| Nitrides are widely used in cutting materials,high temperature structural materials,catalytic materials and other fields,owing to their excellent properties such as high melting point,high strength,high thermal conductivity,corrosion resistance,good thermal shock resistance and unique electronic properties.Conventional preparation methods for nitrides suffer from several shortcomings,such as high reaction temperature and low product purity.Molten salt synthesis method is a simple and reproducible method for preparation of inorganic material powders,which has the advantages of low reaction temperature and short reaction time required,and high purity and small particle size of the final products etc.In this thesis,carbon nitride,aluminium nitride,boron nitride and cabon-doped boron nitride powders were prepared via a molten salt synthesis method.The effects of various processing parameters including salt types,reaction temperatures and holding times on the synthesis of nitride powders were investigated.The results indicate that:(1)Tetragonal carbon nitride hollow tubes(TCNTs)were synthesized by a molten salt method with melamine as the main starting materials,and LiCl-KCl as molten salt medium.As-prepared TCNTs were 2~20 μm long and 50~2000 nm wide and high.A possible salt-assisted self-assembly mechanism is believed to dominate the formation of TCNTs,salt not only provides the liquid phase reaction medium,but also acts as an in-situ template.As-prepared TCNTs exhibited superior photocatalytic activities and adsorption performance due to their higher content of impurity nitrogen,unique one-dimensional hollow structure and larger specific surface area.(2)Aluminum nitride powders were synthesized by a molten salt method with aluminum and melamine as the main starting materials,and LiCl-KCl as molten salt medium.The lowest synthesis temperature of present method was about 1000°C,and the purity of Al N was up to 97%.The morphology of as-prepared Al N is granular with a particle size of about 300 nm.Aluminum nitride powders were synthesized by a molten salt method with aluminum oxide and melamine as the main starting materials,and LiCl-KCl as molten salt medium.The lowest synthesis temperature of present method is about 1200°C,which is more than 300°C lower than that required by the conventional carbonthermal reduction nitridation method.The morphology of as-prepared Al N is irregularly granular and lamellar.(3)Boron nitride powders were synthesized at 1100°C by a molten salt method with borax and melamine as the main starting materials,and NaCl-KCl as molten salt medium.The particle size of the product decrease d with the increase of the mass ratio of molten salt to reactant.When the ratio of molten salt to reactant ran up to 15:1,boron nitride nanosheets with only a few layers were obtained,which thickness was about 1 nm.Boron nitride powders were synthesized by a molten salt method with boric acid and melamine as the main starting materials,and LiCl-KCl as molten salt medium.The lowest synthesis temperature of present method was about 900°C,which is more than 300°C lower than required by the conventional carbonthermal reduction nitridation method.The morphology of as-prepared BN is granular with a particle size of about 50 nm.(4)Carbon-doped boron nitride powders were synthesized at 1100°C by a molten salt method with boric acid,melamine and glucose as the main starting materials.Using LiCl-KCl as molten salt medium is most favourable to the formation of BCN nanosheets,as-prepared BC0.4N samples had a flake structure of about 10 nm thick and the highest specific surface area of 484 m2/g.As-prepared BC0.4N sample had a good adsorption performance for methylene blue. |
