Niobium doped silica titania glass and method of preparation

Patent metadata

Field	Value
Publication number	US-8987155-B2
Application number	US-201313973428-A
Country	US
Kind code	B2
Filing date	Aug 22, 2013
Priority date	Aug 30, 2012
Publication date	Mar 24, 2015
Grant date	Mar 24, 2015

Abstract

This disclosure is directed to a silica-titania-niobia glass and to a method for making the glass. The composition of the silica-titania-niobia (SiO 2 —TiO 2 —Nb 2 O 5 ) glass, determined as the oxides, is Nb 2 O 5 in an amount in the range of 0.005 wt. % to 1.2 wt. %, TiO 2 in an amount in the range of 5 wt. % to 10 wt. %, and the remainder of glass is SiO 2 . In the method, the STN glass precursor is consolidated into a glass by heating to a temperature of 1600° C. to 1700° C. in flowing helium for 6 hours to 10 hours. When this temperature is reached, the helium flow can be replaced by argon for the remainder of the time. Subsequently the glass is cooled to approximately 1050° C., and then from 1050° C. to 700° C. followed by turning off the furnace and cooling the glass to room temperature at the natural cooling rate of the furnace.

First claim

We claim:

1. A silica-titania-niobia glass comprising, in wt., % measured as the oxides, niobia in an amount in the range of 0.005 wt. % to 1.2 wt. %, titania in an amount in the range of 5 wt. % to 10 wt. %, and the remainder of the glass is silica, SiO 2 .

2. The silica-titania-niobia glass according to claim 1 , wherein the titania content is in the range of 6 wt. % to 9 wt. %.

3. The silica-titania-niobia glass according to claim 1 , wherein the silica-titania-niobia has a lower expansivity slope than that of a silica-titania glass having a substantially equivalent titania content.

4. The silica-titania-niobia glass according to claim 1 , wherein the OH content of the glass is less than 200 ppm.

5. The silica-titania-niobia glass according to claim 1 , wherein the OH content of the glass is less than 100 ppm.

6. The silica-titania-niobia glass according to claim 1 , wherein the OH content of the glass is in the range of 10-70 ppm.

7. A method for making a silica-titania-niobia glass having a composition comprising niobia in an amount in the range of 0.005 wt. % to 1.2 wt. %, titania in an amount in the range of 5 wt. % to 10 wt. %, and the remainder of the glass is silica, the method comprising the steps of:
obtaining a silica-titania soot have a titania content in the range of 5-10 wt., %
preparing an aqueous hydroxide solution containing a selected amount of a niobium compound and adjusting the pH to above 12, and adding the silica-titania soot to the solution, the amount of the niobium compound in the solution being such that a silica-titania-niobia glass formed therefrom consists essentially of 0.005 wt. % to 1.2 wt. % niobia, 5 wt. % to 10 wt. % titania, and the remainder of the glass is silica,
mixing the resulting silica-titania soot containing solution for a time of 14-24 hours to form a stable sol, then reducing the pH to less than 10 by the addition of a time dependent buffering, gelling agent to form a gel, and degassing to remove entrapped air;
transferring the degassed sol to a partially-closed container and aging the sol 0.2 to 48 hours at a relative humidity of >75% to form a gel;
opening the container and allowing the gel to air dry for a time in the range of 4-8 days or until the weight of the gel is reduced to less than 70% of the weight of the starting gel;
drying the gel in an oven by slowly heating it to a temperature 100-150° C. for a time in the range of 20-30 hours to form a dried gel material;
slowly heating the dried gel material in a furnace to a temperature of 700-800° C. over a time in the range of 70 hours to 100 hours to slowly remove the organic binders present in the dried material without damaging the dried gel material and thereby forming a silica-titania-niobia glass precursor;
consolidating silica-titania-niobia glass precursor into a glass by heating the precursor to a selected temperature in the range of 1600° C. to 1700° C. in flowing helium over a time in the range of 4 hours to 24 hours, with the provision that the heating be at a rate exceeding 8° C./minute above 1535° C. to avoid crystallization in the glass; and
cooling the consolidated glass from the consolidation temperature to room temperature.

8. The method according to claim 7 wherein after the glass has been consolidated and before the glass is cooled to room temperature, the glass is annealed by lowering the temperature of the glass from the consolidation temperature to a temperature of 1000° C.±100° C. and holding the glass at this temperature for a time in the range of 1-2 hours followed by cooling the glass to a temperature of 750±50° C. at a rate in the range of 1° C. to 10° C. per hour before turning off the furnace and cooling the glass to room temperature at the natural cooling rate of the furnace.

9. The method according to claim 7 , wherein after the glass is cooled and removed from the furnace, the glass is placed in an annealing oven and heated to 1000° C.±100° C. over a time in the range of 1-2 hours and held at 1000° C.±100° C. for a time in the range of 1-2 hours, followed by cooling to 750±50° C. at a rate in the range of 1° C. to 10° C. per hour before turning off the furnace and cooling the glass to room temperature at the natural cooling rate of the furnace.

10. The method according to claim 7 , wherein after the glass has been consolidated and before the glass is cooled and removed from the furnace, the fictive temperature of the glass is controlled by changing the annealing procedure prior to cooling by:
lowering the temperature from the consolidation temperature to 1100° C. and then cooling to a selected temperature of in the range of 700° C. to 900° C. at a rate of less than 2° C./minute;
holding the glass at the selected temperature for a time in the range of 5 hours to 400 hours; and
cooling the glass to a temperature of at most 500° C. at an average cooling rate of at most 150° C./hr.; and
turning off the heat to the furnace and allowing the furnace and glass therein to cool to room temperature at their natural rate.

11. The method according to claim 10 , wherein the average cooling rate is at most 50° C./hr.

12. The method according to claim 10 , wherein the average cooling rate is at most 10° C./hr.

Assignees

• Corning Inc

Inventors

• Annamalai Sezhian
• Dawes Steven Bruce
• Hrdina Kenneth Edward

Classifications

• C03C3/06

  with more than 90% silica by weight, e.g. quartz {(C03C3/045 takes precedence)} · CPC title

• C03C2203/42

  using silicon halides as starting materials · CPC title

• C03B19/12

  by liquid-phase reaction processes · CPC title

• C03C2201/40

  containing transition metals other than rare earth metals, e.g. Zr, Nb, Ta or Zn · CPC title

• C03B2201/40

  doped with transition metals other than rare earth metals, e.g. Zr, Nb, Ta or Zn · CPC title