Crystallization,microstructure and expansivity of spodumene-nepheline glasses

摘要

The crystallization of some glasses within the binary spodumene(LiAlSi_2O_6)-nepheline(NaAlSiO_4)system with and without TiO_2 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_2Al_2Si_2O_8),nepheline,carnegieite,quartz and cristobalite.Crystallization of TiO_2-free glasses was relatively dependent on the nominal ratio and the heat treatments as well,however,the lithium aluminosilicate phases were usually dominant.TiO_2 catalyzed the aluminosilicate phases and precluded the crystallization of silica phases.Inversion of nepheline into carnegieite took place at higher temperatures in TiO_2-free samples,however,carnegieite was also developed in small amounts in TiO_2 containing samples.On the other hand,the beta-eucryptite resisted the entire inversion into beta-spodumene even at higher temperatures(up to 1100 deg C).Glass-ceramics of heterogeneous microstructures were obtained.The CTE values of the glasses investigated decrease from 101 to 86 centre dot 10~(-7)K~(-1)(20 to 500 deg C)with increase in the Li_2O/Na_2O ratio,and those of the corresponding glass-ceramics decrease from 96 to-24 centre dot 10~(-7)K~(-1)(20 to 500 deg C)with increase in the crystallization of beta-eucryptite and/or beta-spodumene.