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US 2002/0157418 A1Published application
Process for reducing or eliminating bubble defects in sol-gel silica glass
OwnerRahul Ganguli, Steven G. Colbern +1inventors
InventorsRahul Ganguli, Steven G. Colbern, Matthew S. Gleason
Life of this patent
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Abstract
This invention resides in a process for making silica articles having few or no visible bubbles by sintering silica gels derived from a sol-gel process. The process incorporates control of pH during hydroxylation and gelation, as well as chlorination at temperatures previously considered unsuitable. The process optionally incorporates addition of dispersant to the silica solution.
Claims24
A process for making synthetic silica glass, comprising:
- mixing together fumed silica, water and acid to form a paste having a pH of less than about 2.2;
- mixing into the paste an alkoxysilane to form a liquid;
- adding a base to the liquid to increase the pH of the liquid to between about 2.8 and about 3.6 to form a sol;
- gelling the sol to form a gel;
- drying the gel using a subcritical drying process to form a dry gel;
- heating the dry gel in an atmosphere comprising chlorine gas to a temperature ranging between about 950° C. and about 1,200° C. for a duration sufficient to chlorinate and dehydroxylate the dry gel;
- heating the dry gel in an atmosphere free of chlorine gas for a duration sufficient to dechlorinate the dry gel;
- and
- heating the dry gel at a temperature and for a duration sufficient to form the synthetic silica glass.
6 more elements
A process for making synthetic silica glass, comprising:
- mixing fumed silica, water and acid to form a paste having a pH of less than about 2.2;
- mixing into the paste a dispersant;
- mixing into the paste an alkoxysilane to form a liquid;
- adding a base to the liquid to increase the pH of the liquid to between about 2.8 and about 3.6 to form a sol;
- gelling the sol to form a gel;
- drying the gel using a subcritical drying process to form a dry gel;
- heating the dry gel in an atmosphere comprising chlorine gas to a temperature ranging between about 950° C. and about 1,200° C. for a duration sufficient to chlorinate and dehydroxylate the dry gel;
- heating the dry gel in an atmosphere free of chlorine gas for a duration sufficient to dechlorinate the dry gel;
- and,
- heating the dry gel at a temperature and for a duration sufficient to form the synthetic silica glass.
7 more elements
A process for making synthetic silica glass, comprising:
- mixing fumed silica powder, water and acid, to form a paste having a pH of about 2.0;
- mixing into the paste a quaternary ammonium salt to a weight percentage of about 0.25 weight percent of the paste;
- mixing into the paste tetra-alkoxysilane to form a liquid;
- adding base to the liquid to increase the pH of the liquid to about 3.0 to form a sol;
- gelling the sol to form a gel;
- drying the sol using a subcritical drying method to form a dry gel;
- placing the dry gel in an atmosphere comprising chlorine gas at a temperature of about 1,050° C. for a duration sufficient to chlorinate and dehydroxylate the dry gel;
- placing the dry gel in an atmosphere essentially free of chlorine gas at a temperature and for a duration sufficient to dechlorinate the dry gel;
- heating the dry gel at a temperature and for a duration sufficient to form the synthetic silica glass;
- and
- heating the silica glass at a temperature less than about 1,734° C. and for a duration sufficient to remove inclusions from the glass.
8 more elements
Dependencies are inferred from the claim text.