Crystallization, microstructure and expansivity of spodumenenepheline glasses

The crystallization of some glasses within the binary spodumene(LiAlSi2O6)-nepheline(NaAlSiO4) system with and without TiO2 has been investigated using X-ray diffraction analysis, scanning electron microscopy and coefficient of thermal expansion (CTE) measurements. The crystalline phases developed were beta-spodumene, beta-eucryptite, LAS(Li(2)Al(2)Si(2)Og), nepheline, carnegieite, quartz and cristobalite. Crystallization of TiO2-free glasses was relatively dependent on the nominal ratio and the heat treatments as well, however, the lithium aluminosilicate phases were usually dominant. TiO2 catalyzed the aluminosilicate phases and precluded the crystallization of silica phases. Inversion of nepheline into carnegieite took place at higher temperatures in TiO2-free samples, however, carnegieite was also developed in small amounts in TiO2 containing samples. On the other hand, the beta-eucryptite resisted the entire inversion into beta-spodumene even at higher temperatures (up to 1100 degreesC). Glass-ceramics of heterogeneous microstructures were obtained. The CTE values of the glasses investigated decrease from 101 to 86 (.) 10(-7) K-1 (20 to 500 degreesC) with increase in the Li2O/Na2O ratio, and those of the corresponding glass-ceramics decrease from 96 to -24 (.) 10-7 K-1 (20 to 500 degreesC) with increase in the crystallization of beta-eucryptite and/or beta-spodumene.