Properties of sodium-based ternary phosphate glasses produced from readily available phosphate salts

Three series of phosphate glasses were produced by melting together sodium phosphate salt (NaH2PO4) and the phosphate salts of either calcium (CaHPO4), magnesium (MgHPO4 · 3H2O) or iron (FePO4 · 2H2O) in a 5% gold/95% platinum crucible at 1200 °C. The glass compositions were confirmed by EDX and XRD analysis. Glass transition temperature (Tg), density and durability in water were determined for all the compositions. Maximum metal oxide contents before devitrification were between 55% and 59% for CaO + Na2O and 59% and 62% for MgO + Na2O. The normalized equivalent for Fe2O3 + Na2O was between 55% and 61%. Density values for the glasses lay between 2.49 and 2.75 g cm−3. Tgs lay between 295 °C and 470 °C. Degradation rates in deionized water at 37 °C lay between 0.03 g cm−2 h−1 for Na phosphate glasses and 9 × 10−6 g cm−2 h−1 for Ca phosphate glasses, 3 × 10−6 g cm−2 h−1 for Mg phosphate glasses and <3 × 10−6 g cm−2 h−1 for Fe phosphate glasses. The effect of metal addition on properties goes as Fe > Mg > Ca for degradation rates and Tg and Fe > Mg ≈ Ca for density. The change in properties with metal addition was seen to be linear for Fe and Ca additions but not with Mg addition. This is in agreement with the anomalous behavior of magnesium phosphate glasses.