Fe-Ti-O exchange at high temperature and thermal hysteresis

Abstract

In this study, the Fe-Ti-O exchange behaviour between the systems hemo-ilmenite (y)FeTiO3-(1 -y)Fe2O3 and titano-magnetite (x)Fe2TiO4-(1 -x)Fe3O4 was investigated in the temperature range from 900 to 1400 K in an inert Ar atmosphere. Starting from a mixture of hematite and ilmenite with a fixed mol per cent, heat treatment generates a self-adjusting chemical equilibrium between hemo-ilmenite and titano-magnetite solid solution by means of interdiffusion and Fe3+→ Fe2+ reduction. Structural and magnetic characterization reveals that hemo-ilmenite is stable at all temperatures, whereas titano-magnetite shows increasing Ti-content with increasing treatment temperature. Heating-cooling cycles were performed for a sample to mimic slow cooling and study its effects on the two solid solutions. The magnetic properties of that sample exhibit thermal hysteresis during these cycles, as the Ti departs from titano-magnetite and thus leads to a new chemical equilibrium. The experimental data provide insight into the dynamics of the formation of Fe-Ti-O phases formed under varying conditions in geological systems. © 2011 The Authors Geophysical Journal International © 2011 RAS.