On the Formation of Calcium Ferrite in Sintered Ore

Abstract

Calcium ferrite phases in the sintered ores whose basicities were about 1.5 were investigated by the polished thin section method and X-ray microanalysis. They were hemicalcium ferrite containing Al₂O₃ of several to ten odd per cent and some of them included the very fine particles of calcium ferrite of ternary system or hematite precipitated in the cooling process. Hemicalcium ferrite was classified in four types, i. e. columnar, long columnar, acicular and dendritic. The formation mechanisms of the particles of each type are as follows: Columnar and long columnar ferrite is formed by the reaction of iron oxide with CaO in molten slag and their shapes depend on firing temperature and cooling rate. Acicular ferrite whose Al₂O₃ content are remarkably high grow from the ash of coarse coke particle. Dendritic ferrite is crystallized from the molten slag whose ratio of CaO to SiO₂is small. The formation of the particle composed of two kinds of calcium ferrite is related to the change of the oxygen potential of the melt during crystallization.