Effect of SiO₂, Al₂O₃ Additions on the Reduction and Resultant Expansion of Synthesized Materials in the Vicinity of CaO·2Fe₂O₃ Composition

Abstract

The reduction of CaO·2Fe₂O₃(CF₂) in which SiO₂, Al₂O₃ were added separately or simultaneously and resultant expansion have been studied in CO-N₂ (4 : 6) mixed gas at 550 °C.
The main results obtained are as follows :
1) In melted material of CF₂-SiO₂ (SiO₂ : 0.52.0 wt%) system, the addition of SiO₂ into CF₂ promotes the formation of 2CaO·SiO₂(C₂S), CaO·Fe₂O₃(CF) and Fe₂O₃. SiO₂ is insoluble in CF₂. The formed Fe₂O₃ increases the reduction and resultant expansion.
2) In melted material of CF₂-CaO (1.87 wt%)-SiO₂ (SiO₂ : 0.52.0 wt%) system, the combined addition of SiO₂ and CaO promotes the formation of CF₂, CF and C₂S. SiO₂ is only slightly soluble in CF. Consequently, the formation of C₂S and the disappearance of Fe₂O₃ restrains the reduction and resultant expansion.
3) In melted material of CF₂-CaO (1.87 wt%)-SiO₂ (1.0 wt%)-Al₂O₃ (Al₂O₃ : 0.58.0 wt%) system, the combined addition of SiO₂, CaO and Al₂O₃ promotes the formation of CF₂-α (SiO₂ : 1.51.8 wt%, Al₂O₃ : ≤8.2 wt%) and CF₂-β (SiO₂ : 1.51.8 wt%, Al₂O₃ :>8.2 wt%).
Both CF₂-α and CF₂-β restrain the reduction, and the former promotes the resultant expansion, inversely, the latter restrains it.