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