Hollow glass microspheres for use in radiation shielding

The production of hollow glass microspheres from Li2O–Al2O3–B2O3 glasses was investigated. The production of hollow, rather than solid, spheres is enabled by the use of blowing agents in the glass, such as sulfate compounds. Irregular glass frit (25–100 μm in diameter) was fed into a propane/oxygen torch and spherodized. Solid spheres were easily obtained for all particle sizes and glass compositions studied, but the yield of spheres with single hollow cavities was very low. Raman scattering spectroscopy was performed on glass frit to determine glass structure and the presence of sulfur-containing groups. Glasses were batched to contain SO3, but Raman spectra show the presence of bands due to SO42-. The Raman spectra presented do not show a clear relationship between glass composition (structure) and the yield of solid or hollow spheres. The solubility of sulfate in lithium aluminoborate glasses is around 1 wt%, based on the appearance of white Li2SO4 inclusions in glasses made to contain 1 wt% SO3 or greater. Sulfate solubility in glass samples was also seen to decrease with increasing Al2O3 content.