Influence of SiO2 and Al2O3 on the activity coefficients of alkalis in melts: An experimental study

Abstract

The simultaneous saturation of silicate melts with variable Al2O3 and SiO2 contents in sodium, potassium, and rubidium was investigated at a total pressure of 1 atm and temperatures of 1300–1470°C using the crucible supported loop technique. It was shown that an increase in both SiO2 and Al2O3 contents in the melt results in a significant decrease in the activity coefficients of the alkalis, and the effect of Al2O3 is especially pronounced in silicic compositions. The extrapolation of the experimental data allowed us to estimate the influence of SiO2 and Al2O3 contents in the melt on the behavior of Li and Cs. Using a numerical experiment, it was shown how the inert and perfectly mobile behavior of alkalis in magmatic processes can be discriminated. A methodic investigation was performed on the loss of Na, K, and Rb from silicic glasses during microprobe analysis depending on beam diameter.