THERMODYNAMIC STUDY OF THE SOLID-LIQUID EQUILIBRIA IN THE SYSTEMS (MPO3)-P-I-PR(PO3)(3) (M-I = NA, RB, CS OR AG)

A previously established equation of a stoichiometric phase liquidus c urve was applied to determination of the phase diagrams of the systems (MPO3)-P-I-Pr(PO3)(3) (with M-I=Na, Rb, Cs or Ag). The temperature, e nthalpy and entropy of fusion were calculated for each solid phase wit h the exception of silver polyphosphate, the crystallization field of which was very limited. The enthalpy of fusion of the polyphosphate Pr (PO3)(3) was determined from the DTA curve. The melting enthalpy of Pr (PO3)(3) calculated from the different binary systems was approximatel y equal to the measured value. The calculated temperatures and composi tions were in good agreement with those determined experimentally.