CRYSTALLIZATION MECHANISMS IN GLASS-CERAMICS

Transmission electron microscopy, electron diffraction, and microprobe X‐ray analysis were used to study crystallization of glasses in the systems Li2O‐SiO2, BaO‐SiO2, and Li2O‐A12O3‐SO2. The ternary system, with 4 mol% TiO2 added to an Li2O‐Al2O3‐4SiO2 composition, crystallizes with a simple morphology of equiaxed grains of the β‐quartz metastable phase which transforms at higher temperatures to the stable β‐spodumene structure. The binary systems exhibit a more complex crystallization morphology dictated by crystal anisotropy, temperature, impurity content, and susceptibility either to intermediate‐phase formation (BaO‐SiO2) or to liquid immiscibility (Li2O‐SiO2). The initial crystal growth units formed in these systems are frequently two‐phase branched morphologies many micrometers in diameter. They may be recrystallized to form polycrystalline glass‐ceramics with submicrometer grain sizes. Copyright © 1979, Wiley Blackwell. All rights reserved