A model for estimating the bulk modulus of polycomponent inorganic oxide glasses

Abstract

A new theory which allows the bulk modulus of polycomponent oxide glasses to be estimated to a precision of about ±7% or better, is described. It is suggested that the bulk modulus is approximately proportional to the product of the reduced Madelung constant, the mean valence charge product weighted by the relative ionicities of the various bonds, the fourth power of the reciprocal molar volume per ion pair, and a factor less than 1 which increases with the mean stiffness of bonds. The relationship can be simplified by assuming that the ionicity and stiffness factors cancel and the important result is that the product expressing the theoretical bulk modulus can be evaluated solely from a knowledge of the coordination numbers in the crystalline forms of the component oxides, and the glass composition and density. A good correlation between this simplified product and the experimental modulus of a large range of phosphate and silicate glasses is obtained, providing that the mean valence charge product does not exceed the value obtaining in the parent glass.