GLASS-TRANSITION OF COVALENT GLASSES

The glass transition temperature T//g of various glasses has been studied in light of their bonding structures. An empirical relationship, ln T//g approximately equals 1. 6Z plus 2. 3, where Z expresses the average coordination number is retained for the glasses consisting of covalent molecules held together by van der Waals forces. This relation can be understood with a dimensional argument for molecular segment motions. It is conjectured that atomic clusters of approximately 10 A in size move at T//g with an activation energy of approximately 0. 15 ev per atom.