Multicomponent phosphate invert glasses with improved processing

Owing to their structure of small phosphate units, phosphate invert glasses have high crystallisation tendencies, which make processing of the melt challenging. The aim was to improve their processing by (1) increasing the number of glass components and (2) incorporating intermediate oxides (TiO2, MgO and ZnO). Glasses (P2O5–CaO–MgO–Na2O) were produced by a melt-quench route. In series 1, TiO2 was partially substituted for Na2O, and the number of components was increased by partially substituting strontium for calcium, zinc for magnesium and potassium for sodium on a molar base. In series 2, the MgO + ZnO content in the multicomponent glass was varied between 0 and 20 mol% in exchange for CaO + SrO. Differential scanning calorimetry showed a significant increase of the processing window in the multicomponent glasses, explained by an increased energy barrier for crystallisation owing to increased entropy of mixing. The MgO + ZnO content also significantly improved the processing window from 117 K (0 mol% MgO + ZnO) to 185 K (20 mol%), owing to their large field strength. These results show that the processing of phosphate invert glasses for biomedical applications can be improved significantly by incorporating ions such as strontium or zinc which are also known to have therapeutic effects.

► Increasing the number of components improves processing of phosphate invert glasses.
► Substituting larger for smaller cations (e.g. Sr for Ca) generally reduces processing.
► When increasing the number of components, even larger cations improve processing.
► Intermediate oxides (MgO, ZnO) also improve processing of phosphate invert glasses.
► New phosphate invert glasses with processing window suitable for sintering and fibre drawing.