PRACTICAL LIMITS ON UP-GRADIENT CRYSTALLIZATION

The kinetic processes relevant to up-gradient crystallization are anal yzed in detail. Crystallization occurs upon moving an amorphous sample up through a temperature gradient which is the reverse of traditional crystallization from the melt. Both nucleation and growth processes a re important to the present technique. To obtain a highly oriented mic rostructure, bulk nucleation must be prevented. Generally, a liquid wi th small nucleation rate and large crystal growth rate is favorable fo r the present route. The model was tested for the lithium diborate gla ss system, which yielded a highly oriented microstructure with only is olated additional nucleation events.