In industrial iron ore sintering, the raw material is heated in a reducing atmosphere and cooled in an oxidizing atmosphere. In order to study the effects of gas atmosphere in industrial sintering, small tablet specimens containing powdered commercial iron ore, limestone, quartz and kaolin were heated in controlled gas atmospheres to examine the effects of gaseous atmosphere, heating temperature and cooling condition on the formation of minerals in sinter. The results obtained are summarized as follows.
In the heating stage of laboratory sintering, with a decrease of partial pressure of oxygen, the magnetite content increases and hematite content decreases. The calcium ferrite content is found also to decrease at the low sintering temperature (1 210°C). However, at a higher sintering temperature (1 255°C), a medium oxygen potential (5×10^-3 atm) produces the most calcium ferrite. In the air cooling stage, magnetite may react with the silicate melt and oxygen to generate a large amount of columnar calcium ferrite.
A typical microstructure of the bond composed of columnar calcium ferrite, granular magnetite grain and glassy silicate in a normal industrial sinter can be simulated reasonably by heating a specimen to 1 255°C for 4 min in the gaseous mixture CO=1%, CO₂=24% and N₂=75% and then cooling it slowly in air.