High-temperature Structure Evolution And Properties Of Micro-nano Boron Nitride Materials

The mechanical property,thermal stability and oxidation resistance of boron nitride?BN?micro/nanomaterials at high temperatures have distinct advantages compared with other kinds of micro/nanomaterials.BN micro/nanomaterials have shown broad application prospects in composite material reinforcements,electronic packaging fillers,etc.However,because of abundant dangling bonds on BN micro/nanomaterials'surface,harsh environments such as high-temperature could affect their microstructures,resulting in changes of properties.The study on the stabilities of BN micro/nanomaterials,especially the microstructure evolutions and properties changes in a harsh environment,is of great significance for the practical applications of BN micro/nanomaterials.In this thesis,we chose BN nanospheres and porous BN microfibers produced in our laboratory as our research objects to carry out the following researches:?1?We have studied the changes of microstructure and luminescent properties of BN nanospheres after heated at high temperature?1400-1600°C?in different kinds of gases?N2,Ar and NH₃?.With the heating temperatures increasing,the contents of C,O impurities in the BN nanospheres gradually decrease.Meanwhile,hollows emerge in the core of BN nanopheres.The lamellar stacking of BN lattice fringes gradually becomes more orderly,and the overall shape gradually changes from a sphere to an angular hexagonal structure.Luminescence results show that the impurities and nitrogen vacancies in the BN nanospheres changed after high temperature treatment in inert gases?N₂ and Ar?,causing new photoluminescence?PL?peaks at 338 nm.However,the BN nanospheres treated in NH₃ gas exhibit a new broadband emission peak at 350-440 nm,probably caused by the introduction of N-H groups at high temperature in NH₃ gas.?2?We have studied the changes of microstructure and gas adsorption properties of porous BN microfibers after heated at high temperature?1400-1600°C?in N₂ and NH₃ gases,respectively.The results show that the contents of C and O impurities in the porous BN microfibers decrease effectively and the crystallinity increase after heated at high temperature in N₂ gas.With the temperature increasing,the amount of micropores in the porous BN microfibers decreases,the mesoporous content increases,and the specific surface area decreases,resulting in a corresponding decrease in the adsorption capacity of CO2.After NH3treatment,the pore structures of the microfibers remains constant,but the CO₂ adsorption capacity is higher than the BN microfibers untreated with NH₃.We believe that the N-H groups introduced by NH₃ treatment play a key role in improving the CO₂ adsorption performance of porous BN microfibers.?3?We have studied the effects of metal ions?concentration and species?on the microstructure and properties of porous BN microfibers in high temperature environment.The adsorption of proper concentration of metal Tb³⁺ions makes the porous BN microfibers in-situ converted into a novel self-assembled BN architecture,assembled from high crystallinity BN nanosheets with diameter of²00 nm and thickness of²0 nm.This BN architecture has super-hydrophobicity and exhibits a strong ultraviolet emission peak from the BN nanostructure and a green emission peak from the Tb³⁺ ions.