Crystallization Of Zblan Glass

The glass transition, onset crystallization, solidus, and liquidus temperatures of a ZBLAN glass have been measured by differential thermal analysis in a sealed Pt ampoule. The onset crystallization was observed at 335 deg C. for apowdered glass, while for a monolithic glass, prepared in situ quenching in the Pt capsule, the onset crystallization was observed at 395 deg C, 135 deg C higher than Tg. Surface induced heterogeneous nucleation is therefore proposed to be important for the crystallization of ZBLAN glasses.