Effect of the CaO/SiO 2 ratio on the controlled solidification of ‘Fe 2 O 3 ’-CaO-SiO 2 melts in air

Abstract

The solidification of liquids having bulk compositions in the high iron region of the ‘Fe₂O₃’-CaO-SiO₂ system having selected CaO/SiO₂ ratios has been investigated. The compositions investigated were selected such that the bulk compositions were within the hematite primary phase field, fully liquid at temperature (1350°C) and pass through the SFC primary phase field on cooling. Specifically, three CaO/SiO₂ ratios (wt/wt) were investigated, 2.78, 3.46 (Nicol S, Jak E, Hayes P. 2019b. Microstructure evolution during controlled solidification of “Fe₂O₃”-CaO-SiO₂ liquids in air. Met. Trans. B. 50:2706–2722) and 4.75 with bulk compositions comprising 69.23, 72.74 and 74.94 wt% Fe₂O₃ respectively. The phases present and their composition was determined with electron probe microanalysis (EPMA) and X-ray diffraction (XRD). During cooling, four stages of solidification were observed at all three CaO/SiO₂ ratios, and an additional two stages at the highest CaO/SiO₂ ratio. Non-equilibrium phase and liquidus compositions were observed. Significantly, the silico ferrite of calcium phase (SFC) was not observed in any of the samples, although the formation of this phase was anticipated from phase equilibrium considerations.