A partial molar volume for La2O3 in silicate melts

Abstract 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 La 2 O 3 leads to an increase in the melt density. From these density data, the partial molar volume of La 2 O 3 in silicate melts has been determined. Distinct values for partial molar volume of La 2 O 3 have been obtained (i.e., 44.01 and 37.04 cm 3 /mol at 1273 K for the La 2 O 3 –Na 2 O–SiO 2 and La 2 O 3 –CaO–MgO–Al 2 O 3 –SiO 2 systems, respectively) indicating a compositional dependence of the partial molar volume of La 2 O 3 . Nevertheless, a single value for the partial molar volume of La 2 O 3 (i.e., 43.47 cm 3 /mol at 1273 K) suffices to describe the molar volume of melts within errors in the entire multi-component system La 2 O 3 –Na 2 O–CaO–MgO–Al 2 O 3 –SiO 2 and for La 2 O 3 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 La 2 O 3 obtained in this study and their differences with the molar volumes of molten La 2 O 3 given in the literature raise the possibility however that this ideality is not maintained within the entire system.