Study On Efficient Preparation&Dispersion And Their Mechnisms Of Boron Nitride Nanotubes

Because of low density, high strength, strong oxidation resistance and other advantages,boron nitride nanotubes （BNNTs） had attracted great interest of researchers. The BNNTspreparation, dispersion and their mechanisms were studied and the products and dispersionsysterm were characterized in the paper.BNNTs with diameter of20-200nm and length of several micrometers were synthesizedby catalyst assisted growth method. The method employed B powders as resourse, Fe₂O₃andCaO as catalysts and atmosphere of NH3. The method need1200℃and2h heatpreservation. The products were characterized by the means of XRD, SEM, TEM, SAED,FTIR and Raman spectroscopy in the paper. The factors of BNNTs growth such as catalystcomposition, temperature, atmosphere and catalyst pretreatment, were studied in the paper.The results indicated that it could not prepare BNNTs with Fe₂O₃as single catalyst and theproducts synthesized with CaO as single catalyst had many defects. However, we preparedgood BNNTs by empoying Fe₂O₃and CaO as co-catalysts. The yield of BNNTs was increasedby higher temperature. The inner structure of BNNTs can be changed by different atmosphere.The pretreatment of catalyst was able to decrease the diameter of BNNTs. The yield ofBNNTs was increased to89.5%by designing orthogonal experiments.The method of magnesiothermic reduction was employed to prepare BNNTs in the paper.The method employed B₂O₃as resourse, Fe₂O₃,CaO and Mg powders as catalysts and need1250℃and6h heat preservation. The products were characterized by the means of XRD,SEM, TEM and SAED. The effects of catalyst composition, temperature and atmosphere onBNNTs were studied in the paper, respectly. The results indicated that the yield of BNNTswas able to be changed by using different composition of catalysts. Higher temperature andlonger heat preservation can improve the BNNTs yield and length of tube body. It was alsoproved that there was no effect of atmosphere on BNNTs. The yield of BNNTs was inceasedto77.8%with the help of orthogonal experiments.The model of BNNTs growth was proposed by studying the phase composition ofproducts and chemical reaction of preparation and refering the growth mechanism of carbonnanotubes （CNTs）. The results indicated that the growth mechanism of the bamboo-liked andcylinder-liked BNNTs were liquid-solid （LS） and vapor-liquid-solid （VLS）, respectly.BNNTs were successfully dispersed in water with the help of ammonium oleate orpolyethylenimine （PEI） as surfactant. The dispersion system was characterized by the meansof Zeat potential, SEM, TEM and FTIR. The dispersion effects of two surfactants werestudied comparatively. The effects of addition of surfactants, pH and ultrasonic time on BNNTs dispersion were researched, respectly. The results showed that the stability of BNNTsdispersion was able to be increased by surfactants. The optimal addition of ammonium oleateand PEI were3%and1.5%, respectly; The optimal pH value of them were8-9and3-7,respectly; the optimal ultrasonic time of them were1h and0.5h, respectly. The dispersionmechanism of BNNTs was studied in the paper. The decomposition of BNNTs in water withultrasonic was researched at last, and the decomposition mechanism of BNNTs was explainedin the paper.