Preparation Of Ultrafine Boron Carbide And Boron Nitride Nanotubes By Continuous Method

In recent years,boron-containing inorganic compound materials have attracted much attention.Among them,boron carbide（B₄C）has been widely used in abrasive tools,high-performance ceramics,ballistic materials,nuclear reactor neutron absorbing materials,etc.due to its excellent physicochemical properties;boron nitride nanotubes（BNNTs）is a novel nanomaterial that is similar in structure to carbon nanotubes but has better performance than carbon nanotubes.However,current domestic and foreign production and preparation technologies have seriously restricted the application of B₄C and BNNTs in the scientific community.Based on the existing synthetic B₄C and BNNTs methods in this laboratory,a synthetic device and process that can be used for continuous production were invented by improving the experimental scheme and improving the production equipment.Ultrafine boron carbide powder was prepared by self-propagating high-temperature synthesis（SHS）,and ultrafine boron carbide powder was used as precursor.Bamboo-like boron nitride was prepared by batch push-chemical vapor deposition（CVD）.nanotube.At the same time,the development status of the synthesis and application of boron nitride hydrogel materials was investigated and summarized.The main innovative research results of this paper are as follows:1.Ultrafine boron carbide powder was prepared by batch push-SHS method using boric acid/glucose/magnesium powder system,The products were characterized by Scanning electron microscopy（SEM）,X-ray diffraction（XRD）and Raman spectrum（Raman）.The results show that the B₄C sample has good crystallinity,uniform particle distribution,uniform morphology and average particle size of 250 nm.2.By using the intermittent push-boat-CVD method,the self-made ultra-fine boron carbide powder is used as the precursor,and the reaction atmosphere is controlled to be an ammonia atmosphere.The bamboo-shaped boron nitride nanotubes are successfully prepared at 1150～1250°C.The products were characterized by Scanning electron microscopy（SEM）,Transmission electron microscopy（TEM）,X-ray diffraction（XRD）,Raman spectrum（Raman）and Fourier Transform infrared spectroscopy（FT-IR）.The results showed that the prepared BNNTs had a wide range of tube diameter distribution,high purity,and the inner hollow structure was tapered.3.A push-type semi-continuous boron nitride nanotube preparation furnace is disclosed,which is composed of an electrically controlled heating part,a furnace structure part,a burner part and a furnace tail,and the solid reactant is made according to the intermittent operation mode.The chemical reaction takes place at the specified temperature in the furnace,and the suction and air intake devices of the burner and the furnace tail can provide different reaction atmospheres as needed,and the preparation furnace is used as a pilot test equipment,and the intermittent push boat method is adopted.A large number of continuous preparations of BNNTs.Experiments were carried out by changing the gas composition,flow rate and reaction temperature.By comparing the structure,morphology and diameter of BNNTs,the ammonia flow rate was determined to be 0.6～1.2 L/min.Continuous heating of the furnace tube to 900～1400°C and constant temperature insulation for 3～6 h is the optimal process parameter range.4.A preliminary exploration has been made in the field of preparation of boron nitride nanosheets,and an attempt has been made on the existing preparation methods.