SOLUBILITY AND THERMODYNAMIC PROPERTIES OF Y(2)O(3) IN LIF-YF(3) MELTS

A systematic investigation was undertaken to measure the solubility of Y2O3 in several LiF-YF3 melts, with the YF3 composition ranging from 20 to 50 mole pct, in the temperature range of 998 to 1273 K. Experimental results showed that the solubility of Y2O3 in the melts increased with increase in temperature and also with increased YF3 content. The activity of Y2O3 was calculated using the free energy of fusion of Y2O3, DELTAG(m,Y2O3)-degrees. The DELTAG(m,Y2O3)-degrees was deduced from the values of enthalpy, heat of fusion, and melting point of Y2O3. From the known values of activity, the activity coefficients of Y2O3 as a function of temperature and melt composition were calculated. Considering the ionic nature of the melt, activity coefficients were also calculated using Temkin's ideal mixing and electrically equivalent fraction methods. The thermodynamic data, such as integral molar enthalpy, entropy, and free energy of formation, were calculated as a function of composition and temperature. The calculated thermodynamic data showed that the melt exhibited a negative deviation from ideal conditions.