Monosized powders for the preparation of high-purity silica glass

Abstract

Very-high purity silica glass for the preparation of optical fibers can be produced by using ceramic powder technology methods. Commercial silica powders, e.g. colloidal pyrogenic silica, are used by other authors for the shaping of a porous green compact which becomes transparent silica glass after purification and sintering. Monosized powders of submicron, spherical silica particles are advantageous in the preparation and sintering of green compacts because they lead to a homogeneous pore structure. Monosized powders are prepared by the hydrolysis of tetraethoxysilane. Particle size distributions and specific surface area measurements indicate the presence of micropores, which are created depending on the reaction conditions. These micropores can be sintered at temperatures far below the usual sintering temperature of the green compacts. The packing density of the spherical particles in green compacts is approximately 66 %, representing a non-agglomerated, close-packed random array of monosized spherical particles. The green compacts of monosized silica powders can be sintered to transparent silica glass.