Production Of An Article Of High Purity Metal Oxide

Abstract

A torch is provided for decomposing a volatile metal chloride by hydrolysis to directly form an oxide article on a mandrel. The torch includes a nozzle which provides an output jet stream of vaporized metal chloride. Sheath openings in the nozzle provide a supply of gas which is relatively inert with respect to the gaseous metal chloride for preventing reaction immediately adjacent the nozzle face. A plurality of slanted nozzle openings are provided in the nozzle for directing angled streams of combustible gas through the sheath stream at a selected region for reaction with the jet stream of gaseous metal chloride. When the gas streams are ignited, a torch flame is provided which may be directly impinged upon a mandrel in order to directly form an oxide article of high purity thereon.

Description

This invention relates to a production of metal oxide by the decomposition of volatile metal chloride, and more particularly to a formation of an article of metal oxide by the vapor phase hydrolysis of volatile anhydrous chlorides of metallic elements from Groups III and IV of the periodic system, and particularly silicon tetrachloride.

It is necessary in the formation of many semiconductor devices to "pull" pull monocrystalline silicon from a melt of very pure silicon. In order to prevent impurities from entering the melt of silicon from the walls of the melt crucible, it has been found advantageous to construct the melt crucible from very pure silica. Further, it has been found desirable to provide the silicon melt crucible with very uniform sidewalls and with a symmetrical configuration in order to ensure a uniform "pull" from the silicon melt.

Silica articles have been heretofore formed by various techniques. For instance, U.S. Pat. No. 2,272,342, issued Feb. 10, 1942, discloses the production of a silica article by the vaporization of silicon tetrachloride or silicon fluoride and the decomposition of the resulting vapor in a flame. The flame is then impinged on a refractory core to deposit a layer of silica, after which the silica is vitrified by the application of high temperature. Additionally, U.S. Pat. No. 3,117,838, issued Jan. 14, 1964, discloses the utilization of a flaming torch for oxidizing a gas mixture including silane in a reactive gas to form molten silica and then directing the molten silica onto a carbon form to grow a body of transparent silica. Such previously developed techniques have not, however, been completely satisfactory with respect to forming an extremely pure silica article having a desired uniform configuration and necessary strength for use as a melt crucible.

It has also heretofore been known to produce finely divided metal oxide from volatile metal chlorides by igniting streams of the vaporized metal chloride and combustible gases within a reactor. The volatile metal chloride is thus oxidized to form finely divided oxide which is withdrawn from the bottom of the reactor. In order to prevent obstruction of the nozzle through which the gas streams are provided to the reactor, it has heretofore been known to provide an intermediate layer of relatively inert gas between the combustible gas and the gaseous metal chloride. Further, in some instances, it has been known to slant the supply of combustible gases toward the gaseous metallic chloride at angles from 45.degree. to 60.degree. to enhance the combustion reaction between the gases. Examples of such systems are disclosed in U.S. Pat. No. 2,240,343, issued Apr. 29, 1941; U.S. Pat. No. 2,394,633, issued Feb. 12, 1946; and U.S. Pat. No. 2,823,982, issued Feb. 18, 1958.

The present invention is an improvement over the torch for providing vapor phase hydrolysis of a volatile metal chloride in a flame which is described and claimed in the copending patent application entitled "Method and Apparatus for Forming an Article of High Purity Metal Oxide," by Michael A. Carrell, filed Jul. 11, 1968, Ser. No. 744,188.

In accordance with the present invention, a volatile metallic chloride is vaporized and entrained in a carrier gas and streamed from a jet nozzle. A stream of combustible gas is formed symmetrically about the jet stream and directed at an angle in the range of 2.degree. to 30.degree. to the axis of the jet stream to provide a preselected reaction region with the jet stream. A stream of sheath gas is provided between the streams to prevent reaction closely adjacent the nozzle. When the gas streams are ignited at the reaction region, a flame is formed which may be directed upon a mandrel to form an article of high purity oxide directly thereupon.

For a more complete understanding of the present invention and further objects and advantages thereof, reference may now be made to the following description taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a somewhat diagrammatic illustration of a torch constructed in accordance with the invention;

FIG. 2 is a sectional view taken generally along the section lines 2-2 of the torch shown in FIG. 1;

FIG. 3 is an end view of the torch shown in FIG. 1;

FIG. 4 is a diagrammatic illustration of the temperature zones of a torch flame formed in accordance with the invention;

FIG. 5 is a sectional view of another embodiment of a nozzle for the torch shown in FIG. 1;

FIG. 6 is a cross-sectional view of yet another embodiment of a nozzle for use with the torch shown in FIG. 1;

FIG. 7 is a front view of the nozzle shown in FIG. 6;

FIG. 8 is a view of yet another embodiment of a nozzle for use with the torch shown in FIG. 1;

FIG. 9 is a graph illustrating variances in deposition rate with the present torch in accordance with changes in the distance between the torch and the mandrel;

FIG. 10 is a graphical illustration of the variance of the deposition rate with the present torch versus variances in the velocity of the central jet stream of the torch; and

FIG. 11 is a graphical illustration of variances in the deposition rate of the present torch in accordance with variances in the flow rate of a combustible gas provided to the torch.

Referring to FIG. 1, the torch designated generally by the numeral 10 emits a flame which provides vapor phase hydrolysis of a gaseous volatile metal chloride to produce a metal oxide which is deposited upon a rotating mandrel. The present torch may be used to decompose any one of a number of the volatile anhydrous chlorides of metallic elements from Groups III and IV of the periodic system, such as titanium tetrachloride, aluminum tetrachloride, and tin tetrachloride. However, in the preferred embodiment of the invention, silicon tetrachloride is decomposed by the torch 10 to form silicon dioxide according to the following equation:

SiCl.sub.4 + 2H.sub.2O -- SiO.sub.2 + 4HC1

A tube or pipe 12, preferably constructed from stainless steel, extends through the length of the torch 10 to provide a passage for vaporized silicon tetrachloride entrained in a carrier gas. A T-connection, designated generally by the numeral 14, is connected about the tube 12 and is sealed at one end to the tube 12 by a collar member 16. A coupling member 18 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 the source of sheath gas in a manner to be later described, which is in this instance oxygen containing gas. 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 one combustible gas, while the inlet 32 is connected to a source of a second combustible gas. The combustible gases are mixed within the 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 the cooling chamber about the torch. An inlet fitting 38 is connected to a suitable supply of cooled fluid which is circulated through the chamber 34 and exhausted via an outlet fitting 40.

Oxygen is supplied through a conduit 42 to the inlet of three flowmeters 44, 46 and 48. Hydrogen is supplied via a conduit 50 to a flowmeter 52. Both the oxygen and hydrogen are dried prior to entering the flowmeters. 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. Oxygen is supplied through a conduit 54 to the inlet portion 24 of the T-connection member 14. Oxygen from the flowmeter 46 is supplied through a conduit 56 to a bubbler unit 58. The bubbler unit 58 comprises a container filled with liquid silicon tetrachloride and includes a diffusing element 60 which bubbles the oxygen upwardly through the silicon tetrachloride, thereby entraining vapors of the silicon tetrachloride within the oxygen. While a bubbler assembly has been shown, it will be understood that a conventional diffuser type gas source could alternatively be utilized. The gaseous silicon tetrachloride entrained in the carrier oxygen gas is passed outwardly through a conduit 62 to the inlet of the pipe 12. Oxygen is supplied from the flowmeter 48 through a conduit 64 to the inlet 30 of the mixing chamber 26. Hydrogen is supplied from the flowmeter 52 through the conduit 66 to the inlet 32 of the mixing chamber 26.

A nozzle assembly 68 is attached to the face of the torch 10 by screws 70. As shown in FIG. 2, four screws 70 pass through the nozzle assembly 68 and into portions of the walls defining chamber 34. Nozzle 68 comprises a unitary circular member having a center opening 72 for receiving the end of pipe 12. As best shown in FIG. 1, the end of pipe 12 is closed, with the exception of a center nozzle aperture 74 defined therein. In a practical torch, a nozzle aperture having a diameter of about .063 inch has been found to provide satisfactory results. Due to the difference in the diameters of pipe 12 and pipe 20, an annular opening 76 is defined concentrically about the nozzle aperture 74. The sheath chamber 22 opens into the opening 76. A plurality of nozzle openings 78 are defined through the nozzle assembly 68. The diameter of these openings is generally the same, or smaller than, the diameter of the nozzle aperture 74.

An important aspect of the present invention is that the nozzle openings 78 slant towards the axis of the jet stream which issues from the nozzle aperture 74. As shown in FIG. 1, each of the nozzle openings 78 makes an angle .phi. with the axis of the jet stream issuing from the jet aperture 74. This angle .phi. may be varied according to the invention for particular desired results, but in any instance is within the range of 2.degree. 30.degree.. In the torch shown in FIG. 1, an angle .phi. of 20.degree. has been shown. As will be later described, the angle nozzle openings 78 provide a very efficient torch flame for the direct deposition of metal oxides.

In operation of the torch 10, silicon tetrachloride entrained in oxygen is passed through the pipe 12 and out the jet aperture 74 as a gaseous jet stream. A concentric sheath of oxygen is passed through the annular opening 76. Eight streams of a combustible mixture of hydrogen and oxygen are directed at an angle in the range from 2.degree. to 30.degree. toward the axis of the jet stream for penetration of the gas sheath and interaction with the gaseous silicon tetrachloride. When the torch is ignited, combustion occurs at this region and the silicon tetrachloride is decomposed by vapor phase hydrolysis to form silicon dioxide. The slanting of the combustible gas through the sheath into the gaseous silicon tetrachloride is believed to provide substantially improved results due to better contact with the reactants within the gas streams to provide a more controlled and directed flame reaction.

FIG. 4 diagrammatically illustrates the theoretical operation of the present torch. The stream of reactant gas fed from the bubbler 58 is surrounded by a circular stream of sheath gas. In the preferred embodiment, the sheath gas comprises oxygen in such quantities as to be initially relatively inert with respect to the silicon tetrachloride bubbler gas. Thus, silicon tetrachloride is not allowed to react with a combustible gas and decompose immediately adjacent the face of the nozzle to thereby cause obstructions of the nozzle apertures. The combustible gas is directed along the dotted lines through the oxygen sheath at a distance below the nozzle face to react with the silicon tetrachloride in the region designated generally by the numeral 80. When the gas streams are ignited, this region 80 is extremely hot, and provides temperatures of in the range of 1,500.degree. C.

A relatively narrow reaction zone is provided by the angled, or focused, combustible gas stream shown in FIG. 4. This relatively short reaction zone is in contrast with previously developed torches without angled gas nozzles which provide relatively wide reaction zones. The provision of the relatively small reaction zone enables excellent contact with the reactant gases and insures efficient production of silicon dioxide. On the other hand, an excessive angle greater than about 30.degree. leads to a reaction 30.degree. too close to the torch, causing deposition on the burner face and a lower efficiency.

The flame from the torch 10 is impinged directly upon a rotating mandrel 82. Mandrel 82 is generally constructed from a substance such as graphite which can withstand the high temperatures of the torch. Improved results are usually obtained by preheating the mandrel before deposition operations. The mandrel 82 is translated along its axis in the direction of the arrow designated as 84 and a layer of high purity silica, shown generally by the numeral 86, is deposited directly upon the mandrel 82. The present torch enables a very smooth deposition of high purity silica, with the resulting article formed having sufficient "green strength" upon cooling to allow the article to be removed from the mandrel 82 and further treated. It is believed that this "green strength" results from a slight sintering together of the silicon dioxide particles during the deposition thereof.

FIG. 5 illustrates another embodiment of a nozzle assembly according to the invention. Substantial advantages are provided by the present torch in that nozzles may be easily changed on the torch body in accordance with the desired uses of the torch. The nozzle assembly shown in FIG. 5 includes an aperture 90 for receiving the end of the pipe 12 and further includes holes 92 for receiving suitable screws for attachment to the torch body.

Whereas the nozzle assembly shown in FIG. 1 included slanted apertures directed at 20.degree. toward the axis of the jet stream, the nozzle shown in FIG. 5 includes nozzle openings 94 which slope at an angle of 10.degree. toward the axis of the jet stream and the longitudinal axis of the torch.

FIGS. 6 and 7 illustrate yet another embodiment of a nozzle assembly 96. Instead of the eight holes for combustible gas previously shown, the nozzle assembly 96 includes 16 holes or openings 98 arranged in a cylindrical configuration. Alternate ones of the openings 98 slant toward the axis of the jet stream issuing from the torch at different angles. For instance, the opening 100 slants downwardly at an angle of 10.degree., while the opening 102 slants downwardly toward the axis of the jet stream at an angle of 20.degree.. Each alternate nozzle opening slants downwardly at a different angle than the openings directly adjacent thereto. Eight nozzle openings will thus slant downwardly at an angle of 10.degree., .degree.while the eight remaining alternate openings slant downwardly at an angle of 20.degree. . It will of course be understood that various other configurations of varying nozzle opening angles may be selected for nozzles according to the invention to meet various operating requirements. Additionally, various nozzle opening angles may be used in combination with different combinations of openings for the combustible gas.

FIG. 8 illustrates an end view of an assembled torch according to the invention which includes four nozzle apertures 106a--106d defined in the end of the pipe 12. In the embodiment shown in FIG. 8, 16 nozzle openings 108 are shown in a symmetrical configuration about the center jet nozzle apertures. Each of the openings 108 is slanted toward the longitudinal axis of the torch in order to pierce the sheath gas issuing from the annular opening 110 in the manner previously described. It will be understood that a variety of other configurations of nozzle openings may also be provided by the invention, as long as the openings are suitable symmetrically arranged.

FIG. 9 is a graphical representation of the effect of variances in the distance between the nozzle of the torch and the mandrel upon the deposition rate of the silicon dioxide and the efficiency of such deposition. Curve 110 represents variances in the deposition rate while curve 111 represents variances in efficiency. This data was obtained from a torch having a flame temperature of in the range of 1,400.degree. C. with a flow rate of 1.5 liters per minute of gaseous silicon tetrachloride entrained in 1 liter per minute of oxygen. A sheath gas flow rate of 1 liter per minute of oxygen was provided, along with a flow of combustible gases at a flow rate of 5.2 liters per minute of oxygen and 30 liters per minute of hydrogen being provided through apertures angled toward the jet stream of silicon tetrachloride at 10.degree..

Inspection of FIG. 9 illustrates that both the efficiency and rate of deposition of silicon dioxide on the mandrel increases at the torch is pulled away from the mandrel; an optimum distance is about 31/4 inches. As this distance then increases, both the rate of deposition and efficiency of deposition substantially decreases. It will be understood that each torch having a different configuration will have an optimum mandrel distance which will be different from torches with other configurations.

FIG. 10 illustrates variations in the deposition rate and efficiency of the torch described with respect to FIG. 9 utilizing the same flow rates, with the exception that the velocity of the bubbler gas is varied. As shown by curve 112, the deposition rate substantially increases as the velocity of the gaseous silicon tetrachloride entrained in carrier gas is increased. However, as shown by curve 114, the efficiency of such deposition begins to fall off at a velocity of about 6 feet per minute .times. 10.sup.3.

FIG. 11 illustrates changes in the deposition rate and efficiency of the torch described with respect to FIG. 9 as the flow rate of hydrogen into the torch is varied. Curve 116 illustrates that as the hydrogen flow rate is increased, the deposition rate increases to a maximum of about 120 grams per hour at about 30 liters per minute flow rate. Thereafter, the deposition rate falls off. Similarly, curve 118 illustrates that the efficiency of the deposition by the torch increases to about 55 percent at about 30 liters per minute flow rate of hydrogen, and thereafter falls off on further increases in flow rate. A similar effect is observed by varying the flow rate of the oxygen fed into the combustion chamber of the torch.

It will thus be observed from an inspection of FIGS. 9--11 that optimum results are obtained by varying various parameters of the flow rates of the gases fed into the torch and the distance from the torch to the mandrel. For any particular torch configuration, each of these parameters may be adjusted to a maximum to give utmost performance of the torch.

The following examples will further explain the use of the present torch, but should not serve to limit the utilization of the torch.

EXAMPLE 1

A torch was constructed in accordance with FIG. 1 with eight cylindrical holes each sloping at 20.degree. toward the longitudinal axis of the torch for supplying combustible gas through the sheath of oxygen to the gaseous silicon tetrachloride. The torch was connected to a gas system similar to that shown in FIG. 1 and then ignited. A nonrotating graphite mandrel was disposed about 31/4 inches from the torch nozzle and the flame issuing from the torch was impinged upon the graphite mandrel for 20 minutes. The temperature of the flame approximately one-fourth inch from the mandrel was in the range of 1,500.degree. C. One liter per minute of oxygen and 1.56 liters per minute of gaseous silicon tetrachloride entrained in the oxygen was fed to the torch. To provide this supply of gas, a conventional bubbler was maintained at a temperature of approximately 50.degree. C. and at a pressure of 5 pounds per square inch. The percentage of silicon tetrachloride entrained in the oxygen carrier gas was about 60 percent. The diameter of the center nozzle aperture of the torch was .063 inch. One liter per minute of oxygen was provided to the torch for use as a sheath gas, while 5.2 liters per minute of oxygen and 30 liters per minute of hydrogen were mixed in a torch to provide the combustion gas. The resulting velocity of the gas jet stream of gaseous silicon tetrachloride from the torch was about 4.17 feet per minute .times. 10.sup.3. After 20 minutes of deposition by the flame, the actual deposition of silicon dioxide on the graphite mandrel was measured to be 41 grams. By comparing this deposition with the theoretical computation of 76.8 grams, an efficiency of deposition of 53 percent was computed. This percentage was contrasted to a deposition efficiency of 46 percent by the utilization of a torch with the identical parameters above enumerated, but with eight holes which were not slanted toward the axis of the jet stream. This increase in efficiency of deposition, and in the rate of deposition, is thought to be because the penetration of the sheath gas by the combustion gases increases the uniformness of reaction of the gases and provides a more limited and intense reaction zone.

EXAMPLE 2

The identical torch described in example 1 was utilized at the same distance from the graphite mandrel for the same deposition time. The same gas flow rates were provided into the torch, with the exception that 2 liters per minute of oxygen was provided to the torch for use as a sheath gas and 8 liters per minute of oxygen was provided for mixture with the hydrogen within the torch. After 20 minutes of deposition with the torch, 44.2 grams of silicon dioxide were deposited on the mandrel for a deposition efficiency of 58 percent.

EXAMPLE 3

In some instances, it has been found that a reduction in the velocity of the sheath gas may increase the efficiency of deposition of silicon dioxide. In this deposition example, the identical torch previously described was utilized with the same flow rates of the gases thereto and at the same distance from the mandrel as that described in example 2, with the exception that 1.5 liters per minute of oxygen was provided to the torch for use as the sheath gas. In this instance, after a 20 minute run, 53.3 grams of silicon dioxide were deposited on the mandrel for a deposition efficiency of 69 percent.

EXAMPLE 4

Increase in the velocity of the jet stream of gaseous silicon tetrachloride also was found to provide good results with the torch described in examples 1--3. The gas flows to the torch were maintained as described in example 3, except that 2 liters per minute of oxygen was provided to the bubbler and 2.86 liters per minute of gaseous silicon tetrachloride was entrained in the oxygen, with 1 liter per minute being used as a sheath gas. After 20 minutes of deposition at 3 inches from the mandrel, 72.9 grams of silicon dioxide were deposited on the graphite mandrel to provide an efficiency of 52 percent.

EXAMPLE 5

Effective deposition was found to be provided with the utilization of the torch shown in FIG. 1 with a nozzle having 16 holes for the combustion gas each slanted at 20.degree. toward the axis of the jet stream. In this example, the torch was held 31/4 inches from the mandrel for a period of 20 minutes, with an effective flame temperature one-fourth inch from the mandrel of slightly over about 1,400.degree. C. One liter per minute of oxygen was fed to a bubbler and entrained 1.56 liters per minute of silicon tetrachloride therein. One liter per minute of oxygen was provided to the torch for use as a sheath gas. 5.2 liters per minute of oxygen was supplied to the torch for mixture with 30 liters per minute of hydrogen to form a combustive mixture. The bubbler was maintained at a temperature of 50.degree. C. and at a pressure of 5 pounds per square inch to provide 60.9 percent silicon tetrachloride within the gaseous mixture. This mixture was passed outwardly through a .063 inch diameter jet nozzle to provide a jet stream having a velocity of 4.17 feet per minute .times. 10.sup.3. The use of this torch after 20 minutes provided 39.2 grams of silicon dioxide upon the graphite mandrel for a deposition efficiency of 51 percent.

EXAMPLE 6

Excellent results were also obtained by the use of a torch connected as shown in FIG. 1 with a nozzle having eight holes for combustible gas, each hole being slanted toward the axis of the jet stream at an angle of 10.degree.. The torch was held from the mandrel about 3 1/4 inches and ignited for about 20 minutes. The resulting flame of the torch one-fourth inch from the mandrel surface was measured to be slightly under 1,400.degree. C. One liter per minute of oxygen was fed to a bubbler to entrain 1.56 liters per minute of silicon tetrachloride therein. One liter per minute of oxygen was fed to the torch for use as a sheath gas about the jet stream. 5.2 liters per minute of oxygen was mixed within the torch with 30 liters per minute of hydrogen to form the combustible gas mixture. After 20 minutes, 55.2 grams of high purity silicon dioxide were deposited upon the mandrel to provide an efficiency of 72 percent. This efficiency is a marked improvement over a torch utilizing the conventional nozzle to provide parallel streams of combustible gas and jet stream of reactant gas.

EXAMPLE 7

The torch described in example 6 was held the same distance from the mandrel and was provided with the same flow of gases thereto, with the exception that 8 liters per minute of oxygen was mixed with 30 liters per minute of hydrogen to provide the combustible gas mixture. A 20 minute deposition of the resulting torch flame provided 60.5 grams of high purity silicon dioxide for an efficiency of 78 percent.

EXAMPLE 8

A torch similar to that described with respect to example 7 was utilized, with the exception that only 0.6 liter per minute of oxygen was provided to the bubbler for entrainment with 2.28 liters per minute of silicon tetrachloride to provide a relatively high 79.2 percent gaseous silicon tetrachloride. A 20 minute deposition with the resulting torch deposited 78 grams of high purity silicon dioxide upon the mandrel for an efficiency of 76 percent.

EXAMPLE 9

This example shows the results obtained with holes at an angle of 5.degree.. A run was made using a torch constructed similar to and employing the same reactants as employed in Example 1 with the following exceptions. The eight cylindrical holes sloped at an angle of 5.degree. toward the longitudinal axis of the torch. The nonrotating graphite mandrel was disposed 41/4 inches from the torch nozzle. The temperature of the flame approximately one-fourth inch from the mandrel was in the range of about 1,400.degree. C. The gaseous silicon tetrachloride was entrained in the oxygen stream at the rate of 1.57 liters per minute per liter of oxygen fed to the torch. The velocity of the gas example stream of gaseous silicon tetrachloride from the torch was about 4.19 feet per minute .times. 10.sup.3. After 20 minutes of deposition by the flame, the actual deposition of silicon dioxide on the graphite mandrel was measured to be 44.9 grams. By comparing this deposition with the theoretical computation of 77.3 grams, an efficiency of 58 percent was computed.

EXAMPLE 10

This example shows the results obtained by employing double angled holes of, respectively, 10.degree. and 5.degree.. The run was made with similar torch construction and the same reactants as employed in example 1 with the differences noted hereinafter. The torch was constructed with the eight cylindrical holes having alternating angles of, respectively, 10.degree. and 5.degree. toward the horizontal axis of the torch for supplying combustible gas through the sheath of oxygen to the gaseous silicon tetrachloride. A nonrotating graphite mandrel was disposed 41/4 inches from the torch nozzle. Gaseous silicon tetrachloride was entrained in the oxygen fed to the torch in the ratio of 1.53 liters per minute per liter of oxygen. The velocity of the gas jet stream of gaseous silicon tetrachloride from the torch was about 4.12 feet per minute .times. 10.sup.3. After 20 minutes of deposition by the flame, the actual deposition of silicon dioxide on the graphite mandrel was measured to be 45.3 grams. By comparing this deposition with the theoretical computation of 75.4 grams, an efficiency of 60 percent was computed.

The present invention thus provides a technique for forming high purity metal oxides upon a mandrel by the vapor phase hydrolysis of a volatile metallic chloride by flame which provides improved deposition efficiency over prior techniques. While the invention has been disclosed with respect to the deposition of high purity silicon dioxide by the decomposition of silicon tetrachloride, it will be understood that other volatile anhydrous chlorides of metallic elements from Groups III and IV of the periodic system, such as for example, titanium tetrachloride, zirconium tetrachloride and the like, could additionally be advantageously utilized with the present invention.

Although the specific embodiments of the present invention have been described in some detail, it will be understood that various modifications and changes will be suggested to one skilled in the art, and it is intended to encompass such modifications and changes which fall within the true scope of the invention as defined in the appended claims.

Claims

I claim:

1. A torch for decomposing a volatile metal chloride by vapor phase hydrolysis to form an oxide article on a surface comprising: a. a torch housing including a passage having a nozzle aperture for providing an output jet stream of the vaporized volatile metal chloride; b. a first chamber defined within said torch for receiving a supply of gas which is relatively inert with respect to said volatile metal chloride, said chamber having an opening adjacent said nozzle aperture for providing a sheath stream of said gas around said jet stream sufficient to prevent residue from being formed on said nozzle aperture when the torch is ignited; and c. a second chamber defined within said torch housing for receiving a supply of combustible gas and including slanted nozzle openings, each alternate nozzle opening having a substantially different slant angle from that of adjacent openings, for directing angled streams of combustible gas through said sheath stream for reaction with said jet stream at a preselected region to provide efficient deposition of said oxide article directly upon said surface.

2. The torch of claim 1 wherein said volatile metal chloride comprises silicon tetrachloride and said combustible gas comprises a mixture of oxygen and hydrogen.

3. The torch of claim 1 wherein said nozzle aperture is circular, said opening in said second chamber is an annular opening concentrically disposed about said nozzle aperture, and said slanted nozzle openings are circular and are disposed symmetrically about said annular opening.

4. The torch of claim 3 and further comprising at least six slanted nozzle openings disposed in a circle about said annular opening, each of said nozzle openings having an area no greater than said nozzle aperture.

5. The torch of claim 1 wherein said slanted nozzle openings slope toward the axis of said jet stream at an angle within the range of 2.degree. to 30.degree..

6. The torch of claim 1 and further comprising a chamber enclosing said second chamber and having inlet and outlet means for circulation of a cooling fluid therethrough.

7. The torch of claim 1 wherein said slanted nozzle openings are defined in nozzle removable from said torch housing.

8. A torch for forming a silica article directly upon a mandrel by hydrolysis of silicon tetrachloride entrained in a carrier gas comprising: a. a torch housing having a central passage therethrough with an inlet for receiving gaseous silicon tetrachloride entrained in a carrier gas and having a nozzle aperture to provide an output jet stream of gaseous silicon tetrachloride entrained in a carrier gas; b. a sheath chamber defined in said torch housing including an inlet for receiving a relatively inert gas and having an annular opening disposed about said nozzle aperture to provide a circular stream of said inert gas around said jet stream; and c. a mixing chamber disposed about said sheath chamber including inlets for combustible gases and a plurality of outlet openings slanted toward the axis of said jet stream, each alternate outlet opening having a substantially different slant angle from that of adjacent openings, to penetrate said circular stream at a selected region for reaction with said jet stream, whereby a silica article may be formed by directly impinging the flame resulting from ignition of said torch on the mandrel.

9. The torch of claim 8 wherein said outlet openings from said mixing chamber slant towards the axis of said jet stream at an angle within the range of 2.degree. to 30.degree..

10. The torch of claim 9 comprising at least six said outlet openings disposed in a circular configuration around said nozzle aperture.