Fundamental Conditions for Glass Formation

JSGT 1947 V31 T245-T253

The fundamental condition for glass formation is the existence of strongly bonded large networks or long chains of atoms in the liquid. Such chains or networks will not only prevent or hinder the orientation or arrangement of atoms in the chains or networks themselves but also that of other atoms not in the networks in the liquid near the melting point or liquidus temperature. Thus, a liquid structure will persist even after the liquid has been cooled below the melting point or liquidus temperature and indeed farther down to such temperatures that free long-range movement of atoms becomes impossible. In order to obtain such long chains or large networks, it is necessary that (1) the bond strength of atoms in the chains or networks be very strong; (2) small ring formation of these strongly bonded atoms be at a minimum; and (3) the relative numbers of various atoms in the chains or networks be such that at least a continuous chain is configuratively and structurally possible. At the same time, the co-ordination numbers of the glass-forming atoms must be as small as possible to keep the bond strong. The general treatment is applied to all kinds of glasses, particularly oxide glasses. For the latter, the bond strengths of all M–O single-bond linkages have been calculated and are here tabulated for the first time. It was found that the bond strength of all the glass-formers is greater than 80 k.cal. per Avogadro bond, that of the intermediates between 50 and 80, and that of the modifiers below 50. The transition is continuous and the division into glass-formers, intermediates and modifiers is arbitrary. The table of bond strengths is particularly useful for the synthesis of new glasses and for the study of glass structure.

Kuan-Han Sun