KINETIC-STUDY OF THE FORMATION OF CATION-EXCESS MAGNETITE

A cation-excess magnetite Fe3 + deltaO4, has been found to form in the range 0.00 < delta < 0.09, in the course of the H-2-reduction of magnetite into alpha-Fe at 300 OC. The formation of the cation-excess magnetite described by (3 + delta)Fe3O4 + 4 delta H-2 --> 3Fe(3 + delta)O(4) + 4 delta H2O was studied kinetically. In the temperature range 250-350 degrees C, the rate constants, k(1) and k(2), were determined for the forward and reverse reactions, respectively. The rate of formation of the cation-excess magnetite depended on the partial pressure of H-2 gas. The rate constant, k(1), was estimated to be 10(-13.8) at 300 degrees C and the reaction order was 1.11 with respect to the partial pressure of H-2 gas. The rate of reverse reaction depended on the partial pressure of H2O vapour and the excess of cations in magnetite, delta. The reaction rate constant k, was estimated to be 10(-2.45) at 300 degrees C, and the reaction orders were 0.45 and 0.95 with respect to the partial pressure of H2O vapour and the delta value, respectively. The activation energies of the forward and reverse reactions were evaluated to be 63.8 kJ mol(-1) and 25.5 kJ mol(-1) from the Arrhenius plots.