Influence of Al 2 O 3 and TiO 2 degradation behaviour of sinter and hematite at low temperatures on reduction

It is known that the presence of Al₂O₃ and TiO₂ tends to increase the intensity of the reduction degradation of sinter. To enable a basic understanding of the phenomena taking place, the present work evaluates some aspects of paramount importance, such as: (a) microstructural changes of sinter containing Al₂O₃ and TiO₂ during low temperature reduction; (b) theoretical and experimental volume changes occurring during the hematite to magnetite reduction step as well as the effect of Al₂O₃ and TiO₂ in solid solution with hematite, using absolute dilatometry; and (c) crystal lattice distortions of hematite and magnetite owing to solid solution with Al₂O₃ and TiO₂, determined by line broadening of X-ray diffraction peaks. The results show that hematite containing Al₂O₃ and TiO₂, subjected to a reduction process to the magnetite stage, yields a magnetite phase with a distorted crystal structure. This phenomenon, in association with structural deformation resulting from the volumetric expansion of hematite crystals during reduction, can cause crack generation and propagation in the sinter, leading to disintegration.