Nucleation and early stage crystallization of fluorapatite in apatite-mullite glass-ceramics

The crystallization morphology and activation energy of fluorapatite formation in apatite-mullite glass-ceramics has been examined. A systematic change in the amount of network modifier in the base glass has demonstrated that increasing levels of network modifier cause a corresponding increase in activation energy for fluorapatite crystallization and a decrease in fluorapatite crystal size. Apatite-mullite glass-ceramics are known to phase separate and nucleate prior to crystallization. To separate these effects during activation energy determination, a nucleation hold was used to ensure the activation energy is purely for crystal growth and is not skewed by any phase separation or nucleation occurring. It is postulated that greater amounts of network modifier in the system cause the base glass to phase separate and nucleate to a greater extent during heating thus limiting the crystal growth.