A partial molar volume for La2O3 in silicate melts

The densities of several La-bearing silicate melts distributed along binary joins have been measured using the double-bob Archimedean method. The results show that the addition of La2O3 leads to an increase in the melt density. From these density data, the partial molar volume of La2O3 in silicate melts has been determined. Distinct values for partial molar volume of La2O3 have been obtained (i.e., 44.01 and 37.04 cm3/mol at 1273 K for the La2O3–Na2O–SiO2 and La2O3–CaO–MgO–Al2O3–SiO2 systems, respectively) indicating a compositional dependence of the partial molar volume of La2O3. Nevertheless, a single value for the partial molar volume of La2O3 (i.e., 43.47 cm3/mol at 1273 K) suffices to describe the molar volume of melts within errors in the entire multi-component system La2O3–Na2O–CaO–MgO–Al2O3–SiO2 and for La2O3 concentrations not greater than 7 mol%. In addition, this work points out that the molar volumes behave ideally within the composition range investigated (i.e., linear variation of the molar volume along the binary joins). Distinct values for the partial molar volume of La2O3 obtained in this study and their differences with the molar volumes of molten La2O3 given in the literature raise the possibility however that this ideality is not maintained within the entire system.