Effect of CaO and SiO 2 on swelling and iron whisker formation during reduction of iron oxide compact

The effects of CaO and SiO₂ on swelling and iron whisker growth during iron oxide reduction were investigated. Compacts made up of iron oxide concentrate and SiO₂/CaO sintered for 1 h in air were reduced by CO at 900°C to 80–90%. The reduced compact was broken to be examined for the formation of whisker by SEM. The results showed that the effect of SiO₂ on suppressing swelling is complex, but an increase in %CaO effectively suppressed swelling and long iron whisker growth. The SEM results indicated that the nucleation sites of whisker growth were changed from disperse locations to close clusters with an increase in %SiO₂, while the number of whiskers increased with an increase in %CaO. A conceptual diagram developed in this work presents adequately the effects of SiO₂ and CaO contents on swelling and iron whisker growth.