The Effect of Microstructure on the Physical Properties of Glasses in the Sodium Silicate System

Samples of sodium silicate glasses heat-treated in the region of immiscibility were studied to characterise the physical properties and to determine the dependence of physical properties on microstructure. Independent measurements of the elastic moduli and thermal expansion characteristics were examined. The magnitudes of elastic moduli and coefficients of thermal expansion were controlled by the total amount of soda present. The temperature dependence of the physical properties, however, was greatly influenced by the amount and distribution of the phases present. In general, glasses with two independently interconnected phases were more rigid than homogeneous materials having the same nominal composition. The properties of glasses with a second phase dispersed as particles in a continuous matrix phase were determined primarily by the properties of the continuous phase. The observed behaviour of the physical properties supports the conclusion of three-dimensional interconnectivity of phases developed in the unstable region of immiscibility for sodium silicate glasses.