| Epoxy resin(EP)has been extensively utilized in numerous fields,including aerospace,national defense,and the nuclear industry,due to its high adhesion,outstanding electrical insulation,good processability,and chemical resistance.However,when EP is employed as an electrical insulator in nuclear power plants and spacecraft and as a coating for nuclear containment,it will inevitably be exposed to ionizing radiation.Radiation can cause negative effects on the microstructure and crosslinking network of EP,which can lead to a decline in its performance and lifespan.Therefore,it is crucial to improve the radiation stability of EP in the nuclear industry.Adding nanomaterials to the matrix has been proven to be a simple and effective method for improving the radiation stability of polymer materials.Furthermore,in addition to enhancing the radiation resistance of the matrix,nanomaterials also endow the material with some new characteristics,such as high thermal conductivity and insulation.Boron nitride(BN)is an ideal filler for improving the radiation stability of EP due to its excellent mechanical strength,low density,insulation performance,neutron absorption,and thermal conductivity.Nonetheless,the compatibility between the BN and EP matrix is limited,and microphase separation between BN and EP is prone to occur,making it difficult to maximize its reinforcing effect.In this thesis,we focused on developing the BN/EP composite and modifying BN to achieve the highest possible reinforcing effect.The mechanical and thermal properties of BN/EP before and after irradiation and the influence of BN size and interface on the radiation stability of composites were explored.The main research results are as follows:1.h-BN/EP composite was successfully prepared by the solution blending method.Compared with neat EP,the composites with a small amount of h-BN exhibited higher tensile strength and thermal stability.In addition,the effects of absorbed dose,dose rate,and irradiation atmosphere on the properties of the composites were investigated.Afterγ-ray irradiation,the h-BN/EP composite exhibited stronger radiation resistance,and when the relative tensile strength was reduced by half,the absorbed dose required by h-BN/EP was about 300 kGy higher than neat EP.Finally,the neutron shielding performance of the h-BN/EP composite was studied,and the neutron transmittance of the h-BN/EP composite decreased significantly.This work demonstrates that h-BN can not only effectively improve the radiation resistance of EP,but also be used to improve the neutron shielding performance of materials.2.A mild and large-scale ball milling method was developed to prepare boron nitride nanosheets(BNNS),i.e.,isopropanol(IPA)assisted ball milling exfoliation.Isopropanol(IPA)had two effects:on the one hand,the dispersion of BN in IPA was good,which facilitated the effective effect of shear force on BN;on the other hand,its surface energy was similar to BN,which aided in the exfoliation process.The results demonstrated that the average thickness of IPA-BN prepared by this method was 6 nm,with a high yield of 49%.Furthermore,the crystal structure of BN remained intact.The size of BN had a significant impact on the thermal properties and thermal conductivity of the composite material.The addition of thin IPA-BN significantly reduced the coefficient of thermal expansion(CTE)of the composite material.However,the composite with the addition of thick h-BN/EP showed higher thermal conductivity.In terms of radiation resistance,the addition of 0.2 and 1 wt%of BN with an average thickness of 6 nm to 300 nm had a limited effect on the properties of the composites under γ-irradiation.3.Carbon-doped boron nitride(BCN)with a large number of active groups on the surface was prepared by thermal polymerization,and the as-prepared BCN was further functionalized by two silane coupling agents to improve the interface compatibility between the filler and EP.Compared with BCN,the interface interaction between the modified BCN and EP matrix was stronger,and the modified BCN/EP composite exhibited higher tensile strength and thermal stability.After γ-ray irradiation,the radiation resistance of the modified BCN/EP composite was significantly enhanced,and the tensile strength was 32.5%higher than neat EP after irradiation at 900 kGy.In addition,the modified BCN/EP maintained a high glass transition temperature(120℃)and thermal conductivity.This work shows that the interface effect between the filler and the matrix is very important in improving the radiation resistance of the material,which will help to develop composite materials with better radiation resistance.4.The Ag ions were reduced to form nanoparticles loaded on h-BN by γ-ray radiation method.The thermal conductivity and the radiation resistance of composites under simultaneous thermal heating and γ-ray irradiation were investigated.The experimental results indicated that the bridging effect of Ag nanoparticles loaded on BN greatly reduced the thermal resistance between BN,resulting in enhanced thermal conductivity of the composites.In addition,appropriate loading and smaller size were found to be beneficial for improving the thermal conductivity of composites.The AgBN/EP exhibited excellent thermal stability and high T_g.Compared with neat EP,the initial decomposition temperature and T_g of Ag-BN/EP increased by 5.5 and 5.1℃,respectively,which was advantageous for enhancing the stability of the material at high temperatures.Furthermore,the properties of the composite were improved under simultaneous heating and irradiation,because thermal oxidation promoted intermolecular crosslinking.However,The Ag-BN/EP composite exhibited minimal changes in performance after simultaneous heating and irradiation,demonstrating excellent stability. |
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