Thermal stability of a low Tg phosphate glass investigated by DSC, XRD and solid state NMR

The thermal stability of a low Tg phosphate glass (Tg = 339 °C), formulated in the ZnO–Na2O–P2O5 system, is investigated in this contribution by Differential Scanning Calorimetry (DSC), X-Ray diffraction (XRD) and solid state Nuclear Magnetic Resonance (NMR). DSC measurement indicates a very important Tx − Tg value (197 °C) for the investigated composition compared to other low Tg phosphate glasses found in literature. XRD and 1D 31P solid state NMR were used to monitor the isothermal crystallization process occurring at 60 °C above Tg (400 °C). The mixture of phases formed after crystallization cannot be identified by XRD but 2D MAS-NMR experiment provides valuable information about the composition and the structure of the unknown sample.

Research Highlights
► The glass exhibits a very large Tx-Tg compared to other phosphate glasses.
► 2D 31P NMR reveals a complex mixture of crystalline compounds.
► Strong correlations exists between T and the crystallization kinetics.