Kinetic study on preparation of substoichiometric titanium oxide via carbothermal process

Abstract

Gibbs free energy was applied to analyze the carbothermal reduction process of TiO2. The phase stable diagram of Ti–C–CO was drawn, and it can be found that TiO2 will be reduced to Ti–O Magneli phase, TinO2n–1 (3 < n < 10) or Ti3O5 first and then further reduced to TiC. However, in the present study, it was found that Ti4O7 can be reduced to TiC directly when the temperature was lower than 800 K and lg(p co/p θ ) < −1.1. The reduction route was proved by the results of non-isothermal TG–DTA combined XRD. The isothermal analysis of carbothermal reduction process of TiO2 via TG–DTA under the temperature of 1363, 1413, 1463 and 1513 K was performed. The whole reduction process was divided into two sections: Initially it was rate controlled by an interfacial reaction, and later was rate controlled by three-dimensional diffusion. The modified mathematical expressions were deduced. They fit the experimental curves well. Their activation energy of steps was 241.1 and 323.4 kJ mol−1, respectively.