A method for controlling alkali-metal oxide activities in one-atmosphere experiments and its application to measuring the relative activity coefficients of NaO0.5 in silicate melts

Abstract

The activity of alkali metal oxides can be controlled in one-atmosphere wire-loop experiments at high temperature by suspending a crucible containing alkali silicate melt beneath the samples. The method has been applied to measuring the activity coefficient of NaO0.5 in a series of CMAS-NaO0.5 melts relative to that in the anorthite-diopside eutectic composition at 1400 °C, using a reservoir of NaO0.5-SiO2 melt. The results show that this relative activity coefficient decreases strongly with SiO 2, increases with CaO and MgO, but is insensitive to AlO0.5. This latter behavior is inconsistent with " quasi-crystalline" models of melt thermodynamics that hypothesize Na-Al species. Show more