Fabrication of hollow glass microspheres in the Na2O-B2O3-SiO2 system from metal alkoxides

Hollow glass microspheres (HGS) for laser fusion targets were fabricated in the system Na₂O-B₂O₃-SiO₂ from NaOCH₃, B(OCH₃)₃ and Si(OC₂H₅)₄. Gel powders prepared from metal alkoxides and urea liberate H₂O, CO₂ and NH₃ gases, evolution of which takes place completely at about 500° C. The precursor of HGS is formed by the encapsulation of these gas components in the glass layer formed at the surface of the powder. HGS are produced from the gel powders having both a melting temperature lower than about 1000° C and a viscosity at that temperature lower than 10⁵ P. In the Na₂O-B₂O₃-SiO₂ system, the compositions from which HGS are produced are those containing 55–75 wt% SiO₂ and 0–20 wt% B₂O₃. HGS ranging from 100–500m diameter and 0.5–7.0m wall thickness are obtained by change of urea content.