On the Formation and Constitution of Calcium-Ferrite

Abstract

We studied the formation, constitution, melting point, and micro-structures of Ca-ferrite prepared from the mixtures of CaO and Fe₂O₃ by chemical- and X-ray analyses. Main results obtained are as follows. 1) Ca-ferrite has two kinds of compound which are represented by CaOFe₂O₃ (monocalcium-ferrite) and 2CaOFe₂O₃ (dicalcium-ferrite). 2) CaOFe₂O₃ is formed over 700° and the formation is completed at about 1000℃. 3) When the sample contains excess CaO, 2CaOFe₂O₃ is formed over 1000℃ by the reaction of CaOFe₂O₃ and excess CaO and this reaction is completed at about 1200℃. 4) CaOFe₂O₃ dissolves Fe₂O₃ at high temperature and the sample containing 60 mol% of Fe₂O₃ shows single phase at 1200℃. 5) The compound represented by 3CaOFe₂O₃ or CaO2Fe₂O₃ cannot be observed by X-ray examination ; the former is nothing but a mixture of CaO and 2CaOFe₂O₃, and the latter, simply a mixture of solid solution of CaOFe₂O₃ and Fe₂O₃ and free Fe₂O₃. 6) CaOFe₂O₃ melts at 1220° and is dissolved in hot 1 : 1 HCl by heating while 2CaOFe₂O₃ melts at 1280C° and is dissolved immediately in cold dil HCl, and they both have paramagnetic property. 7) CaOFe₂O₃ forms fine hexagonal crystals near its melting point and shows growth steps, but 2CaOFe₂O₃ is apt to become glassy and its definite crystal forms are difficult to recognize under microscope.