Crystallization of FeSiO3 in iron-containing sodium borosilicate glass

Abstract

FeSiO3 is a pyroxene mineral – ferrosilite. It remains unclear whether FeSiO3 can be synthesized at atmospheric pressure, as most mineral-focused research leans toward the improbability of such a phenomenon. However, in our previous studies of synthetic glasses melted under atmospheric pressure, the FeSiO3 phase was observed. In this work, FeSiO3 crystallization was studied in more detail in the low-alkali synthetic glass of the Na2O-B2O3-SiO2-Fe2O3-FeO system by XRD, DTA, SEM and Mössbauer spectroscopy depending on the duration of heat treatment (700 °C, 2–130 h). The glass was synthesized using conventional melting at atmospheric pressure at 1500 °C in air. Additional heat treatment caused the formation of magnetite (79–0416), iron metasilicate (FeSiO3, 76–1638), and cristobalite. Increasing the duration of heat treatment led to the growth of FeSiO3 spherical inclusions to more than 2000 nm, and the oxidation of magnetite to hematite. The crystallization of iron metasilicate with an anorthite (triclinic) structural type at atmospheric pressure in synthetic borosilicate glass during thermal treatment at 700 °C was established. The possible reasons for the formation of the FeSiO3 phase are discussed.