WO1998015499A1 - Method of inhibiting gelling of siloxane feedstocks and a gel inhibited feedstock - Google Patents
Method of inhibiting gelling of siloxane feedstocks and a gel inhibited feedstock Download PDFInfo
- Publication number
- WO1998015499A1 WO1998015499A1 PCT/US1997/017495 US9717495W WO9815499A1 WO 1998015499 A1 WO1998015499 A1 WO 1998015499A1 US 9717495 W US9717495 W US 9717495W WO 9815499 A1 WO9815499 A1 WO 9815499A1
- Authority
- WO
- WIPO (PCT)
- Prior art keywords
- feedstock
- siloxane
- end capping
- comprised
- silica
- Prior art date
Links
Classifications
-
- C—CHEMISTRY; METALLURGY
- C03—GLASS; MINERAL OR SLAG WOOL
- C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
- C03B19/00—Other methods of shaping glass
- C03B19/14—Other methods of shaping glass by gas- or vapour- phase reaction processes
- C03B19/1415—Reactant delivery systems
-
- C—CHEMISTRY; METALLURGY
- C03—GLASS; MINERAL OR SLAG WOOL
- C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
- C03B2207/00—Glass deposition burners
- C03B2207/30—For glass precursor of non-standard type, e.g. solid SiH3F
- C03B2207/32—Non-halide
Definitions
- the present invention relates to the formation of silica. More particularly, the present invention relates to a silicon containing feedstock for use in manufacturing silica and a method of treating feedstocks used in the formation of silica.
- Various processes are known in the art that involve the production of silica glass from vaporous reactants. Such processes require a feedstock containing silicon, a means for transporting the feedstock and an oxidant to a reaction site, and a means of decomposing the feedstock in order to convert the feedstock into silica.
- An apparatus used in such a process usually consists of a liquid feedstock reservoir, a means of converting said liquid feedstock into a vapor and delivering said feedstock vapor to a conversion site burner wherein the feedstock vapor is converted by flame hydrolysis into silica soot.
- Silica soot produced by such a burner is then collected on a deposition surface.
- Such collected silica may be simultaneously or subsequently heat treated to form a fused, non-porous, transparent, high purity silica glass article.
- SiCU silicon tetrachloride
- SiCl silicon-containing feedstocks
- U.S. Patent No. 5,043,002 to Dobbins et al. the disclosure of which is hereby incorporated by reference, discloses the use of such siloxanes as feedstocks.
- polyalkylsiloxanes such as polymethylsiloxanes, and in particular polymethylcyclosiloxanes with octamethylcyclotetrasiloxane (OMCTS) as the preferred silicon-containing feedstock, in the formation of silica.
- OCTS octamethylcyclotetrasiloxane
- cyclic siloxanes and in particular octamethylcyclotetrasiloxane (OMCTS)
- OCTS octamethylcyclotetrasiloxane
- Such cyclic siloxane feedstocks are sensitive to cracking and polymerization during vaporization and delivery to a decomposition site.
- the cyclic structure of octamethylcyclotetrasiloxane may open up. Such opened siloxane rings will join or polymerize with other siloxane species to form higher weight siloxane species.
- Such polymerized higher weight siloxane species normally have boiling points exceeding the vaporizing and delivery temperatures of the silica manufacturing process and are thus deposited during vaporizing and delivery as troublesome gels.
- This gelling of the siloxane feedstock causes manufacturing difficulties due to the clogging and restriction of the feedstock flow during storage, vaporization, delivery and decomposition. Such gelling tends to foul heat transfer surfaces and plug the piping of delivery systems, leading to disturbance of the silica manufacturing process.
- Such gel formation creates great difficulty in controlling, monitoring and metering the amount and rate at which a silicon-containing feedstock is utilized in a silica manufacturing process.
- the present invention is directed to a silica forming feedstock which is resistant to gelling and to a method of inhibiting the gelling of siloxane feedstocks.
- the invention inhibits the gelling of siloxane feedstocks during the silica manufacturing process by end capping the siloxane feedstock.
- the invention includes a silica forming feedstock of polyalkylsiloxane and an end capping compound which inhibits the polymerization of the polyalkylsiloxane.
- FIG. 1 is a Fourier Transform Infrared (FTLR) Spectra Analyses of an embodiment and components of the invention.
- FTLR Fourier Transform Infrared
- FIG. 2 is a Fourier Transform Infrared (FTLR) Spectra Analyses of an embodiment and components of the invention.
- FTLR Fourier Transform Infrared
- FIG. 3 is a Fourier Transform Infrared (FTLR) Spectra Analyses of an embodiment and components of the invention.
- FTLR Fourier Transform Infrared
- FIG. 4 is a Gel Permeation Chromatography (GPC) Analyses of an embodiment and components of the invention.
- the invention is directed to a method of inhibiting the gelling of siloxane feedstocks, used in manufacturing and forming silica, by end capping the siloxane feedstock.
- end capping the siloxane feedstock the polymerization of the siloxane feedstock is restrained.
- restraining the polymerization of the siloxane feedstock the formation of gels during the silica producing process is inhibited.
- the invention discloses a polyalkylsiloxane silica forming feedstock which includes an end capping compound which inhibits polymerization of the feedstock and formation of gels during the silica manufacturing process.
- the inventors mean that the normally polymerizing ends of the siloxane compound are preferentially reacted with a compound which prevents these normally polymerizing ends from polymerizing with other siloxanes and forming higher molecular weight siloxane polymers.
- the kinetics governing the preferential reaction of the end capping compounds with the normally polymerizing ends are quicker than the kinetics of the siloxane polymerization reaction.
- Octamethylcyclotetrasiloxane is a preferred siloxane containing halide free feedstock. Octamethylcyclotetrasiloxane is decomposed to form silica which is utilized in the fabrication of optical fibers, planar waveguides, lightwave optical circuits, bulk fused silica, high purity fused silica members and other silica glass based products. Although the use of an octamethylcyclotetrasiloxane feedstock is preferred, it has disadvantages due to the octamethylcyclotetrasiloxane ring structure's tendency to open up during vaporization from a liquid and delivery of the vaporized feedstock to the decomposition site where it is converted to silica (Si0 2 ).
- Octamethylcyclotetrasiloxane molecules may open up and subsequently polymerize with other octamethylcyclotetrasiloxane molecules under the temperature and other environmental conditions, including operating pressures, that are present in the silica manufacturing process, particularly the steps of vaporization of the feedstock, delivery of the vaporized feedstock to the decomposition site, and decomposition of the feedstock into silica.
- Such polymerization converts the octamethylcyclotetrasiloxane molecules into higher molecular weight siloxane polymers.
- These higher molecular weight siloxane polymers are not very volatile and tend to form gels which plug the vaporization, delivery, and decomposition systems of the silica manufacturing process.
- the inventors have discovered that such polymerizing and gelling of the octamethylcyclotetrasiloxane feedstock can be inhibited and prevented by introducing an end capping chemical compound into the liquid feedstock before the feedstock is vaporized.
- an end capping chemical compound By introducing an end capping chemical compound into the liquid feedstock, octamethylcyclotetrasiloxane molecules which open up are end capped and prevented from polymerizing with other present siloxanes.
- the end capping compound will react with the normally polymerizing octamethylcyclotetrasiloxane opened ring ends to form an octamethylcyclotetrasiloxane end capped complex which will not polymerize with other siloxanes present in the silica manufacturing process.
- the presently preferred end capping compound of the invention is triethyl borate.
- Triethyl borate introduced into the feedstock is able to effectively end cap the octamethylcyclotetrasiloxane thus preventing the polymerizing and gelling of this siloxane feedstock.
- Triethyl borate is preferred in that it can serve as a boron source compound for boron oxide which is utilized as a dopant in many silica compositions and products such as optical waveguides, planar waveguides, and lightwave optical circuits.
- triethyl borate can be attributed to boron which is electron deficient which makes the triethyl borate molecule very reactive toward nucleophilic reagents, which contain atoms such as oxygen which have lone pairs of electrons.
- triethyl borate's boiling point and vapor pressure are compatible with those of octamethylcyclotetrasiloxane.
- Triethyl borate has a boiling point of 117- 118° C. Having such a boiling point over 100° C is beneficial since it allows the triethyl borate to be present both as a vapor and a liquid at above 100° C temperatures and pressures typically utilized in the silica manufacturing process. Normally a temperature of 120° C or higher is needed to vaporize an octamethylcyclotetrasiloxane liquid feedstock.
- Octamethylcyclotetrasiloxane ring opening typically begins to occur in the 150° C to 200° C temperature range for the commercially available high purity grade octamethylcyclotetrasiloxane used in the formation of high purity silica.
- Triethyl borate's compatibility with octamethylcyclotetrasiloxane in terms of solubility and boiling points allows this end capping compound to be present and effective in the liquid and vapor states experienced by octamethylcyclotetrasiloxane molecules during vaporization and delivery. It is preferred to introduce the liquid end capping compound into the siloxane feedstock when the siloxane feedstock is in the liquid state.
- liquid triethyl borate into the liquid octamethylcyclotetrasiloxane before the feedstock is vaporized. Due to the compatibility between triethyl borate's and octamethylcyclotetrasiloxane's boiling points, the end capping compound is present and end capping may occur throughout the silica manufacturing steps where octamethylcyclotetrasiloxane is susceptible to polymerization and gelling.
- the triethyl borate When using triethyl borate as an end capping compound, the triethyl borate combines with the opened ring octamethylcyclotetrasiloxane molecule to form a triethyl borate-octamethylcyclotetrasiloxane complex which is vaporizable along with the unopen octamethylcyclotetrasiloxane molecules.
- Such end capped triethyl borate- octamethylcyclotetrasiloxane complexes are resistant to polymerizing and gelling.
- these end capped triethyl borate-octamethylcyclotetrasiloxane complexes travel through the vaporized feedstock delivery system and are then converted to silicon dioxide and boron oxide, without troublesome gelling.
- End capping the siloxane feedstock with triethyl borate is preferred in the manufacturing of planar waveguides, particularly when the siloxane containing feedstock is converted to silica by flame hydrolysis.
- core and clad layers are formed which guide the light.
- the core and clad layers are formed from silica glass compositions that differ from one another in order to provide an appropriate difference in refractive index.
- the inventors utilized the inventive method of end capping a siloxane feedstock in the manufacturing of such a clad glass layer.
- a clad glass liquid feedstock containing approximately 4.30 wt% trimethyl phosphate, 12.80 wt% triethyl borate and 82.70 wt% octamethylcyclotetrasiloxane was mixed together and pumped to a vaporizer.
- This triethyl borate end capped siloxane feedstock was vaporized, and the vaporized feedstock was delivered to a burner where it was converted into silica.
- Gel Permeation Chromatography (GPC) and Fourier Transform Infrared (FTLR) analysis were performed on this borate end capped siloxane containing feedstock, which showed that polymerization of the feedstock did not occur during vaporization.
- FIG. 1 shows the FTLR spectra of individual components octamethylcyclotetrasiloxane 20, triethyl borate 21, trimethyl phosphate
- FIG. 2 compares the FTLR spectra of octamethylcyclotetrasiloxane 24, the vaporized concentrated liquid clad glass feedstock mixture GPC Sample 25, vaporized octamethylcyclotetrasiloxane concentrate GPC Sample 26, and polymerized octamethylcyclotetrasiloxane 27 in descending order.
- Evidence of the siloxane in the vaporized concentrated liquid clad glass feedstock mixture are the bands in the FTLR spectrum at 810 cm “1 (Si-CH 3 ), 1070 cm “1 (Si-O-Si), 1254 cm “1 (Si-CH 3 sym. def.) and 2850-2980 cm (CH stretch).
- the bands between 1320-1640 cm “1 are due to triethyl borate and trimethyl phosphate with additional borate bands between 740-780 cm “1 .
- FIG. 3 compares the FTLR spectra of the clad glass feedstock mixture 28, the vaporized concentrated liquid clad glass mixture GPC Sample 29, the clad glass feedstock mixture solid precipitate 30, and the clad glass feedstock mixture solid precipitate after exposure to air 31, in descending order.
- Evidence of a siloxane borate complex can be seen in the clad glass feedstock mixture solid precipitate FTLR spectra
- FIG. 4 shows the Gel Permeation Chromatography (GPC) traces of an octamethylcyclotetrasiloxane concentrate 32, a vaporized octamethylcyclotetrasiloxane concentrate 33, and the vaporized concentrated liquid clad glass mixture 34.
- GPC Gel Permeation Chromatography
- Trace 32 shows the GPC trace obtained for the high molecular weight siloxanes of a typical octamethylcyclotetrasiloxane feedstock.
- Trace 33 shows the GPC trace of the high molecular weight siloxanes obtained from vaporized octamethylcyclotetrasiloxane.
- Trace 34 shows the GPC trace of the vaporized concentrated liquid clad glass mixture which is flat in the high molecular weight siloxane region on the left hand side of FIG. 4 but contains the low molecular weight cyclics on the right hand side as represented by the small double peaks.
- This end capping reaction can be attributed to boron's electron deficiency, which makes the end capping molecule very reactive toward nucleophilic reagents having atoms with lone pairs of electrons, such as oxygen.
- triethyl borate is the preferred end capping compound for octamethylcyclotetrasiloxane in silica forming processes used in the manufacturing of boron containing waveguides
- other end capping compounds can be used to end cap siloxane feedstocks to inhibit gelling.
- Trisopropyl borate which has a boiling point in the range of 134-14TC
- tributyl borate which has a boiling point of 233 °C
- siloxane feedstocks such as octamethylcyclotetrasiloxane
- boron containing compounds such as tri-tert-butyl borate, trimethyl boroxine, dichloro phenylborane, dihydroxy phenylborane, and alkyl boron chloride can be used as end capping compounds.
- alkoxides containing other Periodic Table Group ILIA elements can be used as end capping compounds.
- Particular end capping compounds should be chosen having vapor pressures or boiling points compatible with the siloxane feedstock whose polymerization and gelling is being inhibited under the conditions of the silica manufacturing process.
- the end capping compound should be sufficiently soluble in the siloxane feedstock. In particular, it is beneficial to have the end capping compound present with the siloxane feedstock when the siloxane is most likely to polymerize, such as at high temperatures. In addition, end capping compounds should be chosen in view of the elements that are required to be present or absent in the formed silica. Further, the composition of the silica forming feedstock in terms of the percentage of end capping compound should be chosen in view of the percentage of elements that are required to be present or absent in the formed silica and the degree of gell formation that is to be inhibited.
- a silica forming feedstock comprised of siloxane and 0.5 wt% to 12 wt% triethyl borate is preferred to result in a silica glass with minimal boron content while inhibiting gell formation.
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- Engineering & Computer Science (AREA)
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- Materials Engineering (AREA)
- Organic Chemistry (AREA)
- Silicon Polymers (AREA)
Abstract
Description
Claims
Priority Applications (4)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
CA002267794A CA2267794A1 (en) | 1996-10-08 | 1997-09-25 | Method of inhibiting gelling of siloxane feedstocks and a gel inhibited feedstock |
EP97910721A EP0931018A4 (en) | 1996-10-08 | 1997-09-25 | Method of inhibiting gelling of siloxane feedstocks and a gel inhibited feedstock |
JP10517578A JP2001502312A (en) | 1996-10-08 | 1997-09-25 | Method for inhibiting gelation of siloxane raw material and raw material in which gelation is inhibited |
AU48022/97A AU4802297A (en) | 1996-10-08 | 1997-09-25 | Method of inhibiting gelling of siloxane feedstocks and a gel inhibited feedstock |
Applications Claiming Priority (2)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
US2800896P | 1996-10-08 | 1996-10-08 | |
US60/028,008 | 1996-10-08 |
Publications (1)
Publication Number | Publication Date |
---|---|
WO1998015499A1 true WO1998015499A1 (en) | 1998-04-16 |
Family
ID=21841034
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
PCT/US1997/017495 WO1998015499A1 (en) | 1996-10-08 | 1997-09-25 | Method of inhibiting gelling of siloxane feedstocks and a gel inhibited feedstock |
Country Status (6)
Country | Link |
---|---|
EP (1) | EP0931018A4 (en) |
JP (1) | JP2001502312A (en) |
CN (1) | CN1232436A (en) |
AU (1) | AU4802297A (en) |
CA (1) | CA2267794A1 (en) |
WO (1) | WO1998015499A1 (en) |
Cited By (5)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
EP1491655A2 (en) | 2003-06-23 | 2004-12-29 | Air Products And Chemicals, Inc. | Stabilizers to inhibit the polymerization of substituted cyclotetrasiloxane |
GB2405404A (en) * | 2003-08-28 | 2005-03-02 | Advanced Tech Materials | Stabilised cyclosiloxanes for use as precursors for low-dielectric constant thin films |
US7342295B2 (en) | 2002-11-21 | 2008-03-11 | Advanced Technology Materials, Inc. | Porogen material |
WO2013092553A1 (en) * | 2011-12-19 | 2013-06-27 | Heraeus Quarzglas Gmbh & Co. Kg | Method for producing synthetic quartz glass |
WO2018014934A1 (en) * | 2016-07-18 | 2018-01-25 | Prysmian S.P.A. | Method for manufacturing silicon dioxide preforms employed in the production of optical fibers |
Citations (3)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US3213048A (en) * | 1965-10-19 | Process for preparing organo- polysiloxane compositions | ||
US5098747A (en) * | 1989-06-16 | 1992-03-24 | Wacker-Chemie Gmbh | Coating compositions containing (poly)borosiloxanes and a process for preparing vitreous coatings |
US5231058A (en) * | 1989-12-27 | 1993-07-27 | Semiconductor Process Laboratory Co. Ltd. | Process for forming cvd film and semiconductor device |
Family Cites Families (3)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US3998865A (en) * | 1975-03-12 | 1976-12-21 | General Electric Company | Process for the stabilization of hexamethyl-cyclotrisiloxane and the stabilized compositions resulting therefrom |
US5043002A (en) * | 1990-08-16 | 1991-08-27 | Corning Incorporated | Method of making fused silica by decomposing siloxanes |
BR9611969A (en) * | 1995-12-19 | 1999-02-17 | Corning Inc | Process and apparatus for forming fused silica by combustion of liquid reagents |
-
1997
- 1997-09-25 WO PCT/US1997/017495 patent/WO1998015499A1/en not_active Application Discontinuation
- 1997-09-25 CN CN97198564.2A patent/CN1232436A/en active Pending
- 1997-09-25 AU AU48022/97A patent/AU4802297A/en not_active Abandoned
- 1997-09-25 EP EP97910721A patent/EP0931018A4/en not_active Withdrawn
- 1997-09-25 JP JP10517578A patent/JP2001502312A/en not_active Ceased
- 1997-09-25 CA CA002267794A patent/CA2267794A1/en not_active Abandoned
Patent Citations (3)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US3213048A (en) * | 1965-10-19 | Process for preparing organo- polysiloxane compositions | ||
US5098747A (en) * | 1989-06-16 | 1992-03-24 | Wacker-Chemie Gmbh | Coating compositions containing (poly)borosiloxanes and a process for preparing vitreous coatings |
US5231058A (en) * | 1989-12-27 | 1993-07-27 | Semiconductor Process Laboratory Co. Ltd. | Process for forming cvd film and semiconductor device |
Cited By (11)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US7423166B2 (en) | 2001-12-13 | 2008-09-09 | Advanced Technology Materials, Inc. | Stabilized cyclosiloxanes for use as CVD precursors for low-dielectric constant thin films |
US7300995B2 (en) | 2001-12-21 | 2007-11-27 | Air Products And Chemicals, Inc. | Stabilizers to inhibit the polymerization of substituted cyclotetrasiloxane |
US7342295B2 (en) | 2002-11-21 | 2008-03-11 | Advanced Technology Materials, Inc. | Porogen material |
EP1491655A2 (en) | 2003-06-23 | 2004-12-29 | Air Products And Chemicals, Inc. | Stabilizers to inhibit the polymerization of substituted cyclotetrasiloxane |
EP1491655A3 (en) * | 2003-06-23 | 2007-06-20 | Air Products And Chemicals, Inc. | Stabilizers to inhibit the polymerization of substituted cyclotetrasiloxane |
GB2405404A (en) * | 2003-08-28 | 2005-03-02 | Advanced Tech Materials | Stabilised cyclosiloxanes for use as precursors for low-dielectric constant thin films |
DE102004041641A1 (en) * | 2003-08-28 | 2005-07-28 | Advanced Technology Materials, Inc., Danbury | Stabilized cyclosiloxanes for use as precursors for low dielectric constant thin films |
GB2405404B (en) * | 2003-08-28 | 2008-07-16 | Advanced Tech Materials | Stabilized cyclosiloxanes for use as CVD precursors for low-dielectric constant thin films |
WO2013092553A1 (en) * | 2011-12-19 | 2013-06-27 | Heraeus Quarzglas Gmbh & Co. Kg | Method for producing synthetic quartz glass |
WO2018014934A1 (en) * | 2016-07-18 | 2018-01-25 | Prysmian S.P.A. | Method for manufacturing silicon dioxide preforms employed in the production of optical fibers |
US11124442B2 (en) | 2016-07-18 | 2021-09-21 | Prysmian S.P.A. | Method for manufacturing silicon dioxide preforms employed in the production of optical fibers |
Also Published As
Publication number | Publication date |
---|---|
CN1232436A (en) | 1999-10-20 |
CA2267794A1 (en) | 1998-04-16 |
AU4802297A (en) | 1998-05-05 |
EP0931018A4 (en) | 2000-02-23 |
JP2001502312A (en) | 2001-02-20 |
EP0931018A1 (en) | 1999-07-28 |
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