| Powdered samples of glasses in the system Na20-Be0-Si02, which were homogeneous
and clear under optical microscope, exhibited phase separation when heated at or above liquidus
for short durations (l-2 hrs) and quenched in mercury ; some glasses in the system Na20-Si02
a/so showed similar phenomena. The same glasses, when heated for longer durations (50-75 hrs),
no longer retained the droplets of a second glass, though some high-silica compositions did stand
this test of time. Possible origin of this phenomenon is discussed. |
