Collection of Czechoslovak Chemical Communications - digital archive 

Abstract

From the calculations of heterogenous chemical equilibria in the systems Si-Cl and Si-Cl-H the equilibrium composition of the gas phase and the amount of deposited or reacted solid silicon have been determined. For these calculations, the method based on the minimization of the Gibbs energy of the system and critically judged and selected values of input thermodynamic data have been used. The calculations have been performed for the temperature range 1 000-1 600 K, for the pressure 101.325 kPa and 10.133 kPa and for various input compositions of the gaseous phase. In the case of the system Si-Cl, the reaction of solid leading to the formation of silicon subchlorides takes place at all conditions investigated. At atmospheric pressure and at temperatures in the neighbourhood of 1 300 K, the dominant components of the gas phase are the following substances: SiCl₄, SiCl₃ and SiCl₂. The dependence of the amount of deposited solid silicon on temperature and on the initial composition of the gas phase in the system Si-Cl-H shows–in the investigated range of variables – a maximum, the position of which depends on the total pressure of the system. At atmospheric pressure, at temperatures around 1 300 K and at the initial molar ratio Cl/H = 0.01, the dominant components of the gas phase are the following substances: SiCl₄, SiCl₃, SiCl₂, SiHCl₃, SiH₂Cl₂ and HCl. The substance SiHCl which has been included into the equilibrium calculations for the first time, is present in a significant amount at higher temperatures and especially at lower pressure.