Supercritical Of Co <sub> 2 </ Sub> Low Temperature Synthesis And Characterization Of Silicon Carbide - Alkali Metal System

The ScCO₂-alkali metal system, which is used to convert CO₂ into useful carbon-based materials, belongs to green chemistry system. The purpose of this dissertation is to establish a route for synthesizing silicon carbide at low temperatures in the ScCO₂-alkali metal system, and to investigate photoluminescence and dilute magnetic properties of 3C-SiC semiconductor synthesized at low temperatures. The details are summarized as follows:Firstly, the trait of pressure variation and reaction character of ScCO₂-alkali metal system during the reaction process was studied. The curves of CO₂ pressure vs temperature (P-T) with different CO₂ densities were respectively measured and plotted. Especially, by investigating the influence of metallic Na and its volume on the curve of P-T (CO₂ density = 1.0 g/mL), the pressure variation vs time at different heating temperatures, some interesting results were obtained, laying the foundation for the synthesis of high-temperature phase materials.Secondly, silicon carbide was synthesized at low temperature of 460℃ in the ScCO₂-metallic Na system, using cheap FeSix alloy, industrial CO₂ gas and metallic Na. The synthesis conditions of silicon carbide were explored by changing grain size, weight of FeSix alloy, metallic Na volume, heating rate, heating temperature and heating time. The influence of the synthesis conditions on crystal types and yield of silicon carbides was also investigated. Besides, silicon carbide was also synthesized at 500℃ using FeSix alloy, basic magnesium carbonate and metallic Na, the two kinds of reaction systems by using basic magnesium carbonate and CO₂ as carbon sources respectively were compared. The optimized synthesis conditions of silicon carbide were brought forward after discussion of the results. Magnesium carbonate as carbon source for synthesis of silicon carbide in the ScCO₂-metallic Na system with FeSix alloy as silicon source is more advantageous than CO₂. The smaller grain size of FeSix alloy and more weight of metallic Na are two favorable conditions to form silicon carbonate; As using CO₂ and FeSix alloy (≤500) as carbon source and silicon...