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.