MELT CRYSTALLIZATION OF ZINC ALKALI PHOSPHATE-GLASSES

Melt crystallization of two zinc alkali phosphate glasses was studied with X-ray diffraction (XRD) experiments to accelerate efforts to melt process these glasses with organic polymers. The inorganic glasses di ffered markedly in chemical durability (water sensitivity) and crystal lization rates. They were studied at room temperature prior to and aft er melt processing with XRD experiments and in situ at melt temperatur es without flow in a novel differential scanning calorimeter/XRD appar atus. The glasses were found to be amorphous at room temperature and s emi-crystalline above their glass-transition temperatures. Higher temp eratures and shear (mixing) rates increased the crystallization rate o f the glasses. The non-durable (water-sensitive) glass was observed to contain significant levels of crystalline matter after melt processin g at 400 degrees C. This process-induced crystallization of the glasse s must be controlled, possibly during processing and/or glass formulat ion, otherwise it may lead to formation of unwanted phase-separated de fects in the glass. If high levels of the crystalline matter are prese nt during melt processing, they may lead to irreversible plugging of t he processing equipment.