Mechanism of Ferrite Spinel Formation Revisited

Data on the volume changes of the starting reagents and reaction products were used to analyze the reactions taking place in the ferrite-forming systems MgO–Fe₂O₃, Mn_0.75Mg_0.25O–Fe₂O₃, and NiO–Fe₂O₃ in the temperature range 1255–1315°C. It was shown that, under these conditions, there is no oxygen transport through the gas phase. The possible formation of Fe²⁺ ions is attributed to partial electron compensation for the charge on the M²⁺ cations as a result of counterdiffusion. The presence of excess Fe in the spinel phase at the intermediate stages of ferrite formation is due to the transformation of -Fe₂O₃ into -Fe₂O₃ at a certain M²⁺ concentration.