Changes in Relation Between Refractive Index and Young's Modulus as the Result of Successive Heat Treatments

The relation between refractive index and elastic modulus is found to be a sensitive indicator of the nucleation and separation of submicroscopic phases in glass. In a study of the changes in properties with heat treatments of a wide variety of glasses containing SOa, B20s, and ZnO as major constituents, it was observed that large decreases in Young's moduli were not accompanied by decreases in refractive indices of the magnitude usually observed. The abnormal changes in properties resulted from a sequence of two heat treatments. The results indicate that during the first heat treatment an immiscible phase is nucleated which, on subsequent heat treatment at a higher temperature, develops into heterogeneous regions producing changes in the relation between the refractive index and the elastic modulus.