Claims
- 1. 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.
- 2. A method in accordance with claim 1 wherein the sol has an effective silica concentration in the range of about 1-12 moles of SiO.sub.2 per liter.
- 3. A method in accordance with claim 2 wherein the soluble silicate compound is an alkali silicate compound, and wherein the sol has an effective SiO.sub.2 concentration of 3-12 moles per liter.
- 4. A method in accordance with claim 3 wherein the solid phase of the sol additionally comprises colloidal SiO.sub.2.
- 5. A method in accordance with claim 3 wherein the sol is gelled by the addition of a gelling agent thereto which is effective to reduce the pH of the sol to a value at which SiO.sub.2 will precipitate therefrom as a semisolid gel.
- 6. A method in accordance with claim 5 wherein the gelling agent is selected from the group consisting of formaldehyde, paraformaldehyde, formamide, glyoxal, methyl formate, methyl acetate, ethyl formate, and ethyl acetate.
- 7. A method in accordance with claim 3 wherein the TiO.sub.2 is provided as an aqueous colloidal TiO.sub.2 suspension containing quaternary ammonium ions and having a pH above about 9.
- 8. A method in accordance with claim 7 wherein the colloidal TiO.sub.2 in the sol is present in a concentration providing a TiO.sub.2 content in the range of about 7-10% of the total effective concentration of TiO.sub.2 and SiO.sub.2 in the sol.
- 9. A method in accordance with claim 8 wherein the gel has a pore size of 2000-3000 .ANG..
- 10. A method in accordance with claim 2 wherein the step of removing alkaline constituents from the semisolid gel comprises the immersion of the semisolid gel in an aqueous acidic medium.
- 11. A method in accordance with claim 2 wherein the step of drying the dealkalized gel comprises heating the gel to a temperature in the range of about 1000.degree.-1100.degree. C. to volatilize water and organic constituents therefrom.
- 12. A method in accordance with claim 2 wherein the step of drying comprises microwave heating.
- 13. A method in accordance with claim 2 wherein the step of firing the gel comprises heating the gel to a temperature in the range of about 1350.degree.-1700.degree. C. to consolidate the gel to a dense, non-porous glass.
BACKGROUND OF THE INVENTION
The government has rights in this invention under contract number F19628-85-C-0048 awarded by the U.S. Air Force.
US Referenced Citations (3)