Patent Description:
The present disclosure generally relates to methods of soot capture.

Optical articles may be manufactured by pyrogenically producing and depositing ultra-high purity, nanoscale glass particles (soot) on a target. However, soot deposition efficiency is often less than desirable with a portion of the soot being captured in a pollution abatement system. "Scrubber" type pollution abatement systems have been used to capture small particles from various gas exhausts for pollution abatement purposes, but the resultant collection of particles is often contaminated and has few uses. Further, the soot produced may have changes in concentration or composition resulting in variation in articles produced from the soot.

<CIT> discloses a method for production of glass material for a light-transmitting fiber. <CIT> and <CIT> show additional prior art.

The invention provides a method of capturing soot according to claim <NUM>.

According to another feature of the present disclosure, a method of capturing soot includes the steps of: combusting a first precursor comprising a silicon-containing compound and a second precursor in a burner to produce a soot stream comprising soot; passing water as a vapor and aerosol into the soot stream proximate the burner such that the soot is captured in the water and forms a slurry; recirculating the slurry through the soot stream such that the slurry is from about <NUM> wt% to about <NUM> wt% soot; and mixing a second slurry with the slurry, wherein the second slurry has a different soot wt% than the slurry.

The following is a description of the figures in the accompanying drawings. The figures are not necessarily to scale, and certain features and certain views of the figures may be shown exaggerated in scale or in schematic in the interest of clarity and conciseness.

Additional features and advantages of the disclosure will be set forth in the detailed description which follows and will be apparent to those skilled in the art from the description, or recognized by practicing the invention as described in the following description, together with the claims and appended drawings.

In this document, relational terms, such as first and second, top and bottom, and the like, are used solely to distinguish one entity or action from another entity or action, without necessarily requiring or implying any actual such relationship or order between such entities or actions.

It will be understood by one having ordinary skill in the art that construction of the described disclosure, and other components, is not limited to any specific material.

For purposes of this disclosure, the term "coupled" (in all of its forms: couple, coupling, coupled, etc.) generally means the joining of two components (electrical or mechanical) directly or indirectly to one another. Such joining may be permanent in nature, or may be removable or releasable in nature, unless otherwise stated.

As used herein, the term "about" means that amounts, sizes, formulations, parameters, and other quantities and characteristics are not and need not be exact, but may be approximate and/or larger or smaller, as desired, reflecting tolerances, conversion factors, rounding off, measurement error and the like, and other factors known to those of skill in the art. When the term "about" is used in describing a value or an end-point of a range, the disclosure should be understood to include the specific value or end-point referred to. Whether or not a numerical value or end-point of a range in the specification recites "about," the numerical value or end-point of a range is intended to include two embodiments: one modified by "about," and one not modified by "about. " It will be further understood that the end-points of each of the ranges are significant both in relation to the other end-point, and independently of the other end-point.

The terms "substantial," "substantially," and variations thereof as used herein are intended to note that a described feature is equal or approximately equal to a value or description. For example, a "substantially planar" surface is intended to denote a surface that is planar or approximately planar. Moreover, "substantially" is intended to denote that two values are equal or approximately equal. In some embodiments, "substantially" may denote values within about <NUM>% of each other.

It is also important to note that the construction and arrangement of the elements of the disclosure, as shown in the exemplary embodiments, is illustrative only. Although only a few embodiments of the present innovations have been described in detail in this disclosure, those skilled in the art who review this disclosure will readily appreciate that many modifications are possible (e.g., variations in sizes, dimensions, structures, shapes and proportions of the various elements, values of parameters, mounting arrangements, use of materials, colors, orientations, etc.) without materially departing from the novel teachings and advantages of the subject matter recited. For example, elements shown as integrally formed may be constructed of multiple parts, or elements shown as multiple parts may be integrally formed, the operation of the interfaces may be reversed or otherwise varied, the length or width of the structures, and/or members, or connectors, or other elements of the system, may be varied, and the nature or number of adjustment positions provided between the elements may be varied. It should be noted that the elements and/or assemblies of the system may be constructed from any of a wide variety of materials that provide sufficient strength or durability, in any of a wide variety of colors, textures, and combinations.

Referring now to <FIG>, depicted is an article <NUM>. The article <NUM> may be composed of a glass, a glass-ceramic or ceramic material. The article <NUM> may include Si, Al, Ti, Zn, Ge, Er, Nd, Bi, Sb, Yb, Rb, oxides thereof and/or combinations thereof. According to various examples, the article <NUM> may be doped within one or more halogens (e.g., F) and/or OH. It will be understood that the glass article <NUM> may include SiO<NUM> at balance with the other constituents of the glass article <NUM>. The article <NUM> may be a variety of components. For example, the article <NUM> may be a lens, a photomask blank, optical fibers, a glass substrate, planar-waveguides, other components and/or combinations thereof.

The composition of the article <NUM> may have a low variation across the article <NUM>. For example, the composition of one or more of the constituents of the glass article <NUM> may vary over between any two points of the article <NUM> by about ± <NUM> wt%, or about ± <NUM> wt%, or about ± <NUM> wt%, or about ± <NUM> wt%, or about ± <NUM> wt%, or about ± <NUM> wt%, or about ± <NUM> wt%, or about ± <NUM> wt%, or about ± <NUM> wt%, or about ± <NUM> wt%, or about ± <NUM> wt%, or about ± <NUM> wt%, or about ± <NUM> wt%, or about ± <NUM> wt%, or about ± <NUM> wt% or any and all values and ranges therebetween. The variation in composition across the article <NUM> may be expressed as a standard deviation and is calculated as the square root of variance by determining the variation between each composition relative to the average composition of the article <NUM> at each point measured. The compositional standard deviation of one or more of the constituents of the article <NUM> may be from about <NUM> wt% to about <NUM> wt%, or from about <NUM> wt% to about <NUM> wt%, or from about <NUM> wt% to about <NUM> wt%, or from about <NUM> wt% to about <NUM> wt% or any and all values and ranges therebetween.

The article <NUM> may have a length L and/or width W of from about <NUM> to about <NUM>, or from about <NUM> to about <NUM>, or from about <NUM> to about <NUM>, or from about <NUM> to about <NUM>, or from about <NUM> to about <NUM> or any and all values and ranges therebetween. The article <NUM> may have a thickness T of about <NUM>, or about <NUM>, or about <NUM>, or about <NUM>, or about <NUM> or any and all values and ranges therebetween. It will be understood that the article <NUM> may be larger than the above-noted dimensions and may be sectioned or cut to provide one or more articles <NUM> of the above-noted sizes. The compositional variations noted above apply to article <NUM> having any of the sizes (length, and/or width and/or thickness) disclosed herein.

According to various examples, the article <NUM> may be free or substantially free of gas seeds, solid inclusions (e.g., compositional or optical inhomogeneities) or other defects.

Referring now to <FIG>, depicted is a soot generation and capture system <NUM> used in the formation of the article <NUM>. The system <NUM> includes a container <NUM> defining a chamber <NUM> and a burner <NUM>. According to various examples, a cooling jacket may be positioned around the container <NUM> and configured to remove heat from the system <NUM>. In the depicted example, the burner <NUM> is positioned at a top of the chamber <NUM>, but it will be understood that the burner <NUM> may be positioned at other locations within the chamber <NUM> of the container <NUM>. For example, the system <NUM> may be positioned horizontally or on an incline such that that the burner <NUM> may be positioned on a side of the system <NUM>. The burner <NUM> is configured to burn or oxidize one or more vapors or precursors to produce a soot stream <NUM> of a soot <NUM>. The soot stream <NUM> exits the burner <NUM> at an outlet <NUM>. A slurry nozzle <NUM> is positioned proximate the outlet <NUM> of the burner <NUM> and is configured to spray a capture medium <NUM> into the soot stream <NUM>. The capture medium <NUM> contacts with the soot stream <NUM> at an impact region <NUM>. For example, a tip of the slurry nozzle <NUM> where the capture medium <NUM> is sprayed from may be within a distance of about <NUM>, or about <NUM>, or about <NUM>, or about <NUM> from the outlet <NUM> of the burner <NUM>. A condensate nozzle <NUM> is positioned proximate the outlet <NUM> of the burner <NUM> and the slurry nozzle <NUM>, and is configured to spray a condensate <NUM> into the soot stream <NUM>. It will be understood that while the capture medium <NUM> and the condensate <NUM> are described as being sprayed into the soot stream <NUM>, the capture medium <NUM> and/or the condensate <NUM> may be added to the soot stream <NUM> in a nebulized form, in an ultrasonically vaporized form, as a stream of liquid, other methods and/or combinations thereof without departing from the teachings provided herein. According to various examples, the condensate nozzle <NUM> may be positioned further away from the outlet <NUM> of the burner <NUM> than the slurry nozzle <NUM> (i.e., downstream from the slurry nozzle <NUM>) or closer to the outlet <NUM> of the burner <NUM> than the slurry nozzle <NUM> (i.e., upstream of the slurry nozzle <NUM>). As will be explained in greater detail below, the capture medium <NUM> and the condensate <NUM> sprayed from the slurry nozzle <NUM> and the condensate nozzle <NUM>, respectively, are configured to capture the soot <NUM> of the soot stream <NUM> to form a slurry <NUM>. Although the slurry <NUM> is depicted as collecting within the chamber <NUM>, it will be understood that the slurry <NUM> may be held in a separate holding chamber without departing from the teachings provided herein. The slurry <NUM> is formed as the condensate <NUM> and/or the capture medium <NUM> intermix in or combine with the soot stream <NUM> at the impact region <NUM> to capture the soot <NUM>. The formation of the slurry <NUM> is further aided as the slurry <NUM>, soot stream <NUM>, capture medium <NUM> and condensate <NUM> are passed through a constriction <NUM> defined by a blockage <NUM>. The system <NUM> may also include a heat exchanger <NUM>, a condenser <NUM> and a pollution abatement system <NUM> as explained in greater detail below.

Referring now to <FIG> and <FIG>, depicted is a method <NUM> of capturing the soot <NUM>. The method <NUM> may begin with a step <NUM> of combusting a first precursor and/or a second precursor in the burner <NUM> to produce the soot stream <NUM> including the soot <NUM>. Although described herein as including two precursors, it will be understood that the method <NUM> may equally include a single precursor or more than two precursors (e.g., up to five or more separate precursors) which are combusted in the burner <NUM> without departing from the teachings provided herein. The first and/or second precursors may be in the form of liquids, vapors and/or gasses.

According to various examples, the first precursor may include a silicon-containing compound. The silicon-containing compound may include octamethylcyclotetrasiloxane (OMCTS), other siloxane compounds, organosilanes, silicon carbide (SiC), silicon monoxide (SiO), silicon nitride (Si<NUM>N<NUM>), silicon tetrabromide (SiBr<NUM>), silicon tetrachloride (SiCl<NUM>), silicon tetraiodide (SiI<NUM>), silica (SiO<NUM>), silicon tetraisocyanate (Si(NCO)<NUM>), other silicon-bearing compounds and/or combinations thereof. The silicon-containing compound is configured to combust and produce SiO<NUM> soot <NUM>.

According to various examples, the second precursor may include a titanium-containing compound. The titanium-containing compound may include titanium isopropoxide (Ti(OC<NUM>H<NUM>)<NUM> (TPT)), titanium ethoxide (Ti(OC<NUM>H<NUM>)<NUM>), titanium <NUM>-ethylhexyloxide (Ti[OCH<NUM>CH(C<NUM>H<NUM>)C<NUM>H<NUM>]<NUM>), titanium cyclopenthyloxide (Ti(OC<NUM>H<NUM>)<NUM>), titanium amides (Ti(NR<NUM>)<NUM>), , other titanium-bearing compounds and/or combinations thereof. Additionally or alternatively, the second precursor may include a compound configured to produce soot <NUM> including at least one of Ge, Er, Al, Nd, Bi, Sb, Ti, Yb and/or Rb when combusted. Further, it will be understood that one or more precursors or vapors of the dopants outlined above may be supplied to the burner <NUM>. It will be understood that the relative molar amounts of the first precursor and the second precursor supplied to the burner <NUM> may be roughly equal to the desired composition (e.g., Si and Ti) of the article <NUM>.

The first precursor and the second precursor may be separately converted to vapor form and carried to a mixing manifold by a carrier gas, such as nitrogen. The mixture passes via fume lines, into a flame produced by the burner <NUM>. The burner <NUM> may also have a fuel (e.g., CH<NUM>) and an oxidizer (e.g., O<NUM>) carried to the flame in order to facilitate combustion. The combustion of the first precursor and the second precursor in the burner <NUM> produces the soot stream <NUM> carrying the soot <NUM>. The soot <NUM> may have a size (i.e., largest diameter, linear dimension, or length) of from about <NUM> to about <NUM>, or from about <NUM> to about <NUM>, or from about <NUM> to about <NUM>, or from about <NUM> to about <NUM>, or from about <NUM> to about <NUM> or any and all values and ranges therebetween. In examples where dopants are provided to the burner <NUM>, the soot <NUM> may also include particles of the dopants.

As the burner <NUM> is combusting the first and second precursors, a step <NUM> of passing or directing the capture medium <NUM> into the soot stream <NUM> proximate the outlet <NUM> of the burner <NUM> such that the soot <NUM> is captured in the capture medium <NUM> and forms the slurry <NUM> is performed. The outlet <NUM> of the burner <NUM> and the tip of slurry nozzle <NUM> may have a distance from one another of about <NUM> meter or less, or about <NUM> (<NUM> foot) or less, or about <NUM> (<NUM> inch) or less or about <NUM> or less. At a beginning of the method <NUM>, the capture medium <NUM> may start in the bottom of the chamber <NUM> and be pumped to the slurry nozzle <NUM>. It will be understood that the as yet unused capture medium <NUM> may also be stored exterior to the chamber <NUM> without departing from the teachings provided herein. The capture medium <NUM> may be composed of deionized water or other liquids capable of withstanding the elevated temperatures of the soot stream <NUM>. As will be explained in greater detail below, as the capture medium <NUM> becomes increasingly laden with the soot <NUM>, the capture medium becomes the slurry <NUM> which is a suspension of the soot <NUM> in the capture medium <NUM>. Further, as the system <NUM> may later recirculate the capture medium <NUM> containing the soot <NUM> (i.e., now the slurry <NUM>) through the soot stream <NUM> from the slurry nozzle <NUM>, it may be said that the capture medium <NUM> and/or the slurry <NUM> is recirculated through the soot stream <NUM>.

The capture medium <NUM> is passed or directed into the soot stream <NUM> at the impact region <NUM>. The impact region <NUM> is the area at which the capture medium <NUM> first contacts or mixes with the soot stream <NUM> to form the slurry <NUM>. The distance between the outlet <NUM> of the burner <NUM> and the impact region <NUM> may be about <NUM> or less, or about <NUM> or less, or about <NUM> or less or any and all values and ranges therebetween. For example, the impact region <NUM> may be from about <NUM> to about <NUM> from the outlet <NUM> of the burner <NUM>. As the impact region <NUM> may be proximate the outlet <NUM> of the burner <NUM>, the soot <NUM> may have an elevated temperature in the impact region <NUM> and as the capture medium <NUM> contacts the soot <NUM>. For example, the soot <NUM> may have a temperature of about <NUM>° C or greater, or about <NUM>° C or greater, or about <NUM>° C or greater, or about <NUM>° C or greater, or about <NUM>° C or greater, or about <NUM>° C or greater, or about <NUM>° C or greater, or about <NUM>° C or greater, or about <NUM>° C or greater or any and all values and ranges therebetween. For example, the temperature of the soot <NUM> in the impact region <NUM> may be from about <NUM>° C to about <NUM>° C, or about <NUM>° C to about <NUM>° C, or about <NUM>° C to about <NUM>° C or about <NUM>° C to about <NUM>° C, or about <NUM>° C to about <NUM>° C.

The capture medium <NUM>, and therefore the slurry <NUM> formed when the capture medium <NUM> combines with the soot <NUM>, may include one or more dispersants configured to increase the particle separation or reduce clumping of the soot <NUM> within the capture medium <NUM>. As used herein, a dispersant is a surface-active substance present in a suspension, which is usually a colloid, to improve the separation of particles (e.g., the soot <NUM>) and to prevent settling or clumping so that a uniform dispersion of particles (e.g., the soot <NUM>) is present in the slurry <NUM>. According to various examples, the one or more dispersants may include a surfactant. The dispersant may include ammonium citrate, polyurethanes, polyacrylates, anionic dispersants, cationic dispersants, electroneutral dispersants, nonionic dispersants, other dispersants and/or combinations thereof. Additionally or alternatively, the capture medium <NUM>, and therefore the slurry <NUM>, may include one or more organic bases. The organic base may include tetramethylammonium hydroxide, choline hydroxide, organolithium compounds, Grignard reagents (e.g., alkyl, vinyl, or aryl-magnesium halides), amines, tetraalkylammonium hydroxides, phosphonium hydroxides, metal alkoxides, metal amides, metal silanoates, other bases and/or combinations thereof. The capture medium <NUM> and/or slurry <NUM> may have a pH of from about <NUM> to about <NUM>, or from about <NUM> to about <NUM>, or from about <NUM> to about <NUM>, or from about <NUM> to about <NUM>, or from about <NUM> to about <NUM>. Further, one or more pollution abatement compounds may be added to the capture medium <NUM>. For example, a pollution abatement compound may include one or more compounds which is configured to capture, sequester, neutralize, decompose and/or otherwise reduce pollutants in the soot stream <NUM>. For example, in situations where the soot stream <NUM> includes HCl, NOx, volatile organic compounds or the like, pollution abatement compounds such as oxidizers may be included in the capture medium <NUM>.

According to various examples, the capture medium <NUM> is sprayed from the slurry nozzle <NUM> into the soot stream <NUM> as both a vapor and an aerosol. In a vapor, the capture medium <NUM> is in a gas phase and a temperature lower than its critical temperature. As such, the capture medium <NUM> can be condensed to a liquid. In an aerosol, the capture medium <NUM> is a suspension of fine liquid droplets. The droplets of the aerosolized capture medium <NUM> may have a diameter about <NUM> or less, about <NUM> or less, about <NUM> or less, about <NUM> or less, about <NUM> or less, about <NUM> or less, about <NUM> or less, about <NUM> or less, about <NUM> or less, about <NUM> or less, or about <NUM> or less. As the capture medium <NUM> and the soot stream <NUM> mix or combine, the particles of the soot <NUM> impact on the droplets of the aerosolized capture medium <NUM> and get collected as the slurry <NUM> as they follow in the chamber <NUM>. Further, as the vapor phase of the capture medium <NUM> mixes or combines with the soot stream <NUM>, the vapor phase of the capture medium <NUM> may condense on the soot <NUM> as the temperature of the soot stream <NUM> cools. As such, the soot <NUM> with the condensed capture medium <NUM> may agglomerate to form droplets which may in turn condense with other droplets (e.g., aerosolized capture medium <NUM> and soot <NUM> and/or condensed capture medium <NUM> on the soot <NUM>) to form the slurry <NUM> which is collected at the bottom of the chamber <NUM>.

Once the capture medium <NUM> has been sprayed into the soot stream <NUM>, a step <NUM> of passing the soot stream <NUM> and the capture medium <NUM> through the constriction <NUM> defined by the blockage <NUM> is performed. The constriction <NUM> is an aperture or opening defined by the blockage <NUM>. The blockage <NUM> may take a variety of configurations. Although depicted as a separate component than the container <NUM>, it will be understood that the blockage <NUM> may be part of the container <NUM> (i.e., inward-facing walls or baffles) without departing from the teachings provided herein. The blockage <NUM> may define one or more tapered or slanted surfaces leading to the constriction <NUM> in order to guide the soot stream <NUM>, soot <NUM>, capture medium <NUM>, condensate <NUM> and slurry <NUM> to the constriction <NUM>. The constriction <NUM> may have a generally circular, oval, oblong, triangular, square, rectangular, pentagonal or higher order polygon shape. Further, the blockage <NUM> may define a plurality of constrictions <NUM> such that the blockage <NUM> is a mesh or screen. According to various examples, the constriction <NUM> is smaller than a diameter of the soot stream <NUM>. As such, movement of the soot stream <NUM>, soot <NUM>, capture medium <NUM>, condensate <NUM> and slurry <NUM> through the constriction <NUM> may generate turbulence, an increased speed of the soot stream <NUM> and the capture medium <NUM>, and generally create conditions which increase the mixing of the soot stream <NUM>, soot <NUM>, capture medium <NUM>, condensate <NUM> and slurry <NUM>. For example, the increased speed of the soot stream <NUM> as it passes through the constriction <NUM> may increase the impact velocity between the capture medium <NUM> and the soot <NUM> such that the soot <NUM> is captured. Such a feature may be advantageous in increasing the amount of soot <NUM> from the soot stream <NUM> which is captured within the capture medium <NUM> by the above-noted processes to form the slurry <NUM>. The constriction <NUM> of the blockage <NUM> may extend for a length to ensure sufficient mixing of the soot stream <NUM>, soot <NUM>, capture medium <NUM>, condensate <NUM> and slurry <NUM>.

As explained above, capture of the soot <NUM> by the capture medium <NUM> results in the formation of the slurry <NUM>. The slurry <NUM> is collected in a bottom portion of the chamber <NUM>. The slurry <NUM> collected after the first time the capture medium <NUM> and the soot stream <NUM> are introduced may have a concentration of soot <NUM> of from about <NUM> wt% to about <NUM> wt%, or from about <NUM> wt% to about <NUM> wt%, or from about <NUM> wt% to about <NUM> wt%, or from about <NUM> wt% to about <NUM> wt%, or from about <NUM> wt% to about <NUM> wt%, or from about <NUM> wt% to about <NUM> wt% or any and all values and ranges therebetween.

Once an appreciable amount of slurry <NUM> has been captured at the bottom of the chamber <NUM>, a step <NUM> of recirculating the slurry <NUM> through the soot stream <NUM> is performed. During step <NUM>, the slurry <NUM> may be pumped from the bottom of the chamber <NUM> or other holding tank, through the heat exchanger <NUM> and back through the slurry nozzle <NUM>. The heat exchanger <NUM> may cool the slurry <NUM> from a temperature of from about <NUM>° C to about <NUM>° C to a temperature of from about <NUM>° C to about <NUM>° C, or from about <NUM>° C to about <NUM>° C. For example, upon exiting heat exchanger <NUM>, the slurry <NUM> may have a temperature of about <NUM>° C, or about <NUM>° C, or about <NUM>° C, or about <NUM>° C, or about <NUM>° C, or about <NUM>° C, or about <NUM>° C, or about <NUM>° C, or about <NUM>° C, or about <NUM>° C, or about <NUM>° C, or about <NUM>° C, or about <NUM>° C, or about <NUM>° C, or about <NUM>° C, or about <NUM>° C, or about <NUM>° C, or about <NUM>° C, or about <NUM>° C, or about <NUM>° C, or about <NUM>° C or any and all values and ranges therebetween.

Similar to the capture medium <NUM>, the slurry <NUM> may be sprayed into the soot stream <NUM> in an aerosol and/or vapor form. The slurry <NUM>, when sprayed into the soot stream <NUM>, functions similarly to the capture medium <NUM> in collecting soot <NUM> from the soot stream <NUM> by impacting the soot <NUM> (i.e., aerosolized slurry <NUM>) and/or condensing on the soot <NUM> (i.e., vapor form slurry <NUM>). By recirculating and spraying the slurry <NUM> into the soot stream <NUM>, the wt% of soot <NUM> present in the slurry <NUM> may be increased. The slurry <NUM> is recirculated through the soot stream <NUM> until the slurry <NUM> has a wt% of soot <NUM> of from about <NUM> wt% to about <NUM> wt%, or from about <NUM> wt% to about <NUM> wt%, or from about <NUM> wt% to about <NUM> wt%, or from about <NUM> wt% to about <NUM> wt%, or from about <NUM> wt%. For example, the slurry <NUM> may be recirculated through the soot stream <NUM> until the slurry <NUM> has a wt% of soot <NUM> of about <NUM> wt%, or about <NUM> wt%, or about <NUM> wt%, or about <NUM> wt%, or about <NUM> wt%, or about <NUM> wt%, or about <NUM> wt%, or about <NUM> wt%, or about <NUM> wt%, or about <NUM> wt%, or about <NUM> wt%, or about <NUM> wt%, or about <NUM> wt%, or about <NUM> wt%, or about <NUM> wt%, or about <NUM> wt%, or about <NUM> wt%, or about <NUM> wt%, or about <NUM> wt%, or about <NUM> wt%, or about <NUM> wt%, or about <NUM> wt%, or about <NUM> wt%, or about <NUM> wt%, or about <NUM> wt%, or about <NUM> wt%, or about <NUM> wt%, or about <NUM> wt%, or about <NUM> wt%, or about <NUM> wt%, or about <NUM> wt% or any and all values and ranges therebetween. It will be understood that the slurry <NUM> may be recirculated through the soot stream <NUM> a single time or a plurality of times in order to reach the final wt% of soot <NUM> in the slurry <NUM>. The final wt% of soot <NUM> in the slurry <NUM> may be based on a predetermined amount of soot <NUM> in the slurry <NUM> and/or until the viscosity of the slurry <NUM> becomes too great to be handled by pumps (e.g., pumps moving the slurry <NUM>) and/or slurry nozzle <NUM>.

Simultaneously with step <NUM> and/or step <NUM>, a step <NUM> of condensing the soot stream <NUM> and the capture medium <NUM> to the condensate <NUM> and a step <NUM> of passing the condensate <NUM> through the condensate nozzle <NUM> and into the soot stream <NUM> proximate the outlet <NUM> of the burner <NUM> may be performed. In operation, a portion of the soot stream <NUM>, the soot <NUM>, the capture medium <NUM> and/or the slurry <NUM>, may not be captured and collect at the bottom of the chamber <NUM> as the slurry <NUM>. Such an uncaptured portion may still exist as a gas or vapor phase in the chamber <NUM>. As such, the remaining portion of the soot stream <NUM> and the capture medium <NUM> and/or slurry <NUM> may be passed through the condenser <NUM>. The condenser <NUM> is configured to condense vaporized liquids (e.g., the capture medium <NUM>, water or byproducts present as a result of the combustion at the burner <NUM>, and or slurry <NUM>) into the condensate <NUM>. As such, the condensate <NUM> may contain a mixture of the capture medium <NUM> and/or water (or other liquids) and any soot <NUM> still present in the soot stream <NUM>. The condensate <NUM> is passed back into the soot stream <NUM> proximate the outlet <NUM> of the burner <NUM> through the condensate nozzle <NUM>. It will be understood that similar to the slurry <NUM>, the condensate <NUM> may be passed cooled to a predetermined temperature. Similar to the slurry nozzle <NUM>, the condensate nozzle <NUM> is configured to pass the condensate <NUM> as an aerosol and/or as a vapor. Use of the condenser and the condensate nozzle <NUM> may be advantageous in retaining the amount of capture medium <NUM> within the system <NUM> (i.e., as it is not exhausted out of the system <NUM>) while simultaneously being used to capture additional soot <NUM> from the soot stream <NUM>. Gases of the soot stream <NUM> may then be passed to the pollution abatement system <NUM> where any remaining soot <NUM> present in the gases may be filtered out or scrubbed and the gases exhausted.

Once the slurry <NUM> has a predetermined wt% of the soot <NUM> in the slurry <NUM>, the slurry <NUM> may be removed from the system <NUM> and stored.

Referring now to <FIG>, depicted is an article forming method <NUM>. In the depicted example, the forming method <NUM> may be referred to as a "sol-gel" process, but it will be understood that the article forming method <NUM> may be a variety of manufacturing processes of the article <NUM> using the soot <NUM> and/or the slurry <NUM>. As such, the sol-gel process is only one of many examples of the article forming method <NUM>. For example, the soot <NUM> may be utilized in a soot pressing process (e.g. to form optical fiber preforms or substrates) and/or the slurry <NUM> may be used as a feedstock in suspension plasma spraying for a coating application.

Variations in the operation of the system <NUM> may cause the composition (e.g., the relative wt% of SiO<NUM> to TiO<NUM> of soot <NUM> or the wt% of soot <NUM> in the slurry <NUM> to vary from process run to process run. As such, the composition of the slurry <NUM> may deviate from that of the desired composition of the article <NUM> or the wt% of soot <NUM> in the slurry <NUM> may deviate from a desired soot wt% for formation of the glass article <NUM>. In such an example, the article forming method <NUM> may begin with an optional step <NUM> of mixing a second slurry (i.e., formed during a different process run of the system <NUM> or method <NUM>) with the slurry <NUM>. In such an example, the second slurry may have a different soot wt% than the slurry <NUM>, or may have a different compositional make up (e.g., different relative amounts of SiO<NUM> and TiO<NUM> and/or different dopants or constituents) compared to the slurry <NUM>. Such a feature may be advantageous in achieving the desired composition of the slurry <NUM> and the desired wt% of soot <NUM> in the slurry <NUM>. Further, mixing of various batches of the slurry <NUM> may be advantageous in decreasing the production of slurry <NUM> which is ultimately wasted due to non-conformity with predetermined specifications.

Once the slurry <NUM> is at a predetermined wt% of soot <NUM> and has a predetermined composition (i.e., through use of a single slurry <NUM> or the mixing of slurries <NUM>), a step <NUM> of filtering the slurry <NUM> through a filter or a mesh screen may performed. Filtering of the slurry <NUM> is configured to remove contaminants and/or to break agglomerations of the soot <NUM> present in the slurry <NUM> into smaller (e.g., less than <NUM>) particle aggregate sizes. In such an operation, the mesh screen may be composed of stainless steel or other materials which will not contaminate the slurry <NUM>. According to various examples, the mesh screen may be configured to filter out particle aggregates having a size (i.e. longest linear dimension) of about <NUM> or greater. Filtering of the slurry <NUM> can be assisted by applying a pressure differential across the mesh screen (i.e., pressure filtration or vacuum filtration). If the contaminants are large or numerous enough such that the openings of the mesh screen get plugged, the mesh screen can be cleaned manually or by temporarily reversing the flow of the slurry <NUM> through the mesh screen to dislodge the contaminants. Additionally or alternatively, Stokes settling can separate large or dense contaminants or particle aggregates from the slurry <NUM>. Filtering of the slurry <NUM> may advantageously result in a stirring of the slurry <NUM>. Stirring of the slurry <NUM> may improve the compositional homogeneity by preventing stratification and/or agglomeration of certain types of soot <NUM> (e.g., SiO<NUM> vs TiO<NUM> particles). It will be understood that step <NUM> may be carried out by recirculating the slurry <NUM> in the system <NUM> for some amount of time after the soot generation has been stopped (i.e., the burner <NUM> is no longer producing the soot stream <NUM>) or by using a separate mixing vessel. It will be understood that step <NUM> of filtering the slurry <NUM> may be performed a plurality of times during the method <NUM> without departing from the teachings provided herein.

Next, a step <NUM> of generating a vacuum over the slurry <NUM> is performed. Generation of the vacuum has the effect of removing adsorbed or trapped gases from the soot <NUM> by holding the slurry <NUM> in a vacuum. In other words, the slurry <NUM> is degassed in step <NUM>. The soot <NUM> that is generated by the combustion process at the burner <NUM> has a relatively high surface area and therefore may adsorb gas at its surface. This gas is entrained into the slurry <NUM> as the soot <NUM> is captured, but can be removed by evacuating the space above the slurry <NUM>. According to various examples, the generation of the vacuum above the slurry <NUM> may take place in a dedicated vessel downstream of system <NUM>. The vacuum level above the slurry <NUM> may be modulated in order to accelerate the breaking up of bubbles forming at the surface of the slurry <NUM>. The vacuum over the slurry <NUM> may have a pressure of from about <NUM> atm to about. <NUM> atm, or from about <NUM> atm to about <NUM> atm, or from about <NUM> atm to about <NUM> atm, or from about <NUM> atm to about <NUM> atm, or from about <NUM> atm to about <NUM> atm, or from about <NUM> atm to about <NUM> atm, or from about <NUM> atm to about <NUM> atm, or from about <NUM> atm to about <NUM> atm, or from about <NUM> atm to about <NUM> atm, or from about <NUM> atm to about <NUM> atm or any and all values and ranges therebetween. Step <NUM> of generating the vacuum may be performed for about <NUM> seconds, or about <NUM> minute, or about <NUM> minutes, or about <NUM> minutes, or about <NUM> minutes, or about <NUM> minutes, or about <NUM> minutes, or about <NUM> minutes, or about <NUM> minutes, or about <NUM> minutes or about <NUM> minutes, or about <NUM> minutes or greater than about <NUM> minutes. It will be understood that step <NUM> of generating the vacuum over the slurry <NUM> may be performed a plurality of times during the forming method <NUM>.

Once the slurry <NUM> is degassed, a step <NUM> of adding a pH modifier to the slurry <NUM> is performed. It will be understood that the pH modifier may also be known as a pH shifter. The pH modifier is configured to reduce the pH of the slurry <NUM>. In a typical embodiment, the slurry <NUM> is basic (e.g., due to the presence of a base or dispersant). The pH of the slurry <NUM> may be greater than <NUM>, or greater than <NUM>, or greater than <NUM>, or greater than <NUM>, or greater than <NUM>. Reducing the pH of the slurry <NUM> toward neutral (e.g. to a pH less than <NUM>, or less than <NUM>, or less than <NUM>, or less than <NUM>, or less than <NUM>) over some period of time. Shifting of the pH of the slurry <NUM> from basic to neutral may promote gelling or an increase of viscosity of the slurry <NUM>. The pH modifier may include esters, formaldehyde, paraformaldehyde, formamide, glyoxal, methyl formate, methyl acetate, ethyl formate, ethyl acetate, organic acids, other pH modifiers and/or combinations thereof. The pH modifier may be added in small amounts to avoid developing regions of high concentration within the slurry <NUM> which would cause premature gelling at localized positions. Once the pH modifier is added to the slurry <NUM>, the slurry <NUM> may optionally be filtered, stirred or degassed again.

Next, prior to full gelation of the slurry <NUM>, a step <NUM> of casting the slurry <NUM> into a receptacle is performed. The receptacle may be near net shape to the ultimate shape of the glass article <NUM>, or may be a shape from which the glass article <NUM> may be easily singulated. The receptacle may have a smooth surface which is in contact with the slurry <NUM> in order to prevent sticking or adherence of the slurry <NUM> to the receptacle. According to various examples, a mold release agent may be applied to the surface of the receptacle prior to the casting of the slurry <NUM> into the receptacle. The mold release agent may be dry polytetrafluoroethylene lubricant, wax, other dry lubricants, a wet lubricant, other lubricants and/or combinations thereof. The casting of the slurry <NUM> may be carried out so that gasses are not generated and/or entrained in the slurry <NUM> as it is cast into the receptacle. Casting of the slurry <NUM> into the receptacle with minimal entrained gasses may be accomplished by maintaining an unbroken stream of slurry <NUM> when transferring the slurry <NUM> from a container into the receptacle.

Once the slurry <NUM> is within the receptacle, a step <NUM> of gelling the slurry <NUM> to form a gelled body is performed. During gelling of the slurry <NUM>, the receptacle may be covered tightly and the slurry <NUM> is allowed to gel. Gelling of the slurry <NUM> to form the gelled body may take from about <NUM> hour to about <NUM> hours, or from about <NUM> hours to about <NUM> hours, or from about <NUM> hours to about <NUM> hours. Gelling of the slurry <NUM> into the gelled body may be carried out at a temperature of from about <NUM>° C to about <NUM>° C, or from about <NUM>° C to about <NUM>° C, or from about <NUM>° C to about <NUM>° C, or from about <NUM>° C to about <NUM>° C, or from about <NUM>° C to about <NUM>° C, or from about <NUM>° C to about <NUM>° C, or from about <NUM>° C to about <NUM>° C, or from about <NUM>° C to about <NUM>° C, or from about <NUM>° C to about <NUM>° C or any and all values and ranges therebetween. The gelling of the slurry <NUM> may be increased as temperatures above ambient temperatures (e.g., about <NUM>° C) are used. Gelling of the slurry <NUM> may be complete once the pH of the slurry <NUM> is about <NUM> or less, or about <NUM> or less, or about <NUM> or less, or about <NUM> or less, or about <NUM> or less, or about <NUM> or less, or about <NUM> or less, or about <NUM> or less or any and all values and ranges therebetween. Shrinkage of the slurry <NUM> during the gelling process may occur and can cause cracking of the gelled body, especially where the gel tends to adhere to the receptacle. Minimization of this cracking may be achieved through the above-noted use of a mold release material and/or the receptacle having smooth surfaces in contact with the slurry <NUM>. According to some examples, the slurry or gelled body is released from the receptacle as soon as it is gelled sufficiently to withstand removal.

Next, a step <NUM> of drying the gelled body to form a green body is performed. Step <NUM> may begin while the gelled body is still positioned in the receptacle or after the gelled body has been removed from the receptacle. In examples where drying of the gelled body begins in the receptacle, a lid of the receptacle may be raised (e.g., from about <NUM> to about <NUM>) to allow the evaporation of moisture in the gelled body. At this point the gelled body may shrink by a few percent (e.g., from about <NUM>% to about <NUM>% linearly). Regardless of whether or not the gelled body begins drying in the receptacle, the gelled body may be removed from the receptacle and placed on a substrate. The substrate may be composed of ultrahigh molecular weight high-density polyethylene with a plurality of polytetrafluoroethylene tape strips. The gelled body may be allowed to dry in air (e.g., at ambient temperatures) for an extended period of time (e.g., from about <NUM> days to about <NUM> days) until a water content within the gelled body reaches a predetermined amount and the gelled body becomes the green body. For example, the gelled body may be air dried until a water content of the gelled body is about <NUM> wt% or less, or about <NUM> wt% or less, or about <NUM> wt% or less, or about <NUM> wt% or less, or about <NUM> wt% or less, or about <NUM> wt% or less, or about <NUM> wt% or less, or about <NUM> wt% or less, or about <NUM> wt% or less, or about <NUM> wt% or less, or about <NUM> wt% or less, or about <NUM> wt% or less, or about <NUM> wt% or less or any and all values therebetween. Once the gelled body reaches the predetermined water content, the gelled body may be heated to remove the remaining water. According to various examples, the gelled body may be heated to from about <NUM>° C to about <NUM>° C for an extended period of time (e.g., about <NUM> hours) in air to remove the remaining water. Organic materials remaining in within the green body after the drying process may be removed by heating the green body to an elevated temperature for a period of time. For example, the green body may be heated to a temperature of from about <NUM>° C to about to <NUM>° C, or from about <NUM>° C to about <NUM>° C, or about <NUM>° C. The green body may be heated for a time period of from about <NUM> hours to about <NUM> hours, or from about <NUM> hours to about <NUM> hours or about <NUM> hours.

Next, a step <NUM> of consolidating the green body to form the glass article <NUM> is performed. Consolidation of the green body to form the glass article <NUM> may be performed in a reduced-pressure atmosphere (e.g., less than or equal to about <NUM> Torr oxygen) and/or in an inert gas (e.g., helium, argon, neon, etc.). The green body may be consolidated at a temperature of from about <NUM>° C to about <NUM>° C, or from about <NUM>° C to about <NUM>° C, or from about <NUM>° C to about <NUM>° C, or from about <NUM>° C to about <NUM>° C. For example, consolidation may take place at a temperature of about <NUM>° C, or about <NUM>° C, or about <NUM>° C, or about <NUM>° C, or about <NUM>° C, or about <NUM>° C, or about <NUM>° C, or about <NUM>° C, or about <NUM>° C, or any and all values and ranges therebetween. Doping can be achieved by adding a partial pressure of steam or other dopants during the consolidation.

In SiO<NUM> and TiO<NUM> compositional examples, consolidation of the green body may result in a translucent glass article <NUM> due, for example, to the presence of titania nanocrystals. These nanocrystals can be dissolved in the glass article <NUM> through a step <NUM> of heating the glass article <NUM>. The heating (i.e., or reheating since the glass article <NUM> had already been consolidated under heat) of the glass article <NUM> may be at a temperature of from about <NUM>° C to about <NUM>° C, or from about <NUM>° C to about <NUM>° C, or from about <NUM>° C to about <NUM>° C. For example, the article <NUM> may be reheated to a temperature of about <NUM>° C, or about <NUM>° C, or about <NUM>° C, or about <NUM>° C, or about <NUM>° C, or about <NUM>° C, or about <NUM>° C, or about <NUM>° C, or about <NUM>° C or any and all values and ranges therebetween. The reheating of the article <NUM> may be carried out for about <NUM> minutes, or about <NUM> minutes, or about <NUM> minutes, or about <NUM> minutes, or about <NUM> minutes, or about <NUM> minutes, or about <NUM> minutes, or about <NUM> minutes, or about <NUM> minutes, or about <NUM> minutes, or about <NUM> minutes, or about <NUM> minutes, or about <NUM> minutes, or about <NUM> minutes, or about <NUM> minutes, or about <NUM> minutes, or about <NUM> minutes, or about <NUM> minutes, or about <NUM> minutes, or about <NUM> minutes or any and all values and ranges therebetween. It will be understood that step <NUM> may be carried out for a time period of about <NUM> hours or greater without departing from the teachings provided herein. Reheating of the article <NUM> may result in the dissolution of the titania nanocrystals and produce a clear glass article <NUM>. The glass article <NUM> may then be trimmed, ground and polished. Further, the glass article <NUM> may be cut or singulated to form a plurality of glass articles <NUM>.

Use of the presently disclosed soot generation and capture system <NUM>, method <NUM> and forming method <NUM> may offer a variety of advantages.

First, use of the slurry nozzle <NUM> and the condensate nozzle <NUM> proximate the outlet <NUM> of the burner <NUM> may reduce the temperature of the soot stream <NUM> and soot <NUM> prior to reaching the pollution abatement system <NUM>. Gases and soot <NUM> of the soot stream <NUM> are generated at high temperatures (e.g., about <NUM>° C) at the burner <NUM> during combustion. Particles of soot <NUM> which reach the pollution abatement system <NUM> at these elevated temperatures may damage bags, filters and other components. By spraying the capture medium <NUM>, slurry <NUM> and condensate <NUM> into the soot stream <NUM> proximate the burner <NUM>, the temperature of the gases and soot <NUM> which eventually reach the pollution abatement system <NUM> may be drastically decreased such that damage to the pollution abatement system <NUM> may be minimized and/or eliminated. Further, as the system <NUM> is cooled by the capture medium <NUM>, the present disclosure may offer a more compact and space efficient design than conventional air-cooled systems.

Second, as the soot <NUM> is captured in the capture medium <NUM> and is mixed, stirred or otherwise homogenized, better compositional uniformity of the resulting glass article <NUM> may be achieved. Conventional photomask blanks are produced by burning a combined flow of OMCTS and TPT and either collecting or depositing the resultant particles. As the ratio of the OMCTS and TPT can vary over time, compositional variations of Si and/or Ti within the particles of soot <NUM> collected or deposited may result in non-uniform regions within a single photomask or the composition of the photomasks may vary across a production run. As such, each conventional individual photomask may need to be validated for composition and each may require a unique post-fabrication heat treatment to achieve the target properties (e.g., clarity and/or cross-over temperature). Using the present disclosure, the soot <NUM> generated from an entire run of the method <NUM> would be captured into the slurry <NUM> which would then be homogenized by mixing the slurry <NUM>. Such a feature may be advantageous in ensuring that the composition of the articles <NUM> produced using the method <NUM> all have the same composition and thus the same heat treatment cycle and optical properties.

Third, capturing of the soot <NUM> in the capture medium <NUM> leads to less agglomeration of the soot <NUM>. In conventional soot generation processes, the particles of the soot <NUM> are captured onto fiber bags across which a pressure differential is applied. The particles are pressed onto the bags until an air pulse knocks the pressed soot off the bags and into a collection hopper. This pressing action, along with potentially high moisture levels from the combustion by-products, can cause the particles to form agglomerates that survive the pressing process. The agglomerates may result in gas seeds and/or compositional inhomogeneities in the final article <NUM>. Use of the method <NUM> allows for agglomerates to be dispersed away by mechanical mixing or removed by filtration of the slurry <NUM>.

Fourth, use of the forming method <NUM> and system <NUM> allow for greater flexibility to adjust the composition of the slurry <NUM> and the resulting article <NUM>. For example, the composition (e.g., SiO<NUM> to TiO<NUM> ratio and/or soot wt%) of the slurry <NUM> may be adjusted up or down by mixing a second slurry with a different composition with the slurry <NUM>. Such adjustments may allow very precise control of the composition for tuning the final properties of the glass article <NUM>.

Fifth, use of the present disclosure may offer less contamination relative to conventional processes. In conventional soot pressing processes, there may be no remediation possible to any contaminants that enter the burner exhaust gases and the dry soot is difficult to sift efficiently. Such contaminants include dust from the manufacturing environments, fibers from the collection bags, large soot agglomerates and other contaminants. As the present disclosure offers the liquid slurry <NUM>, contaminants may be removed or filtered by various methods (e.g., the mesh screen, Stokes settling).

Sixth, use of the system <NUM> and forming method <NUM> may offer near net shape articles <NUM>. Conventional processes produce large articles which are pressed, consolidated, remelted, and then cut into the photomask shapes. Use of the present disclosure offers the ability to cast near-net shape articles <NUM> which may need only minor trimming and polishing to form the article <NUM>.

Seventh, use of the forming method <NUM> may offer higher quality glass articles <NUM>. In conventional article formation, contaminants cannot be removed from the soot after generation and capture, and end up in the photomask blanks in the form of inclusions. Also, large pressed parts are difficult to press to a uniform density such that voids can form that result in gas seeds in the final article <NUM>. Finally, gas diffusion in and out of a large pressed soot part may take much longer than in a small thin part such that the removal of trapped gas and/or residual organic matter within the pressed part is significantly more time-consuming than for small parts. Use of the method <NUM> allows contaminants to be filtered while still in the slurry <NUM>, the density of the green parts to be uniform with little to no void formation, and for adsorbed gas to be removed during the evacuation of the slurry <NUM> (e.g., step <NUM>). The resulting glass article <NUM> may be free of gas seeds after consolidation so that only a mild reheat (e.g., to temperatures about <NUM>° C) may be necessary to obtain transparent glass.

Eighth, the forming method <NUM> may allow for ease of doping of the glass article <NUM>. Conventional soot pressing processes produce large (e.g., from about <NUM> to about <NUM>) pressed soot bodies that may require OH doping by consolidating in a steam-containing atmosphere. These large parts may have relatively low thermal conductivity and long diffusion distances such that a long doping duration may be needed to achieve thermal uniformity throughout the part and to diffuse the dopant (e.g., water) uniformly. Use of the method <NUM> and system <NUM> may produce green bodies which are thin and therefore have a short diffusion distance which results in faster heating and uniform diffusion of the optional dopants.

Ninth, as the soot <NUM> is captured within the capture medium <NUM> proximate the outlet <NUM> of the burner <NUM>, a lower amount of total gas needs to be passed through the burner <NUM> as compared to conventional designs. In conventional designs, the combustion of source chemicals to produce soot often produces insufficient volumetric flow of gas to move the soot to a requisite capture point or a pollution scrubbing system. As such, ambient air often needs to be drawn to aid in carrying the soot. Often, ambient air contains contaminants which lead to defects in products made from the soot. Use of the presently disclosed system <NUM> avoids the contaminant issue as little to no ambient air is necessary to transport the soot <NUM>. For example, as the capture medium <NUM> is introduced to the soot stream <NUM> proximate the outlet <NUM> of the burner <NUM>, the soot <NUM> does not need to be carried a great distance and as such little to no ambient air which may contain contaminants is needed.

Tenth, as the soot <NUM> is stored in the capture medium <NUM> as the slurry <NUM>, the system <NUM> may offer a more compact and space efficient storage of the soot <NUM> as compared to conventional designs. Conventional storage of soot is often inefficient as the soot has a high surface area and low packing density. Such features lead to large volumes of relatively low weight soot storage. Use of the presently disclosed system <NUM> allows for the soot <NUM> to be stored in a more compact form as the slurry <NUM> thereby decreasing the overall required area for storage of the soot <NUM>.

Modifications of the disclosure will occur to those skilled in the art and to those who make or use the disclosure. Therefore, it is understood that the embodiments shown in the drawings and described above are merely for illustrative purposes and not intended to limit the scope of the disclosure, which is defined by the following claims.

Claim 1:
A method of capturing soot (<NUM>), comprising:
combusting a first precursor in a burner (<NUM>) to produce a soot stream (<NUM>) comprising soot (<NUM>), the first precursor including a compound configured to produce soot (<NUM>) including at least one of Ti, Si, Mg, Fe, P and/or Ca when combusted;
passing a capture medium (<NUM>) into the soot stream (<NUM>) proximate the burner (<NUM>) such that the soot (<NUM>) is captured in the capture medium (<NUM>) and forms a slurry (<NUM>); and
recirculating the slurry (<NUM>) through the soot stream (<NUM>) such that the slurry (<NUM>) is from about <NUM> wt% to about <NUM> wt% of the soot (<NUM>),
wherein the capture medium (<NUM>) is passed or directed into the soot stream (<NUM>) at an impact region (<NUM>), wherein the impact region (<NUM>) is the area at which the capture medium (<NUM>) first contacts the soot stream (<NUM>) to form the slurry (<NUM>), wherein a distance between an outlet (<NUM>) of the burner (<NUM>) and the impact region (<NUM>) is <NUM> or less, wherein the soot stream (<NUM>) exits the burner (<NUM>) at the outlet (<NUM>).