Comparison of the effects of titania and tantalum oxide nucleating agents on the crystallization of Li2O sm-bullet Al2O3 sm-bullet 6SiO2 glasses

This paper reports the crystallization mechanism in Li2O-Al2O3-SiO2 (1:1:6) glasses investigated with TiO2 or Ta2O5 as nucleation agents, by differential thermal analysis, x-ray diffractometry, and transmission electron microscopy. Phase separation occurred prior to crystallization in all of the glasses studied. Both TiO2 and Ta2O5 additives promoted nucleation and crystal growth in the bulk glasses by causing the precipitation of crystalline precursor phases dispersed within phase-separated glass, which acted as heterogeneous nucleation sites for β-quarts (ss) (solid solution) formation. Upon reheating glasses with Ta2O5 s the nucleating agent, phase separation occurred, followed by LiTa3O8 and Ta2O5 nucleation and limited growth as the first-formed crystalline phases, and then crystallization of β-quartz structured solid solution, which nucleated and grew from the LiTa3O8/Ta2O5 crystallites