Phase Equilibria in the Fe_2O_3-P_2O_5 System

摘要

Four ferric phosphate compounds were identified in the Fe_2O_3-P_2O_5 system and the liquidus surfaces in the subsystems Fe_3PO_7-FePO_4, FePO_4-Fe_4(P_2O_7)_3 and Fe_4(P_2O_7)_3-Fe(PO_3)_3 were determined. The results are significantly different from those presented by Wentrup in 1935. Fe_3PO_7 is the stable ferric oxo-phosphate compound, not Fe_4P_2O_(11), and Fe_3PO_7 decomposes in air at 1090°C. The congruent melting point of FePO_4 (1208°C) is similar to what was reported, but Fe_4(P_2O_7)_3 melts congruently at 945℃, about 300°C lower than claimed by Wentrup. Fe(PO_2)_3, for which the melting temperature has not been previously reported, melts congruently at 1205 C. Eutectic points exist at 58.0 mol% Fe_2O_3 (1070°C), 42.7% Fe_2O_3 (925°C), and 37.0% Fe_2O_3 (907°C). The latter two eutectic points bracket the conventional glass-forming range for iron phosphate melts under consideration as alternative hosts for nuclear wastes.