Crystallization of sol-gel-derived lithium aluminosilicate (LAS) glass ceramic powders

The gel to glass ceramic conversion of a sol-gel-derived LAS powder was characterized by its gel to glass conversion, nucleation, crystallization and microstructural development. At T_g the gel converts to a glass with a dense skeletal structure and at ∼ 800°C to fully dense, amorphous particles. Crystallization at 860°C to a ß-quartz solid solution is independent of nucleating agents, gel powder particle size and heat treatment. In contrast, crystallization of a melt glass derived from the gel was dependent on nucleation heat treatment, reaching a minimum crystallization temperature of 860°C. As the glass transition temperature and glass structure before crystallization are approximately the same for the gel and melt-derived powders, the lower crystallization temperature of the gel is attributed solely to its surface excess free energy and its effect on nucleation.