Formation of Calcium Ferrites under Controlled Oxygen Potentials at 1273 K

Abstract

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.