Classifications

• • C—CHEMISTRY; METALLURGY
  • C03—GLASS; MINERAL OR SLAG WOOL
  • C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
  • C03B19/00—Other methods of shaping glass
  • C03B19/14—Other methods of shaping glass by gas- or vapour- phase reaction processes
  • C03B19/1415—Reactant delivery systems
  • C03B19/1423—Reactant deposition burners
• • C—CHEMISTRY; METALLURGY
  • C03—GLASS; MINERAL OR SLAG WOOL
  • C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
  • C03B37/00—Manufacture or treatment of flakes, fibres, or filaments from softened glass, minerals, or slags
  • C03B37/01—Manufacture of glass fibres or filaments
  • C03B37/012—Manufacture of preforms for drawing fibres or filaments
  • C03B37/014—Manufacture of preforms for drawing fibres or filaments made entirely or partially by chemical means, e.g. vapour phase deposition of bulk porous glass either by outside vapour deposition [OVD], or by outside vapour phase oxidation [OVPO] or by vapour axial deposition [VAD]
  • C03B37/01413—Reactant delivery systems
  • C03B37/0142—Reactant deposition burners
• • C—CHEMISTRY; METALLURGY
  • C03—GLASS; MINERAL OR SLAG WOOL
  • C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
  • C03B2201/00—Type of glass produced
  • C03B2201/06—Doped silica-based glasses
• • C—CHEMISTRY; METALLURGY
  • C03—GLASS; MINERAL OR SLAG WOOL
  • C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
  • C03B2201/00—Type of glass produced
  • C03B2201/06—Doped silica-based glasses
  • C03B2201/20—Doped silica-based glasses doped with non-metals other than boron or fluorine
  • C03B2201/28—Doped silica-based glasses doped with non-metals other than boron or fluorine doped with phosphorus
• • C—CHEMISTRY; METALLURGY
  • C03—GLASS; MINERAL OR SLAG WOOL
  • C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
  • C03B2201/00—Type of glass produced
  • C03B2201/06—Doped silica-based glasses
  • C03B2201/30—Doped silica-based glasses doped with metals, e.g. Ga, Sn, Sb, Pb or Bi
• • C—CHEMISTRY; METALLURGY
  • C03—GLASS; MINERAL OR SLAG WOOL
  • C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
  • C03B2201/00—Type of glass produced
  • C03B2201/06—Doped silica-based glasses
  • C03B2201/30—Doped silica-based glasses doped with metals, e.g. Ga, Sn, Sb, Pb or Bi
  • C03B2201/34—Doped silica-based glasses doped with metals, e.g. Ga, Sn, Sb, Pb or Bi doped with rare earth metals, i.e. with Sc, Y or lanthanides, e.g. for laser-amplifiers
• • C—CHEMISTRY; METALLURGY
  • C03—GLASS; MINERAL OR SLAG WOOL
  • C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
  • C03B2201/00—Type of glass produced
  • C03B2201/06—Doped silica-based glasses
  • C03B2201/30—Doped silica-based glasses doped with metals, e.g. Ga, Sn, Sb, Pb or Bi
  • C03B2201/40—Doped silica-based glasses doped with metals, e.g. Ga, Sn, Sb, Pb or Bi doped with transition metals other than rare earth metals, e.g. Zr, Nb, Ta or Zn
• • C—CHEMISTRY; METALLURGY
  • C03—GLASS; MINERAL OR SLAG WOOL
  • C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
  • C03B2201/00—Type of glass produced
  • C03B2201/06—Doped silica-based glasses
  • C03B2201/30—Doped silica-based glasses doped with metals, e.g. Ga, Sn, Sb, Pb or Bi
  • C03B2201/50—Doped silica-based glasses doped with metals, e.g. Ga, Sn, Sb, Pb or Bi doped with alkali metals
• • C—CHEMISTRY; METALLURGY
  • C03—GLASS; MINERAL OR SLAG WOOL
  • C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
  • C03B2201/00—Type of glass produced
  • C03B2201/06—Doped silica-based glasses
  • C03B2201/30—Doped silica-based glasses doped with metals, e.g. Ga, Sn, Sb, Pb or Bi
  • C03B2201/54—Doped silica-based glasses doped with metals, e.g. Ga, Sn, Sb, Pb or Bi doped with beryllium, magnesium or alkaline earth metals
• • C—CHEMISTRY; METALLURGY
  • C03—GLASS; MINERAL OR SLAG WOOL
  • C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
  • C03B2207/00—Glass deposition burners
  • C03B2207/04—Multi-nested ports
  • C03B2207/06—Concentric circular ports
• • C—CHEMISTRY; METALLURGY
  • C03—GLASS; MINERAL OR SLAG WOOL
  • C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
  • C03B2207/00—Glass deposition burners
  • C03B2207/04—Multi-nested ports
  • C03B2207/08—Recessed or protruding ports
• • C—CHEMISTRY; METALLURGY
  • C03—GLASS; MINERAL OR SLAG WOOL
  • C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
  • C03B2207/00—Glass deposition burners
  • C03B2207/04—Multi-nested ports
  • C03B2207/12—Nozzle or orifice plates
• • C—CHEMISTRY; METALLURGY
  • C03—GLASS; MINERAL OR SLAG WOOL
  • C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
  • C03B2207/00—Glass deposition burners
  • C03B2207/04—Multi-nested ports
  • C03B2207/14—Tapered or flared nozzles or ports angled to central burner axis
• • C—CHEMISTRY; METALLURGY
  • C03—GLASS; MINERAL OR SLAG WOOL
  • C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
  • C03B2207/00—Glass deposition burners
  • C03B2207/20—Specific substances in specified ports, e.g. all gas flows specified
• • C—CHEMISTRY; METALLURGY
  • C03—GLASS; MINERAL OR SLAG WOOL
  • C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
  • C03B2207/00—Glass deposition burners
  • C03B2207/20—Specific substances in specified ports, e.g. all gas flows specified
  • C03B2207/22—Inert gas details
• • C—CHEMISTRY; METALLURGY
  • C03—GLASS; MINERAL OR SLAG WOOL
  • C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
  • C03B2207/00—Glass deposition burners
  • C03B2207/30—For glass precursor of non-standard type, e.g. solid SiH3F
  • C03B2207/32—Non-halide
• • C—CHEMISTRY; METALLURGY
  • C03—GLASS; MINERAL OR SLAG WOOL
  • C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
  • C03B2207/00—Glass deposition burners
  • C03B2207/30—For glass precursor of non-standard type, e.g. solid SiH3F
  • C03B2207/34—Liquid, e.g. mist or aerosol
• • C—CHEMISTRY; METALLURGY
  • C03—GLASS; MINERAL OR SLAG WOOL
  • C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
  • C03B2207/00—Glass deposition burners
  • C03B2207/42—Assembly details; Material or dimensions of burner; Manifolds or supports
• • C—CHEMISTRY; METALLURGY
  • C03—GLASS; MINERAL OR SLAG WOOL
  • C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
  • C03B2207/00—Glass deposition burners
  • C03B2207/46—Comprising performance enhancing means, e.g. electrostatic charge or built-in heater
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
  • Y02P40/00—Technologies relating to the processing of minerals
  • Y02P40/50—Glass production, e.g. reusing waste heat during processing or shaping
  • Y02P40/57—Improving the yield, e-g- reduction of reject rates

Definitions

• the present invention relates to the formation of soot used in the manufacture of glass and, more particularly, to a method and apparatus for the delivery of liquid precursors to a flame during flame hydrolysis.
• Such processes involve the production of metal oxides from vaporous reactants.
• Such processes require a feedstock solution or precursor, a means of generating and transporting vapors of the feedstock solution (hereafter called vaporous reactants) and an oxidant to a conversion reaction site (also known as a soot reaction zone to those skilled in the art), and a means of catalyzing oxidation and combustion coincidentally to produce finely divided, spherical aggregates, called soot.
• This soot can be collected on any deposition receptor in any number of ways ranging from a collection chamber to a rotating mandrel.
• the collected soot may be simultaneously or subsequently heat treated to form a non-porous, transparent, high purity glass article.
• This process is usually carried out with specialized equipment having a unique arrangement of nozzles and burners.
• HCI hydrochloric acid
• Defects typically are in the form of small (i.e. 0.1 to 4.0 mm in diameter) bubbles in a glass body. They are often formed in fused silica by an impurity, such as uncombusted gelled polyalkylsiloxane. A very small particle of siloxane gel can be the initiation site for such a defect. Since siloxane decomposes at high temperature after being deposited on the glass body; it can give off gases that cause the formation of the defect.
• Clustered 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-shaped cluster. Typically, a large particle of gel is the initiation site for a clustered defect.
• the gel particle After the gel particle has struck the porous preform, it causes a raised area to stand out on the preform surface. Because the clustered defect is a raised site, more heat transfer passes to this site. Due to this increased heat transfer, more thermophoresis occurs at the site, causing the imperfection to grow and leave behind a string of defects. As a result of the clustered defect, the affected portion of the optical waveguide preform cannot be consolidated normally, and the consequent irregularity in the blank yields a defective optical waveguide.
• U.S. Patent Application Serial No. 08/767,653 discloses that clustered defects can be reduced by delivering a liquid siloxane feedstock to a conversion site, atomizing the feedstock at the conversion site, and converting the atomized feedstock at the conversion site into silica. Because the precursors are delivered directly into a burner flame as a liquid rather than a vapor, the vapor pressure of the precursors is no longer a limiting factor in the formation of soot for optical waveguides.
• the external atomizers and their methods of use disclosed in Application Serial No. 08/767,653 are not without limitation. External atomizers typically have a liquid discharge orifice that is co-planer or substantially co-planar with the burner face.
• the liquid and the atomizing gases come together at the surface of the burner. Since the flame is generated adjacent the face of the burner, atomization must occur very quickly if the liquid is to be dispersed into droplets prior to reaching the flame. For this to occur, very high atomizing gas velocities are required. While these high gas velocities can disperse the liquid into small droplets, they do so by creating turbulence, which in turn adversely affects the soot deposition rate. Additionally, external atomizers rely on a very small atomizing gas annulus positioned around the liquid exit orifice to provide the high velocity atomization gas that impinges on the liquid.
• the liquid exit orifice on the burner face of the external atomizer is generally provided with a knife-edge to facilitate rapid mixing of the atomizing gases and the liquid stream discharged from the orifice
• the liquid exit orifice diameter is limited to a dimension which is greater in size than preferred.
• the liquid exit orifice must be centrally positioned within the annulus to avoid the problem of non-concentricity. Any slight misalignment, and the flame will be non-concentric. Non-concentricity results in poor soot deposition and is a serious problem during laydown. Accordingly, tolerances must be tight, which in turn increases manufacturing costs.
• the present invention is directed to an improved method and apparatus for delivering a liquid precursor to a burner flame to form soot used in the manufacture of glass.
• the liquid precursor capable of being converted by thermal oxidative decomposition to glass, is provided and introduced directly into the flame of a combustion burner, thereby forming finely divided amorphous soot.
• the amorphous soot is typically deposited on a receptor surface where, either substantially simultaneously with or subsequent to its deposition, the soot is consolidated into a body of fused glass.
• the body of glass may then be either used to make products directly from the fused body, or the fused body may be further treated, e.g., by forming an optical waveguide such as by drawing to make optical waveguide fiber as further described in U.S. Patent Application No. 08/574,961 entitled, "Method for Purifying Polyalkylsiloxanes and the Resulting Products", the specification of which is hereby incorporated by reference.
• the burner assembly for delivering the precursor directly to the burner flame as an atomized liquid includes a novel recessed injector orifice that delivers a precision stream of liquid into a chamber where the stream is exposed to a low velocity atomizing gas.
• the introduction of the gas and liquid stream into the chamber increases the pressure within the chamber causing the liquid stream to be discharged as an aerosol from an exit orifice at the burner face of the atomizing burner assembly, which, in operation, generates a conversion site flame.
• the small liquid droplets of the aerosol are thus fed into the flame to convert the compound by thermal oxidative decomposition to finely divided amorphous soot.
• a receptor surface such as a rotating mandrel is positioned in close proximity to the atomizing burner assembly to permit deposition of the soot on the receptor surface.
• the principal advantage of the present invention is the provision of an arrangement and method which substantially reduces the clogging of the orifices on the face of the burner assembly by using lower atomizing gas velocities than other atomizing burner assemblies known in the art, while at the same time, atomizing an equivalent liquid flow rate.
• lower atomizing gas velocities By using lower atomizing gas velocities, turbulence is reduced at the soot reaction zone, and thus the soot deposition rate is greatly improved.
• gelling of the precursor is prevented in that exposure of the precursor to the high temperature environments of a vaporizer and vapor delivery system are avoided.
• soot improves the yield and quality of the soot produced and also reduces the maintenance requirements of the production system. Additionally, because the precursor does not have to reach the vapor phase prior to its exposure to the burner flame, elements never before used to form soot for use in the manufacture of the preforms can now be converted by oxidation or flame hydrolysis to soot for use in the manufacture of glass preforms, including elements selected from Groups IA, IB, IIA, IIB, IIIA, IIIB, IVA, VA, and the rare earth series of the Periodic Table of Elements.
• the invention in another aspect, includes a burner assembly formed from a housing having a burner face with multiple gas orifices and an atomization orifice.
• An injector chamber resides within the housing and a plurality of gas passageways within the housing communicate with the gas orifices.
• An injector having an injector orifice is positioned within the injector chamber such that the injector orifice is remotely spaced from the atomization orifice.
• the injector together with the housing, forms a pressurization chamber within the burner assembly.
• the burner assembly includes and injector constructed and arranged to deliver liquid precursors, and a housing substantially surrounding the injector.
• the housing has a burner face, which includes an orifice rim defining an atomization orifice.
• the orifice rim is shaped such that turbulence is reduced as the liquid precursor is discharged from the atomization orifice.
• FIG. 1 is a block diagram of a reactant delivery system in accordance with the present invention.
• FIG. 2 is a top plan view 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 plan view 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 plan view of a preferred embodiment of the liquid orifice insert of the present invention.
• FIG. 7 is a side cross sectional view of the liquid orifice insert of the present invention taken along line 7 — 7 of FIG. 6.
• FIG. 8 is a schematic representation of liquid precursor droplets being discharged into a flame from the exit orifice of the preferred embodiment of the atomizing burner assembly of the present invention.
• FIG. 9 is a partial cross-sectional view of a low turbulence embodiment of the burner assembly of the present invention illustrating the rounded orifice rim.
• FIG. 1 schematically depicts an exemplary system for delivering a liquid precursor to atomizing burner assembly 10 of the present invention. It will be understood by those skilled in the optical fiber art that there are other systems and variations of the depicted system in which the present invention can be incorporated to perform the functions described and claimed herein.
• a liquid siloxane precursor such as, for example, a polymethylcyclosiloxane is stored in precursor tank 12.
• Precursor tank 12 is in fluid communication with atomizing burner assembly 10 via a liquid precursor transporting conduit system that can, if desired, include metering pump 14, filter 16, and optional preheater 18.
• the siloxane liquid precursor from tank 12 is transferred through the liquid precursor-transporting conduit by pump 14 through filter 16 to optional preheater 18.
• the liquid delivered through filter 16 is under sufficient pressure to substantially prevent and inhibit its volatilization in preheater 18, which is optionally employed to warm the liquid reactant prior to its introduction into atomizing burner assembly 10, and avoids the high temperatures of a vaporizer which typically promotes gel formation.
• Burner assembly 10 preferably is provided with an inner shield gas, a reaction gas, and a mixture of methane and oxygen for the flame, as described, for example, in U.S. Patent No. 4,165,223 to D.R. Powers, the specification of which is hereby incorporated by reference. It is to be understood, however, that other gases, such as hydrogen in addition to, or other than methane and oxygen can be and often are used to support the burner flame.
• the liquid precursor is conveyed from filter 16 or optional preheater 18 to the atomizing burner assembly 10, which as the name implies, atomizes the liquid precursor, provides the combustion source, and delivers the atomized liquid as an aerosol into the combustion source, which in the preferred embodiment, is a flame.
• the precursor is described as being a "liquid” or as being in "liquid form”. What is meant by these terms is that the precursor is in a substantially liquid state.
• Some small portion of the reactant may be in vapor form, particularly where preheater 14 is employed in the system, or where a nitrogen blanket over the liquid is employed. A small portion of the reactant can be in vapor form as delivered to the combustion site or soot reaction zone without adversely affecting the operation of the invention.
• the precursor can contain small amounts of solids provided the solids are small enough to be burned upon entering the flame produced by atomizing burner assembly 10.
• the details of the present invention are described below.
• atomizing injectors and nozzles capable of forming small droplets of liquid are known in the atomization art as disclosed in Atomization and Sprays, by Arthur H. Lefebure, Hemisphere Publishing Co., 1989, which is incorporated herein by reference.
• Atomizers can be operated by various energy sources and may be categorized as, for example, internal, external, air-blast, air-assist, jet, swirl, jet-swirl, pneumatic, rotary, acoustic, ultrasonic, electrostatic, and combinations of the same.
• atomizing burner assembly 10 includes a housing 20 formed from a cover 22, a sealing plate 24, and a base 26 (FIG. 3).
• the cover 22 is mounted to the base 26 with fasteners 28 such as hex nuts, such that the sealing plate 24 is interposed therebetween.
• the cover 22 is frustoconical in shape and has a centrally positioned burner face 30.
• a plurality of concentric rows of gas orifices are positioned on burner face 30 such that their common center corresponds to the location of atomization orifice 32.
• Inner shield gas orifices 34 form the row closest atomization orifice 32, followed next 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 greater or fewer rows of gas orifices can be used with and will enable the present invention.
• injector 44 also forms a part of the preferred embodiment of the atomizing burner assembly 10. Injector 44 is centrally positioned within injector chamber 46 formed in housing 20 of atomizing burner assembly 10, and when seated within burner assembly 10, injector 44 and housing 20 define a pressurization chamber 56 therein. As shown clearly in FIGS. 4 through 7, injector 44 includes an elongated liquid tube 45 having a threaded bore 58 (FIGS. 4 and 5) adapted to removably receive a liquid orifice insert 48 (FIGS. 6 and 7).
• circumferential row of atomization gas orifices 54 is positioned around the circumference of and on the head of injector 44 and surrounds threaded bore 58.
• Atomization gas passageways 60 place atomization gas orifices 54 in fluid communication with injector chamber 46 which is fed atomization gas 70 from gas passageway network 42.
• atomization gas 70 is delivered from gas passageways 60, through atomization gas orifices 54, to pressurization chamber 56 where atomization gas 70 mixes with a stream of liquid discharged from injector 44, as will be described in greater detail below.
• FIGS. 6 and 7 show the detail of liquid orifice insert 48.
• Liquid orifice insert 48 is preferably threaded for mating with threaded bore 58 in the head of liquid tube 45, and is fitted with injector orifice insert 50 having a precision injector orifice 52. Because it is removable, insert 50 can easily be changed in the event it becomes partially plugged with soot, or if a different injector orifice size is required or desired for other applications.
• Injector orifice insert 50 is preferably made from 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 (Al 2 0 3 ) meets this requirement.
• injector orifice insert 50 is cut to provide an injector orifice 52 having a diameter of between about 0.001 inches and 0.010 inches.
• injector orifice 52 has a diameter of less than or equal to .006 inches.
• liquid tube 45 has a centrally positioned injector passageway 62 which communicates with insert channel 64 when liquid orifice insert 48 is positioned within threaded bore 58. In this way, liquid precursor 66 from tank 12 can pass to and through precision injector orifice 52. In operation, as shown in FIG.
• liquid precursor 66 is delivered through liquid tube 45, liquid orifice insert 48, subsequently through injector orifice 52, and then into pressurization chamber 56 as a fine stream of liquid 68.
• atomization gas 70 is delivered through atomization gas passageways 60 into pressurization chamber 56. Due in large part to the torroidal shape of chamber 56 and the reduced size of atomization orifice 32 as compared to the volume of chamber 56, liquid stream 68 is accelerated through pressurization chamber 56 and is discharged from atomization orifice 32 as an aerosol.
• liquid stream 68 is ripped into numerous droplets 76 of extremely small size and is directly delivered as an aerosol to flame 72 created adjacent burner face 30 by the combustion of reaction gas 84 delivered through reaction gas orifices 36 and 38, and flame gas 74 delivered through flame gas orifices 40. Where flame 72 and the aerosol meet and react is known as the soot reaction zone. Thermal oxidative decomposition of the aerosol in the soot reaction zone produces finely divided amorphous soot 78, which is deposited on rotatable mandrel 80. Droplets 76 are combusted in the soot reaction zone above burner face
• flame 72 fueled by, preferably, a combination of methane and oxygen.
• the methane and oxygen form the flame gas 74, which is preferably conducted through flame gas orifices 40 to the soot reaction zone.
• a reaction gas 84 such as oxygen is delivered 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 for better combustion.
• a shield gas 82 such as nitrogen, argon, helium or another inert gas, but preferably nitrogen, is delivered through shield gas orifices 34 to inhibit the premature reaction of droplets 76 with flame 72, and thus prevent soot build-up on burner face 30.
• Atomization gas 70 may consist of nitrogen, or other inert gases, or mixtures thereof.
• the atomizing gas 70 is a mixture of elements such as nitrogen and oxygen; however, it has been found that the most preferable gas is oxygen alone, as it reduces the formation of defects in the soot blank.
• oxygen is the most preferred atomizing gas to be used in atomizing burner assembly 10. Using oxygen as the atomizing gas allows for better mixing of liquid precursor 66 with the oxygen before conversion to soot. Use of this atomizing gas results in quicker heating of the liquid and helps provide the oxygen needed for the reaction.
• the velocity of the oxygen atomizing gas can be significantly lowered, at least by about 50%, compared to the velocity of the atomizing gas when pure nitrogen is employed. This reduction in gas velocity consequently reduces burner flame turbulence and thus soot blank defects.
• the construction and arrangement of pressurization chamber 56 further reduces the velocity requirements of atomization gas 70, and thus, flame turbulence is reduced even further.
• FIG. 9 illustrates a preferred atomizing burner assembly 10 design for reducing flame turbulence associated with the delivery of liquid precursors into a flame.
• This embodiment of the present invention differs from the embodiment shown in FIG. 8 in that the portion of cover 22 housing liquid orifice insert 48 has a rounded or curved orifice rim 90 bounding and defining atomization orifice 32.
• Rounded orifice rim 90 reduces flame turbulence 94 produced adjacent burner face 30 and atomization orifice 32, which in turn facilitates better atomization, and reduces soot build up (not shown) on burner face 30. Accordingly, clogging of atomization orifice 32 and thus the need for frequent burner face cleaning are reduced.
• elements such as potassium and calcium present in certain optical waveguide precursors no longer solidify and deposit on the surface of burner face 30 around atomization orifice 32 as has been found with burner assembly's having a knife-edge rim, such as that shown in FIG. 8.
• orifice rim 90 is preferably a non-linear surface and is more preferably a rounded surface.
• orifice rim 90 is preferably shaped to have a radius 92, which is between about 1/4 to 2/3 of the diameter of atomization orifice 32. More preferably, radius 92 is about 1/2 of the diameter of atomization orifice 32. Accordingly, if the atomization orifice 32 diameter is approximately 0.03 inches, the radius 92 of orifice rim 90 defining atomization orifice 32 will preferably be approximately 0.015 inches.
• rounded surfaces other than semi-circular rounded surfaces will also reduce flame turbulence 94, and thus, curved rounded orifice rims 90 having non-uniform radial dimensions are also intended to be a part of the invention of the burner assembly described herein.
• the apparatus can also be provided with dopant supply tank 19, shown in FIG. 1 , which contains a compound capable of being converted by oxidation or flame hydrolysis to P 2 O ⁇ or to a metal oxide whose metallic component is selected from Groups IA, IB, MA, MB, IIIA, IIIB, IVA, IVB, VA, and the rare earth series of the Periodic Table.
• dopant supply tank 19 shown in FIG. 1 , which contains a compound capable of being converted by oxidation or flame hydrolysis to P 2 O ⁇ or to a metal oxide whose metallic component is selected from Groups IA, IB, MA, MB, IIIA, IIIB, IVA, IVB, VA, and the rare earth series of the Periodic Table.
• These oxide dopants combine with the soot generated by burner assembly 10 to provide doped soot, which can be subsequently formed into optical waveguide fibers.
• the dopant can be supplied to precursor tank 12 and mixed with the precursor in tank 12, or alternatively, the dopant can be delivered from supply tank 19 to atomizing burner assembly 10 via a separate metering pump and optionally a filter (not shown) analogous to the delivery system used for the precursor stored in precursor tank 12.
• the preferably halide-free, silicon-containing precursor preferably is a polyalkylsiloxane, for example, hexamethyldisiloxane. More preferably, the polyalkylsiloxane is a polymethylcyclosiloxane. Most preferably, the polymethylcyclosiloxane such as hexamethylcyclotrisiloxane, octamethylcyclotetrasiloxane, decamethylcyclopentasiloxane, dodecamethylcyclohexasiloxane, and mixtures thereof.

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Manufacturing & Machinery (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Organic Chemistry (AREA)
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• Life Sciences & Earth Sciences (AREA)
• Geochemistry & Mineralogy (AREA)
• General Life Sciences & Earth Sciences (AREA)
• General Chemical & Material Sciences (AREA)
• Manufacture, Treatment Of Glass Fibers (AREA)
• Glass Melting And Manufacturing (AREA)
• Gas Burners (AREA)

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• 1999
  • 1999-06-24 ZA ZA9904171A patent/ZA994171B/xx unknown
  • 1999-07-22 BR BR9912802-0A patent/BR9912802A/pt not_active Application Discontinuation
  • 1999-07-22 ID IDW20010543A patent/ID28392A/id unknown
  • 1999-07-22 WO PCT/US1999/016616 patent/WO2000007949A1/en not_active Application Discontinuation
  • 1999-07-22 CA CA002339278A patent/CA2339278A1/en not_active Abandoned
  • 1999-07-22 CN CN99809377A patent/CN1311762A/zh active Pending
  • 1999-07-22 AU AU52233/99A patent/AU759821B2/en not_active Ceased
  • 1999-07-22 EP EP99937392A patent/EP1121332A1/en not_active Withdrawn
  • 1999-07-22 JP JP2000563585A patent/JP2002522333A/ja not_active Withdrawn

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