Carbon oxidation at high temperature during carbothermal reduction of titanium dioxide

Abstract

Carbothermal reduction of titanium dioxide is a very complex reaction. It comprises several successive or simultaneous reactions, interest being focused on the sequence: which is itself composed of two reactions: the first being a quasi-equilibrium which fixes the partial pressure of carbon dioxide for the second reaction, slow and kinetically limiting. The overall reaction rate is identical to that of carbon oxidation. Hence, this method allows a study of the kinetic behaviour of carbon at high temperatures (here, 1523 K) under low partial pressures of carbon dioxide (10^-2–10³ Pa) which are unusual conditions. The degree of conversion of carbon α vs. time t follows the kinetic law: where the constant K determines the specific rate v of the reaction. Changes of the partial pressure of carbon dioxide, to which carbon is exposed, are obtained by imposing variable partial pressures of carbon monoxide (0–10⁵ Pa). The resulting relationship v=f(P): shows that the oxidation of carbon is governed by the desorption of the carbon dioxide. This work proves the feasibility of a study of the carbon oxidation at low partial pressures of CO₂ and for high temperatures and casts new light on the kinetics of the carbothermal reduction of titanium dioxide.