The Vitreous State

Abstract

The tendency of glass forming substances to supercooling is discussed in connection with the existence of large or irregular groups in the melts of such substances. If the size of these groups makes their direct addition to the crystal lattice difficult, and if the forces within them are so strong as to prevent a rapid disintegration of the groups, the melt will tend to supercooling and glass formation. In the inorganic glasses consisting of oxides of metalloids or the corresponding acids or salts, the formation of large or irregular groups is caused by the strong tendency of these metalloids to coordinate oxygen in a definite way. If the number of available oxygen atoms is smaller than necessary for the formation of discrete polyhedral groups with the required coordination, the polyhedra will be linked together sharing oxygen atoms. The resulting groups will delay crystallization and thus cause the formation of glass.