Sublimation Kinetics of Zirconium Tetrachloride (ZrCl_4) for Producing Zr Sponge

摘要

Sublimation of ZrCl_4 is important for the production of nuclear grade metallic Zr in Kroll's process. The sublimation kinetics of ZrCl_4 was investigated by TGA under both isothermal and non-isothermal conditions. The sublimation rate of ZrCl_4 increased with increasing temperature under isothermal conditions. ZrCl_4 sublimation was confirmed to be a zero-order process under isothermal conditions, whereas it was first-order kinetics under non-isothermal conditions. The activation energy of ZrCl_4 sublimation under isothermal conditions was 21.7 kJ/mol. The activation energy for non-isothermal sublimation was 101.4 kJ/mol and 108.1 kJ/mol with the Kissinger method and Flynn-Wall-Ozawa method, respectively. These non-isothermal activation energies were very close to the heat of sublimation (103.3 kJ/mol). Sublimation occurs by two elementary steps: surface reaction and desorption. Therefore, the overall activation energy of ZrCl_4 sublimation is 104.8(±3.4) kJ/mol. The activation energy of the surface reaction and desorption steps are proposed to be 83.1 kJ/mol and 21.7 kJ/mol, respectively.