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 NaH_2PO_4 as a starting material, providing an intrinsic Na_2O:P_2O_5 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 deg 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 deg 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 percent A1_2O_3 content. A1_2O_3 incorporation above this value caused a reduction in the value of the T_g.
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