Abstract:
Burners ( 40 ) for producing fused silica boules are provided. The burners employ a tube-in-tube ( 301-306 ) design with flats ( 56, 50 ) on some of the tubes ( 305, 301 ) being used to limit the cross-sectional area of certain passages ( 206, 202 ) within the burner and/or to atomize a silicon-containing, liquid source material, such as OMCTS. To avoid the possibility of flashback, the burner has separate passages for fuel ( 205 ) and oxygen ( 204, 206 ), i.e., the burner employs nozzle mixing, rather than premixing, of the fuel and oxygen. The burners are installed in burner holes ( 26 ) formed in the crown ( 20 ) of a furnace and form a seal with those holes so that ambient air cannot be entrained into the furnace through the holes. An external air cooled jacket ( 60 ) can be used to hold the temperature of the burner below a prescribed upper limit, e.g., 400° C.

Description:
This application claims the benefit of Provisional application ser. No. 60/095,741 filed Aug. 7, 1998. 
    
    
     U.S. GOVERNMENT RIGHTS 
     The government of the United States of America has rights in this invention pursuant to Subcontract No. B299143 awarded by the Regent of the University of California under prime contract No. W-7405-ENG-48 awarded by the U.S. Department of Energy. 
    
    
     FIELD OF THE INVENTION 
     This invention relates to fused silica glass and, in particular, to burners for producing silica soot from which such glass can be made. As used herein, the term “silica glass” includes glass which is pure or may contain one or more dopants, as does the term “silica soot”. 
     BACKGROUND OF THE INVENTION 
     An effective method for making fused silica glass comprises the steps of: (1) generating silica soot particles using soot producing burners, and (2) collecting and consolidating the particles on a rotating substrate to form a glass “boule”. Such boules can have diameters on the order of five feet (1.5 meters) and thicknesses on the order of 5-10 inches (13-25 cm). The process is typically carried out in a furnace which has a rotatable base, an outer ring wall, and a crown which carries the soot producing burners. 
     FIG. 1 shows the front face  8  of a soot producing burner  7  which has been used in the past to produce fused silica boules. This burner has five zones or regions  10 ,  12 ,  14 ,  16 , and  18  through which gases of different compositions pass to (1) supply the raw material(s) from which the soot particles are produced, and (2) generate a flame of suitable size and temperature to (a) convert the raw material(s) into soot particles and (b) generate sufficient heat to consolidate the particles as they are collected at the surface of the boule. 
     For the burner of FIG. 1, region  10  is referred to as the “fume tube” and carries, for example, a mixture of nitrogen gas and a vaporized silicon-containing compound, regions  12  and  18  are known as the inner and outer shields, respectively, and carry oxygen, and regions  14  and  16  are referred to as the “premix rings” and carry a mixture of fuel (e.g., methane) and oxygen. The diameter of outer shield  18  is typically about 1.1 inches (2.8 cm), while the overall dimensions of front face  8  are typically about 3.4 inches by 3.4 inches (8.5 cm by 8.5 cm). 
     Historically, the vaporized silicon-containing compound supplied to fume tube  10  was silicon tetrachloride or a mixture of silicon tetrachloride and chlorides of other materials, e.g., titanium tetrachloride, when a doped glass was desired. As a result of environmental concerns, silicon tetrachloride has now been replaced with halide-free, silicon-containing compounds, of which octamethylcyclotetrasiloxane (OMCTS) is a particularly preferred example since in addition to providing silicon, it is also provides energy for the burner&#39;s flame. In the same manner, organometallic compounds have been substituted for chloride compounds in the production of doped glasses. 
     FIG. 2 shows the manner in which burners of the type shown in FIG. 1 have been positioned relative to the furnace&#39;s crown  20 . With regard to the present invention, it is significant to note that burner  7  is spaced from the outer face  22  of the crown (the “cold” face of the crown) by gap  24 . This gap, which in practice is about a quarter inch in height, allows air to be inspirated into the furnace so as to cool burner hole  26  and prevent soot buildup on the walls of the hole. The entrained air also ensures that complete combustion of the fuel occurs in burner flame  38 . 
     In addition to illustrating the spatial relationship between burner  7  and crown  2 , FIG. 2 also shows the connection of feed lines  28 ,  30 , and  32  to the burner, as well as lines  34  and  36  which carry cooling water to and from the burner. 
     Although burners and burner/crown configurations of the type shown in FIGS. 1 and 2 have worked successfully in practice, they have had some drawbacks. In particular these burners have suffered from the following problems: 
     (1) Maintenance Problem 
     Because of their relatively large frontal areas exposed to furnace conditions, the previously used burners tend to collect deposits on burner face  8  which must be removed to avoid variations in the burner&#39;s flame characteristics and/or the soot produced by the burner. In particular, large frontal areas make a burner subject to recirculation effects whereby soot which is not deposited on the boule recirculates back and fouls the face of the burner. 
     (2) Water Cooling Problem 
     The large frontal areas of the previously used burners also result in substantial heat transfer from the hot furnace to the burner, thus requiring water cooling of the burners. This is especially so in view of the fact that the burners are made out of aluminum. (It should be noted that the heat transfer occurs both through burner hole  26  and through the crown material itself since the crown is desirably made as thin as possible.) The need for water cooling makes the burners more complex to build and operate. 
     (3) Furnace Atmosphere Control Problem 
     The inspiration of air through the burner holes in the crown makes it more difficult to control the composition of the atmosphere within the furnace. Variations in the furnace atmosphere can result in variations in the properties (e.g., hydrogen content) of the glass boules produced by a furnace, both between different parts of a single boule and between different boules. 
     (4) Emissions Problem 
     The inspiration of air through the burner holes can also result in elevated levels of NO x  in the exhaust gases exiting the furnace since N 2  is the major constituent of the inspirated air and furnace temperatures are high enough for NO x  production, e.g., above 1600° C. 
     (5) Energy Consumption Problem 
     Inspiration of ambient air through the burner holes leads to an increase in the amount of energy which must be inputted to the furnace to keep it at its operating temperature. 
     (6) Potential Safety Problem 
     The feeding of a premix of fuel and oxygen to regions  14  and  16  makes these regions and the feed lines leading thereto susceptible to flame flashback. 
     As discussed below, the burners of the present invention address and provide solutions to each of these problems. 
     DESCRIPTION OF THE PRIOR ART 
     The use of halide-free, silicon-containing compounds to form fused silica glasses by soot deposition is discussed in Dobbins et al., U.S. Pat. No. 5,043,002, and Blackwell et al., U.S. Pat. No. 5,152,819. The incorporation of a dopant, specifically, titanium, in such glasses is discussed in Blackwell et al., U.S. Pat. No. 5,154,744. The contents of these prior patents are incorporated herein by reference. 
     PCT Patent Publication No. WO 97/22553, published on Jun. 26, 1997, discloses soot producing burners which can be used with halide-free, silicon-containing compounds such as octamethylcyclotetrasiloxane (OMCTS). The halide-free, silicon-containing compound is preferably provided to the burner as a liquid, atomized in the burner by an integral atomizer, and then directly converted into soot particles by the burner&#39;s flame. See also pending U.S. applications Ser. No. 08/767,653 and Ser. No. 08/903,501, filed Dec. 17, 1996 and Jul. 30, 1997, respectively, the contents of both of which are incorporated herein by reference. 
     Miller et al., U.S. Pat. No. 5,110,335 discloses a burner for producing soot from silicon tetrachloride which includes an ultrasonic nozzle which when operated at a frequency of 120 kilohertz converts liquid silicon tetrachloride into a fine mist. 
     Brown et al., U.S. Pat. No. 5,092,760 discloses an oxygen/fuel burner which atomizes liquid fuel by means of an integral atomizer. Brown et al., U.S. Pat. Nos. 5,405,082 and 5,560,758, disclose oxygen/fuel burners for use in glass conditioning. These burners employ a tube-in-tube construction and, during use, are sealed to the wall of a glass distribution channel. Brown et al., U.S. Pat. No. 4,986,748 discloses a further construction for an oxygen/fuel burner. Significantly, with regard to the present invention, the burners of these various Brown et al. patents are concerned with heat production, not with the production of silica soot. Among other things, such heat producing burners do not have to be concerned with soot build-up on the burner face or with the adverse effects of the burner&#39;s internal operating temperature on the heat-sensitive raw material(s) used to produce silica soot. 
     SUMMARY OF THE INVENTION 
     In view of the foregoing, it is an object of the present invention to provide improved burners for producing silica soot. More particularly, it is an object of the invention to provide improved burners which overcome some and preferably all of the above problems of previously used soot producing burners. 
     The invention achieves these and other objects by providing soot producing burners and furnaces employing such burners which have some or all of the following properties: 
     (1) The burner uses a tube-in-tube design so as to reduce the frontal area of the burner and thus minimize the soot build-up problem. For example, the frontal area of a burner constructed in accordance with the invention can be about 0.32 square inches (2.1 square centimeters) whereas burners of the type shown in FIGS. 1 and 2 had frontal areas of about 1.8 square inches (11.4 square centimeters). 
     The tube-in-tube design produces a plurality of passages for carrying liquid and/or gaseous materials, namely, a first passage constituting the bore of the innermost (first) tube, a second passage defined by the outer surface of the first tube and the inner surface of the next innermost (second) tube (the first pair of tubes), a third passage defined by the outer surface of the second tube and the inner surface of the third tube (the second pair of tubes), and so on. In this way, “n” tubes define “n” passages. 
     Not all passages need extend throughout the entire length of the burner. For example, as discussed below, the first tube may end prior to the face of the burner, whereupon the contents of the first passage merge with the contents of the second passage. The innermost passage at the face of the burner is then defined by the inner surface of the second tube, rather than the inner surface of the first tube. 
     (2) To provide a focused, relatively uniform flow pattern, one or more of the passages produced by the tube-in-tube design can include flats in, for example, the vicinity of the burner&#39;s face which serve to guide the flow of gas out of the burner. These flats can be oriented at an angle with respect to the burner&#39;s face, e.g., at an angle of approximately 75 degrees with respect to the burner&#39;s axis (see FIG.  4 ). The flats are preferably formed on the outer surface of the inner tube of the pair of tubes which defines the passage. Alternatively, although less preferred for manufacturing reasons, the flats can be formed on the inner surface of the outer tube of the pair of tubes which defines the passage. It should be noted that in either case, sizing the tubes so that they make contact at the corners of the flats in the case of flats on the inner tube or at the centers of flats in the case of flats on the outer tube results in a passage of limited cross-sectional area. This contacting also aids in centering the inner tube within the bore of the outer tube. 
     (3) Flats can also serve to atomize a liquid raw material, e.g., liquid OMCTS or a mixture of liquid OMCTS and one or more liquid dopants. In particular, in accordance with these aspects of the invention, the liquid raw material is subjected to shear forces as it passes through a restriction zone formed by flats. Preferably, the passage which carries the liquid raw material has a cross-sectional area which decreases as the raw material approaches the restriction zone and a cross-sectional area which increases after the raw material has passed through the restriction zone. Such changes in cross-sectional areas can be achieved by, for example, tapering one or both of the tube surfaces which define the passage. In addition to the restriction zone, the passage carrying the liquid raw material preferably merges with a passage carrying gas, e.g., a passage carrying oxygen, downstream of the restriction zone to further enhance the atomization of the liquid raw material. 
     In comparison to orifices, flats have the advantage of being able to achieve atomization for low flow rates of a liquid raw material, e.g., flow rates less than about 10 grams/minute. 
     (4) To minimize soot deposition on the face of the burner, it has been found that the passage which provides soot producing raw material(s) to the burner flame needs to extend beyond the face of the burner. Preferably, this passage is the center passage of the burner and the passages surrounding the center passage, which carry fuel and oxygen, are angled towards the center passage to further reduce soot build up on the burner face. 
     (5) The burners are sealed to the crown of the furnace so as to substantially completely eliminate inspiration of air into the furnace at the locations of the burners. Preferably, inspiration is completely eliminated although in some cases, minor amounts of leakage of air at the crown/burner interface can be tolerated without encountering the various problems discussed above which result from large amounts of air passing through a burner hole. 
     (6) Cooling of such sealed burners is accomplished by the flow of gases through the burner. In particular, oxygen is flowed through the outermost passage of the burner where the greatest amount of heat transfer from the crown occurs. In addition, the burner can be equipped with an external air cooled jacket to further reduce its internal operating temperature. 
     (7) The burner has completely separate passages for fuel (e.g., methane, natural gas, hydrogen, etc.) and oxygen so that the mixing of fuel and oxygen does not occur until after these materials have exited the burner face, thus eliminating the possibility of flashback. That is, the burner of the invention uses “nozzle mixing” of the fuel and oxygen rather than “premixing” of these materials. 
     By means of these features, the invention provides improved burners which are economical to build, use, and service, and which allow for more efficient and controlled production of fused silica boules. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic drawing of the front face of a prior art burner for producing silica soot. 
     FIG. 2 is a schematic side view of a prior art burner showing the spaced relationship between the burner and the furnace crown. 
     FIG. 3 is a schematic side view of a burner constructed in accordance with the present invention showing the sealed relationship between the burner and the furnace crown. 
     FIG. 4 is a cross-sectional view of a first embodiment of the nozzle portion of the burner of FIG.  3 . 
     FIG. 4A shows the face of the burner of FIG.  4 . 
     FIG. 5 is a cross-sectional view of the manifold portion of the burner of FIG.  3 . 
     FIG. 6 is a cross-sectional view of an internal atomizer constructed in accordance with the invention. 
     FIG. 7 is a cross-sectional view along lines  7 — 7  in FIG.  6 . 
     FIG. 8 is a cross-sectional view along lines  8 — 8  in FIG.  6 . 
     FIG. 9 is a cross-sectional view along lines  9 — 9  in FIG.  6 . 
     FIG. 10 is a cross-sectional view of a second embodiment of the nozzle portion of the burner of FIG.  3 . 
     FIG. 10A shows the face of the burner of FIG.  10 . 
     FIG. 11 is a cross-sectional view of a third embodiment of the nozzle portion of the burner of FIG.  3 . 
     FIG. 12 is a schematic diagram illustrating the use of an air cooled jacket to reduce the burner&#39;s internal operating temperature. 
     FIG. 13 is a cross-sectional view of an alternate internal atomizer constructed in accordance with the invention. 
     FIG. 14 is a cross-sectional view along lines  14 — 14  in FIG.  13 . 
    
    
     The foregoing drawings, which are incorporated in and constitute part of the specification, illustrate the preferred embodiments of the invention, and together with the description, serve to explain the principles of the invention. It is to be understood, of course, that both the drawings and the description are explanatory only and are not restrictive of the invention. 
     The reference numbers used in the drawings correspond to the following: 
     
       
         
               
               
             
           
               
                   
               
             
             
               
                  1-6 
                 flow arrows 
               
               
                  7 
                 previously used soot producing burner 
               
               
                  8 
                 front face of previously used soot producing burner 
               
               
                  10 
                 fume tube of previously used soot producing burner 
               
               
                  12 
                 inner shield of previously used soot producing burner 
               
               
                  14 
                 premix ring of previously used soot producing burner 
               
               
                  16 
                 premix ring of previously used soot producing burner 
               
               
                  18 
                 outer shield of previously used soot producing burner 
               
               
                  20 
                 furnace crown 
               
               
                  22 
                 outer face of furnace crown 
               
               
                  24 
                 gap between previously used soot producing burner and 
               
               
                   
                 furnace crown 
               
               
                  26 
                 burner hole 
               
               
                  28 
                 feed line 
               
               
                  30 
                 feed line 
               
               
                  32 
                 feed line 
               
               
                  34 
                 line for cooling water 
               
               
                  36 
                 line for cooling water 
               
               
                  38 
                 burner flame 
               
               
                  40 
                 burner of present invention 
               
               
                  42 
                 manifold portion of burner 40 
               
               
                  44 
                 nozzle portion of burner 40 
               
               
                  46 
                 chamfered surface of nozzle 44 
               
               
                  48 
                 restriction zone 
               
               
                  50 
                 flats on tube 301 
               
               
                  52 
                 spaces formed by flats 50 
               
               
                  54 
                 restriction rod 
               
               
                  56 
                 flats on tube 305 
               
               
                  58 
                 spaces formed by flats 56 
               
               
                  60 
                 air cooled jacket 
               
               
                  62 
                 air inlet of air cooled jacket 
               
               
                  64 
                 air outlet of air cooled jacket 
               
               
                  66 
                 internal plenum of air cooled jacket 
               
               
                  68 
                 external plenum of air cooled jacket 
               
               
                  70 
                 air flow arrow 
               
               
                  72 
                 annular ring for atomization 
               
               
                  74 
                 burner axis 
               
               
                 101-106 
                 entrance ports 
               
               
                 201-206 
                 passages 
               
               
                 301-306 
                 tubes 
               
               
                 403-406 
                 drilled apertures 
               
               
                   
               
             
          
         
       
     
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     As discussed above, the present invention relates to improved burners for use in producing fused silica boules. FIG. 3 is a schematic drawing showing the overall construction of such a burner. As shown therein, burner  40  includes manifold portion  42  and nozzle portion  44 . The nozzle portion forms a seal with crown  20  at chamfered surface  46 . 
     Manifold portion  42  has six entrance ports for receiving processing gases, fuel, and the raw material(s) which forms the soot. As shown in FIG. 5, the burner includes six tubes which by means of the tube-in-tube construction form six passages for carrying the gases, fuels, and raw materials (collectively, the “source materials”). Table 1 sets forth the correspondence between the source materials, the entrance ports, the passages, and the tubes. 
     FIGS. 6-9 illustrate the use of a restriction zone  48  formed by flats  50  on the outer surface of tube  301  to apply shear to the liquid raw material flowing in passage  202 . For OMCTS, the spaces  52  between the outer surface of tube  301  and the inner surface of tube  302  at the restriction zone can, for example, have a maximum thickness of 0.005 inches (0.13 millimeters). All other dimensions being held constant, the use of more or less flats will respectively decrease or increase this maximum thickness. Using routine experimentation, persons skilled in the art can readily determine a suitable number of flats for any particular application of the invention. 
     As also shown in FIGS. 6-9, the cross-sectional area of passage  202  decreases as the liquid raw material approaches the restriction zone and then increases after the raw material has passed through the restriction zone. As shown in FIG. 6, these decreases and increases in cross-sectional area can be achieved by providing the outer surface of tube  301  and the inner surface of tube  302  with tapers which begin at different locations and have different taper angles. For example, the outer surface of tube  301  can begin tapering closer to the face of the burner and can have a taper angle of, for example, 5° while the inner surface of tube  302  can begin tapering farther from the burner face and can have a taper angle of, for example, 3½°. In this way, these surfaces converge before the restriction zone and diverge after that zone. Other taper configurations can, of course, be used in the practice of the invention. For example, the outer surface of tube  301  can have a taper angle of 4° when used with the embodiment of FIG.  11 . 
     FIGS. 6-9 also illustrate (1) the merger of passage  202  with passage  201  downstream of the restriction zone and (2) the use of a restriction rod  54  to reduce the cross-sectional area of passage  202  after the merger and to also reduce the cross-sectional area of passage  201  prior to the merger. The use of this restriction rod in combination with the merger of passage  201  with passage  202  further enhance the atomization of the liquid raw material. In particular, the merger and the restriction rod enhance atomization through the application of relatively high pressure  02  to the droplets of liquid raw material created at the restriction zone. 
     Other configurations for restriction zone  48  include the following: 
     (1) Rather than using flats  50 , tube  301  can be positioned relative to tube  302  to form a thin annular ring which serves to atomize the liquid raw material. This approach is illustrated in FIGS. 13 and 14, where the annular ring is identified in FIG. 14 by the reference number  72 . A suitable thickness for such an annular ring is approximately 0.004 inches (0.1 millimeters). Such a thickness can be readily achieved by retracting tube  301  relative to tube  302  by about {fraction (3/64)} of an inch (1.2 millimeters). 
     (2) The passages which carry the liquid raw material and the atomizing oxygen can be reversed, e.g., passage  201  can carry the liquid raw material and passage  202  can carry the oxygen. In this case, flats  50  serve to reduce the cross-sectional area of passage  202  and, along with the taper on the inner surface of tube  302 , serve to guide the oxygen into the stream of liquid raw material so as to break the stream into droplets. 
     (3) Variations (1) and (2) can be combined, i.e., the flats can be removed and the passages which carry the liquid raw material and the atomizing oxygen can be reversed. 
     FIGS. 4 and 4A show the nozzle portion of burner  40  downstream of restriction zone  48 . To reduce the cross-sectional area of passage  206 , tube  305  includes flats  56 . The spaces  58  between the outer surface of tube  305  and the inner surface of tube  306  formed by these flats can, for example, have a maximum thickness of 0.01 inches (0.25 millimeters). As with flats  50 , the use of more or less flats will respectively decrease or increase this maximum thickness. Using routine experimentation, persons skilled in the art will readily be able to determine a suitable number of flats for any particular application of the invention. 
     FIGS. 10 and 10A show a variation of FIGS. 4 and 4A wherein passage  203  has been omitted. Corresponding changes are made to the manifold portion of the burner (not shown). 
     FIG. 11 shows a further variation in which passage  202  extends beyond the face of the burner and passages  203 ,  204 ,  205 , and  206  are angled towards passage  202  to fully develop (streamline) the gas flows exiting the burner face and thus improve the burner&#39;s flame characteristics. The amount of extension of passage  202  beyond the face of the burner will depend upon the particular application of the invention. In general, this extension will be about 0.25 inches (6.4 millimeters). 
     As can be seen in FIG. 11, passage  204  narrows as it approaches the face of the burner, while passage  205  widens. The inclination of the inner and outer surfaces of tubes  302 ,  303 ,  304 ,  305 , and  306  relative to the burner&#39;s axis is set forth in Table 2. The values given in this table are for natural gas as the fuel and OMCTS as the silicon-containing raw material. Different angles may be required for other fuels and source materials. Based on the disclosure herein, the particular angles and dimensions to be used for any particular application of the invention can be readily determined by those skilled in the art using routine experimentation. 
     FIG. 11 also illustrates the use of drilled apertures  403 ,  404 ,  405 , and  406  to form portions of passages  203 ,  204 ,  205 , and  206 , respectively. These apertures facilitate the manufacture of the various tubes making up the burner through a combination of drilling the apertures and machining the tube surfaces to achieve the desired part configurations. 
     Although not shown in FIG. 11, the atomization apparatus of FIGS. 6-9 or the variations thereof discussed above can be incorporated in this burner in the same manner as it is incorporated in the burners of FIGS. 4 and 10. On the other hand, the burner of FIG. 11, as well as those of FIGS. 4 and 10, can be used without an internal atomizer. In such a case, the soot producing material, e.g., OMCTS, is provided to entrance port  102  in vaporized form, optionally mixed with, for example, nitrogen, from which it passes to the face of the burner through passage  202 . Entrance port  101  and tube  301  are then not included as part of the burner. 
     FIG. 12 illustrates the use of an external air cooled jacket  60  for providing additional cooling to the burner in cases where the internal flow of gases through the burner is not sufficient to keep the burner&#39;s internal operating temperature at a desired value. Air cooled jacket  60  has an air inlet  62  which is connected to an internal plenum  66 . It also has a series of air outlets  64  which are connected to external plenum  68 . The cross-sectional area of the external plenum is preferably greater than the cross-sectional area of the internal plenum to accommodate the increase in volume of the cooling air as it is heated by contact with the outer surface of tube  306 . 
     FIG. 12 also illustrates the mating of the burner of FIG. 11 with the furnace&#39;s crown. Since the front end of the nozzle of this burner is already slanted, a chamfer is not required to provide a suitable surface for sealing engagement with burner hole  26 . It should be noted that the burner of FIGS. 11 and 12, as well as those of FIGS. 4 and 10, are self-aligning with respect to burner hole  26 . This feature provides more efficient furnace assembly compared to the prior art burner of FIGS. 1 and 2 which had to be aligned with the burner hole. Also, impingement of the burner flame on the walls of the burner hole is less likely with the burners of the invention than with the previously used burners. 
     The burner of FIGS. 11 and 12 was tested using the flow rates and source material temperatures set forth in Table 3. Room temperature air was supplied to air cooled jacket  60  at a rate of 15 cubic feet per hour. A thermocouple was mounted to the face of tube  306  and recorded temperatures in the range of 350-400° C. during operation of the burner. These temperatures are well within the operating range of a burner constructed of, for example, stainless steel and are suitable for use with OMCTS as the liquid raw material. With tube  302  extending beyond the face of the burner and with  0   2  flowing in passage  203 , essentially no build up of soot on the face of the burner was observed. Soot build up, however, was observed when either of these preferred features of the burner was omitted. 
     A glass boule was prepared using vaporized OMCTS in a nitrogen carrier and the apparatus of FIGS. 11 and 12. The flow rates used are shown in Table 4. The burner was found to work successfully in all respects and to produce high quality glass. 
     Various materials can be used to construct the burners of the present invention. For example, manifold  42  can be constructed of aluminum, tube  306  of FIGS. 4 and 10 can be made of a refractory material, e.g., alumina, tube  306  of FIGS. 11 and 12 can be made of stainless steel, and all other tubes can likewise be made of stainless steel. Other materials can, of course, be used in the practice of the invention. 
     Although preferred and other embodiments of the invention have been described herein, further embodiments may be perceived by those skilled in the art without departing from the scope of the invention as defined by the following claims. 
     
       
         
               
               
               
               
               
               
             
           
               
                 TABLE 1 
               
               
                   
               
               
                   
                   
                   
                   
                 Passage 
                   
               
               
                   
                   
                   
                   
                 Cross- 
               
               
                   
                   
                   
                   
                 Sectional 
                 Tubes Which 
               
               
                 Source 
                 Flow 
                 Entrance 
                   
                 Area in 
                 Define 
               
               
                 Material 
                 Arrow 
                 Port 
                 Passage 
                 inches 2  (cm 2 ) 1   
                 Passage 
               
               
                   
               
             
             
               
                 O 2   
                 1 
                 101 
                 201 
                 0.0034 (0.02) 
                 Inner surface 
               
               
                   
                   
                   
                   
                   
                 of 301. 
               
               
                 Liquid 
                 2 
                 102 
                 202 
                 0.0034 (0.02) 
                 Inner surface 
               
               
                 raw 
                   
                   
                   
                   
                 of 302 and 
               
               
                 material, 
                   
                   
                   
                   
                 outer surface 
               
               
                 e.g., 
                   
                   
                   
                   
                 of 301. 
               
               
                 OMCTS 
               
               
                 O 2  or an 
                 3 
                 103 
                 203 
                  0.015 (0.09) 
                 Inner surface 
               
               
                 inert gas, 
                   
                   
                   
                   
                 of 303 and 
               
               
                 e.g., 
                   
                   
                   
                   
                 outer surface 
               
               
                 argon 2   
                   
                   
                   
                   
                 of 302. 
               
               
                 O 2   
                 4 
                 104 
                 204 
                  0.037 (0.24) 
                 Inner surface 
               
               
                   
                   
                   
                   
                   
                 of 304 and 
               
               
                   
                   
                   
                   
                   
                 outer surface 
               
               
                   
                   
                   
                   
                   
                 of 303. 
               
               
                 Fuel, 
                 5 
                 105 
                 205 
                  0.05 (0.32) 
                 Inner surface 
               
               
                 e.g., 
                   
                   
                   
                   
                 of 305 and 
               
               
                 natural 
                   
                   
                   
                   
                 outer surface 
               
               
                 gas, 
                   
                   
                   
                   
                 of 304. 
               
               
                 methane, 
               
               
                 or 
               
               
                 hydrogen 3   
               
               
                 O 2   
                 6 
                 106 
                 206 
                  0.098 (0.63) 
                 Inner surface 
               
               
                   
                   
                   
                   
                   
                 of 306 and 
               
               
                   
                   
                   
                   
                   
                 outer surface 
               
               
                   
                   
                   
                   
                   
                 of 305. 
               
               
                   
               
             
          
         
       
     
       1 The values for cross-sectional area are calculated at the burner face except for passage  201  where the cross-sectional area is calculated at lines  8 — 8  or  9 — 9  in FIG.  6 . The cross-sectional area of passage  202  represents the area with restriction rod  54  in place, i.e., it represents the cross-sectional area at lines  7 — 7  in FIG. 6.  
       2 The use of an inert gas as flow  3  tends to delay combustion and thus move the burner&#39;s flame away from the burner&#39;s face which may be advantageous for some applications.  
       3 The cross-sectional area of passage  205  is adjusted depending on which fuel is used. In particular, hydrogen requires a larger cross sectional area than methane or natural gas, e.g., twice the cross-sectional area.  
     
       
         
               
               
               
             
           
               
                   
                 TABLE 2 
               
               
                   
                   
               
               
                   
                 Surface 
                 Inclination Angle α 1   
               
               
                   
                   
               
             
             
               
                   
                 Inner surface of tube 302 
                 3.5° to the right of the burner face; 
               
               
                   
                   
                 0° to the left of the burner face. 
               
               
                   
                 Outer surface of tube 302 
                   4° 
               
               
                   
                 Inner surface of tube 303 
                   4° 
               
               
                   
                 Outer surface of tube 303 
                 6.5° 
               
               
                   
                 Inner surface of tube 304 
                   8° 
               
               
                   
                 Outer surface of tube 304 
                  10° 
               
               
                   
                 Inner surface of tube 305 
                   8° 
               
               
                   
                 Outer surface of tube 305 
                  10° 
               
               
                   
                 Inner surface of tube 306 
                  10° 
               
               
                   
                 Outer surface of tube 306 
                  15° 
               
               
                   
                   
               
               
                   
                   1 Measured with respect to the burner&#39;s axis 74 shown in FIG. 11. The angle α equals 90° minus the angle β shown in FIG. 11.  
               
             
          
         
       
     
     
       
         
               
               
               
               
             
           
               
                 TABLE 3 
               
               
                   
               
               
                   
                   
                 Source Material 
                 Source Material 
               
               
                 Source Material 
                 Passage 
                 Flow Rate 
                 Temperature (° C.) 
               
               
                   
               
             
             
               
                 O 2   
                 201 
                   7 slpm 
                 15 
               
               
                 OMCTS 
                 202 
                 6.5 g/min 
                 15 
               
               
                 O 2   
                 203 
                  10 slpm 
                 15 
               
               
                 O 2   
                 204 
                  20 slpm 
                 15 
               
               
                 Natural Gas 
                 205 
                  20 slpm 
                 15 
               
               
                 O 2   
                 206 
                  20 slpm 
                 15 
               
               
                   
               
             
          
         
       
     
     
       
         
               
               
               
               
             
               
               
               
               
             
           
               
                 TABLE 4 
               
               
                   
               
               
                   
                   
                 Source Material 
                 Source Material 
               
               
                 Source Material 
                 Passage 
                 Flow Rate 
                 Temperature (° C.) 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 OMCTS 
                 202 
                 6.5 g/min 
                 175 
               
               
                 N 2   
                 202 
                   5 slpm 
                 175 
               
               
                 O 2   
                 203 
                  10 slpm 
                 15 
               
               
                 O 2   
                 204 
                  20 slpm 
                 15 
               
               
                 Natural Gas 
                 205 
                  20 slpm 
                 15 
               
               
                 O 2   
                 206 
                  20 slpm 
                 15