Stability of SFC (silico-ferrite of calcium): solid solution limits, thermal stability and selected phase relationships within the Fe2O3-CaO-SiO2 (FCS) system

Quenching experiments have been performed to investigate the thermal stabil ity, solid solution limits, and selected phase relationships of SFC (silico -ferrite of calcium) within the Fe2O3-CaO-SiO2 (FCS) system. Experiments we re performed in air over the temperature interval 1050-1260 degrees C using a combination of synthetic oxide mixtures and SFC compositions which had b een pre-synthesized at 1200 degrees C. SFC forms a solid solution along a trend line between the theoretical end-m embers CF3 and C4S3 The maximum solid solution range occurs between composi tions containing approximately 7.0 through to 11.7 wt% C4S3 component. The solution range is valid between 1060 degrees C and 1240 degrees C. Above 12 40 degrees C the compositional range narrows until the liquidus is reached. The maximum liquidus temperature for SFC is composition dependent with the highest melting point (T = 1252 degrees C) recorded from a sample containi ng 9.0 wt% C4S3. Determination of ferrous iron content in SFC shows a range between 0.24 -0. 37 wt% at 1200 degrees C compared to 0.40-0.64 wt% at 1250 degrees C. The a bsolute Fe2+ content is both temperature and composition dependent, with hi gher ferrous iron values measured at high temperature and high CIS; content s. EPMA data, combined with the ferrous iron measurements, indicate a coupl ed substitution mechanism in SFC represented by the reaction 2(Fe3+) = (Ca2 +, Fe2+) + Si4+. Data obtained in the present investigation combined with those available in the literature enable the construction of a series of isothermal sections showing phase relationships within the broader FCS system. These diagrams m ay be used as a guide to improving the understanding of fundamental sinteri ng phase relations in the high iron corner of the FCS ternary system, as we ll as providing some insight into the compositional and thermal conditions required to maximize the stability of SFC phase in iron ore sinter.