US3109747A

US3109747A - Method and apparatus for forming silica

Info

Publication number: US3109747A
Application number: US149695A
Authority: US
Inventors: Alton G Foote
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1961-11-02
Filing date: 1961-11-02
Publication date: 1963-11-05
Anticipated expiration: 1980-11-05

Description

Nov.' 5', Y1963 A. G. Foo-rE METHOD AND APPARATUS Foa FORMING sILIcA Filed Nov. 2, 1961 ...www

oO 2 $6395 A n S/L lm TE a@ ITM/@Deter Alflcm G FQOcL-e b9 mr His Atflo neg United States Patent O 3,109,7 47 METHOD AND APPARATUS FOR FORMING SILICA Alton G. Foote, Wiclrliie, Ohio, assignor to General Electric Company, a corporation of New York Filed Nov. 2, 1961, Ser. No. 149,695 8 Claims. (Cl. 117-18) The invention relates generally to a method and apparatus for forming iinely divided silica by the combustion of liquid organo-silicon compounds reducible by burning to silica, and has particular application -to the forming of light-diffusing coatings on the interior surfaces of hollow glassware such as electric lamp bulbs.

The formation of highly efficient light-diffusing coatings of fine particles of amorphous silica is disclosed and claimed in U.S. Patent 2,545,896, Iipkin. For many years such coatings have been formed by apparatus such as that disclosed in U.S. Patent 2,679,822, Kuehler, for example, 'and comprising a burner wherein liquid tetraethyl orthosilicate is fed upwardly in a central tube or conduit the upper end of which is heated during operation to a temperature suilicient to vaporize the liquid silicate where it is mixed with oxygen and burned inside the bulb to produce a white fume or smoke of amorphous silica particles which vare deposited on the inner bulb surface. 'l'lhe source of heat for warming the burner and keeping it Ihot is the ethyl silicate-oxygen tire, and full operating temperature is attained only after bulbs have been loaded over the burner.

While the coatings obtained in that manner are entirely satisfactory, the processing and equipment does have the disadvantage that the burners must be operated continuously in order to maintain them at proper temperature. There is also a problem of gumming of the burner due to running ot some of the liquid silicate over the top of the burner which causes it to dry up and lform a hard crust.

It is therefore an object of the invention to provide a method and apparatus for burning liquid organo-silicon compounds in a manner such that the ilame can readily be turned on and ol `at will, thereby effecting an economy of operation by permitting the burner to be turned oil during periods when there is no bulb present and without requiring a Warming up period when the burner is again turned on.

It is another important object to provide a method and apparatus which operates effectively with :a liquid cornpound such -as condensed ethyl silicate which is substantially -less expensive than the tetraethyl orthosilicate heretofore employed but which is subject to fractionization.

In accordance with the invention, the liquid silicate is brought -under pressure into a heated zone and released through an orifice into a hot conduit where it is immediately vaporized due to the reduction in pressure. The vapor is mixed with oxygen as it yleaves the tube and is ignited. This arrangement prevents fractionization and permits the burning of condensed ethyl silicate, as well as tetraethyl orthosilicate. It will be understood that condensed ethyl silicate consists of tetraethyl orthosilicate and about l to 15% by weight polysilicates, for example, polyethoxy siloxanes.

For a further understanding of the invention reference is directed to the following detailed description taken in conjunction with the drawing wherein:

FIG. 1 is a somewhat ydiagrammatic perspective view of a burner arrangement for practicing the invention;

FIG. 2 is an elevation of a burner of somewhat modified construction; and

FIG. 3 is a fragmentary side View at right angles to FIG. 2.

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Referring to FIG. l of the drawing, the burner comprises a block or base member 1 of material of vgood heat conductivity, such as brass, which is heated in any convenient manner, for example, by cartridge type electric resistance heaters which are contained in wells in the body of the block and are controlled by a suitable thermostat (not shown), which may be recessed in the block `2l, to maintain the block at a desired temperature. Into the block 1 there are inserted the lower ends of concentric tubes 4, 5 and 6 of such size and thermal conductivity that the center tube `6 is maintained at a temperature close to that of the block v1. 'Ihe combustible liquid silicate is brought into a passage 7 in the block 1 under pressure, and is released into the center tube 6 through an orifice 8 by means of a needle valve `9 which meters the `quantity of silicate fed into tube 6 and also `functions as an on-ol valve. An igniter or pilot llame is provided by feeding a small amount of combustible gas, preferably hydrogen, into the tube 5 through a passage 10 and allowing it to burn at the top of the tube 5.

A burner cap 11 is litted closely on the upper ends of tubes 4 and 5. A combustion supporting gas, preferably oxygen, is fed into the passage 12 and into the outer tube 4 to the lip 13 on cap 11 where it emerges from the apertures 14. The size and direction of the apertures 14 may be varied to control to some extent the direction of the flames and yconsequently the distribution of the smoke or fume in the lamp bulb.

The lamp bulb 15 is supported to enclose the burner cap 111 and to be rotated about its axis and reciprocated vertically Iin any suitable manner, as is known in the art. A portion of a bulb support member is indicated at 16.

During operation, the liquid organo-silicate is introduced under pressure of at least about tive pounds per square inch above atmospheric, preferably about iiteen pound-s per square inch, into the heated zone or chamber 7 which -is maintained at a temperature in the range of about to 220 C., preferably about 190 to 195 C., as measured by means of a thermocouple in the vicinity of the orifice `8. The liquid silicate in chamber 7 is released through the oniiice ytlfto atmospheric pressure in the central tube `6 so that it is immediately vaporized without fractionizat-ion. The vapor flows upward in tube 6 and from the upper end thereof Where it is mixed with oxygen from the apertures 1'4 in cap 11, and is ignited by the pilot llame of hydrogen issuing from tube 5. The oxygen is preferably supplied in excess to assure complete combustion of the silicate. The fume or smoke of tine amorphous silica formed by the burning of the silicate vapor is caused to deposit on the inner sur-face of the bulb 15; the remaining products of combustion liow out downwardly around the tube 4 and through the lower end of the bulb l15.

The burner sho'wn in FIG. 2 comprises a block or base member 20 which carries the three '

concentric tubes

21, 22 and 23 for flow of oxygen, hydrogen and silicate vapor, respectively. The liquid silicate is introduced into the block 20 under pressure through passage 24 and is released from a heated chamber 25 through orifice 26 into the center tube 23 by means of the needle valve 27. The hydrogen for the igniter or pilot flame is introduced into tube 22 through passage 28, and the oxygen -is supplied to outer tube 21 through passage 29. The burner cap 3i] is like that shown in FIG. l. The temperature of the block 20 is controlled by a resistance heating element 31 and associated thermostatic lswitch 32 (FIG. 3) contained in a recess in the block.

In the arrangement illustrated in FIG. 2, the needle valve `27 is carried by a exible diaphragm 33 and is held open by the pressure of the liquid silicate on the Vupper sur-face of the diaphragm in the opening 34. When it is desired to stop operation of the burner, the needle valve 27 is closed by the application of air pressure to the under surface of the diaphragm 33y through the passage 35. The size of the needle'valve opening may be adjustedby a stud 36 engageable with the lower end of the needle 27. y

It will be evident that the burner is of the surface mix type since the oxygen and fuel are kept apart until they exit from the burner. No liquid reaches the top of the burner so that the only buildaup on the burner is a soft smoke deposit that can be brushed oliE rather than having to be chipped off as is the case with dried liquid. In addition to effecting a saving of about one-fourth to onethird of the amount of liquid silicate used in coating a given number of bulbs, there is the further advantage that the method and apparatus disclosed herein makes it possible to utilize a lower cost fuel such as condensed ethyl silicate without the fractionization and gumming which resulted when employing burners of the type here- Y tofore employed in the art.

What l cla-im as new and desired to secure by Letters Patent of the United States is:

1. The method of forming tinely divided silica by the combustion of a liquid organo-silicon compound reducible by burning to silica, which comprises introducing the compound under pressure above atmospheric into a heated zone maintained at a temperature in the approximate range of 180'-220f 1C. and wherein the said compound remains a liquid, releasing a ilow of the liquid compound to a conned heated path at atmosphenic pressure to cause it to be immediately vaporized and maintained in Vapor form to the end of the path where it is mixed with oxygen and ignited to form a fume including iinely divided silica as one of the products of combustion, and collecting the silica on a surface exposed to the fume.

2. The method of forming silica as set -iorth in claim 1 wherein the pressure of the liquid organo-silicon compound in said heated zone is at least about iive pounds per square inch above atmospheric. Y

3. The method olf forming silica as set forth in claim l wherein the pressure of the liquid organo-silicon compound in said heated zone is approximately fteen pounds per square inch.

4. rl'he method of forming silica as set forth in claim 1 wherein'the .said liquid organosilicon compound is condensed ethyl silicate.

5. The method of forming silica as set forth in claim 1 wherein the said liquid organo-silicon compound is tetraethyl orthosilicate.

`6. The method of coating the interior of an electric lamp bulb `with a layer of finely divided silica by the combustion of an organo-silicon 'compound reducible by burning to silica, which comprises introducing the said liquid compound under pressure above atmospheric into a heated zone maintained at a temperature in the approximate range of -220 C. and wherein the said compound remains a liquid,V releasing a iiow of the liquid compound to a confined heated path at atmospheric pressure to cause it to be immediately vaporizied and maintained in vapor form to the end of the path in the interior of the bulb and mixing it ther-eat with a ilow of oxygen, igniting the said flow of vapor within the bulb to form a fume including finely divided silica as one of the products of combustion, and collecting a layer of the said silica on the interior of the bulb.

7. A burner for forming tinely divided silica by the combustion of a liquid organo-silicon compound reducible by burning to silica, comprising a block member having a chamber therein, means to heat and maintain said block member at a temperature in the approximate range of IBO-220 C., means to supply a quantity of said liquid compound to said chamber at a pressure above atmospheric, a conduit mounted in said block member to be heated therefrom and communicating with said chamber through an orice, means to release a iiow of the liquid compound from said chamber to said conduit through said onice whereby it is immediately vaporized, and means to ignite the -ow of vapor issuing lfrom said conduit.

8. A burner for forming finely 'divided sil-ica by the combustion of a liquid organo-silicon compound reducible by burning to silica, comprising a block member having a chamber therein, means to heat and maintain said block member adjacent said chamber at a temperature in the approximate range of ISO-220 C., means to supply a quantity of said liquid compound to said chamber at a pressure above atmospheric, a vertically extending Ilirst conduit having its lower end mounted .in said block member tobe heated therefrom and communicating with said chamber through an orifice, means to release a ilow of the liquid Ycompound from said chamber to said conduit through said oritice whereby it is immediately vaporized, a second conduit concentrically surrounding said 4lirst conduit to the upper end thereof, means to supply a ow of hydrogen to the space between said rst and second conduits to provide for a pilot ame at the upper end thereof for ignition of the vapor issuing from said rst conduit, a third conduit concentrically surrounding said second conduit to the upper end thereof, and means to supply a flow olif oxygen to the spacebetween said second and third conduits for admixture with the vapor issuing from said first conduit.

Liebhafslky et al. Jan. 3, 1961

Claims

1. THE METHOD OF FORMING FINELY DIVIDED SILICA BY THE COMBUSTION OF A LIQUID ORGANO-SILICON COMPOUND REDUCIBLE BY BURNING TO SILICA, WHICH COMPRISES INTRODUCING THE COMPOUND UNDER PRESSURE ABOVE ATMOSPHERIC INTO A HEATED ZONE MAINTAINED AT A TEMPERATURE IN THE APPROXIMATE RANGE OF 180-220*C. AND WHEREIN THE SAID COMPOUND REMAINS A LIQUID, RELEASING A FLOW OF THE LIQUID COMPOUND TO A CONFINED HEATED PATH AT ATMOSPHERIC PRESSURE TO CAUSE IT TO BE IMMEDIATELY VAPORIZED AND MAINTAINED IN VAPOR FORM TO THE END OF THE PATH WHERE IT IS MIXED WITH OXYGEN AND IGNITED TO FORMA FUME INCLUDING FINELY DIVIDED SILICA AS ONE OF THE PRODUCTS OF COMBUSTION, AND COLLECTING THE SILICA ON A SURFACE EXPOSED TO THE FUME.