The Density of Silicate Glasses as a Function of Composition*

Abstract

The volume per gram atom of oxygen in a well-annealed silicate glass is given quite accurately by the equation V_O=k+b_Si+c_SiN_Si+∑c_MN_M, where k is a very small constant characteristic of the annealing technique, N_Si and N_M are the numbers of Si or other “metal” atoms per atom of oxygen, b_Si and c_Si are constants which are different for different ranges of N_Si values, and c_M are constants valid (insofar as can be determined from present data) for all values of N_M. For boron-containing glasses separate terms are required for tetrahedrally surrounded and for triangularly surrounded atoms, the relative numbers of which depend on the relative amounts of Si, B and O. With the aid of the above equation, one can calculate densities from compositions simply and quite accurately. The empirical results obtained are interpreted theoretically.