Research For Preparation And Properties Of Nano Boron Carbide Based On Graphene Oxide

With the rapid development of nuclear energy and nuclear technology,the research of high-performance neutron absorption materials for radiation protection has become an essential subject in the field of nuclear technology.Boron carbide?B₄C?possesses various superior properties,such as high neutron absorption cross-section,low secondary radiant energy after neutron capture,easy shielding,etc.Due to its attractive combination of these properties,B₄C plays a crucial role in neutron absorption materials.However,boron carbide exhibits poor sintered compactness and fracture toughness.The combination of nanosized boron carbide and a toughening agent is currently an effective improvement method.Graphene oxide?GO?with a layered structure,high specific surface area,and an abundance of chemical groups to provide plenty of active sites for the reaction and lower the reaction temperature.The excellent dispersibility of GO in the ceramic matrix can improve the mechanical properties of materials.The GO can be used as a carbon source to prepare nano-boron carbide to improve the neutron absorption performance of the material.In addition,it can also be used as a toughening component to enhance the sintered compactness and fracture toughness of boron carbide.Therefore,in this thesis,graphene oxide was used as a carbon source to react with different boron sources to prepare nano-boron carbide,and its related properties were studied.The main research contents are as follows:?1?The GO-B₂O₃ system was used as the research object.Nano-boron carbide was prepared by the carbothermal reduction method.The effects of C/B molar ratio?C/B₂O₃=1.25,1.5,1.75,2.0,2.25?and reaction temperature?1300-1400°C?on the crystal structure of B₄C were investigated.The phase,morphology,and morphology of prepared B₄C were characterized by X-ray diffraction?XRD?,field emission scanning electron microscopy?SEM?,Fourier transform infrared spectroscopy?FT-IR?,and Raman spectroscopy.The results showed that a precursor with a C/B₂O₃ molar ratio of 1.25 was reacted at 1400°C for4 h to obtain rod-shaped B₄C with a diameter of about 1-2?m and a length of about 20?m.The crystal structure of the rod-shaped B₄C is rhombohedral.?2?The GO-B₂O₃-B system was used as the research object.Nano-boron carbide was prepared by the carbothermal reduction method.The effects of reaction temperature?1300-1400°C?and reaction time?1-4 h?on the crystal structure of B₄C were studied.XRD,SEM and XPS were used to study the phase,the morphology and the structure,respectively.The results show that the precursor with a C/B₂O₃/B molar ratio of 2:1:1 was reacted at1400°C for 3 h to obtain boron carbide particles with a particle size of about 500 nm.?3?The GO-B system was used as the research object.Nano-boron carbide was prepared by a solid-phase thermal reaction method.The effects of B/C molar ratio?C/B=3.6,3.8,4.0,4.2,4.4?,reaction temperature?1300-1450°C?and reaction time?1-4 h?on the crystal structure of B₄C were investigated.The phase,morphology,and morphology of prepared B₄C were characterized by XRD,SEM,and FT-IR.The neutron shielding properties of the neutron shielding composites with B₄C content of 0 wt%,5 wt%,10 wt%,15 wt%,20 wt%,and 25 wt%were measured using a Suanni small-angle neutron scattering spectrometer.The B₄C nano-powders were sintered at 1800-1900°C to produce B₄C ceramics by vacuum hot pressing,and its mechanical properties were tested by a nano-indenter.The results show that a precursor with a B/C molar ratio of 4 was reacted at 1450°C for 4 h to obtain boron carbide nanosheets with edge lengths of about 200-500 nm and a thickness of about 100 nm.The neutron-shielding performance test results show that neutron transmittance with a B₄C nanosheets content of 25 wt%was 94.83%lower?from 56.47%to 2.92%?than with epoxy resin,and the total macroscopic cross-section was 518.41%greater(from 0.2857±0.0023cm^-11 to 1.7668±0.0004 cm^-1).The mechanical test results show that when the sintering was1800°C,the relative density,fracture toughness and hardness of ceramics made from homemade B₄C nanosheets were increased by 3.6%,23.1%,and 12.8%,respectively,compared with ceramics made from commercial available B₄C powders.This study provides a new method for the preparation of boron carbide nanosheets with excellent neutron absorption performance and sintering activity.