US 4,883,521 AGranted

Method for the preparation of silica glass

AssigneeShin-Etsu Chemical Co., Ltd.

InventorsTakaaki Shimizu, Syuji Tanaka

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Abstract

An improved sol-gel method is proposed for the preparation of a transparent silica gel block, in which a deposit of fine silica particles having a controlled particle diameter as prepared by hydrolyzing an alkoxy silane in the presence of ammonia is dispersed in a silica sol solution prepared in an acidic condition and settled therein to form a structure of closest-packing prior to gelation, drying, sintering and vitrification so that silica glass blocks can be obtained with low volume shrinkage from the wet gel in an improved yield without cracks, bubbles and haziness. The improvement can be further enhanced when two separately prepared deposits of silica particles having larger and smaller particle diameters are dispersed as combined in the silica sol solution, especially, when the particle diameter in one deposit is not exceeding 22.5% of that in the other deposit.

Claims11

Dependent claims

A method for the preparation of transparent silica glass which comprises the successive steps of:

(a) hydrolyzing an alkoxy silane compound in the presence of a basic catalyst to prepare a dispersion containing spherical particles of silica;
(b) removing the basic catalyst from the dispersion by distillation so as to bring the pH of the dispersion to 8 or below;
(c) settling the silica particles in the dispersion;
(d) discarding the supernatant from the dispersion to obtain a first deposit of the silica particles;
(e) dispersing the first deposit of silica particles in a silica sol solution of a hydrolyzate of an alkoxy silane compound obtained by the hydrolysis thereof in the presence of an acidic catalyst to prepare a dispersion of the silica particles in the silica sol solution;
(f) adjusting the pH of the dispersion to have a value of 2 to 6;
(g) settling the silica particles in the dispersion;
(h) discarding the supernatant from the dispersion to obtain a sexcond deposit of the silica particles;
(i) heating the second deposit of the silica particles to obtain a wet gel thereof;
and
(j) drying, sintering and vitrifying the wet gel of silica particles to give a block of transparent silica glass.

8 more elements

Dependencies are inferred from the claim text.