Melt Crystallization of Zinc Alkali Phosphate Glasses

C. E. Crowder, J. U. Otaigbe, M. A. Barger, R. L. Sammler, B. C. Monahan, and C. J. Quinn

The Dow Chemical Company

Midland, MI, USA

Abstract

Melt crystn. of two zinc alkali phosphate glasses was studied with X-ray diffraction (XRD) expts. to accelerate efforts to melt process these glasses with org. polymers. The inorg. glasses differed markedly in chem. durability (water sensitivity) and crystn. rates. They were studied at room temp. prior to and after melt processing with XRD expts. and in situ at melt temps. without flow in a novel differential scanning calorimeter/XRD app. The glasses were found to be amorphous at room temp. and semi-cryst. above their glass-transition temps. Higher temps. and shear (mixing) rates increased the crystn. rate of the glasses. The non-durable (water-sensitive) glass was obsd. to contain significant levels of cryst. matter after melt processing at 400 ° C. This process-induced crystn. of the glasses must be controlled, possibly during processing and/or glass formulation, otherwise it may lead to formation of unwanted phase-sepd. defects in the glass. If high levels of the cryst. matter are present during melt processing, they may lead to irreversible plugging of the processing equipment.