The kinetics of reduction at relatively low temperatures with hydrogen of pure and doped metastable non-stoichiometric magnetite
with 1 at% Mn, Co, Ni and Cu and also with 5 at % Ni and Cu have been investigated by using isothermal thermogravimetry in
the temperature range 300–400°C. With increase in the concentration of the dopant (5 at% Ni and Cu), the reactivity increases.
The activation energies for pure magnetite varies from 7 to 9 kcal/mole with the preparation temperature of precursorf Fe2O3 (250–400°C), being the lowest for those prepared at the lowest temperatures. The corresponding activation energies for the
reduction of doped samples (Fe, M)3−zO4, it depends, apart from their porosity and surface areas, on the nature of the solute atom, amount of disorder, whether it
occupies the tetrahedral (A) or octahedral (B) sites in the non-stoichiometric spinel and possibly on hydrogen ‘Spill over’