CRYSTAL NUCLEATION KINETICS IN A 40CAO-40P2O5-20B2O3 GLASS - A STUDY OF HETEROGENEOUSLY CATALYZED CRYSTALLIZATION

The crystallization mechanism and nucleation kinetics in a 40CaO-40P2O5-20B2O3 glass were studied using differential thermal analysis, X-ray diffraction, optical microscopy and scanning electron microscopy/energy dispersive analysis of X-rays. After heat treatments at temperatures around the glass transformation temperature, T(g), the first phase to precipitate was BPO4 and subsequently the phase 4CaO . P2O5 appeared by heterogeneous nucleation on the BPO4. The kinetics of nucleation were studied as a function of temperature. The maximum nucleation rate occurred at 620-degrees-C, which is close to T(g). The crystallization peak height from differential thermal analysis was also used to determine the temperature of the maximum nucleation rate.