Effect of Small Fraction of Spherical Porosity on Elastic Moduli of Glass

During the preparation of a glass for other purposes~ it was observed that glass specimens could be obtained containing perfectly spherical porosity.This note xeports on the effect of these spherical pores on the overall elastic moduli of the glass.The glass used was of the same composition as the 11 D-glass 11 (15% Na 2 0J 15% B 2 0 3 J 70% Si0 2 ) employed in a previous investigation.1 An intimate mix of sodium carbonate~ boric acid, and silica was melted in a platinum crucible at 1300°C.The evolution of carbon dioxide and water vapor provided the gases for bubble formation.The relative amount of bubbles in the melt was an inverse function of the length of time the crucible was held at temperature.The melt was held at temperature from about 20 to 40 min# depending on the bubble content desired.Glass specimens ( 5 x 1 I 2 x 1 I 2 in.) were cast in suitable graphite molds preheated to 650°C.