| The precursor conversion method is used to prepare ceramic design cross-linked polymer compounds.By designing,changing and optimizing the molecular structure,a new type of ceramic with the required composition and physical and chemical properties is obtained,and this method of synthesis was found the advantages of simple preparation process,designable molecular structure,and lower synthetic environment requirements,and is widely used in the preparation of ceramic materials.Among the many silicon carbide ceramic materials,boron-containing silicon carbide ceramics are reported excellent thermal and oxygen stability and excellent chemical stability,therefor these polymers have always been the research hotspot of silicon carbide ceramics.However,the preparation of common SiBCN ceramic precursors was required a relatively high anhydrous and oxygen-free environment,while the SiBCN（O）ceramics were reported the similar chemical stability and relatively loose reaction conditions which can be used as a new type of structural ceramics.This thesis was reported a new method for synthesizing polysilazaborazanes.Through the molecular design,borohydride reaction,the raw materials like borane-methyl sulfide complex and1,1,3,3-tetramethyl-1,3-divinyldisilazane were synthesized a vinyl-functional group of silazane compound named BSZ12.And the BSZ12 can be used as a crosslinking agent to cross-link which can be synthesized with perhydropolysilazane to prepare polysilazaborazane.As a compound with polyvinyl functional groups,the multiple reactive cross-linking sites in BSZ12 can be used as a cross-linking agent to react and polymerize with Si-H bond.The structure of the synthesized product was determined by FT-IR,1H-NMR,11B-NMR and other characterization methods.Poly[imino（methylsilylene）]has a lot of Si-H groups,which can be cross-linked and polymerized with BSZ12 in a heating oxygen environment to obtain cross-linked polymers CPBCS3-1,CPBCS5-1,and CPBCS10-1 with different proportions.The reaction process of CPBCSs was proved by FT-IR and other characterization methods,and the surface properties of CPBCSs and mechanical properties were proved.At the same time,it is proved by the TG curves that the residual carbon rate in air and argon atmosphere at 1000℃is 77%and 71%,respectively.SiBCN（O）ceramics were prepared with CPBCSs,and the inorganic transformation process in the cracking process was determined through analysis,and XRD,Raman spectroscopy,and XPS proved that the ceramics cracked at1000℃will start to appear from the original amorphous structure at high temperature.Crystallization,β-SiC crystals begin to appear at 1400°C,and a carbothermal reduction reaction will occur when the temperature rises to1800°C,accompanied by a crystal form transformation to formα-SiC crystals. |
