Fluoride Assited Preparation Of Boron Nitride Nano-materials

Hexagonal boron nitride nanomaterials（also called“White graphite”）own the similar crystal structure to the graphite and share many of the properties,including exceptional thermal conductivity,extraordinary strength durability and so on.Compared with their carbon nanocounterparts,BN nano-material has excellent temperature and chemical stability,greater neutron adsorption properties,special electrical isolation with band gap,and it would be used in electric,photonic and aerospace field as coating,isolation substrate,electronic heat sink,polymer composite,ultraviolet emitter and neutron adsorption materials.However,it is restricted by the synthesis of the raw materials to improve the depth study and application research.so improving the synthesis method and realizing controllable process are still the research highlights as well as getting high product.In the thesis,with the traditional CVD method,we compare the results of growthBN nanomaterials from different fluoride precursors by changing the experiment data,such as temperature and catalyst.We firstly have developed a process to create a virtually perfect collapsed boron nitride nanotube and boron nitride cystic nanomaterials at relatively lower temperature,with the ammonium tetrafluoroborate（NH₄BF₄）being the boron source and anhydrous MgCl₂ being the catalyst.With the advantage of horizontal furnace,meaning that the heating zone could be artificially moved to adjust the feeding speed of the precursor,we synthesis uniform collapsed BNNTs with high purity and highly crystaline,and eventually produce boron nitride cystic,a random network structure by optimizing the catalyst,protecting gas,synthesis and annealing temperature.Additionally,it shows potential applications in the hydrogen storage and adsorption of pollution reflecting from the characterization of gas adsorption-desorption test.Then we realized the presentation of the synthesis of tubular precursor for BNNTs in a setup of horizontal furnace,by using BF_3`NH₃ as a source of B,MgCl₂ as a catalyst.During this period,By takeing the advantages of the characteristics of horizontal furnace’s moving capability,by adjusting the annealing temperature of the furnace,the types of shielding gas and other various aspects influence conditions,we successfully prepared the BNNTs with high purity,great crystalline and uniform distribution,Additionally,we had conduct the further analysis to the growth mechanism of BNNTs,the analysis exhibits that the growth of BNNTs tends to follow the VS growth mechanism with MgF₂ being the model.This method overcomes the disadvantages of expensive raw materials in the existing preparation of BNNTs and achieved the preparation of pure phase BNNTs with low-cost high yield.Andthe gas adsorption properties were inestigated.