Synthesis And Characterization Of Novel BN(Si、C) Organic Precursor

Hexagonal boron nitride （h-BN） meets all kinds of special application requirementof aerospace wave-transmitting materials and devices owing to its good heat resistance,thermal stability as well as excellent wave-transmitting performance. Therefore,hexagonal boron nitride can be utilized to in the preparation of high-performancewave-transmitting materials and devices, and the hexagonal boron nitride fiber can beutilized as the reinforcement of the ceramic matrix composites. Hexagonal boron nitridematerials have become one of the hottest research direction of material researchers andengineers all over the world. Nowadays, polymer derived ceramics route is of greatefficiency, and getting a precursor with excellent spin ability is of great importance. Inthis research, B-trichloroboranzine/N-methyl aniline/dichloromethylsilane system andB-trichloroboranzine/N-methyl aniline/dichlorodimethylsilane system are studied indetails as the boron nitride （silicon/carbon） precursor.B-trichloroboranzine was synthesized using BCl₃and NH₄Cl as raw materials andtoluene as solvent by means of appropriate synthesis conditions. The synthesisconditions were improved and the reaction time reduced to a certain extent. TCB areused as B, N source, and N-methyl aniline as a seal agent.B-trichloroboranzine/N-methyl aniline/dichloromethylsilane system andB-trichloroboranzine/N-methyl aniline/dichlorodimethylsilane system were tried toprepare boron nitride （silicon/carbon） precursor. However, the fiber could not befabricated from the precursor by melting-drawing method. The time of sealing, the timeof cross linking, the temperature of cross linking, the reduced pressure distillationtemperature and molar ratio of raw materials were studied in details to understandpolymerization mechanism of the precursor. The microstructure and chemicalcomposition of the boron nitride （silicon/carbon） precursor were characterized byX-Ray diffraction, Fourier Transform Infrared Spectroscopy, X-Ray PhotoelectronSpectroscopy and Scanning Electronic Microscope. XRD patterns obtained failed tofind the corresponding materials in the standard map. The precursor was composed bySilicon, boron, carbon, nitrogen, oxygen, chlorine. And the results of FT-IRdemonstrated that the molecular structure of the precursor was the same as the design.The thermal decomposition behavior of the boron nitride （silicon/carbon） precursorwas studied as well. And the product obtained was characterized to analyze the chemicalcomposition, surface micro topography, and the structure. The outcome of the thermalgravimetric analysis demonstrated that the ceramic yield was about32percent on1200℃. Hexagonal boron nitride was obtained after the process of high-temperaturenitriding, and the crystallization improved as the nitriding temperature as well as thenitriding time. According to the outcome of the Energy Diffraction Spectrum, Carboncontent was less than8percent after the1400℃-nitriding。A bamboo-like nanostructure was found after the1400℃-nitriding. The diameter was about200nm, and the lengthwas microns. And the bamboo-like nanostructure was totally composed by hexagonalboron nitride in different orientation.