Title:
PRODUCTION OF METAL OXIDES
United States Patent 3642521


Abstract:
High-purity metal oxide articles are produced by a process wherein a vaporous stream containing a volatile compound of the metal is intimately contacted with a vaporous combustible stream containing water to form a reactant stream which is ignited to form the metal oxide by vapor phase reaction with the volatile metal compound. The ignited reactant stream is impinged upon a deposition surface to form the high-purity metal oxide article. In a preferred embodiment, a vapor stream of silicon tetrachloride is contacted with another vapor stream of hydrogen, oxygen, and water vapor (up to about 2 moles of water vapor per mole of silicon tetrachloride) to form a resultant stream which is combusted to form a high-purity silicon dioxide product upon the deposition surface.



Inventors:
Moltzan, Herbert J. (Dallas, TX)
Walker, Jack (Richardson, TX)
Application Number:
04/869843
Publication Date:
02/15/1972
Filing Date:
10/27/1969
Assignee:
TEXAS INSTRUMENTS INC.
Primary Class:
Other Classes:
65/30.1, 65/120, 65/421, 118/320, 264/81, 423/325, 427/425, 427/426, 427/453
International Classes:
C03B19/14; C23C16/40; C23C16/453; (IPC1-7): B05B7/08
Field of Search:
117/105.2 23
View Patent Images:



Primary Examiner:
Kendall, Ralph S.
Assistant Examiner:
Weston, Caleb
Claims:
We claim

1. A process for producing a metal oxide article comprising:

2. The method of claim 1 wherein said metal is selected from Groups IIA, IIIA, IVA, IIIB, IVB, and VB of the Periodic Table.

3. The method of claim 1 wherein water is present in said second stream in quantities up to about the stoichiometric amount necessary to convert said metal halide to said metal oxide.

4. The method of claim 3 wherein said second stream consists essentially of molecular hydrogen, molecular oxygen, and water vapor.

5. The method of claim 4 wherein water is present in said second stream in amounts up to about 2 moles of water per mole of said metal halide in said first stream.

6. The method of claim 5 wherein said metal halide is silicon tetrachloride.

7. The method of claim 6 wherein said second stream is contacted with said first stream at a first selected region and interaction between said first and second streams in prevented within a selected second region.

8. The method of claim 7 wherein said interaction is prevented by streaming a supply of initially relatively inert gas between said first stream and second stream.

9. The method of claim 8 wherein said second stream is slanted toward the axis of said first stream at an angle within the range of about 2° to about 30°.

10. In a process of producing an article of an oxide of a metal selected from Groups IIA, IIIA, IVA, IIIB, IVB, and VB of the Periodic Table wherein a jetstream consisting essentially of a vaporous halide of said metal is ejected from a nozzle and contacted with a combustible gas stream and ignited to cause vapor phase hydrolysis of said halide of said metal, and then directed upon a surface to form said metal oxide article thereon, the improvement comprising infusing water into said combustible gas stream prior to said contacting.

11. The method of claim 10 wherein the water is infused in said combustible gas in quantities up to about the stoichiometric amount necessary to convert the metal halide to the corresponding metal oxide.

12. The method of claim 11 wherein said combustible gas stream consists essentially of molecular hydrogen, molecular oxygen and water vapor.

13. The method of claim 11 wherein said combustible gas stream consists essentially of a vaporous hydrocarbon, molecular oxygen and water vapor.

14. The method of claim 12 wherein said water vapor is present in said combustible gas stream in quantities up to about 2 moles water per mole of said metal halide in said jetstream.

15. The method of claim 14 wherein said metal halide is silicon tetrachloride.

Description:
This invention relates to the production of metal oxide articles. In another aspect, this invention relates to an improved process for the production of metal oxide articles by hydrolysis of volatile metal halides.

Various processes are known in the art for the production of metal oxides from vaporous reactants. These processes generally include the vapor phase oxidation and hydrolysis of vaporous metal halides. For example, it is known to produce silicon dioxide by the following hydrolysis reaction:

SiCL4 +2H2 O ➝ SiO2 +4HCL

The conventional vapor phase processes which are utilized to carry out the above reaction require the use of burners or jet assemblies for feeding the reactant gases and vapors to a reaction space. Generally, very sophisticated equipment including jet nozzle assemblies are used in order to provide the moisture for the hydrolysis reaction by the simultaneous combustion of hydrogen and oxygen. Thus, the contact of the vaporous metal halide stream with the oxygen and hydrogen combustion containing stream must be conducted under very controlled conditions so that the metal oxide product formed from the ignition of the combined streams will not prematurely form upon the nozzle tip and cause unwanted deposition buildup. Additionally, the proportion of reactants and method of admixing the same must be closely controlled in order to obtain reasonable yields of the metal oxide product.

One object of this invention is to provide an improved process for the formation of metal oxide articles.

Another object of this invention is to provide an improved process for production of metal oxide articles from vaporous metal halide which results in a conversion of substantially all of the metal halide to high purity metal oxide by vapor phase hydrolysis.

According to the invention, metal oxides are produced by a process wherein a stream containing a vaporous metal halide is contacted with a reactant stream containing water and combustible constituents which are ignited to yield the metal oxide. The ignited stream is directed against a suitable deposition surface to form a metal oxide article thereon. Preferably, the reactant stream containing the combustible constituents has up to about 2 moles of water vapor per mole of metal halide. The combusting constituents for the production of pure metal oxides are preferably hydrogen and oxygen. If desired, the combusting constituents can comprise a hydrocarbon and oxygen.

This invention can be understood more easily from a study of the drawings in which:

FIG. 1 is a partial schematic view illustrating a suitable nozzle for carrying out the process of this invention;

FIG. 2 is a sectional view of the nozzle illustrated in FIG. 1 showing connection to the various reactant streams; and

FIG. 3 is an end view of the nozzle of FIG. 2.

Now referring to FIG. 1, torch 10 provides a means for admixing the reactants and providing a flame for producing vapor phase hydrolysis of a gaseous metal halide to produce a corresponding metal oxide deposit 100 on a substrate such as mandrel 101 according to this invention.

Any volatile metal halide known in the art can be used in the practice of this invention. Preferred metal halides include halides of the metals of Groups IIA, IIIA, IVA, IIIB, IVB and VB of the Periodic Table as set forth on page B-2 of the Handbook of Chemistry and Physics, Chemical Rubber Publishing Co., 45th ed. (1964). The preferred metal halides are the chlorides, bromides, and iodides, and most preferred are the chlorides. In addition, these halides of silicon are particularly preferred. In a preferred embodiment of this invention, high purity metal oxide is formed by vapor phase hydrolysis of a silicon tetrahalide, preferably silicon tetrachloride, to form silicon dioxide.

The combusting constituents of the combustible gas stream used in this invention are preferably molecular hydrogen and molecular oxygen. However, other combusting constituents can be used within the scope of this invention such as, for example, a vaporous hydrocarbon and oxygen. Generally, any hydrocarbon which has an atmospheric boiling point below that of nonleaded gasoline can be utilized. However, it is usually preferred to use the normally vaporous hydrocarbons such as methane, ethane and propane.

The flame produced from torch 10 is shown diagrammatically as comprising a very hot central portion 102 wherein a vaporized metal halide stream 103 within an annular stream of a relatively inert sheath gas 104 is combined with an annular combustible gas stream 105 containing water, at point 106 such that intermixing between the combustible gas stream and metal halide there occurs. Thus, the metal halide is not allowed to react with the combustible gas stream and decompose immediately adjacent the face of the nozzle, but rather it combines with and reacts with the combustible stream at point 106. When the two streams are ignited, the region 102 is extremely hot. The heat of combustion provides the necessary temperature to rapidly react the water with the metal halide to form the metal oxide. In one embodiment, water combustion product is also formed which reacts with the metal halide.

The hot central portion 102 can be directed upon any suitable deposition surface such as a graphite surface to receive a coating of metal oxide. As illustrated, mandrel 101 is a rotating, and translating mandrel which is disclosed in copending application Ser. No. 744,188, filed July 7, 1968 (TI 3269). Thus, as mandrel 101 rotates and translates in the directions indicated by the arrows, a layer of high purity metal oxide 100 is formed about the periphery thereof. It is to be noted that any other suitable deposition substrate can be utilized. Additionally, it is within the scope of this invention to deposit a bed of metal oxide within a suitable cavity such as reaction chamber by the process of this invention.

Now referring to FIG. 2, a suitable apparatus is illustrated for carrying out the process of this invention. FIG. 2 includes the improved torch disclosed in copending application Ser. No. 744,153, filed July 11, 1968, (TI 3326) connected to suitable reactant streams according to this invention.

Tube 12, preferably constructed from stainless steel, extends through the length of torch 10 to provide a passage for vaporized metal halide entrained in a carrier gas. A T-connection designated generally by 14 is connected about tube 12 and is sealed at one end to the tube 12 by a collar member 16. A coupling member 18 then fits over a stainless steel tube 20 to provide an annular sheath chamber 22 between the tube 12 and tube 20. An inlet portion 24 of the T-connection 14 is connected to a source of sheath gas as will be described below. This sheath gas is passed into the annular sheath chamber 22.

A mixing chamber 26 is formed by chamber walls 28. An inlet fitting 30 is adapted to be connected to the source of a combustible gas, while the inlet chamber 32 is connected to a source of oxidizing gas, either of which gases can contain the desired amount of water vapor according to this invention. The combustible gases are mixed within chamber 26 in order to limit any possible flashback to the torch housing. An outer annular chamber 34 is formed by annular walls 36 to define a cooling chamber about the torch. An inlet fitting 38 is connected to a suitable supply of cooling fluid which is circulated through chamber 34 and exhausted by an outlet fitting 40.

Now referring to FIGS. 2 and 3, nozzle assembly 68 is attached to the face of the torch 10 by screws 70. As Illustrated, four screws 70 pass through nozzle assembly 68 and into portions of the walls defining chamber 34. Nozzle assembly 68 comprises a unitary circular member having a center opening 72 for receiving the end of tube 12. The end of tube 12 is closed with the exception of a center nozzle aperture 74 defined therein. Due to the difference in the diameters of pipe 12 and pipe 20, an annular opening 76 is defined concentrically about nozzle aperture 74. Sheath chamber 22 communicates with the opening 76. A plurality of nozzle openings 78 are defined through nozzle assembly 68. The diameter of these openings is generally the same, or smaller than, the diameter of nozzle aperture 74.

Each of the nozzle openings 78 makes an angle with the axis of the jetstream issuing from nozzle aperture 74. This angle can be varied according to the particular desired results, and is generally within the range of about 2° to 30°. These angled nozzle openings 78 provide a very efficient torch flame for the direct deposition of metal oxides.

In a preferred embodiment as illustrated in the drawing, oxygen is supplied through conduit 42 to the inlet of three flowmeters 44, 46 and 48. Hydrogen is supplied via a conduit 50 to flowmeter 52. Suitable valves are provided at the output of each of the flowmeters in order to allow accurate regulation of the flow rate of the gases to the torch 10. Oxygen is supplied through conduit 54 to inlet portion 24 of T-connection member 14. Oxygen from flowmeter 46 is supplied through a conduit 56 to a bubbler unit 58. The bubbler unit 58 comprises a container filled with liquid metal halide, e.g., silicon tetrachloride, and includes a diffusing element 60 which bubbles the oxygen upwardly through the metal halide, thereby entraining vapors of the metal halide within the oxygen. While a bubbler assembly has been shown, it will be understood that a conventional diffuser-type gas source can alternatively be utilized. The gaseous metal halide entrained in the carrier oxygen gas is passed outwardly through conduit 62 to the inlet of pipe 12. Oxygen is also supplied from flowmeter 48 through conduit 64 to inlet 30 of mixing chamber 26. Additionally, hydrogen is supplied from flow meter 52 through conduit 66 to bubbler unit 80. Bubbler unit 80 contains water and functions in substantially the same way as bubbler unit 58. Bubbler unit 80 contains diffusing element 81 operatively connected to conduit 66. Bubbler unit 80 functions to bubble hydrogen upwardly through the water, thereby infusing water vapor into the hydrogen which is passed to inlet 32 of mixing chamber 26 via conduit 82.

The quantity of water infused in the hydrogen vapors will be a function of the velocity of the hydrogen flowing through bubbler unit 80, the pressure within the bubbler unit 80, and the temperature of the water contained therein. Conduit 82 is maintained at a temperature sufficient to prevent the infused water vapor within the hydrogen stream from condensing therein. It is to be understood that any other suitable means for infusing water in a combustible feed gas stream to mixing chamber 26 can be used within the scope of this invention. For example, steam can be directly injected into conduit 82 passing to inlet 32. In addition, water infusion means can be directly connected to the interior of chamber 26, or to any of the combustible vapor lines passing thereto, e.g., conduit 64. These units function to infuse sufficient water into the combustible gas mixture to enhance the hydrolysis reaction according to this invention. For example, the amount of water which can be infused into the combustible gas feed generally ranges from trace amounts to about the stoichiometric amount required to react with the metal halide feed. Generally any amount up to about 2 moles of water per mole of metal halide feed can be used. If desired, greater amounts of water can be utilized.

It is to be noted that mixing chamber 26 is shown in FIG. 2 as operatively connected to hydrogen and oxygen feed streams, and in addition to the water feed. This arrangement will produce very pure metal oxide. If it is desired to produce metal oxides of lesser purity, other combustible gas streams can be utilized in the scope of this invention. These gas streams can be passed through either or both of the inlet conduit 64 and/or 82.

In operation of torch 10, metal halide entrained in oxygen is passed through tube 12 and out nozzle aperture 74 as a gaseous jetstream. A concentric sheath of oxygen is passed through annular opening 76. Eight streams of the combustible mixture of hydrogen, oxygen, and water vapor are directed at an angle in the range from about 2° to 30° toward the axis of the jetstream for penetration of the gas sheath and interaction with the gaseous metal halide. When the torch is ignited, combustion occurs at this region of penetration, and the metal is decomposed by vapor phase hydrolysis to form the corresponding metal oxide. The presence of the water vapor within the combustible mixture provides substantially improved conversion of the metal halide. It was heretofore believed that all water utilized in the hydrolysis reaction should be formed as a combustion product of hydrogen and oxygen in the combustible gas feed stream. However, it has been found that the presence of water in the combustible mixture stream significantly increases the metal halide conversion. It is generally necessary to contact the infused water vapor with metal halide a distance spaced from the outlet of the nozzle in accordance with this invention to prevent a premature reaction of the water and formation of metal oxide on the torch which eventually changes the character and usefulness of the flame and the system.

The following example will further explain the subject invention, but it is not intended to limit the scope thereof.

EXAMPLE

The system as illustrated in FIG. 2 was utilized in cooperation with the rotating mandrel as illustrated in FIG. 1. The rotating mandrel was positioned at about 31/4 inches from the end of nozzle assembly 68. Eight nozzle openings 78 each sloping at 20° toward the longitudinal axis of the torch (nozzle aperture 74), were provided through nozzle assembly 68 as illustrated in the drawings. Bubbler unit 58 contained silicon tetrachloride and bubbler unit 80 contained water.

Dry oxygen was supplied to the system via conduit 42 and a dry hydrogen was supplied to the system via conduit 50.

One liter per minute of oxygen with 1.456 liters per minute of gaseous silicon tetrachloride entrained therein was fed to tube 12 via conduit 62. The temperature and pressure of bubbler unit 60 was controlled to provide this entrainment. One liter per minute of oxygen was supplied to annular space 22 via conduit 24 for use as a sheath gas. 5.2 liters per minute of oxygen was supplied to mixing chamber 26 via conduit 64, and 30 liters per minute of hydrogen with about 2.5 grams per minute of water was supplied to mixing chamber 26 via conduit 82 and bubbler unit 80. The temperature and pressure of bubbler unit 80 were controlled to provide the water infusion within the resulting stream.

The resulting velocity of the gas jetstream of gaseous silicon tetrachloride from the torch was about 4.17×103 ft. per minute. The flame was ignited and directed against the rotating graphite mandrel for about 20 minutes. The resulting flame temperature was about 1,500° C. It was found that the conversion of silicon tetrachloride to silicon dioxide was substantially complete.

The above example was repeated except that the water vapor was infused into the oxygen sheath gas stream passed through annular zone 22. The experiment had to be stopped because unwanted deposits of silicon dioxide built up on the face of the nozzle, clogged the nozzle apertures, and substantially changed the character of the flame.

In several subsequent runs, it was found that even trace amounts of water vapor included within the combustible gas stream emitted from nozzles 78 would increase the efficiency of the reaction over conventional processes which utilized dry oxygen-hydrogen combustible gas streams. Improved conversion efficiencies have been found using water contents within the combustible gas stream up to and including the stoichiometric amount required for the conversion of the metal halide to corresponding metal oxide.

While this invention has been described in relation to its preferred embodiments, it must be understood that various modifications will now be apparent to one skilled in the art upon reading the specification, and it is intended to cover such modifications as fall within the scope of the appended claims.