Liquidus of SiO2 in the Li2O-SiO2, Na2O-SiO2, and K2O-SiO2 systems

The phase equilibria in the SiO2-rich region of the Li2O-, Na2O-, and K2O-SiO2 systems at 1550 degrees C to 1650 degrees C were experimentally studied to determine accurate liquidus of SiO2 in the systems. A classical equilibration/quenching method was used, and the equilibrated samples were analyzed by X-ray diffraction (XRD) and electron probe microanalysis (EPMA). Samples were contained in sealed Pt crucibles and held at the target temperatures for 7-21 days to reach equilibrium condition. Sealed Pt crucibles were employed to avoid the volatile loss of alkali oxides during high temperature phase equilibration and hydration upon quenching. Accurate liquidus of SiO2 in alkali-silicate systems was determined for the first time, and the results were analyzed using the limiting slope rule in order to understand the dissolution behavior of alkali oxides in SiO2 melt. It was confirmed that alkali oxide dissolves in SiO2 melt by producing Li+, Na+, and K+ cationic species rather than Li-2(2+), Na-2(2+) and K-2(2+) species.