CALORIMETRIC STUDY OF OLIVINE SOLID-SOLUTIONS IN THE SYSTEM MG2SIO4-FE2SIO4

Solution enthalpies of synthetic olivine solid solutions in the system Mg2SiO4 - Fe2SiO4 have been measured in molten 2 PbO . B2O3 at 979 K. The enthalpy data show that olivine solid solutions have a positive enthalpy of mixing and the deviation from ideality is approximated as symmetric with respect to composition, in contrast to the previous study. Applying the symmetric regular solution model to the present enthalpy data, the interaction parameter of ethalpy (W(H)) is estimated to be 5.3 +/- 1.7 kJ/mol (one cation site basis). Using this W(H) and the published data on excess free energy of mixing, the nonideal parameter of entropy (W(S)) of olivine solid solutions is estimated as 0.6 +/- 1.5 J/mol . K.