Kinetics of thermal decomposition of sodium hexafluorosilicate under isothermal conditions

The results of an experimental study of the thermal decomposition of sodium hexafluorosilicate Na 2 SiF 6 , performed under isothermal conditions at temperatures of 600, 700, 800 and 900 °C, are discussed. It is shown that the kinetics of this process can be described using the Avrami–Erofeev equation with a variable exponent n . The range of this exponent is from 0.541 to 1.545. The average value of the exponent n, calculated for all study variants, was 0.761. As is known, the Avrami–Erofeev equation describes the kinetics of thermal decomposition of a substance in a condensed state, determined by the nucleation process. This suggests that in the case of thermal decomposition of sodium hexafluorosilicate in the temperature range of 600–900 °C, this process is the limiting stage of the overall process. It was found that the decomposition rate of the pyrolytic Na 2 SiF 6 increases with increasing temperature. The average value of activation energy was 63.23 kJ/mol. The average value of pre-exponential factor A was 1.807 10 2 min –1 . The results can be used in the development of equipment for obtaining polycrystalline silicon of semiconductor quality, which is the main raw material for the production of equipment used in micro- and power electronics and photovoltaics.