Hematite to magnetite reduction monitored by Mossbauer spectroscopy and X-ray diffraction

The aim of the present research is to determine the kinetics of the transformation from hematite (alpha-Fe2O3) to magnetite (Fe3O4). The procedure consisted of an isothermal heating in a flow of a H-2-Ar mixture at temperatures between 260 and 360 degrees C. The phase evolution at a given temperature, as a function of the thermal treatment time, was monitored by using room temperature Mossbauer spectroscopy and X-ray diffraction analysis (XRD). In the range of temperatures and times studied the only iron oxide that was formed was magnetite. In order to optimize equipment requirements for the quantification of the reaction products a calibration curve was constructed. This allows to estimate the conversion degree (measured as the percentage of magnetite produced) with a short-run XRD pattern. We calculate an apparent activation energy of 98 +/- 4 kJ/mol from reaction grade-time curves at each temperature. (c) 2006 Elsevier B.V. All rights reserved.