Chlorination of hafnium dioxide by gaseous chlorine in the presence of carbon

Abstract

The thermodynamic simulation of chlorination of hafnium oxide by gaseous chlorine in the presence of carbon at T = 450–1000°C is performed. It is shown that the main reaction products are gaseous hafnium tetrachloride, carbon monoxide, and carbon dioxide; as the temperature increases, the partial pressure of CO increases, while that of CO2 decreases. In the mentioned temperature range, the variations in the enthalpy, entropy, and the Gibbs energy of chlorination reactions are calculated and the composition of the gas phase under the conditions of thermodynamic equilibrium is determined. In the course of studying the kinetics of chlorination of HfO2 in the presence of carbon in the range T = 600–950°C, it is established that its limiting stage depends on the process temperature. Below 700°C, its rate is limited by the chemical reaction on the surface of nonporous solid spherical particles of the body with the formation of the volatile product; above 700°C, it is limited by the mass transfer of gaseous substances.