Study On The Synthesis Of Silicon Nitride, Carbon Nitride And Carbon Nanomaterials

This dissertation concentrates on the synthesis of silicon nitride,carbon nitride and carbon nanostructures through solid phase reaction,solvothermal route at low temperature,thermolysis and solvothermal catalytic methods.As the reactant is very cheap and the reaction condition is mild,these methods are promising in industrial application to some extent.1.The mixtures ofα- andβ-Si₃N₄ nano-crystalline were prepared in 200-350℃using NAN₃,SiCl₄ and Mg powder as the starting materials.The conversion ratio was 54.04%calculated from the amount of limited reactant NAN₃. Orthogonal strategy was performed to find the optimized reaction condition. Magnified experiments were carried out in a 1000 ml autoclave.The conversion ratio was about 50%which indicated that it was a promising process in industrial application.2.Starting from ferro-silicone alloy brezee and ammonium chloride,α-Si₃N₄ nanowires bundles have been obtained at 600℃.The nanowires have about 8 nm in diameter,up to 800 nm in length.The influence of reaction time and temperature on the products was investigated.Using silicon and metallic iron,α-Si₃N₄ olivary microparticles with a diameter of about 300～500 nm have been obtained at 650℃.When silicon and metallic aluminium were used to react with ammonium chloride,α-Si₃N₄ nanowire bundles with diameter of about 8 nm can be also obtained at 600℃.Since all of the starting materials used are relatively cheap,the methods will have potential prospect in industrial application.3.Graphite-like carbon nitride nanowire bundles with diameters of 200-500 nm were synthesized from the solid state thermolysis of melamine at relatively low temperature(400℃).Hexagonal carbon nitride tubes with diameters of 500-800 nm and flake arrays were prepared by heating the nanowire bundles at 550℃in argon atmosphere.The products were characterized in detail and the forming process of tubes and transformation of the molecular structures from s-triazine rings to tri-s-triazine units was analyzed.Compared with other methods,it provides a new simple and mild route for synthesis of carbon nitride with new morphology.4.Carbon nanofibers have been prepared through a simple catalytic route using tetrahydrofuran as the solvent and carbon source,Fe and Ni as catalyst,at 500℃. The carbon nanofibers have the average diameter of 100 nm and lengths ranging from hundreds of nanometers to several micrometers.Carbon micro-capsules with morphology of tobacco pipe have been synthesized through a catalytic solvothermal approach using ethanol as the solvent and carbon source,sodium borohydride as catalyst,at 500℃.The as-prepared carbon micro-capsules have the average diameter of 1μm and lengths of over ten micrometers.Due to the simplicity and large-scale synthesis,this work may have an opportunity to be applied in industrial production of one-demention carbon materials.