Chemical Thermodynamics Of Hydrogen Silicon Synthesis

Through application Reaction and Equilib modules of integrated thermochemical database FactSage software, the complex chemical reactions in the Si-H-Cl system with relation to Trichlorosilane synthesis were studied. The standard Gibbs free energy, standard equilibrium constant, equilibrium gas phase composition, the trichlorosilane conversion rate and yield at various conditions were computed by FactSage software. Also, the Silicon conversion, the trichlorosilane conversion rate and yield with relations to the improvement process of synthesis pressure processes, plus H2diluted and plus SiCl4processes were calculated. Parts of the important calculations were tabularly displayed, they included the ΔrGmθ and Kaθ value of the seventeen reactions at a variety of temperatures, the trichlorosilane conversion rate and yield at a different conditions, and so on. Diagrams of ΔrGmθ and Kaθ for the seventeen chemical reactions in the Trichlorosilane synthesis system have been plotted against thermodynamic temperature T. Graphs of equilibrium gas phase composition, Silicon conversion rate and the trichlorosilanc conversion rate at different temperature, pressure and the charge ratio nHClO/nSiO have been drawn too. The effects of charge ratio nHClO/nSiO temperature and pressure on the SiHCl3equilibrium yield were also graphically presented. In addition, the trichlorosilane conversion rate and yield with relations to the improvement process of synthesis pressure processes, plus H2diluted and plus SiCl4processes have been shown in figure.The results from this thermodynamic of trichlorosilane synthesis study show that:(1) The ΔrGmθ of most of the reactions, including the main reaction, increase with increasing temperature, indicating that higher temperature have a passive effect on the trichlorosilane synthesis process. The ΔrGmθ of most of the reaction is much less than zero (ΔrGmθ≤-41.84kJ·mol-1), indicating that silica powder and HCl gas can react completely. The ΔrGmθ of secondary reaction (2) is far less than the main reaction (1), indicating that the trichlorosilane conversion rate is lower than the SiCl4, which is the main reasons for the lower the trichlorosilane conversion rate.(2) When the charge ratio nHClO/nSiO≤3,the trichlorosilane conversion rate decreases with increasing temperature; when the charge ratio nHClO/nSiO≥4, the trichlorosilane conversion rate increases with increasing temperature. (3) When the ratio of HCl gas to silica powder is low, the yield of SiHCl3decreases with increasing temperature, increases with increasing pressure, increases with increasing HC1gas proportioning; when the ratio of HCl gas to silica powder is high, the yield of SiHCl3increases with increasing temperature, have no changes with increasing pressure, decreases with increasing HCl gas proportioning. Taking all factors into consideration, the optimum operating conditions for trichlorosilane synthesis process were presented as573.15K,0.5atm and the nHClO/nSiO molar ratio of3.4.(4) Improved trichlorosilane synthesis process, for pressurized process, the yield of SiHCl3increases with increasing pressure, the optimum pressure conditions is20atm;for plus H2diluted process, considering the relation between the yield, the equilibrium mole fraction and the ratio of HCl gas to H2, the optimum molar ratio nHClO/nH2O is4; for plus SiCl4process, considering the relation between the yield, the equilibrium mole fraction of SiHCl3and the ratio of HCl gas to SiCl4, the optimum molar ratio nHClO/nSiCl4O is12.