PNNL

Abstract

The aims of this work are to establish the onset of phase separation in the SiO2-B2O3-Na2O glass system doped with P2O5 to understand the mechanism by which phase separation occurs, and the effects of P2O5 on the structure and properties of these glasses. X-ray diffraction (XRD) confirmed a solubility limit of between 3.0 and 4.0 mol% P2O5 as the onset of crystallinity with formation of Na3PO4, and Na4P2O7 in the annealed samples and between 4.0 and 5.0 mol% P2O5 for the quenched samples. Differential Thermal Analysis (DTA) and dilatometry showed modest increases in the glass transition temperature, Tg, with P2O5 additions below the onset of crystallisation and a more substantial increase coinciding with the onset of crystallisation between 3.0 and 4.0 mol% P2O5. High-temperature viscosity measurements showed that increasing the P2O5 content led to increases in viscosity, with the highest P2O5 additions displaying non-Newtonian behavior consistent with the presence of crystals in the melt at 950°C. Raman difference spectra showed that the increase in the P2O5 content resulted in characteristic peak intensities at 729 cm-1, 937 cm-1, 1000 cm-1, 1026 cm-1, 1109 cm-1and 1445 cm-1 which were associated with phosphate species.