Formation of Calcium Ferrites under Controlled Oxygen Potentials at 1273 K

Solid state calcium ferrite formation reactions between different kinds of iron oxides and CaO under various PO2 at 1273 K have been investigated. The calcium ferrite formation rates are evaluated by using thermogravimetric method. The phase identification and quantification of calcium ferrites in the experiment have been carried out by using X-ray diffraction method (the Rietveld method). It has been found that intermediate calcium ferrite phases of CaFe2O4 and CaFe3O5 are formed prior to the Ca2Fe2O5 formation when Fe2O3 and Fe3O4 are used as a starting iron oxide, respectively. When starting from wüstite, intermediate calcium ferrite phases are not formed. The rates of Ca2Fe2O5 formation are found to be different depending on the starting reactant iron oxide phases. The Ca2Fe2O5 formation rate from wüstite is faster than that from Fe3O4, and that from Fe3O4 is faster than that from Fe2O3. It is also found that the Ca2Fe2O5 formation rate starting from Fe3O4 decreases with pO2, but that starting from wüstite is independent from pO2.