Doping of iron phosphate glasses with Al2O3, SiO2 or B2O3 for improved thermal stability

The effects of doping 60 P2O5–40 Fe2O3 (mol%) glasses with 5–10 mol% SiO2, Al2O3 or B2O3 on their thermal stability, iron environments and redox were investigated. Thermal stability improved markedly with 5% dopant addition in the order Al2O3 > SiO2 > B2O3 ≫ base glass. Solubility of pro rata additions when melted at 1150 °C was 5–10% SiO2, <5% Al2O3, and >10% B2O3. It was possible to dissolve 5% Al2O3 by replacing Fe2O3. These additions generally had little effect on dilatometric measurements and iron environments, however the Fe2+/ΣFe redox ratio increased in the order base glass < Al2O3 < SiO2 < B2O3. This behaviour was broadly consistent with the effects of glass basicity. The increased thermal stability of these glasses may improve their suitability for applications such as waste immobilisation or sealing.