The Effect of K₂O, Na₂O and CaO Addition to Fe₂O₃ Single Crystal on Its Reduction

Abstract

The effect of the presence of K₂O, Na₂O, and CaO in Fe₂O₃ on its reduction behavior was investigated.Platelets of Fe₂O₃ single crystals were prepared by the flux method using Na₂B₁O₇, glass as a flux. The size of the crystals was approx. 3 mm in width and 0.3 mm in thickness. In order to make Fe₂O₃ react with K₂O, Na₂O, and CaO, small amounts of Na₂CO₃, K₂CO₃ and CaCO₃ powders were placed on the flat plane (0001) of Fe₂O₃ and heated at 1100-1300°C in air. It was confirmed by EPMA that reaction products of those substances were formed on some parts of the (0001) plane of Fe₂O₃. The Fe₂O₃, crystals were reduced at 750°C in CO and H₂ streams, and surface structures were observed by SEM. The results obtained were as follows. When alkaline metals (as Na₂O, K₂O) were present in Fe₂O₃, abnormal swelling took place during reduction. It was considered that the swelling was caused by the net effects of (1) cracking of the crystal at early stage of the reduction (2) fibrous iron formation and (3) carbon deposition on the reduced iron. The fibrous iron formation was also observed in the grain boundary of calcium ferrite.