Note on the Formation of Glass

JSGT 1919 V03 T282-T285 (4 pages)

Although it has been customary for many years to regard glass as a supercooled liquid, the supposition does not appear to yield much helpful suggestion in glass technology, neither does it conform to the dictionary definition of a liquid as being in a state in which its particles are free to travel about. Comparison with a typical supercooled liquid, such as phenol below its melting point, makes the differences obvious: the former is sufficiently solid to have universal application for the manufacture of vessels, while the latter is a mobile fluid and its crystallisation is marked by the sudden disappearance of the mobility. There is no such sudden change in the solidification of glass; the gradual transition from liquid to solid resembles the setting of a jelly. Indeed, the similarity of glass and gels has previously been pointed out. The structure of gels is now beginning to be understood, and similar considerations appear to explain the formation of glass.

S. C. Bradford