Phase Equilibria in Ferrous Calcium Silicate Slags: Part I. Intermediate Oxygen Partial Pressures in the Temperature Range 1200 °C to 1350 °C

Ferrous calcium silicate slags are used in primary and secondary metallurgical processes (described by the FeO-Fe₂O₃-CaO-SiO₂ system). Despite the industrial and scientific importance of this system, the phase equilibria have not been fully investigated. Characterization of this slag system is necessary to improve the design and optimization of new and existing metallurgical processes, particularly in relation to fluxing practice and operating temperatures. Experimental methods have been developed to investigate the phase equilibria of these slags involving the equilibration of samples at fixed oxygen partial pressures, rapid quenching, and the analysis of the compositions of solid and liquid phases using electron probe X-ray microanalysis (EPMA) with wavelength dispersive detectors. Liquidus and solidus data are reported for the primary phase fields of spinel, pseudo-wollastonite, and tridymite in the temperature range of 1200 °C to 1350 °C at an oxygen partial pressure of 10⁻⁶ atm, and at 1250 °C at an oxygen partial pressure of 10⁻⁵ atm. The resulting data have been used to construct liquidus and solidus isotherms in the “FeO”-CaO-SiO₂ system directly relevant to industrial processes.