Sol-gel method for making ultra-low expansion glass
AssigneeCorning Glass Works
InventorRobert D. Shoup
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Abstract
Ultra-low thermal expansion TiO.sub.2 --SiO.sub.2 glasses are prepared using a sol-gel process wherein a stable alkali silicate solution comprising colloidal TiO.sub.2 and having a pH above 9 is gelled to form a semisolid silicate gel, the gel comprising homogeneously dispersed colloidal TiO.sub.2 but being essentially free of agglomerated TiO.sub.2 particles, washing the gel with aqueous media to remove alkali therefrom, and finally drying and consolidating the gel to a clear, void-free TiO.sub.2 --SiO.sub.2 glass which is substantially free of compositional inhomogeneities and has a thermal expansion coefficient below that of pure fused silica.
Claims13
A method for making a low expansion TiO.sub.2 --SiO.sub.2 glass which comprises the steps of:
- (a) preparing an aqueous sol wherein the liquid phase comprises at least one soluble silicate compound selected from the group of alkali silicates and ammonium silicates, and wherein the solid phase comprises colloidal TiO.sub.2, the sol being formed by combining a TiO.sub.2 sol with a silicate solution containing dissolved SiO.sub.2 compounds, said aqueous sol having a pH of at least 9 and being substantially free of precipitated SiO.sub.2 and TiO.sub.2, the proportion of TiO.sub.2 in the sol being such as to provide a TiO.sub.2 concentration of TiO.sub.2 and SiO.sub.2 ;
- (b) gelling the sol to form a semisolid silicate gelled shape wherein the colloidal TiO.sub.2 is homogeneously distributed;
- (c) removing alkaline constituents from the semisolid gelled shape to provide a dealkalized gel;
- (d) drying the dealkalized gel to remove water and residual volatile solution components and to provide a porous body therefrom;
- and
- (e) firing the porous body to a temperature sufficient to consolidate it to a non-porous TiO.sub.2 --SiO.sub.2 glass article.
Dependencies are inferred from the claim text.