Epitaxial Crystallization of Seeded Albite Glass

Glasses that are extremely difficult to crystallize are generally avoided in making glass-ceramics. It is now possible to crystallize such glasses epitaxially using isostructural seeds. The role of solid-state epitaxy in the crystallization of such albite (NaAlSi₃O₈) glass to glass-ceramic was investigated. The glass was seeded with extremely fine ZrO₂ (nonisostructural) and albite (isostructural) seed crystals. X-ray diffraction results indicated that the albite-seeded glass, heat-treated at 1000°C for 100 h, epitaxially crystallized to albite, while the ZrO₂ and unseeded glasses did not crystallize in identical heat-treatment conditions. In addition, the albite-seeded glass, heat-treated at 905°C for 10 d, crystallized mostly to albite, whereas the ZrO₂ and unseeded glasses at the same conditions contained only a small amount (<5 wt%) of nepheline (NaAlSiO₄). The microstructure of the epitaxially grown glass-ceramics showed that extremely fine crystals (∼0.2 μm thickness) were formed around the seed.