Determination of thermodynamic properties of (Fe,Mg)-pyroxenes at 1000 K by the emf method

Sublattice solid solution model and its application to orthopyroxene (Mg, Fe)2Si2O6

“…Thus, the macroscopic activities on two-unit base can be calculated as and open circles with bars are experimental results of the EMF measurements at temperature of 727 ~ C from Sharma et al (1987). Solid squares with bars are those of the activity measurements at temperature of of 1204 ~ C from Kitayama and Katsura (1968).…”

“…In order to compare the solid solution properties as calculated from the sublattice model with the properties determined by calorimetry and other techniques, it is necessary to calculate the excess functions for the molecular components, as for example, the heats of mixing for the FeSiO3-MgSiO3 binary or for the activity of (1983), the activity-composition measurements of Kitayama and Katsura (1968), EMF measurements of Sharma et al (1987) are compared with the calculated data in the figures. Figure 7 a shows a plot of the excess free energy of mixing at various temperatures against mole fraction.…”

“…We chose a three-order polynomial form (n= 3) in this study, and the temperature-dependent parameters Ai(i = 0, 1, 2, 3) as Sharma et al (1987) By letting X 1 =Xve, Xz=XMg, and optimizing these 20 (4 x 5) parameters based on Ge~c values calculated from the sublattice model at various temperatures and total compositions, we arrived at the results shown in Table 5.…”

“…Figure 7 a shows a plot of the excess free energy of mixing at various temperatures against mole fraction. The experimental EMF data at 1000 K from Sharma et al (1987) are also plotted for comparison. The fit is poor in the middle composition range.…”

“…Low-temperature data 500 ~ C and 600 ~ C are also plotted for comparison. See discussion in the text enthalpy of solution (Chatillon-Colinet et al 1983) and activitycomposition relations (Kitayama and Katsura 1968;Sharma et al 1987) were not included in the optimization, but used for comparison and reproducing the macroscopic thermodynamic properties. Tables 1, 2 and Fig.…”