Importance of Crystallization Hierarchies in Microstructural Evolution of Silicate Glass–Ceramics

Quench studies of in-house melted glasses were used to study the microstructural evolution in Macor-type and Corning Code 9606-type glass–ceramics to elucidate the microstructures of the commercial products. They reveal that phase separation initiates crystallization in both systems which then proceeds via formation of several phases at different scales of size, the first phases to form being those containing the most rapidly diffusing species. This study highlights the concept of crystallization hierarchies whereby crystals form, sometimes simultaneously, sometimes sequentially, on heating glasses, but at different length scales . This is illustrated by the simultaneous nucleation of μ-cordierite nanocrystals and ∼0.2 μm MgAl₂Ti₃O₁₀ rosettes in Corning 9606-type compositions and of ∼0.3 μm chondrodite and 3–4 μm fluorophlogopite laths in Macor-type compositions.