Carbon oxidation at high temperature during carbothermal reduction of titanium dioxide

Carbothermal reduction of titanium dioxide is a very complex reaction. It c omprises several successive or simultaneous reactions, interest being focus ed on the sequence: 2 Ti3O5 + 10 C-->3 Ti2OC + 7 CO which is itself composed of two reactions: 2 Ti3O5 + 13 CO = 3 Ti2OC + 10 CO2 10 C + 10 CO2 --> 20 CO the first being a quasi-equilibrium which fives the partial pressure of car bon dioxide for the second reaction, slow and kinetically limiting. The ove rall reaction rate is identical to that of carbon oxidation. Hence, this me thod allows a study of the kinetic behaviour of carbon at high temperatures (here, 1523 K) under low partial pressures of carbon dioxide (10(-2)-10(3) Pa) which are unusual conditions. The degree of conversion of carbon alpha us. time t follows the kinetic law: 1 - (1 - alpha)(1/3) = Kt where the constant K determines the specific rate v of the reaction. Change s of the partial pressure of carbon dioxide, to which carbon is exposed, ar e obtained by imposing variable partial pressures of carbon monoxide (0-10( 5) Pa). The resulting relationship v = f(P): v = 5.938 x 10(-8) - 9.2447 x 10(-12) P-CO(7/10) / 1.4102 x 10(-3) P-CO + P -CO(-3/10) + 16.615 shows that the oxidation of carbon is governed by the desorption of the car bon dioxide. This work proves the feasibility of a study of the carbon oxid ation at low partial pressures of CO, and for high temperatures and casts n ew light on the kinetics of the carbothermal reduction of titanium dioxide.