Silicon Carbide Synthesis Theory Of Multi-heat-source And Multi-direction-flow System And Its Application

Silicon carbide (SiC) has high density, high purity, high crystallinity and high uniformity,which is widely used in metallurgy, petroleum, chemical industry, aviation, machinery, microelectronics industries. China is a big exporter and production of silicon carbide products in the world. However, high power consumption, high material consumption and low yield, poor quality and unsafe production which have become a major issues to restrict high-speed development of silicon carbide industry in our country. Improving thermal efficiency, reducing energy consumption, and producing the high quality or high value-added SiC products are technical difficulties to be resolved urgently in SiC synthesis. Supported by the National Science Foundation Project (50174046 and 51074123) and the Scientific Research Program by Shaanxi Provincial Education Commission (08JK347and 05JK254), through the numerical simulation, theoretical analysis and experiments, the key theory and method of saving energy, promoting equality, increasing productivity and reducing consumption were systematically studied on the new technology of multi-heat-source and multi-direction-flow system synthesis silicon carbide. The practical results show that the SiC output of the multi-heat-source furnace increased by 48.1% compared with that of an Acheson single-heat-source furnace, the highest grade SiC increased by 30%, and the consumed energy reduced more than 10%. In addition, the frequent spouting was diminished, and the furnace was become more productive and safe. Dissertation research not only provides the theory and the guidance of methodology for SiC synthesis technology, but also has very important significance to promote the exploitation and processing technology of mineral resources in western region. Through the analysis of the heat transfer process of silicon carbide synthesis, the mathematical model of temperature field is founded. The temperature field of SiC-synthesized furnace belongs to unsteady heat conduction which has internal heat source, variable property in plane. The furnace boundary belongs to a given temperature boundary and the heat source boundary belongs to normal heat flux boundary condition. According to chemical reaction degree and common reaction ratio, by the method of linear regression, Linear interpolation, weighted processing, taking the temperature as control condition, thermal physical parameters of equivalent is determined at different temperature conditions.Based on theory analysis of solving transient temperature field by the method of finite element, optimized finite element model is established, and the evolution laws of temperature field in multi-heat-source SiC furnace is studied. Research finds that the high temperature isothermal face expends outside gradually with the prolong of the synthesis time, so the temperature field area compatible to the production of SiC increase gradually, but too long synthesis time not only increase energy consumption, but also generate SiC product yield decreased. So it needs to control the reasonable synthesis time, make the SiC decompose in a proper quantity. Then it can compose abundant high density SiC product. With superficial charge increase, heat source temperature increase and isothermal line of each temperature area move outward gradually, high-temperature region area increase gradually. If the superficial charge is too high, heat source temperature is exorbitant so that SiC synthesized around heat source abundance decomposition. So yield is reduced and energy consumption is increased.Based on the numerical simulation and the industrial tests, diffusion dynamic mechanism for multi-orientation energy flow and material flow in multi-heat-source system is revealed. Research shows that Whether can synthesis high-dense SiC largely depends on diffusion rate of gas phase substance such as silicon steam, SiO,SiO₂,Si₂C,SiC₂ and so on, physical vapor deposition of gas phase materials is the essential reason to result in high purification, high densification and high crystalloid properties of synthesizing SiC crystal. The thermal field superposition and heat shielding among many heat sources are the essential reasons to save energy, increase productivity and reduce consumption for multi-heat source furnace.Based on influnce of the power supply paremetres and furnace size on the temperature field, the judgment model of the heat source number is estiblished. The industrial example in TongHai silicon carbide factory shows that the judgment model can predict the optimal heat-source number of multi-heat-source synthesis furnace better. The judgment model can supply the scientific criterion of the key design parameters for this theoretical practical application in industry. Through the multi-heat-source synthesis experiment, the effect synthetic parameters such as synthesis time, superficial charge on SiC products were investigated, and microstructure of SiC products were analyzed by XRD and SEM ,which are compared with the products synthesizing by single-heat source furnace. The experimental results show that the key to promote quality, save energy, reduce consumption for multi-heat source synthesizing SiC technology lies in the system of multi-heat-source and multi-direction-flow evening the temperature field, which are fit for making SiC high-temperature area larger, making thermal efficiency higher and also can reduce energy consumption and increase productivity and quality of SiC. Based on experimental research, the industrial experiments were launched. The industrial experiments are agree with the numerical simulation and the pilot tests. The evolution of temperature field and dynamic diffusion mechnism of multi-orientation energy flow and material flow are verified.In general, this paper sets up the theoretical system of the multi-heat-source and multi-direction-flow system synthesis silicon carbide materials. The judgment model of the optimal heat-source number is put forward. In the meantime, the optimizing and available way of heat and quality transmitting is obtained of the new technology of multi-heat-source and multi-direction-flow system synthesis SiC. So the theoretical guide is supplied to improve the quantity and quality of SiC product, decrease the energy consumption and produce safely.