An intergrown perovskite-wollastonite phase in some ferrous blast-furnace slags

Abstract

During crystallization of silicate liquids, TiO₂ tends to form its own mineral. Ferrous blast-furnace slags generally have perovskite as the titanium-rich phase. However, a rounded and fibrous phase, crystallizing instead of perovskite, has been observed in some slag samples: it has an apparently late position in the order of crystallization. Detailed electron microprobe analysis and X-ray diffraction have indicated that this unusual phase is composed of intergrown perovskite and wollastonite. However, wollastonite should not be an equilibrium phase in these slags. Therefore, a series of simple high-temperature furnace experiments were conducted to examine possible origins of this intergrowth. Solid solution, liquid immiscibility, and eutectic growth have all been discounted as possible explanations of the intergrowth. However, blast-furnace slags are non-equilibrium products, and their residual liquids crystallize independently. This intergrown perovskite—wollastonite phase has been accounted for as a product of fractional crystallization within the system CaO-MgO-Al₂O₃-TiO₂-SiO₂.