Volume 58 (2018) Issue 4 Pages 642-651
Reducibilities of silico-ferrite of calcium and aluminum (SFCA) have been examined using high temperature X-ray diffraction (XRD) analysis including the effect of hydrogen. Two types of sample were prepared: columnar SFCA covered with slag and acicular SFCA with fine pores, denoted by ‘Columnar SFCA’ and ‘Acicular SFCA’, respectively. These samples were synthesized using chemical reagents and iron ore powders. XRD analysis was applied to the samples heated in a condition simulating a blast furnace. Oxygen partial pressure was controlled by gas mixtures of CO–CO2–He, and there were some cases where 3.9 vol% of hydrogen gas was added to the mixture. The microstructures of the samples before and after heating were observed by electron probe microanalysis (EPMA). XRD profiles indicated: (i) both SFCA samples were reduced to Fe via calcio-wüstite (CW), (ii) the reduction from ‘Acicular SFCA’ to CW took place at lower temperatures than that of ‘Columnar SFCA’ during the heating cycle up to 1000°C, and (iii) CW produced from ‘Acicular SFCA’ was reduced to Fe earlier than CW from ‘Columnar SFCA’ at 1000°C. These results suggest that SFCA and CW phases in ‘Acicular SFCA’ have higher reducibility than those in ‘Columnar SFCA’. This would be because ‘Acicular SFCA’ consists of smaller SFCA particles with fine pores. BSE images have revealed that such microstructures still remained even after the reduction to CW. Additions of hydrogen promoted reduction of ‘Columnar SFCA’ more effectively, and this effect was observed more remarkably in the reduction from CW to Fe than from SFCA to CW.