KR20030005387A - Method of making a titania-doped fused silica preform - Google Patents

Abstract

Titania-doped method for gasifying the liquid TiO ₂ precursor is used to manufacture a fused silica Mi Heng is substantially thermally decomposing the packing liquid TiO ₂ precursor with a carrier gas under conditions sufficient to vaporize the TiO ₂ precursor with no-bed vaporizer Passing through. In addition, the method includes mixing the vaporized TiO ₂ precursor with a vaporized SiO ₂ precursor and conveying the mixture to a vaporization utilization to form the preform. In one embodiment of the present invention, the liquid TiO ₂ and SiO ₂ precursors are simultaneously vaporized in a vaporizer and carried to a vaporization utility to form a preform.

Description

Method of making a titania-doped fused silica preform

Halogenated SiO ₂ precursors are vapor phase deposition, such as modified chemical vapor deposition (MCVD), vapor axial deposition (VAD) and outside vapor deposition (OVD). Has been used in preform manufacturing. In the MCVD, SiO ₂ precursors vaporize to produce oxide particles that react with oxygen to deposit in the fused silica tube. In the VAD and OVD processes, gaseous SiO ₂ precursors are hydrolyzed in the burner and stacked on a rotating maneuvering rod (on bait tube) for VAD or on a rotating mandrel (for OVD). Generate Particles In some OVD systems, the cladding portion of the preform is deposited on the pre-generated preform rather than the mandrel.

Various vaporizers utilized in such a process include US Patent No. 4,212,663 to Asami, US Patent No. 4,314,837 to Blankenship, US Patent No. 4,529,427 to French, Tsuchiya, etc. U.S. Patent No. 4,938,789, Antos et al., U.S. Patent No. 5,078,092, Japanese Patent Application Laid-Open No. 58-125633, and U.S. Patent Nos. 1,559,987, Soubeyrand. Disclosed is the use of a horizontal thin film used for the vaporization of various raw materials in the manufacture of glass particles coated in 5,090,985. None of these systems utilize the specific outflow vaporization system that vaporizes the pyrolytic TiO ₂ precursor used in the present invention.

Optical fibers having at least one outer layer doped with titania exhibit superior strength and ultra low expansion properties compared to homogeneous silica clad fibers. For example, Nordberg, US Pat. No. 2,326,059, discloses a process for producing a large amount of silica, ultra low expansion glass by vaporizing tetrachlorides of Si and Ti into a gas stream of an oxy-gas burner. US Pat. No. 4,501,602 to Miller et al. Discloses a gas phase oxidation process of beta-diketonate composites of metals selected from the IA, IB, IIA, IIB, IIIA, IIIB, IVA, IVB, VA groups, and rare earths of the periodic table. It describes the production of glass and glass / ceramic particles utilized.

However, halogenated SiO ₂ and TiO ₂ precursors produce halogenated byproducts such as halogenated acids (eg hydrochloric acid). These halogenated byproducts are a source of environmental pollution and require recovery and environmentally safe treatment. As a solution to environmental problems, non-halogenated SiO ₂ and TiO ₂ precursors are used as starting materials for preliminary production.

For example, US Pat. No. 5,043,002 to Dobbins et al. Discloses non-halogenated SiO ₂ such as polymethylsiloxane, more preferably polymethylcyclosiloxane, and particularly preferably octamethylcyclotetrasiloxane (OMCTS). A method of producing high purity fused silica glass through oxidation or flame hydrolysis of precursors is disclosed. In addition, US Pat. No. 5,154,744 to Blackwell et al. Discloses OMCTS and a non-halogenated organometallic compound (ie, TiO ₂ precursor), preferably titanium isopropoxide (Ti (OC ₃ H ₇ ) ₄ ), titanium Ethoxide (Ti (OC ₂ H ₅ ) ₄ ), Titanium-2-ethylhexyl oxide (Ti (OCH ₂ (C ₂ H ₅ ) CHCH ₄ H ₉ ) ₄ ), Titanium cyclopentyl oxide (Ti (OC ₃ H ₉ ) ₄ ), titanium amide (Ti (NR ² ) ₄ ), wherein R ² is a titania-doped high purity fused silica glass via oxidation or flame hydrolysis of a gas mixture of methyl, or ethyl groups, or compounds thereof, Disclosed is the preparation of. These liquid OMCTS and the liquid TiO ₂ precursors are vaporized instantaneously in a flash tank heated to 175 ° C. and transported to the oven through a steam line heated with nitrogen, which are then mixed and passed through the flame of the combustion burner. The solution produces crystalline titania-doped fused silica. The amorphous particles are then solidified into a vitreous body. The same non-halogenated, SiO ₂ and TiO ₂ precursors as described above are optionally used in the present invention.

U.S. Pat.Nos. 5,558,687 and 5,707,416 to Cain et al. Disclose a vertical, packed-bed film vaporizer (evaporator) specifically developed for use of non-halogenated SiO ₂ precursors such as OMCTS. . The vaporizer includes a plurality of packed-bed columns surrounding the center tube. A mixture of liquid SiO _{2 and} oxygen is sprayed onto the top layer of the column using a spray nozzle set. The precursor and oxygen flow together in the downward direction of the heated column. The liquid precursor evaporates into oxygen until the dew point is reached and then exits to the bottom layer of the column. At this point, the outflow direction changes from bottom to top, causing high molecular weight material to separate from the gaseous stream. The gaseous stream exits the evaporator through the center tube and is then fed to a burner that produces soot. The same vaporizer as described above is optionally used in the present invention. The two patents do not describe TiO ₂ precursors. Furthermore, there is no mention of whether the vaporizer can vaporize the TiO ₂ precursor at a temperature low enough to substantially inhibit thermal decomposition of the TiO ₂ precursor, in particular while the SiO ₂ precursor is vaporized at the same time.

WO 99/15468 to Maxon et al describes a method for producing titania-doped fused silica glass by flame hydrolysis. The process involves conveying a mixture of SiO ₂ precursor, such as OMCTS, and a TiO ₂ precursor, such as titania alkoxide (e.g., titanium isopropoxide), to the flame in vapor form, passing the mixture through the flame to form SiO ₂ -TiO ₂ particles. Forming a, and depositing in a furnace in which they melt to form a solid glass body. The liquid SiO ₂ and TiO ₂ precursors are deposited in a separation tank and their vapors are mixed and vaporized by passing a carrier gas such as nitrogen through each precursor. Individual bypass streams for the carrier gas are connected with the entrained vapor streams to suppress saturation of the precursors. These two separate vapor streams are mixed mounted in the manifold. In the manifold, the mixed vapor is passed through a steam line to a blast furnace where it passes through a flame burner. Maxon et al. Specify that the titanium alkoxide decomposes into higher order polymers, oxides, and trace elements, and the vapor pressure of the precursor changes. This change in vapor pressure ultimately disturbs the furnace, making it difficult to accumulate glass condensate. Importantly, maxon et al. Insist on increasing the vapor pressure of the alkoxide by using titanium alkoxide at higher temperatures. This lowers the rate of outflow of the conveying vapors and consequently reduces disturbances in the vapor conveying system, minimizing glass accumulation in the furnace. According to maxon et al, decomposition of the TiO ₂ precursor can be avoided through temperature control of the steam line.

Unfortunately, difficulties of preliminary production with non-halogenated TiO ₂ precursors, in particular Titanium Isoproside, continue to this day. Titanium isopropoxide, although having a boiling point of 232 ° C., is thermally unstable at 175 ° C. to produce a high molecular weight gel. In addition, non-halogenated TiO ₂ precursors generally react with oxygen to form contaminants. These gels and contaminants cannot be used for preform production and should be discarded. This waste results in higher preproduction costs due to lower production efficiency and additional waste disposal costs.

Despite the use of non-halogenated SiO ₂ and TiO ₂ precursors to produce titania-doped fused silica preforms, the production of such preforms requires a liquid TiO ₂ precursor without substantial thermal decomposition. Furthermore, at low temperatures where there is no instantaneous vaporization and which can inhibit substantial thermal decomposition of the TiO ₂ precursor, in particular, vaporizing the TiO ₂ precursor at the same time while the SiO ₂ precursor is vaporized produces a titania-doped fused silica preform. Required. The present invention seeks to overcome this drawback in the art.

Summary of the Invention

The present invention relates to a process for vaporizing a liquid TiO ₂ precursor which is convertible to TiO ₂ through thermal decomposition with oxidation or flame hydrolysis. Under the practical conditions effective sikineunde without thermal decomposition of TiO ₂ precursor vaporizing the liquid TiO ₂ precursor packing the liquid TiO ₂ precursor with a carrier gas - to pass through the column bed.

The present invention also relates to a process for providing a reaction vapor comprising vaporized SiO ₂ and TiO ₂ precursors which are individually convertible to SiO ₂ and TiO ₂ via thermal decomposition with oxidation or flame hydrolysis. Under the practical conditions effective sikineunde without thermal decomposition of TiO ₂ precursor vaporizing the liquid TiO ₂ precursor packing the liquid TiO ₂ precursor with a carrier gas - to pass through the column bed. The vaporized TiO ₂ precursor and the carrier gas are mixed with vaporized SiO ₂ to form a reaction vapor / gas mixture.

The invention also relates to a process for vaporizing liquid SiO ₂ and TiO ₂ precursors to provide a reaction vapor. The liquid SiO ₂ and TiO ₂ precursors, which can be converted into SiO ₂ and TiO ₂ individually through thermal decomposition with oxidation or flame hydrolysis, simultaneously form a packed-bed column with a carrier gas under conditions effective to vaporize the respective precursors. Pass through. This is carried out substantially without pyrolysis of these precursors.

The present invention is an improvement on the prior art in at least four aspects. Firstly, the vaporizer minimizes thermal decomposition of temperature sensitive titania precursors and eliminates these wastes and the need for periodic treatment of contaminants by thermal decomposition. Secondly, the process is simpler, as it is carried out with one vaporizer compared to the current method requiring two flash tanks. Third, the process is more robust than conventional systems, as the carrier gas outflow in the vaporizer is essentially independent of the outflow rates of the respective titania and silica precursors. Fourth, current ultra low-expansion glass conveying systems cannot have a coefficient of thermal expansion (CTE) within 2-5 ppb / ° C without a change in atmospheric pressure. Consistent outflow of precursors in existing systems depends on atmospheric pressure, tight control of the outflow rate of the flash tank, and outflow rate of carrier gas. The process of the present invention is independent of all these variables and maintains consistent CTE control that accurately delivers silica and titania precursors to the vaporizer.

The present invention relates to a process for producing titania doped fused silica preforms that can be used for the production of ultra low expansion glass as well as optical or acoustic waveguide fibers.

1 is a block diagram illustrating one embodiment of a vapor delivery system designed in accordance with the present invention.

2 is a schematic, horizontal cross-sectional view of a vaporizer used in the vapor delivery system according to the present invention.

3 is a schematic, horizontal cross-sectional view taken along line 3-3 of FIG.

4 is a block diagram illustrating another embodiment of a steam delivery system designed in accordance with the present invention.

FIG. 5 is a graph showing the theoretical prediction for vaporizing titanium isopropoxide at an outflow rate of 41 g / min, where "good" represents the portion of the operating conditions predicted to be complete vaporization and "bad" is incomplete vaporization Represents the part about the operating condition to be predicted.

FIG. 6 is a graph showing theoretical predictions for vaporizing titanium isopropoxide at effluent rates of 10-80 g / min.

FIG. 7 is a graph showing theoretical values for vaporizing a mixture of titrium isopropoxide and octamethylcyclotetracarboxylic acid. FIG.

FIG. 8 is an enlarged photograph of the graph of FIG. 7.

Looking at the present invention in more detail as follows.

The present invention relates to a process for vaporizing a liquid TiO ₂ precursor used to prepare a titania-doped fused silica preform, such as ultra low expansion glass, or a titania-doped glass. Such TiO ₂ precursors are convertible to TiO ₂ (titania) through thermal decomposition with oxidation or flame hydrolysis.

Referring to FIG. 1, the liquid TiO ₂ precursor is stored in the liquid supply tank 10 and supplied to the vaporizer 13 through the liquid metering pump 12. Pump 12 determines the outflow rate of the liquid TiO ₂ precursor. The carrier gas is stored in the gas supply tank 14 and transferred to the vaporizer 13 by the gas flow outflow regulator 16 at a predetermined outflow rate on its own. In the vaporizer 13, the liquid TiO ₂ precursor is vaporized to produce a vapor / gas mixture of the liquid TiO ₂ precursor and the carrier gas. For example, if the liquid reactant is TPT and the carrier gas is nitrogen, the preferred outflow rate of the carrier gas is between about 2.0 and 9.0 standard liters per minute (slpm) per gram / minute of TiO ₂ precursor, particularly preferably of the TiO ₂ precursor. about 5.0 slpm per gram / minute. From the vaporizer 13, the vapor / gas mixture is conveyed to a vapor utilization section 20 which introduces a gaseous SiO ₂ precursor to form a titania-doped fused silica preform. Without substantial thermal decomposition of TiO ₂ precursor under conditions effective sikineunde vaporize the liquid TiO ₂ precursor packed the liquid TiO ₂ precursor and a carrier gas-bed column (eg, a packed in the vertical direction illustrated in Figures 2 and 3 - Bed Pass through column 22). A gas stream comprising a mixture of gaseous TiO ₂ precursor and carrier gas is passed to packed vapor bed 20, which can exit packed-bed column 22 to form a titania-doped fused silica preform.

Another embodiment of the invention is directed to a method of providing a reaction vapor for preparing a titania-doped silica preform. As shown in FIGS. 1-3, the liquid TiO ₂ precursor is passed through a packed-bed column 22 with a carrier gas under conditions effective to vaporize the liquid TiO ₂ precursor without substantial thermal decomposition. A gas stream comprising a mixture of gaseous TiO ₂ precursor and carrier gas is mixed with a second gas stream comprising gaseous SiO ₂ precursor exiting packed-bed column 22 to form a reaction vapor / gas mixture. The reaction vapor / gas mixture is conveyed to steam utilization 20 to form a titania-doped fused silica preform.

Yet another embodiment of the present invention relates to another method of providing a reaction vapor for producing a titania-doped fused silica preform. 2-4, liquid SiO ₂ (silica) precursors and liquid TiO ₂ (titania) precursors are passed through the packed-bed column 22 together with the carrier gas under conditions effective to simultaneously vaporize each precursor. This is done substantially without thermal decomposition of these precursors. Reaction vapor / gas comprising a mixture of the above gaseous SiO ₂ precursor, gaseous TiO ₂ (titania) precursor, and carrier gas exits packed-bed column 22 to form a titania-doped fused silica preform. It is conveyed to the steam utilization section 20.

In the steam utilization section 20, the reaction vapor / gas mixture passes through the flame of the combustion burner to form molten SiO ₂ of amorphous particles doped with TiO ₂ . Burner structures used in the present invention are disclosed in US Pat. No. 5,599,371 to Kane et al., Which is incorporated herein by reference. In addition to the vapor / gas mixture, these burners are also fed combustible gases such as methane and oxygen. The amorphous particles are deposited on a support (not shown) to form a preform. Thermal decomposition involving oxidation or flame hydrolysis is described in US Pat. No. 3,806,570 to Framenbaum et al., US Pat. No. 3,864,113 to Dumbaugh, Jr. et al. US Pat. No. 3,923,484 to Randall. US Patent No. 5,152,819 to Blackwell et al., And the like, which are incorporated herein by reference. Essentially at the same time depositing or successively here, the amorphous particles of this preform solidify into non-porous bodies. Optionally, the glass can be produced directly without forming a preform. Waveguide fibers can generally be drawn when the non-porous body, especially the non-porous body, is a non-porous, transparent glass body. Waveguide fiber drawing is disclosed in Schultz, US Pat. No. 3,859,073 and in Burke et al. US Pat. No. 3,933,453, incorporated herein by reference.

As described above, the TiO ₂ precursor utilized in the present invention is convertible to TiO ₂ through thermal decomposition involving oxidation or flame hydrolysis. Preferably, such TiO ₂ precursors are non-halogenated titanium alkoxides, titanium amides, or mixtures thereof. Examples of suitable TiO ₂ precursors include titanium-2-ethylhexyloxide, titanium cyclopentyloxide, titanium isopropoxide, titanium methoxide, Ti (NR ₂ ) ₄ , where R ₂ has a methyl, or ethyl group, structure Titanium amide, or mixtures thereof. Titanium isopropoxide (TPT) is the most preferred TiO ₂ precursor.

The SiO ₂ precursor utilized in the present invention is convertible to SiO ₂ through thermal decomposition involving oxidation or flame hydrolysis. In general, as disclosed in US Pat. No. 5,152,819 to Blackwell et al., Which is incorporated by reference herein, the SiO ₂ precursor is an organosilicon-Y compound, where Y is an element of the periodic table, and the Si—Y bond The dissociation energy is not higher than the Si-O bond dissociation energy, and the mixture has no boiling point higher than 350 ° C. Such organosilicon-Y compounds are basically organosilicon-oxygen compounds of Si-O-Si structure, organosilicon-nitrogen compounds of Si-N-Si structure, and basically Si-N-Si- Silosacilaic acid of O-Si structure, or a mixture thereof. Preferably, the SiO ₂ precursor is a non-halogenated polymethylsiloxane, polymethylsilane, polyethylsilane, polyethylsilicane, aminosilane, linear silane acid, cyclosilanic acid, or mixtures thereof. Examples of such SiO ₂ precursors include octamethylcyclotetrasiloxane, hexamethyldisiloxane, octamethyltrisiloxane, hexamethylcyclotrisiloxane, decamethylcyclopentasiloxane, methyltrimethoxysilane, tetraethylorthosilicate, and dimethyldimethic. Methoxysilane, trimethylmethoxysilane, tetramethoxysilane, methyltriethoxysilane, tetraethoxysilane, trisketenimine, nonamethyltrisilaic acid, octamethylcyclotetrasilanic acid, and mixtures thereof. Octamethylcyclotetrasilanic acid (OMCTS) is the most preferred SiO ₂ precursor.

It is known that alkoxides of transition metals are sensitive to light, heat, and moisture, as described in WO 99/15468 by Maxon et al., Incorporated herein by reference. In addition, metal alkoxides are easily hydrolyzed by moisture to form hydroxides and oxides of the metal. Therefore, SiO ₂ precursors, such as OMCTS, should be dehydrated or dried to keep the moisture content preferably below 2 ppm to prevent the formation of white precipitates of TiO ₂ in the system.

The carrier gas is preferably any gas so long as it does not chemically react with SiO ₂ or TiO ₂ precursors. Such gases are nitrogen, helium, neon, argon, krypton, xenon, and mixtures thereof, with nitrogen being most preferred. Oxygen may be utilized as the carrier gas, but is not preferred because of its tendency to react with the TiO ₂ precursor.

4, the liquid TiO ₂ precursor and the liquid SiO ₂ precursor are stored in the liquid supply tanks 10 and 64, respectively. The liquid TiO ₂ and liquid SiO ₂ precursors are simultaneously supplied to the vaporizer 13 by respective liquid metering pumps 12 and 66. The pump 12 determines the outflow rate of the liquid TiO ₂ precursor. Pump 66 determines the outflow rate of the liquid SiO ₂ precursor. The carrier gas is stored in the gas supply tank 14 and transferred to the vaporizer 13 by the gas flow outflow regulator 16 at a predetermined outflow rate on its own. In the vaporizer 13, the liquid TiO ₂ and SiO ₂ precursors are simultaneously vaporized to produce a reaction vapor / gas mixture of TiO ₂ precursor, SiO ₂ precursor and carrier gas. For example, if the TiO ₂ precursor is TPT, the SiO ₂ precursor is OMCTS, and the carrier gas is nitrogen, the preferred outflow rate of the carrier gas is from about 2.0 to 9.0 standard liters per minute per gram / minute of TiO ₂ precursor. , Particularly preferably about 5.0 slpm per gram / minute of TiO ₂ precursor. From the vaporizer 13, the above vapor / gas mixture is introduced into a vapor utilization section 20 in which a titania-doped fused silica preform is formed.

2 and 3 show the preferred structure of the vaporizer 13 used in the embodiments of the invention described in US Pat. Nos. 5,558,687 and 5,707,416 to Kane, which are incorporated by reference herein. The vaporizer 13 uses a plurality of packed-bed columns 22 surrounding the central, vertical, vapor / gas reception tube 24 for vaporization of the liquid TiO ₂ and / or SiO ₂ precursors. The packed-bed column 22 and center tube 24 are preferably made of stainless steel, are about 25 mm in diameter, and 75 cm in length. Other material and component dimensions may be used if desired.

The various packing materials available for the packed-bed column 22 are beads, fibers, rings, saddles, composed of glass, metal, ceramic, or other materials that do not substantially chemically react with the reactants. ), And the like. Preferred packing materials consist of a ceramic component in the form of a saddle and about 6 mm long. The packing provides a large surface area for the packed volume fraction. The lower portion 66 of the packed-bed column is equipped with gratings, screens or the like that can hold the packing material in the column.

As shown in FIG. 1, the liquid TiO ₂ precursor and carrier gas are metered with a continuous spray nozzle 32 located above the vaporizer 13 using a liquid metering pump 12 and a gas flow outflow regulator 16. . As similarly shown in FIG. 4, the liquid precursor and the carrier gas are metered by the spray nozzle 32 using the liquid metering pump 12 and the gas flow outflow regulator 16. The distribution of all liquid precursors or mixtures of these flowing through the upper layer 55 of the packed-bed column 22 is important because the liquid precursors tend to flow in a confined stream if only one portion of the upper layer 54 is supplied. This finite stream reduces the efficiency of the vaporizer 13 by reducing the effective surface area available for vaporization of the liquid precursor. Another method of supplying the liquid precursor and carrier gas to the upper layer of the packed-bed column 22 is to provide a distribution of one or more liquid precursors flowing through the upper layer 54 of the column, although the use of the spray nozzle 32 is preferred. For each packed-bed column 22 one can be used if desired, such as a manifold tube and one tube for each column of carrier gas.

Particular preference is given to a gas spray nozzle 32 which sprays the liquid precursor into the cone of drops 58 produced by the carrier gas. Such a nozzle 32 maintains uniform contact between the liquid precursor and the carrier gas and uniform wet of the bed packing. This type of nozzle 32 normally has a separate inlet (not shown) for the liquid precursor and the carrier gas. In order to maintain uniform operation of the multiple packed-bed columns 22 of FIGS. 2 and 3, the liquid precursor inlet of the nozzle 32 is connected with an air pressure equilibrium manifold (not shown). These manifolds, in order, are respectively connected with the liquid metering pump 12 and the gas flow outflow regulator 16. In the embodiment in which the SiO ₂ and TiO ₂ precursors are simultaneously vaporized with the vaporizer 13, the manifold is connected with the liquid metering pumps 12 and 66 and the gas flow regulator 16, respectively.

The compartment of the nozzle 32 is based on three main elements, including throughput of the liquid precursor, spray type, and carrier gas outflow rate. The nozzle 32 makes it possible to supply sufficient liquid precursor or precursor outflow as required by the system. In addition, the nozzle 32 may be sprayed to uniformly cover the packed-bed. Finally, the outflow rate of the carrier gas required to spray the liquid precursor should be sufficient to prevent dilution of the liquid precursor to below the desired operating level. The outflow rate of the carrier gas must be maintained at a rate sufficient to produce the desired drop of circular spray 58. Other nozzles 32 may be used for various liquid precursor outflow rates. Indeed, a gas spray nozzle 32 having a bore size of about 3 mm, a spray cone 58 of about 60 ° angle, and a dropping pressure flowing through the nozzle 32 at about 10 psig has worked successfully in embodiments of the present invention. Preferred.

Arrows 38, 40, and 42 of FIG. 3 illustrate the outflow form through the vaporizer 13. The liquid precursor, described next, comprises a TiO ₂ precursor and a mixture of TiO ₂ and SiO ₂ precursors. Arrow 38 means that the liquid precursor and the carrier gas simultaneously flow down through the packed-bed column while the liquid precursor or other precursors are vaporized before reaching the bottom 56 of the column. Arrow 40 indicates the upward outflow of the vapor / gas mixture through the center tube 24, and arrow 42 indicates that the outflow direction of the vapor / gas mixture in the phase separator 44 changes from the bottom up. it means. This change in direction effectively removes undesirable gels and gums from the vapor / gas stream. Other attempts to clean the vapor / gas stream may be performed at angles lower than 180 °, eg; 90 °, diverting the stream and placing the filtration material such as the permeation plate and / or asbestos in the stream carrying the impurities from which the conversion has been made, ie outside of the stream as seen from the center of the conversion. As mentioned above, preferably, the stream exiting the packed column can be filtered without changing the direction. Port 48 is provided to remove high molecular weight materials 46 in separator 44.

Arrows 60 and 62 in FIG. 1 describe the outflow of heat transfer oil (eg, silicone oil) from the heat transfer oil transport system 18 to the vaporizer 13. The heat transfer oil 28 is supplied to heat the packed-bed column 22 while flowing around the outer wall 50 of the column. It is also supplied to heat the vapor / gas mixture flowing through the center tube 24 while heating the outer wall 52 of the tube. The vaporizer 13 is heated to a temperature between 110 ° C and 175 ° C, preferably 110 ° C to 140 ° C. If desired, heating fluids other than electrothermal oil may be used to heat the stream, packed-bed column 22 and center tube 24, for example. In addition, even if the heating fluid method is preferred, other heating methods such as electric thermal tapes can be used, since the possibility of occurrence of hot spots in the vaporizer causing polymerization reaction or thermal decomposition of the liquid precursor can be minimized.

The heat transfer oil 28 enters the vaporizer 13 through the port 34 inlet and exits through the port 36 outlet. Within the vaporizer 13, the heat transfer oil 28 defines a confined passageway 30, such as the shell 28 of the vaporizer and the outer walls 50 and 52 of the packed-bed column 22 and the center tube 24. Flows through. A partition (not shown) is included in the passageway 30 so that the heat transfer oil 28 is evenly distributed around the outer walls 50 and 52.

The sheath 26 extends above the nozzle 32 and above the pressure uniform manifold connected to the nozzle 32, resulting in a closed space inside the vaporizer 13. The oil ports 34 and 36, the outlet of the center tube 24, and the port inlet (not shown) that carries the liquid TiO ₂ precursor and carrier gas to the pressure uniform manifold pass through the enclosure 26.

The carrier gas and the liquid precursor are simultaneously heated while passing down through the packed-bed column 22. As their temperature increases, more liquid precursors vaporize into the carrier gas. This process is controlled by the outflow of heat and diffusion of vapor through the carrier gas at the interface between the carrier gas and the liquid TiO ₂ precursor. This process continues with the mixture flowing down through column 22 until all liquid precursors, except for the high molecular weight material of the undesirable liquid precursor, are converted to steam. Thereafter, the temperature increase of the vapor / gas mixture continues as it flows down towards the bottom layer 56 of the column. The packed-bed column 22 equalizes the remaining time of the entire stream while maintaining a uniform velocity. Uniform residence time minimizes pyrolysis of the precursors. The remaining time in the packed-bed column of the TiO ₂ precursor is from 0.5 seconds to 10.0 seconds.

The temperature of the heat transfer oil 28 is set to a certain value that allows the liquid precursor and carrier gas to be heated to a temperature sufficient to vaporize the liquid precursor before reaching the bottom layer 56 of the column. However, the selected temperature should be lower than the pyrolysis temperature of the TiO ₂ precursor. The amount of heat required for various precursors, molar ratios, operating pressure values, and other vaporization volumes is readily determined by those skilled in the art disclosed herein.

The temperature in the vaporizer varies with the absorbed energy of the liquid precursor sprayed and the carrier gas for evaporation and temperature increase. Thus, the temperature distribution in the packed-bed 22 of the vaporizer 13 depends on the temperature of the introduced liquid precursor and the carrier gas. After the liquid precursor and the carrier gas enter the vaporizer 13, the rate of temperature increase (i.e. temperature gradient) along the length of the heated packed-bed 22 is higher for the component entering the ambient temperature compared to the preheated component. . For example, the liquid precursor and carrier gas preheated at 100 ° C. compared to the components entering 25 ° C. significantly reduce the temperature gradient in the vaporizer 13. Preheating is not necessary, but reducing the temperature gradient reduces the length of vaporizer 13 required to fully vaporize a given amount of liquid precursor. Reducing the length of the vaporizer 13 naturally reduces the remaining time in the vaporizer 13 of the liquid precursor. This, then sequentially, reducing the amount of time that the TiO ₂ precursor (140 ℃) exposed to a high temperature to reduce the thermal decomposition of TiO ₂ precursor. Importantly, when TPT and OMCTS react at high temperatures (eg 140 ° C.) for a short period of 2 to 5 seconds, no noticeable reaction or pyrolysis between these precursors occurs. The precursor remaining time in the general vaporizer 13 is about 1 second.

After leaving the phase separator 44, the pure vapor / gas mixture moves up through the center tube 24. In the vaporizer 13, the vapor / gas mixture is generally conveyed to a vapor utilization section 20 which introduces a vapor phase SiO ₂ precursor to form a titania-doped fused silica preform.

Each of the pumps (13 and 66), or Rota meter (not urbanization negative) for a high flow of TiO ₂ and SiO ₂ precursor mixture for the TiO ₂ and the outflow amount of TiO ₂ and SiO ₂ precursor into the vaporizer of the SiO ₂ precursor Adjust with Optionally, the outflow rate can be measured by controlling the time for weight loss in each precursor reservoir per unit time.

5 to 8, the theoretical prediction of the operating temperature required for the TPT used the following Equation 1 combined with the vapor pressure for the temperature relationship of the TPT shown in Equation 2 below.

[Equation 1]

Outflow rate of TiO ₂ precursor = CG (VP / (P _atm -VP)

Here, the outflow rate of the TiO ₂ precursor is grams / minute, CG is the slpm outflow rate of the carrier gas (nitrogen), VP is the vapor pressure of the TiO ₂ precursor in Torr, and P _atm is the atmospheric pressure (Torr).

[Equation 2]

Log (P) = 8.972-2997.96 / T

Where P is the pressure in Torr and T is the absolute temperature in Kelvin. Equation 2 was experimentally demonstrated by measuring the vapor pressure of TPT at various temperatures from 120 ° C. to 140 ° C. according to ASTM standard E 1719-95 entitled “Standard Test Method for Vapor Pressure of Liquids Using a Viscometer”.

5 shows the theoretical prediction at 41 g / min, which separates the operating conditions into two parts. The “good” part includes the operating conditions, ie the temperature and the gas outflow rate, in which a complete vaporization can theoretically occur. The "bad" part indicates the operating conditions under which incomplete vaporization occurs. 6 is the same graph for TPT effluent rate of 10-80 g / min.

Three conclusions can be drawn from FIGS. 5 and 6. First, because of the pressure sufficient to carry the TiO ₂ precursor down, no TiO ₂ precursor (eg TPT) requires a carrier gas for the outflow rate at temperatures above the precursor's boiling point (232 ° C.). Secondly, as the outflow rate of the carrier gas increases, the operating temperature of the vaporizer 13 decreases. Finally, the operating temperature of the vaporizer 13 or the outflow rate of the carrier gas must be increased to vaporize the increased TiO ₂ precursor.

Experiments were carried out in a vaporizer with a nitrogen outlet rate of 10-15 sipm and a TPT amount of 30-50 g / min at 170 ° C. The results are summarized in Table 1 below and show that complete vaporization occurs at a temperature of 5 ± 2 ° C. above the theoretical value. This exhibits excellent heat transport and predictable vaporization in the vaporizer 13.

The liquid mixture of TPT and OMCTS vaporizes in a high stage in the vaporizer 13. Theoretical predictions for the runoff of the mixture of TPT and OMCTS are shown in FIGS. 7 and 8. Table 1 also shows that the vaporizer 13 was operated in a theoretically predicted manner. The mixture is injected at 105 g / min through a vaporizer at 161.5 ° C. with a nitrogen carrier gas at an effluent rate of 16.5 slpm. Theoretically, a difference of about 7 ° C. for these conditions predicted a required temperature of 154.5 ° C., indicating that sufficient heat transport is possible even with relatively high outflow rates.

Unlike two separate feed tanks, the ability to vaporize the TiO ₂ and SiO ₂ precursor mixture through a single vaporizer 13 simplifies the prefabrication process. Surprisingly, it is possible to greatly reduce the carrier gas outflow. In general, existing systems utilizing feed tanks require about 0.8 to 1.2 slpm for liquid precursor 0.8 to 1.2 g / min. The process of the present invention requires only 0.2 to 0.3 slpm of nitrogen for the outflow rate of the same precursor. Therefore, the vaporizer 13 can be more independent of the feed tank system in controlling the outflow rate of the carrier gas, the TiO ₂ precursor, and the SiO ₂ precursor. The method of the present invention is more robust than conventional feed tank processes because the rate of nitrogen outflow in vaporizer 13 is surprisingly independent of the rate of outflow of liquid precursors. Also unexpectedly, vaporization occurs at values that are theoretically predicted close, indicating that the interaction of TPT and OMCTS is minimal. Interactions were expected to change the dew point and / or gel formation of these precursors, but were not observed.

Example 1

Continuous experiments were performed including passing a liquid TPT or a mixture of TPT and OMCTS in a 1.0: 5.0 weight ratio through a vaporizer.

The results of these experiments are shown in Table 1 below. The term "preheat" means that the carrier gas (eg nitrogen) is preheated to 120 ° C. and the liquid phase is preheated to 100 ° C., which is the vaporizer temperature at the outlet of the vaporizer. The term "good" means full vaporization and the term "bad" refers to incomplete vaporization. The TPT used has a small amount of degradation, which can be seen in the brownish-orange color. This suggests that the high molecular weight (MW) component is dissolved in TPT. The high MW component does not vaporize and acts like a dye. As the TPT passes through the vaporizer, the brownish-orange color is recovered to the separator. If the vaporization is successful, this output material becomes transparent. However, if complete combustion fails, a brownish-orange color liquid and TPT accumulate in the separator and exit the vaporizer, resulting in a brownish-orange color in the vapor stream. When this method is used for a mixture of OMCTS and TPT, it is diluted with OMCTS to have a less sensitive color.

Vaporization ingredient Nitrogen outflow (slpm) Carburetor Temperature (℃) Liquid precursor (s) outflow (g / min) good TPT 14.85 170 Preheat 39 Bad TPT 14.2 169 preheat 48 good TPT 14.85 170 Preheat 35 good TPT 14.2 176 Preheat 50.5 Bad TPT 13.9 175 Preheat 55 good TPT 14.85 172 Preheat 36 Bad TPT 14.85 171 Preheat 47 good TPT 14.85 171.2 Preheat 39 Bad TPT 14.85 169 preheat 41 good TPT 14.85 170.6 Preheat 35 Bad TPT 14.85 173.9 Preheat 35 good TPT 14.85 179.9 41 Bad TPT 14.85 168 40 good TPT 15.2 171.8 34 Bad TPT 11.6 171.4 34 good TPT 11.6 172.2 31 Bad TPT 10.19 172 31 good TPT 10.19 170 27 good mixture 16.5 161.5 Preheat 105 Bad mixture 19.85 156.6 Preheat 120 good mixture 14.3 143 Preheat 45 Bad mixture 14.2 131.5 Preheat 47

As described above, the present invention has been described in more detail through the above embodiments, but the scope of the present invention is not limited thereto.

Claims (33)

Providing a liquid TiO ₂ precursor that is convertible to TiO ₂ through thermal decomposition involving oxidation or flame hydrolysis; Providing a carrier gas; Providing a packed-bed column; And The without substantial thermal decomposition vaporize the liquid TiO ₂ precursor and packing the liquid TiO ₂ precursor and a carrier gas under conditions effective to produce a gas stream (gas stream) comprising a mixture of the liquid TiO ₂ precursor and a carrier gas-bed A method of vaporizing a liquid TiO ₂ precursor comprising passing through a column. The method of claim 1, wherein the TiO ₂ precursor is titanium alkoxide, titanium amide, or a mixture thereof. The method of claim 1 wherein the carrier gas is selected from the group consisting of nitrogen, helium, neon, argon, krypton, xenon, and mixtures thereof. The method of claim 1, wherein the method further comprises heating the packed-bed column. The method of claim 1, wherein the method further comprises heating the TiO ₂ precursor and carrier gas prior to passing the liquid TiO ₂ precursor and carrier gas through the packed-bed column. Providing a first gas stream containing a vapor phase SiO ₂ precursor capable of conversion to SiO ₂ through pyrolysis accompanied by oxidation or flame hydrolysis; Providing a liquid phase TiO ₂ precursor capable of conversion to silicon oxide through pyrolysis involving oxidation or flame hydrolysis; Providing a carrier gas; Providing a packed bed column; Without substantial thermal decomposition vaporize the liquid TiO ₂ and the gas phase TiO ₂ precursor and a first liquid phase of the TiO ₂ precursor and a carrier gas under conditions effective to produce a second gas stream containing a mixture of carrier gas pack-pass the bed column Making a step; And Mixing the second gas stream with the first gas stream to form a reaction vapor / gas mixture. The method of claim 6, wherein the TiO ₂ precursor is titanium alkoxide, titanium amide, or a mixture thereof. The TiO ₂ precursor of claim 6, wherein the TiO ₂ precursor is titanium-2-ethylhexyloxide, titanium cyclopentyloxide, titanium isopropoxide, titanium methoxide, Ti (NR ₂ ) ₄ , wherein R ₂ is a methyl, or ethyl group. , Titanium amide having a structure, or a mixture thereof. The method of claim 6, wherein the SiO ₂ precursor is polymethylsiloxane, polymethylsilane, polyethylsilane, polyethysilicate, aminosilane, linear silaic acid, cyclosilanic acid, or mixtures thereof. The method of claim 6, wherein the SiO ₂ precursor is octamethylcyclotetrasiloxane, hexamethyldisiloxane, octamethyltrisiloxane, hexamethylcyclotrisiloxane, decamethylcyclopentasiloxane, methyltrimethoxysilane, tetraethylorthosilicate , Dimethyldimethoxysilane, trimethylmethoxysilane, tetramethoxysilane, methyltriethoxysilane, tetraethoxysilane, trisketenimine, nonamethyltrisilaic acid, octamethylcyclotetrasilanic acid, and mixtures thereof Method selected from the group. 7. The method of claim 6, wherein the carrier gas is selected from the group consisting of nitrogen, helium, neon, argon, krypton, xenon, and mixtures thereof. 7. The method of claim 6, wherein the method further comprises heating the packed-bed column. The method of claim 6, wherein the method further comprises heating the TiO ₂ precursor and carrier gas prior to passing the liquid TiO ₂ precursor and carrier gas through the packed-bed column. 13. The method of claim 12, wherein the packed-bed column is heated to a temperature between 110 ° C and 175 ° C. 7. The method of claim 6, wherein the TiO ₂ precursor further comprises having a residence time between 0.5 seconds and 10.0 seconds in a packed-bed column. The method of claim 6, wherein the method further comprises separating high molecular weight impurities from the second gas stream. 17. The method of claim 16, wherein said separating comprises changing the outflow direction of the second gas stream. The method of claim 6, wherein the method comprises passing a reaction vapor / gas mixture into a flame of a combustion burner to produce molten SiO ₂ of amorphous particles doped with TiO ₂ ; Depositing amorphous particles on a support to form a preform; And And solidifying the preform, which comprises essentially amorphous particles, either at the same time or continuously, into a non-porous body. 19. The method of claim 18, wherein the non-porous body is a non-porous transparent vitreous, and the method further comprises drawing waveguide fibers from the non-porous body. Providing a liquid phase SiO ₂ precursor convertible to SiO ₂ through thermal decomposition with oxidation or flame hydrolysis; Providing a liquid phase TiO ₂ precursor convertible to TiO ₂ through pyrolysis accompanied by oxidation or flame hydrolysis; Providing a carrier gas; Providing a packed-bed column; And Substantially heat vaporizing the liquid phase SiO ₂ and TiO ₂ precursor without decomposing and, gaseous SiO ₂ precursor, gas phase TiO ₂ precursor, and under conditions effective to produce a reaction vapor / gas containing a mixture of the carrier gas of the liquid SiO ₂ precursor Passing the liquid TiO ₂ precursor, and carrier gas, through a packed-bed column. The method of claim 20, wherein the TiO ₂ precursor is titanium alkoxide, titanium amide, or a mixture thereof. 21. The method of claim 20, wherein the TiO ₂ precursor is titanium-2-ethylhexyloxide, titanium cyclopentyloxide, titanium isopropoxide, titanium methoxide, Ti (NR ₂ ) ₄ , wherein R ₂ is a methyl, or ethyl group , Titanium amide having a structure, or a mixture thereof. 21. The method of claim 20, wherein the SiO ₂ precursor is polymethylsiloxane, polymethylsilane, polyethylsilane, polyethilicate, aminosilane, linear silaic acid, cyclosilanic acid, or mixtures thereof. The method of claim 20, wherein the SiO ₂ precursor is octamethylcyclotetrasiloxane, hexamethyldisiloxane, octamethyltrisiloxane, hexamethylcyclotrisiloxane, decamethylcyclopentasiloxane, methyltrimethoxysilane, tetraethylorthosilicate, Dimethyldimethoxysilane, trimethylmethoxysilane, tetramethoxysilane, methyltriethoxysilane, tetraethoxysilane, trisketenimine, nonamethyltrisilaic acid, octamethylcyclotetrasilanic acid, and mixtures thereof Characterized in that it is selected from. The method of claim 20 wherein the carrier gas is selected from the group consisting of nitrogen, helium, neon, argon, krypton, xenon, and mixtures thereof. The method of claim 20, wherein the method further comprises heating the packed-bed column. 27. The method of claim 26, wherein the packed-bed column is heated to a temperature between 110 ° C and 175 ° C. 21. The method of claim 20, wherein the method comprises heating at least one of the liquid SiO ₂ precursor, the liquid TiO ₂ precursor and the carrier gas before passing the liquid SiO ₂ and TiO ₂ precursor and carrier gas through the packed-bed column. Method further comprising a. The method of claim 20, wherein the TiO ₂ precursor further comprises having a remaining time between 0.5 seconds and 10.0 seconds in a packed-bed column. 21. The method of claim 20, wherein said separating further comprises changing the outflow direction of the second gas stream. 31. The method of claim 30, wherein said separating comprises changing the outflow direction of the reaction vapor / gas mixture. The method of claim 20, wherein the method comprises passing a reaction vapor / gas mixture into a flame of a combustion burner to produce molten SiO ₂ of amorphous particles doped with TiO ₂ ; Depositing amorphous particles on a support to form a preform; And And solidifying the preform, which comprises essentially amorphous particles, either simultaneously or sequentially, into a non-porous body. 33. The method of claim 32, wherein the non-porous body is a non-porous transparent vitreous, and the method further comprises drawing waveguide fibers from the vitreous.