MXPA01001383A - Method and apparatus for forming soot for the manufacture of glass - Google Patents

Abstract

The present invention is directed to a method and apparatus for forming soot used in making glass, and in particular, optical waveguides. A liquid precursor (66) is first fed into orifice (52) of a liquid orifice insert (48) within an injector (44) positioned within an atomizing burner assembly, and is thereafter discharged from the injector into a pressurization chamber (56). An atomization gas (70) is also fed into the pressurization chamber (56) to mix with the liquid precursor liquid stream (68) which breaks into droplets (76). The liquid precursor and atomization gas are forced under pressure out of an atomization orifice (32) on the face of the burner (30) assembly. Flame gas (74), reaction gas (84) and shield gas (82) are ejected from burner orifices (40, 38, 36 and 34) to produce the flame. The atomized liquid precursor thus discharged is fed into the flame (72) produced at the face of the burner assembly where the atomized liquid precursor reacts with the flame to form soot (78) on arotating mandrel (80).

Description

METHOD AND APPARATUS FOR FORMING HOLLIN FOR GLASS MANUFACTURE FIELD OF THE INVENTION The present invention relates to the formation of soot used in the manufacture of glass and, particularly, to a method and apparatus for the supply of liquid precursors to a flame during flame hydrolysis. Although the invention is subject to a wide range of applications of glass soot deposition, it is especially suitable for making soot for use in the manufacture of optical waveguides, and will be especially described in that regard.

BACKGROUND OF THE INVENTION Various methods involving the production of metal oxides from vaporous reagents are known in the art. Such procedures require a solution of supply materials or precursor, a means for generating and transporting vapors from the solution of supply material (hereinafter, so-called vaporous reagents) and an oxidant to a conversion reaction site (also known as a soot reaction zone for those skilled in the art), and a means to catalyze oxidation and combustion at the same time to produce finely divided spherical aggregates, called soot. This soot can be collected at any deposition receiver in any number of ways from a rotating mandrel chamber. The collected soot can be heat treated simultaneously or subsequently to form a transparent and non-porous high purity glass article. Normally, this procedure is performed with specialized equipment that has a unique arrangement of nozzles and burners. Much of the initial research that led to the development of such procedures focused on the production of homogeneous silica. The selection of suitable supply material was an important aspect of this work. Subsequently, at that time it was determined that a material capable of generating a vapor pressure of between 200-300 millimeters of mercury (mm Hg) at temperatures below about 100 ° C would be useful in making said homogeneous silica. The high vapor pressure of silicon tetrachloride (SiCU) suggested its usefulness as a source of steam convenient for soot generation and launched the discovery and use of a series of similar supply materials based on chloride. This factor, more than any other, is responsible for the currently accepted use of SiCU, GeCU, POC and BCI3 as sources of steam supply material. However, the use of these and other halide-based supply materials as sources of steam has its disadvantages. The main disadvantage is the formation of hydrochloric acid (HCl) as a by-product of oxidation. HCl not only deteriorates substrates of deposition and the reaction team, but also the environment. Overcoming this disadvantage, among others, led to the use of halide-free compounds as precursors or supply materials for the production of soot for optical waveguides. Although the use of halide-free silicon compounds as sourcing materials for production of fused silica glass, as described in the U.S. Patents. No. 5,043,002 and 5,152,819, prevents the formation of HCl, other problems continue, particularly when the glass is designed for the formation of optical waveguides and high purity silica soot. It has been found that, during the supply of a vaporized polyalkylsiloxane supply material to the burner, the high molecular weight species can be deposited as gels in the line carrying the vaporous reactants to the burner, or within the same burner. This leads to a reduction in the rate of deposition of the soot which is subsequently consolidated into a preform from which an optical waveguide fiber is stretched. This also leads to imperfections in the preform that often produces defective and / or non-usable optical waveguide fiber from the affected portions of the preform. A further problem encountered in forming silica soot using siloxane sourcing materials is the deposition of particles having high molecular weights and high boiling points in the optical waveguide preform. The composition of these particles results in "defective" or "grouped defect" imperfections that adversely affect the optical quality and structure of optical waveguides formed using silica soot. Usually, the defects are in the form of small bubbles (ie 0.1 to 4.0 mm in diameter) in a glass body. They are often formed in silica fused by an impurity, such as gelled polyalkylsiloxane without burning. A very small particle of siloxane gel may be the site of initiation of such a defect. Because the siloxane decomposes at high temperature after being deposited in the glass body; This can emit gases that causes the formation of the defect. The grouped defects are larger glass defects found in optical waveguide fiber preforms, and often occur as a series of defects in the form of a line or a funnel or flower cluster. Normally, a large gel particle is the initiation site for a pooled defect. After the gel particle has collided with the porous preform, causes a raised area to protrude from the preform surface. Because the grouped defect is a high site, more heat transfer passes to this site. By virtue of this increased heat transfer, more thermophoresis occurs at this site, causing the imperfection to grow and leave behind a chain of defects. As a result of When the defect is grouped, the affected portion of the optical waveguide preform can not be consolidated normally, and the consequent irregularity in the preform produces a defective optical waveguide. For example, in the case of a typical preform of 100 consolidated waveguide fiber kilometers, which has a diameter of 70 millimeters (mm) and a length of the surface of the kilometers of optical waveguide fiber during stretching. In the case of a larger consolidated preform, the negative impact of a single grouped defect is proportionately greater. In a consolidated preform of 250 kilometers, which has a diameter of 90 mm and a length of 1.8 m, a defect grouped in the surface of the preform, will normally result in the loss of 8 kilometers of optical waveguide fiber during stretching. The patent application of E.U.A. Serial No. 08 / 767,653, discloses that pooled defects can be reduced by supplying a liquid siloxane supply material to a conversion site, atomizing the supply material at the conversion site and converting the atomized supply material into silica. at the conversion site. Because the precursors are supplied directly in a burner flame as a liquid instead of a vapor, the vapor pressure of the precursors is no longer a limiting factor in the formation of soot for optical waveguides. However, external atomizers and their methods of use described in the application Serial No. 08 / 767,653 are limited. Normally, external atomizers have a liquid discharge orifice that is coplanar or substantially coplanar with the face of the burner. As a result, the liquid and atomizing gases collect on the surface of the burner. Because the flame is generated adjacent to the face of the burner, atomization must occur very quickly if the liquid will be dispersed in droplets before reaching the flame. For this to occur, very high speeds of the atomizing gas are required. Although these high gas velocities can disperse the liquid into small droplets, they do so by creating turbulence, which in turn, adversely affects the rate of soot deposition. In addition, external atomizers rely on a very small ring of atomizing gas placed around the liquid exit orifice to supply the high velocity atomizing gas that collides with the liquid. As a result, the close proximity of the liquid outlet orifice and the soot reaction zone, causes both the liquid exit orifice and the atomizing gas ring of the external atomizers to be susceptible to soot formation and clogging. When the ring or outlet of the liquid is partially obstructed by this soot formation, the flame, and therefore the soot stream, becomes non-uniform and the rate of soot deposition is affected. Due to the small size of these openings, cleaning the external atomizer is difficult and time-consuming. Moreover, because the burners are turned off during cleaning operations, the production downtime has a significantly adverse economic impact on operations. The external atomizerIn addition, it is expensive to manufacture and limited in flexibility. Because the liquid outlet orifice on the face of the external atomizer burner is generally provided with a cutting edge to facilitate rapid mixing of the atomizing gases and the stream of liquid discharged from the orifice, the day of the liquid outlet orifice it is limited to one dimension which is larger in size than the preferred one. In addition, the liquid outlet orifice must be positioned centrally within the ring to avoid the problem of non-concentricity. Any slight misalignment, and the flame will not be concentric. Non-concentricity results in low soot deposition and is a serious problem during sedimentation. Consequently, the tolerances must be rigorous, which in turn increases manufacturing costs. Therefore, there is a need for alternative methods and apparatus for depositing precursor glass soot, especially for optical fiber and other applications related to waveguides.

BRIEF DESCRIPTION OF THE INVENTION The present invention relates to an improved method and apparatus for supplying a liquid precursor to a burner flame to form soot used in the manufacture of glass. The liquid precursor, capable of being converted into glass by thermal oxidant decomposition, is supplied directly into the flame of a combustion burner, thereby forming finely divided amorphous soot. The amorphous soot is normally deposited on a receiving surface where, either substantially simultaneously with or subsequent to its deposition, the soot is consolidated into a fused glass body. The glass body can then be used to either make products directly from the fused body, or the fused body can be subsequently treated, for example, by forming an optical waveguide such as by stretching to make guide fiber 5 of optical wave as further described in the US patent application No. 08 / 574,961 entitled "Method for Purifying Polyalkylsiloxanes and the Resulting Products", the disclosure of which is incorporated herein by reference. 10 The burner assembly to deliver the precursor directly to the burner flame as an atomized liquid, includes a novel hollow injection orifice that supplies a precision stream of liquid into a chamber where the stream is exposed to an atomizing gas. low speed. The introduction of gas and liquid stream in the chamber, increases the precision within the chamber causing the liquid stream to discharge as an aerosol from an outlet hole in the face of the burner of the atomizer burner assembly, which in the operation, generates a flame of the site Of conversation. The small drops of spray liquid are then fed into the flame to convert the composed by thermal oxidant decomposition in finely divided amorphous soot. Generally, a receiving surface, such as a rotating mandrel, is placed in close proximity to the assembly of ^ ^ 9 -? ^? ^^^? ^^ MltSÍMS ^ í &». JÍ! > A ^ - - - - ^ J 'atomizer burner to allow soot on the receiving surface. The main advantage of the present invention is the provision of an arrangement and method, which substantially reduces the obstruction of the holes in the face of the assembly * the burner by using lower speeds of atomizing gas than other atomizer burner assemblies known in the art. technique, while at the same time, atomize an equivalent liquid flow velocity. By using lower atomizing gas velocities, turbulence in the soot reaction zone is reduced, and thus the rate of soot deposition is greatly improved. In addition, by supplying the precursor to the flame as a liquid and not as a vapor, the gelling of the precursor is prevented since the exposure of the precursor to the high temperature environments of a vaporizer and steam supply system is prevented. This improves the performance and quality of the soot 15 produced and further reduces the maintenance requirements of the production system. In addition, because the precursor does not have to reach the vapor phase before its exposure to the burner flame, the elements never before used to form soot for use in the manufacture of the preforms, can now be converted into soot by oxidation or flame hydrolysis for use in the manufacture of glass preforms, including the elements selected from groups IA, IB, HA, IIB, IIIA, IIIB, IVA, VA, and the series of rare earths of the Periodic Table of Elements. ? ff * N ^ * S ~ s & t fe-jTs «ft39 ¡ás¡ & í £ 8¡í tb &? In another aspect, the invention includes a burner assembly formed from a housing having a burner face with multiple gas orifices and a spray orifice. An injection chamber resides within the housing and a plurality of gas access paths within the housing communicates with the gas orifices. An injector having an injection orifice is positioned within the injection chamber so that the injection orifice is remotely spaced from the atomization orifice. The injector, together with the housing, forms a pressurization chamber within the burner assembly. In another aspect of the present invention, the burner assembly includes an injector constructed and arranged to deliver liquid precursors, and a housing substantially surrounding the injector. The housing has a burner face, which includes a hole edge defining a spray orifice. The orifice edge is configured so that turbulence is reduced as the liquid precursor is discharged from the atomization orifice. Additional features and advantages of the invention are set forth below in the detailed description, and in part will be apparent from the description and claims when read together with the accompanying drawings. Other advantages of the invention will be appreciated and achieved through the method and apparatus particularly pointed out in the written description and claims thereof, as well as in the accompanying drawings. a-tea It will be understood that both the foregoing and the explanatory and general description have the power to provide an additional explanation for the invention, and in no way attempt to limit the invention, which is defined by the appended claims. Moreover, the accompanying drawings are included to provide a further understanding of the invention and are incorporated and constitute a part of this description, illustrate one embodiment of the invention, and together with the description serve to explain the principles of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a block diagram of a reagent delivery system according to the present invention. Figure 2 is a top horizontal projection of a preferred embodiment of the burner assembly of the present invention. Fig. 3 is a side cross-sectional view of the burner assembly of the present invention taken along line 3-3 of Fig. 2. Fig. 4 is a top horizontal projection of a preferred embodiment of the liquid tube of the present invention. Fig. 5 is a side cross-sectional view of the liquid tube of the present invention taken along line 5-5 of Fig. 4; Fig. 6 is a top horizontal projection of a preferred embodiment of the liquid orifice insert; the present invention. Figure 7 is a side cross-sectional view of the orifice insert of the liquid of the present invention taken along line 7-7 of Figure 6. Figure 8 is a schematic representation of drops of liquid precursor that are discharged. in a flame from the outlet orifice of the preferred embodiment of the atomizer burner assembly of the present invention.

Figure 9 is a partial cross-sectional view of a low turbulence embodiment of the rotor assembly of the present invention illustrating the round edge of the hole.

DETAILED DESCRIPTION OF THE INVENTION Reference will now be made in detail to the present preferred embodiment of the invention, an example of which is illustrated in the accompanying drawings, in which like reference characters indicate similar parts in all different views. The atomizer burner assembly and soot-forming method for use in the manufacture of optical waveguides of the present invention form a portion of a larger system as shown in Figure 1. Figure 1 schematically describes an exemplary system for supplying a liquid precursor to an atomizer burner assembly 10 of the present invention. It will be understood by those skilled in the art of optical fibers, that there are other systems and variations of the system described in which, the present invention can be incorporated to perform the functions described and claimed herein. In accordance with one aspect of the present invention, a liquid siloxane precursor such as, for example, a polymethylcyclosiloxane is stored in the precursor tank 12. The precursor tank 12 is in fluid communication with the atomizer burner assembly 10 through of a liquid precursor conveyor conduit system which may, if desired, include a metering pump 14, filter 16 and an optional preheater 18. The siloxane liquid precursor in tank 12 is transferred through the conveyor conduit of liquid precursor by the pump 14 through the filter 16 to the optional preheater 18. The liquid supplied through the filter 16 is under sufficient pressure to prevent and substantially inhibit its volatilization in the preheater 18, which is optionally used to heat the reagent of the liquid before its introduction into the atomizer burner assembly 10, and avoids the high temperatures of a vaporizer, which normally promotes gel formation. Preferably, the burner assembly 10 is provided with an internal protective gas, a reaction gas and a mixture of methane and oxygen for the flame, as described for example, in the patent of E.U.A. No. 4,165,223 for D.R. Powers, whose description is incorporated herein by reference. However, it will be understood that other gases, such as hydrogen may be used in addition to or in place of methane and oxygen, and are often used to support the burner flame. The liquid precursor is conveyed from the filter 16 or optional preheater 18 to the atomizer burner assembly 10, which as the name implies, atomizes the liquid precursor, provides the combustion source and supplies the atomized liquid as an aerosol in the source of combustion, 'which in the preferred embodiment is a flame. Throughout the description, the precursor is described as a "liquid" or as in "liquid form". What he is referring to with these terms is that the precursor is in a * ^^ ii ^^ fe ^ wSsi? ¡^^ j »^ ¿g * ^^ * ^^ i íife» ^^ É & been substantially liquid. Some small portion of the reagent may be in vapor form, particularly when the preheater 14 is used in the system, or when a blanket of nitrogen is used on the liquid. A small portion of the reagent may be in the form of vapor as it is delivered to the combustion site or soot reaction zone without adversely affecting the operation of the invention. Also, the precursor may contain small amounts of solids since the solids are small enough to be burned upon entering the flame produced by the atomizer burner assembly 10. The following are described below. details of the present invention. Different types of atomization nozzles and nozzles capable of forming small droplets of liquid are known in the art of atomization as described in Atomization and Sprays. by Arthur H. Lefebure, Hemisphere Publishing Co., 1989, which is incorporated herein for reference. The atomizers can be operated through different energy sources and can be categorized, for example, as internal, external, by air jet, with the help of air, by jet, by swirling action, by swirling action, tires, rotating, acoustic, ultrasonic, electrostatic, and combinations thereof.

Different types of these and other atomizers are further described in Liquid Atomization. by L. Bayvel and Z. Orzechowski, Taylor & Francis, (1993), which is also incorporated herein as a reference. The assembly of sUéafe-j »- s Áa ?. SB * - Jtí »? ^! S ^ Mlí¿ ^ S ^ aiití ^^^ iß ^ la *? Laeí? £ A3J &S '^. -mwfc- »preferred atomizer burner of the present invention, incorporates in its design an internal air atomizer. The preferred embodiment of the atomizer burner assembly of the present invention is shown in Figures 2 to 8 and is generally designated by the reference number 10. As seen in the top view described in Figure 2, the atomizer burner assembly 10 it includes a housing 20 formed from a cover 22, a sealing plate 24 and a base 26 (figure 3). The cover 22 is mounted to the base 26 with fasteners 28 such as hexanol nuts, so that the sealing plate 24 is interposed therebetween. As shown, the cover 22 is frusto-conical in shape and has a centrally located burner face 30. A plurality of concentric rows of gas holes are positioned on the face of the burner 30, so that its common center corresponds to the location of the hole Attrition 32. The orifices of the internal protection gas 34 form the row closest to the atomization orifice 32, followed by a pair of rows of reaction gas orifices 36 and finally by a row of flame gas orifices 40. It will be understood by those skilled in the art that more or fewer rows of gas orifices may be used to facilitate the present invention. As shown in the cross-sectional view of Figure 3, the gas orifices 34, 36, 38 and 40 communicate with the gas supply lines (not shown) through a network of gas access roads 42, some of which can not be seen in the current view. An injector 44 also forms part of the preferred embodiment of the atomizer burner assembly 10. The injector 44 is centrally located within the injection chamber 46 formed in the inlet 20 of the atomizer burner assembly 10, and when installed within the burner assembly 10, the injector 44 and housing 20 define a pressurization chamber 56 therein. As clearly shown in Figures 4 to 7, the injector 44 includes an elongated liquid tube 45 having a threaded hole 58 (Figures 4 and 5) adapted to movably receive a liquid orifice insert 48 (Figures 6 and 5). 7). As illustrated in figure 4, the circumferential row of atomization gas orifices 54 is positioned around the circumference of and on the head of the injector 44 and surrounds the threaded hole 58. The atomizing gas access paths 60 place the atomization gas orifices 54 in fluid communication with the injection chamber 46, which is atomization gas fed 70 from the gas access path network 42. As illustrated in FIG. 8, the atomization gas 70 is supplied from the gas access paths 60, through the atomization gas orifices 54, to the pressurization chamber 56 wherein the atomizing gas 70 is mixed with a stream of liquid discharged from the injector 44, as will be described in more detail below. Figures 6 and 7 show the detail of the liquid orifice insert 48. Preferably, the liquid orifice insert 48 is threaded to match the threaded hole 58 in the head of the liquid tube 45, and is fitted with the insert of injection port 50 having a precision injection orifice 52. Because it is movable, the insert 50 can be easily changed in the case where it is partially clogged with soot, or if an injection port size is required for other apps. The injection orifice insert 50 is preferably made of a material that can be cut to exacting specifications. In the preferred embodiment of the invention, it has been found that a jewel such as a ruby (Al2 O3) meets this requirement. Typically, the injection orifice insert 50 is cut to provide an injection orifice 52 having a diameter between about 0.002 cm and 0.025 cm. Preferably, the injection orifice 52 has a diameter less than or equal to 0.015 cm. The insert of injection hole model No. RB-22012 manufactured by Bird Precision of Waltham, Massachusetts, meets these requirements, but other injection orifice inserts 50 of other manufacturers can be used. As shown in Figures 3 and 5, the liquid tube 45 has a centrally positioned injector port 62, which communicates with the insert channel 64 when the liquid orifice insert 48 is positioned within the threaded hole 58. In this manner, the liquid precursor 66 of the tank 12 can pass to and through the precision injection port 52. In operation, as shown in FIG. 8, the liquid precursor 66 is supplied through the liquid tube 45, orifice insert Liquid 48, subsequently through the injection port 52, and then in the pressurization chamber 56 as a fine stream of the liquid 68. At the same time, the atomizing gas 70 is supplied through atomization gas access ways. 60 in the pressurization chamber 56. Due largely to j. Ax £ klSk »> ' AO JMM- ». ' part to the toroidal shape of the chamber Sfjg ^ the reduced size of atomization orifice 32 compared to the volume of the chamber 56, the liquid stream 68 is accelerated through the pressurization chamber 56 and is discharged from the atomization orifice 32 like a spray. When atomization occurs, the liquid stream 68 is divided into numerous droplets 76 of extremely small size and is supplied directly as an aerosol to the flame 72 created adjacent to the face of the burner 30 by combustion of the reaction gas 84 supplied through of the reaction gas orifices 36 and 38, and the flame gas 74 is supplied through the flame gas orifices 40. Where the flame 72 and the aerosol come together and react, it is known as the reaction zone of soot. The thermal oxidant decomposition of the aerosol in the soot reaction zone produces finely divided amorphous soot 78, which is deposited on the rotating mandrel 80. The drops 76 are burned in the soot reaction zones on the face of the burner 30 by the flame 72 burned, preferably, by a combination of methane and oxygen. Methane and oxygen form the flame gas 74, which is preferably conducted through the flame gas orifices 40 to the soot reaction zone. A reaction gas 84 such as oxygen is supplied to the soot reaction zone through reaction gas orifices 36 and 38 to provide an oxygen rich environment for the flame 72, and thus, provide better combustion. . A protective gas 82, such as nitrogen, argon, helium or other inert gas, but preferably nitrogen, is supplied through gas orifices of protection 34 for inhibiting the premature reaction of droplets 76 with the flame 72, and thus preventing the formation of soot on the face of the burner 30. The atomization gas 70 may consist of nitrogen, or other inert gases, or mixtures thereof. It is also possible that the atomizing gas 70 is a mixture of elements such as nitrogen and oxygen; however, it has been found that the most preferred gas is only oxygen, since it reduces the formation of defects in the soot preform. An advantage of the preferred embodiment thus configured and operated is that the atomizer burner assembly 10 of the present invention produces a narrower soot stream than the external atomizer burner assemblies currently known in the art. To reduce the velocity of atomizing gas 70 and avoid surface defects in the soot preform, oxygen is the most preferred atomizing gas to be used in atomizer burner assembly 10. Using oxygen as the atomizing gas allows a better precursor mixture of liquids 66 with oxygen before the conversion to soot. The use of this atomizing gas results in a faster heating of liquid and helps provide the oxygen necessary for the reaction. Therefore, the velocity of the oxygen atomizing gas can be significantly decreased, by at least about 50%, compared to the velocity of the atomizing gas when pure nitrogen is used. This reduction in gas velocity consequently reduces the burner flame turbulence and thus the soot preform defects. The The construction and arrangement of the pressurizing chamber S 56 further reduces the speed requirements of the atomization atomizer 70, and thus, the flame turbulence is further reduced. Figure 9 illustrates a preferred design of atomizer burner assembly 10 to reduce the flame turbulence associated with the supply of liquid precursors in a flame. This embodiment of the present invention differs from the embodiment shown in FIG. 8, since the cover portion 22 that houses the liquid orifice insert 48 has a curved or round hole edge 90 that defines and defines the atomization orifice 32. The round hole edge 90 reduces the flame turbulence 94 produced adjacent the burner face 30 and atomization orifice 32, which in turn, facilitates better atomization and reduces soot formation (not shown) on the face of the burner. burner 30. As a result, the seal of the atomization orifice 32 is reduced and thus, the need for frequent cleaning of the burner face. In this way, elements such as potassium and calcium present in certain optical waveguide precursors no longer solidify and deposit on the burner face surface around the atomization orifice 32, as has been found with burner assemblies having a sharp edge, such as that shown in Figure 8. As discussed above, the orifice edge 90 is preferably a non-linear surface and preferably is a round surface. During mounting, the orifice edge 90 is preferably configured to have a radius 92, which is between about 1/4 a i: < i? ru.,?, .jlJi = k afc-aaffi ^ 2/3 of the diameter of atomization orifice 32? Preferably, the radius 92 is about 1/2 of the diameter, of the atomization orifice 32. Accordingly, if the diameter of the atomization orifice 32 is about 0.076 cm, the radius 92 of the orifice edge 90 that defines the 5 spray orifice 32, preferably will be about 0.038 cm. However, it will be understood that round surfaces, unlike semicircular round surfaces, will also reduce flame turbulence 94, and thus also curved round hole edges 90 having non-uniform radial dimensions, are intended to be part of the invention of the burner assembly described herein. The apparatus may also be provided with a dopant supply tank 19, shown in Figure 1, which contains a compound capable of being converted by oxidation or flame hydrolysis, into P2Od or into a metal oxide whose metal component is selected from groups IA, IB, HA, IIB, IIIA, IIIB, IVA, IVB, VA, and the series of rare earths of the Periodic Table. These oxide dopants combine with the soot generated by the burner assembly 10 to provide impurified soot, which can subsequently be formed into optical waveguide fibers. The dopant can be supplied to the precursor tank 12 and mixed with the precursor in the tank 12, or alternatively, the dopant can be supplied from the supply tank 19 to the atomizer burner assembly 10 through a separate metering pump and optionally Ss * ÍÉ »3- ?,« MStsSMé ». v ^^^^ sSeA ^ S ß ^^ - f ^ áJ ^ i-aaM ^. A "f" jwMS-j?! £ a-fa filter (not shown) analogous to the delivery system used for the precursor stored in the precursor tank 12. According to the invention, the precursor containing silicon free of halide, preferably is a polyalkylsiloxane for example, hexamethyldisiloxane. Preferably, the polyalkylsiloxane is a polymethylcyclosiloxane. Preferably, the polymethylcyclosiloxane such as hexamethylcyclotrisiloxane, octamethylcyclotetrasiloxane, decamethylcyclopentasiloxane, dodecamethylcyclohexasiloxane, and mixtures thereof. It will be obvious to the person skilled in the art, that different modifications and variations may be made in the method and apparatus for forming soot for use in the manufacture of optical waveguides of the present invention without departing from the spirit or scope of the invention. Thus, it is intended that the present invention encompass the modification and variations of this invention as long as they fall within the scope of the appended claims and their equivalents. In addition, the corresponding structures, materials, acts and equivalents of all additional means or function elements of steps in the claims below, are intended to include any structure, material or act to perform the functions in combination with other elements claimed according to is specified in this.

Claims (21)

NOVELTY OF THE INVENTION CLAIMS

1. - A method for forming soot for use in the manufacture of glass, said method consists of the steps of: a) supplying a liquid precursor to an injector having a hollow injection orifice within a burner assembly, said burner assembly having an atomization orifice; b) discharging said liquid precursor through the injection port in a chamber defined by said burner assembly and said injector; c) introducing a gas into said chamber to increase the pressure therein; d) discharging said liquid precursor from the atomization orifice as an aerosol; and e) reacting said aerosol in a flame produced by said burner assembly.

2. The method according to claim 1, further comprising the step of adjusting said injector with a movable liquid orifice insert that defines a precision orifice having a diameter less than 0.027 cm.

3. The method according to claim 1, further characterized in that step c) comprises introducing an inert gas into said chamber.

4. - The method according to claim 3, further characterized in that step c) further comprises introducing nitrogen into said chamber.

5. The method according to claim 1, further characterized in that step c) further comprises introducing oxygen into said chamber.

6. The method according to claim 1, further characterized in that said gas consists essentially of oxygen and nitrogen.

7. The method according to claim 1, further characterized in that said liquid precursor comprises a metal.

8. The method according to claim 1, further characterized in that said liquid precursor comprises a siloxane.

9. The method according to claim 8, further characterized in that said siloxane is octamethylcyclotetrasiloxane.

10. The method according to claim 7, further characterized in that said metal comprises a metal selected from groups IA, IB, HA, IIB, IIIA, IIIB, IVA, IVB, VA, and the series of rare earths of the Periodic Table of Elements.

11. A burner assembly for supplying a liquid precursor in a flame as an aerosol to form soot to make optical waveguides, said burner assembly comprising: a housing that '* 3í¿d amM ¡? Ati £ 2.2 *? í ?. i? i '-!,. ¿N¿ü s? ** it! »" I .ti »-fa« .-. { has a burner face which defines a plurality of gas orifices and an atomization orifice, said housing defining an injection chamber and a plurality of gas access paths, the gas access paths being in fluid communication with the orifices of the gas. gas and the injection chamber; and an injector having a first end defining an injection orifice in fluid communication with the liquid precursor, said injector being positioned within the injection chamber and, together with said housing, defining a pressurization chamber wherein the orifice injection is remote from the atomization orifice.

12. The burner assembly according to claim 11, further characterized in that said injector comprises a liquid tube and a liquid orifice insert.

13. The burner assembly according to claim 12, further characterized in that said liquid orifice insert is loosely meshed with said liquid tube.

14. The burner assembly according to claim 12, further characterized in that said liquid tube includes a plurality of atomization gas orifices spaced circumferentially around said liquid orifice insert.

15. The burner assembly according to claim 12, further characterized in that said liquid orifice insert comprises a material defining a precision orifice.

16. - The burner assembly according to claim 15, further characterized in that said material comprises a jewel.

17. The burner assembly according to claim 11, further characterized in that the injection chamber is frustoconical and said atomization orifice is greater than said injection orifice.

18. The burner assembly according to claim 11, further characterized in that the portion of the burner face defining the atomization orifice is configured to reduce turbulence.

19. A burner assembly for the liquid supply of optical waveguide precursors, said burner assembly comprising: an injector constructed and arranged to supply the liquid precursor; and a housing substantially surrounding said injector, said housing having a burner face that includes an orifice edge defining an atomization orifice, the orifice edge being configured so that turbulence is reduced as the liquid precursor is discharged from the atomization orifice.

20. The burner assembly according to claim 19, further characterized in that the orifice edge is round.

21. The burner assembly according to claim 20, further characterized in that the round hole edge has a radius of between about 1/4 to 2/3 of the diameter of the atomization orifice.