Behavior of calcium chloride in reduction process of titanium dioxide by calcium vapor

摘要

CaCl_2 has played an indispensible role in many extraction processes for metallic titanium from titanium dioxide. In this paper, behavior of CaCl_2 in reduction process of titanium dioxide by calcium vapor was investigated and analyzed by means of XRD (X-ray diffraction), SEM (Scanning electron microscope), EDS (Energy Dispersive Spectrometer), DSC-TG (Differential Scanning Calorimetry-Thermogravimetry) and thermodynamic calculation. The results show CaCl_2 has a strong moisture absorption behavior and easily transforms CaCl_2.nH_2 (n = 6, 4 and 2). Then CaCl_2.nH_2 would dehydrate to be CaCl_2.H_2O step by step and CaCl_2.H_2O as an unstable compound would further dehydrate to be CaCl_2 or decompose to be CaClOH and CaO with temperature increasing. Additionally, CaCl_2 could volatilize on the experimental condition as well. When CaCl_2 was added in TiO_2 as raw materials, these above behaviors of CaCl_2 and CaCl_2.H_2O could not only discharge some gas or vapor to make raw material of TiO_2 porous, but also would conduct TiO_2 to form CaTiO_3 phase in raw material. The above facts would help the calciothermic reduction process of TiO_2 more easily proceed.