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, Mn0.75Mg0.25O-Fe2O3, and NiO-Fe2O3 in the temperature range 1255-1315degreesC. 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 alpha-Fe2O3 into gamma-Fe2O3 at a certain M2+ concentration.