Fabrication of Hollow Glass Microspheres for Laser Fusion Targets from Metal Alkoxides

Abstract

Fabrication of hollow glass microspheres for laser fusion targets was tried using the gel powders prepared from metal alkoxides. The gel was prepared by hydrolysis of the solution containing Si(OC₂H₅)₄, B(OCH₃)₃ and NaOCH₃ with HCl solution. It was dried, crushed and sieved to obtain the powders fanging from 44 to 63μm. Such powders were dropped into the vertical type electric furnace which was held at appropriate temperatures.
When the gel powder was rapidly heated, the surface of it transformed to the glass to form the shell in which gases contained in the gel powder were encapsulated. During passing through the furnace, the shell expanded to be a hollow glass microsphere.
The expansion rate of the hollow glass microsphere was calculated on the hypothesis that the expansion of microsphere was governed by the pressure of gases encapsulated and the viscous relaxation of the glassy shell. It was estimated that the time required for the microsphere to expand to the final size was about 0.1s at 1300°C and the gases effective for expansion were those contained within a third of radius of the gel powder.
When the highest temperature of furnace was held at 1300°-1500°C, the hollow glass microspheres ranging from 80 to 100μm in diameter with the wall thickness of 1.0μm were obtained. Their sphericity and the wall thickness uniformity were satisfactory for the laser fusion target requirements.