Solubility and thermodynamic properties of Y2O3 in LiF-YF3 melts

A systematic investigation was undertaken to measure the solubility of Y₂O₃ in several LiF-YF₂ 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 Y₂O₄ 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, . The 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.