Residual glass and crystalline phases in a barium disilicate glass–ceramic

• The crystalline and amorphous phases in a barium disilicate glass were characterized and quantified by XRD and TEM.
• The BS2-10 sample was constituted by two main crystalline phases, which consists of 2 polymorphic forms: h-BS2 and l-BS2.
• The orthorhombic BS2 phase (l-BS2) was predominant at 1100 °C.
• The complete polymorphic transformation from h-BS2 to l-BS2 was achieved at 1100 °C.
• Nevertheless, our XRD and TEM results demonstrated that BS2-11 contains a minor amount of residual glass.

Investigations about the presence of residual glass are scarce, despite its fundamental role in the crystallization kinetics and luminescent properties of barium disilicate glass–ceramics (BaO·2SiO2–BS2) with a quasi-stoichiometric composition. Non-isothermal (DTA/DSC) experiments have demonstrated that BS2 presents a polymorphic transformation, where the h-BS2 (monoclinic structure) phase is completely transformed in l-BS2 (orthorhombic structure) at temperatures higher than 1020 °C (10 °C/min). In this study, BS2 monolithic samples were heat-treated at 1000 °C (BS2-10) and 1100 °C (BS2-11) in a DSC furnace at a heating rate of 10 °C/min. In addition, the crystalline and amorphous phases were characterized and quantified by Transmission Electron Microscopy (TEM) and X-ray Diffraction (XRD) experiments, respectively. Although the complete polymorphic transformation from h-BS2 to l-BS2 was achieved at 1100 °C, our results demonstrated that BS2-11 contains a minor, albeit not negligible, amount of residual glass.