Inversion Temperature of Leucite Formed in SiO₂-Al₂O₃-K₂O Noncrystalline Materials

Abstract

The noncrystalline materials of the system SiO₂-Al₂O₃-K₂O were heat-treated at 1200°C-1600°C, and the inversion temperature of tetragonal→←cubic phases, the lattice constants and the amount of leucite crystals precipitated in the noncrystalline materials were measured by using DTA apparatus and X-ray diffractometer.
It was found that the inversion temperature varied in the wide rage of 404°C to 628°C with the atomic ratio δ=Si/Si+Al+K of the noncrystalline material and the crystallization temperature. Each leucite precipitated in the noncrystalline materials with δ<0.5 showed a constant inversion temperature 621±7°C corresponding to that of the leucite with stoichiometric composition. Inversion temperature of leucite precipitated in the noncrystalline materials with δ>0.5 lowered with the increase of δ and with the decrease of crystallization temperature and the lattice parameter c/a tend to decrease with inversion temperature.
It was concluded that in the case of δ>0.5, the leucite crystals having the composition of (KAl)_1-xSi_2+xO₆ (x>0) had a higher symmetrical lattice than the stoichiometric one and the lattice defects which might be caused by the defficiencies of potassium ions increasing with δ.
The shift of AlK_α peak of the leucite crystals prepared was also measured by the X-ray fluorecence spectrometer. The results indicated that the aluminum ions in the leucite crystals were in fourfold coordination.