The effect of production regime and crucible materials on the thermal properties of sodium phosphate glasses produced from salts

Abstract Changes in the thermal properties of sodium phosphate glasses during melt production have been investigated using Pt/Au and fused alumina crucibles. Glasses were produced from NaH₂PO₄ as a starting material, providing an intrinsic Na₂O:P₂O₅ ratio of 1:1 and giving an O/P = 3, that is, a metaphosphate. In Pt/Au crucibles, glass transition temperatures rose to a plateau value of 295°C at a rate determined by melt temperature. No contamination of the glass by platinum or gold was detected or indicated in the results. E_a for the reaction was found to be 66.4 kJ mol⁻¹. In fused alumina crucibles, glass transition temperatures rose to over 450°C, with these values showing some convergence at higher furnace temperatures. Extensive erosion of the alumina crucibles was observed. The amount of alumina incorporation within the glasses correlated well with the rise in glass transition temperature up to a maximum of 15.5 mol % Al₂O₃ content. Al₂O₃ incorporation above this value caused a reduction in the value of the T_g. © 2004 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 71B: 22–29, 2004