Chemical Composition and Tensile Strength of Glasses in the B2O3-PbO and B2O3-SiO2-Na2O Systems

Abstract

Measurements were made of the tensile strength, Vickers hardness, Young's modulus and surface tension in lead borate glasses and sodium borosilicate glasses. The data of the tensile strength had small variation and no size effect as Thomas' results. NMR spectra of B¹¹ were measured in borosilicate glasses and the fraction of 3- and 4-coordinated boron were determined. From these measurements, the following conclusions were obtained. 1) It was observed that the tensile strength of B₂O₃ glass is 60kg/mm², which is very small compared to that of SiO₂ glass. The reason for this weakness may be that the glass has weak cohesive force between the layers in which boron atoms form planar BO₃triangles. 2) The tensile strength of these glasses shows the change with the composition similar to Vickers hardness and Young's modulus. NMR measurements of B^II in the borosilicate glasses can explain the change of the observed tensile strength with the composition. From these facts, it is proper to consider that there is a relation between the strength and the structure of glass. 3) The experimental values of the tensile strength of sodium borosilicate glasses were compared with the theoretical values calculated by using the observed values of Young's modulus and surface tension in Orowan's equation. The experimental values are about one fourth of the theoretical values, although the dependence of both values on the composition are similar. It may be said that the experimental values have not yet reached the intrinsic strength.