic materials with adjustable micro-nanostructures,such as fibers,coatings,porous media or complex shape parts with the help of traditional polymer molding methods.Therefore,UHTCs are considered to be the most attractive materials for aerospace applications and have received extensive attention from the scientific community.In this work,SiZrC polymer precursors were synthesized to introduce Si and Zr elements into the polyvinyl butyraldehyde ester(PVB)backbone by sol-gel method,and the content of PVB was about 10 wt.%.PVB molecular structure as the main chain in the polymer network structure of ceramic precursors,and the Si atoms are added to the PVB side chain through the-OH part,the Zr atoms are crosslinked with Si atoms according to the corresponding Zr/Si molar ratio.The SiZrC polymer precursor with the Zr/Si molar ratio of 3 reached a weight yield of 61.68%after pyrolysis at 1400℃.The results show that the ZrC nanoparticles were evenly distributed on the surface of SiC ceramics,and the outer layer was coated with a carbon layer with higher crystallinity.Subsequently,SiZrBC ultra-high temperature ceramics(UHTCs)were successfully prepared by sol-gel method using stoichiometric phenyl trichlorosilane,dimethyl thioborane and zirconium tetrachloride.Fourier transform infrared spectroscopy determined the macromolecular network structure of precursors mainly Si-O-Si,Si-O-B,B-O,Si-C6H5,Si-O-Zr after solgel process and the FT-IR spectroscopy and X-ray diffraction were used to determine the phase transition and condensed matter structures of SiZrBC ceramics during pyrolysis at 1400-1500℃.The main phases of SiZrBC ceramics are SiC and ZrB2 with the B/Zr molar ratio of 6.At the same time,the morphological and elemental analysis of SiZrBC ceramics was carried out using scanning electron microscopy.The results show the rodshaped SiC and needle-like ZrC blocks gradually disappeared,the powdered ZrB2 ceramics gradually increased with the in crease of the B/Zr molar ratio.Meanwhile,the micro/nanostructure of complex ceramic samples was further investigated by transmission electron microscopy,all samples showed strong crystallinity,and the diffraction ring strength of ZrB2 crystals gradually increased as the molar ratio of B/Zr increased.When the B/Zr molar ratio is 6,it is clearly indicated that the crystalline phase includes β-SiC,ZrC,ZrB2,and the nanoceramics of each phase are uniformly dispersed in the matrix.In addition,the matrix is coated with amorphous carbon layers.Therefore,in this study,the controllable microstructure adjustment of ceramic phase composition was realized by regulating the composition of the precursor preparation,molecular composition and different pyrolysis process parameters.The UHTCs will have the ability to improve or expand their application in future aerospace and other related fields,and paved a novel way for the structural and functional applications of UHTCs series.