Synthesis of hercynite by reaction sintering

Hercynite was synthesized by a reaction sintering method using industrial alumina, mill scale, and carbon black as starting materials in the presence of nitrogen and solid carbon at high temperatures. Phase and microstructure changes during the synthesis were investigated. The specimen sintered at 1450 °C consisted of hercynite (FeO·Al2O3), Al2O3, Fe2O3, Fe3O4 and others. In contrast, the specimens sintered at 1550 and 1650 °C only showed hercynite phase, which exhibited typical octahedral or cubic structures. The results showed that by controlling the atmosphere and the addition of reactants, the transformation from Fe3O4 to FeO was controlled, and the reduction of FeO by carbon was restrained, which extended the temperature range at which FeO could exist stably, thus making it feasible to prepare high-purity hercynite by a reaction sintering method. The firing temperature of high-purity hercynite should be above 1550 °C.