Effect of the CaO/SiO2 ratio on the controlled solidification of ‘Fe2O3’-CaO-SiO2 melts in air

Abstract

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.