Silica glass containing TiO2 and process for its production

• US 20070042893A1
• Filed: 10/31/2006
• Published: 02/22/2007
• Est. Priority Date: 07/01/2004
• Status: Active Grant

• Current Assignee: AGC, Inc.
• Original Assignee: Asahi Glass Company, Limited (AGC, Inc.)
• Inventors: Kikugawa, Shinya, Koike, Akio, Iwahashi, Yasutomi, Takimoto, Yasuyuki
• Granted Patent: US 7,419,924 B2
• Time in Patent Office: Days
• US Class Current: 501/54
• CPC Class Codes: C03B 19/1453 Thermal after-treatment of the shaped article, e.g. dehydrating, consolidating, sintering
• CPC Class Codes: C03B 2201/12 doped with fluorine C03B2201/14 takes precedence
• CPC Class Codes: C03B 2201/23 doped with hydroxyl groups
• CPC Class Codes: C03B 2201/42 doped with titanium
• CPC Class Codes: C03C 2201/12 containing fluorine C03C2201/14 takes precedence
• CPC Class Codes: C03C 2201/23 containing hydroxyl groups
• CPC Class Codes: C03C 2201/42 containing titanium
• CPC Class Codes: C03C 3/06 with more than 90% silica by weight, e.g. quartz C03C3/045 takes precedence

Abstract

It is to provide a silica glass containing TiO₂, having a wide temperature range wherein the coefficient of thermal expansion is substantially zero.

A silica glass containing TiO₂, which has a TiO₂ concentration of from 3 to 10 mass %, a OH group concentration of at most 600 mass ppm and a Ti³⁺ concentration of at most 70 mass ppm, characterized by having a fictive temperature of at most 1,200° C., a coefficient of thermal expansion from 0 to 100° C. of 0±150 ppb/° C., and an internal transmittance T_400-700 per 1 mm thickness in a wavelength range of from 400 to 700 nm of at least 80%. A process for producing a silica glass containing TiO₂, which comprises porous glass body formation step, F-doping step, oxygen treatment step, densification step and vitrification step.

Claims

1. A silica glass containing TiO₂, which has a TiO₂ concentration of from 3 to 10 mass %, a OH group concentration of at most 600 mass ppm and a Ti³⁺ concentration of at most 70 mass ppm, characterized by having a fictive temperature of at most 1,200°

C., a coefficient of thermal expansion CTE_0-100 from 0 to 100°

C. of 0±

150 ppb/°

C., and an internal transmittance T_400-700 per 1 mm thickness in a wavelength range of from 400 to 700 nm of at least 80%.

2. The silica glass containing TiO₂ according to claim 1, which has a F concentration of at least 100 mass ppm.

3. The silica glass containing TiO₂ according to claim 1, which has an internal transmittance T_300-3000 per 1 mm thickness in a wavelength range of from 300 to 3,000 nm of at least 70%.

4. The silica glass containing TiO₂ according to claim 1, which has a temperature range of at least 4.0°

C. wherein the coefficient of thermal expansion is 0±

5 ppb/°

C.

5. A process for producing a silica glass containing TiO₂, which comprises:

a step of forming a porous TiO₂—

SiO₂ glass body by depositing and growing on a target TiO₂—

SiO₂ glass particles obtained by flame hydrolysis of glass-forming materials (porous glass body formation step);

a step of heating the porous TiO₂—

SiO₂ glass body to a densification temperature to obtain a TiO₂—

SiO₂ dense body (densification step); and

a step of heating the TiO₂—

SiO₂ dense body to a vitrification temperature to obtain a high transmittance glass body (vitrification step);

and the process further comprises, after vitrification step;

a step of cooling the high transmittance glass body at a temperature of at least 1,200°

C. to 500°

C. at an average cooling rate of at most 150°

C./hr, or a step of holding the high transmittance glass body at a temperature exceeding 600°

C. for a predetermined time and then cooling it to 500°

C. at an average cooling rate of at most 150°

C./hr (annealing step).

6. The process for producing a silica glass containing TiO₂ according to claim 5, which further comprises, between vitrification step and annealing step, a step of heating the high transmittance glass body to a temperature of at least a softening temperature and forming it into a desired shape to obtain a formed glass body (forming step).

7. A process for producing a silica glass containing TiO₂, which comprises:

a step of forming a porous TiO₂—

SiO₂ glass body by depositing and growing on a target TiO₂—

SiO₂ glass particles obtained by flame hydrolysis of glass-forming materials (porous glass body formation step);

a step of heating the porous TiO₂—

SiO₂ glass body to a densification temperature to obtain a TiO₂—

SiO₂ dense body (densification step); and

a step of heating the TiO₂—

SiO₂ dense body to a vitrification temperature to obtain a high transmittance glass body (vitrification step);

and the process further comprises, between porous glass body formation step and densification step;

a step of holding the porous TiO₂—

SiO₂ glass body in an atmosphere containing oxygen and F to obtain a F-containing porous glass body (F-doping step); and

a step of holding the F-containing porous glass body in an atmosphere containing at least 15% of oxygen to obtain a porous TiO₂—

SiO₂ glass body having an oxygen treatment applied thereto (oxygen treatment step).

8. The process for producing a silica glass containing TiO₂ according to claim 7, which further comprises, after vitrification step, a step of cooling the high transmittance glass body at a temperature of at least 1,200°

C. to 500°

C. at an average cooling rate of at most 150°

C./hr, or a step of holding the high transmittance glass body at a temperature exceeding 500°

C. for a predetermined time and then cooling it to 500°

C. at an average cooling rate of at most 150°

C./hr (annealing step).

9. The process for producing a silica glass containing TiO₂ according to claim 8, which further comprises, between vitrification step and annealing step, a step of heating the high transmittance glass body to a temperature of at least a softening temperature and forming it into a desired shape to obtain a formed glass body (forming step).