Inversion Temperatures of Fe-leucite Crystals Formed in SiO₂-Fe₂O₃-K₂O Glasses

Abstract

The glasses of SiO₂-Fe₂O₃-K₂O system were heat-treated at 800°C-1100°C, and the inversion temperature and the lattice constants of Fe-leucite crystals precipitated in the glass were measured by using DTA apparatus and X-ray diffractometer.
It was found that the change of inversion temperature was closely related with the atomic ratio δ=Si/(Si+Fe+K) of the mother glass composition. Each Fe-leucite crystal precipitated in the glasses with δ<0.5 showed a constant inversion temperature 552±8°C corresponding to the inversion temperature of the Fe-leucite with the ideal composition. Inversion temperature of Fe-leucite crystal precipitated in the glass with δ>0.5 lowered with the increase of δ. The lower crystallization temperature was, the more steep the degree of lowering was. It was also observed that there is a linear relationship between the inversion temperature and the lattice parameter c/a, when δ>0.5.
It was considered that in the case of δ>0.5, Fe-leucite crystal having the composition of (KFe)_1-xSi_2+xO₆(x>0) had a higher symmetrical lattice than the ideal one and the lattice defects which might be caused by the defficiencies of K⁺ increasing with δ.
The influence of other phases such as residual glass, hexagonal KFeSiO₄ crystals and hematite crystals on the inversion temperature was not observed.