Thermal expansion properties of some vitreous and crystalline silicate materials

Abstract

The thermal expansion coefficient (α) of some multi-component silicate glasses with special reference to their respective crystalline products have been measured using an ORTON automatic recording dilatometer. The glass compositions are of the Li 2O(Al 2O 3)-MgO(CaO,ZnO)-SiO 2 type where MgO may be replaced by CaO or ZnO, and Al 2O 3 may replace Li 2O. The expansion coefficients of the glasses increased on replacement with ZnO or CaO/MgO. However, the α-values of the glasses markedly decreased on Al 2O 3/Li 2O replacement. The change in the expansion coefficient of the glasses is discussed in relation to factors such as polarization, field strength and the ionic radii of the incorporated cations, and their effects on the geometrical arrangement of the building units of the glassy network. The expansion coefficients changed markedly on conversion of the glasses into glassceramic materials. In such cases the data obtained were correlated to the nature, composition and concentration of all phases formed in the materials.