UNITED STATES DEPARTMENT OF COMMERCE
`United States Patent and Trademark Office
`
`April 04, 2016
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`THIS IS TO CERTIFY THAT ANNEXED IS A TRUE COPY FROM THE
`RECORDS OF TIDS OFFICE OF THE FILE WRAPPER AND CONTENTS
`OF:
`
`APPLICATION NUMBER: 111762,654
`FILING DATE: June 13, 2007
`PATENT NUMBER: 7,780,890
`ISSUE DATE: August 24, 2010
`
`By Authority of the
`Under Secretary of Commerce for Intellectual Property
`and Director of the United States Patent and Trademark Office
`
`-~.-::r-9 ~
`} "<--z____.-~
`/_
`"
`-
`P.R. GRANT
`Certifying Officer
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`ASPEN0000904
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`ALISON – Ex. 1002
`Alison v. Aspen
`IPR2017-00152
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`

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`ADVANCED GEL SHEET PRODUCTION
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`Docket No: 1008-05
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`CROSS REFERENCE TO RELATED APPLICATIONS
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`5
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`This application is a continuation application of, and incorporates by reference the entirety of
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`pending U.S. patent application Ser. No. 10/876,1 03, which was filed on Jun. 23, 2004, and
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`which claimed priority from, and incorporated by reference the entirety of U.S. Provisional
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`Patent Application Ser. No. 60/482,359, which was filed on Jun. 24, 2003, and which is now
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`1. Field of the Invention
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`abandoned.
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`DESCRIPTION
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`This invention relates to the preparation of solvent filled gel sheets in a continuous fashion. Such
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`gel sheets are used in manufacturing aerogel blankets, aerogel composites, aerogel monoliths and
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`other aerogel based products.
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`2. Description of Related Art
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`Aerogels describe a class of material based upon their structme, namely low density, open cell
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`20
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`structures, large surface areas (often 900 m2/g or higher) and sub-nanometer scale pore sizes.
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`Supercritical and subcritical fluid extraction technologies are commonly used to extract the fluid
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`from the fragile cells of the material. A variety of different aerogel compositions are known and
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`may be inorganic or organic. Inorganic aerogels are generally based upon metal alkoxides and
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`include materials such as si.lica, carbides, and alumina. Organic aerogels include, but are not
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`limited to, urethane aerogels, resorcinol formaldehyde aerogels, and polyimide aerogels.
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`Low-density aerogel materials (0.01-0.3 glee) are widely considered to be the best .solid thermal
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`insulators, better than the best rigid foams with thermal conductivities of 10-15 mW/m-K and
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`Docket No: 1008-05
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`below at 100° F. and atmospheric pressure. Aerogels function as thermal insulators primarily by
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`minimizing conduction (low density, tortuous patb for heat transfer through the solid
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`nanostructure), convection (very small pore sizes minimize convection), and radiation (IR
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`absorbing or scattering dopants are readily dispersed throughout the aerogel matrix). Depending
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`on the formulation, they can function well at cryogenic temperatures to 550° C. and above.
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`Aerogel materials also display many other interesting acoustic, optical, mechanical, and chemical
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`properties that make them abundantly useful.
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`Low-dens ity insulating materials have been developed to solve a number of thermal isolation
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`problems in applications in which the core insulation experiences significant compressive forces.
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`For instance, polymeric materials have been compounded with hollow glass microspheres to
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`create syntactic foams, which are typically very stiff, compression resistant materials. Syntactic
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`materials are well known as insulators for underwater oil and gas pipelines and support
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`equipment. Syntactic materials are relatively inflexible and of high thermal conductivity relative
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`to flexible aerogel composites (aerogel matrices reinforced by fiber). Aerogels can be formed
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`from flexible gel precursors. Vari.ous flexible Layers, including flexible fiber-reinforced aerogels,
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`can be readily combined and shaped to give pre-forms that when mechanically compressed along
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`one or more axes, give compressively strong bodies along any of those axes. Aerogel bodies that
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`are compressed in this manner exhibit much better thermal insulation val.ues than syntactic
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`foams. Methods to produce these materials rapidly will facilitate large-scale use of these
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`materials in underwater oil and gas pipelines as external insulation.
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`Conventional methods for gel sheet and/or fiber-reinforced composite gel sheet production
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`formed via sol-gel chemistry described in the patent and scientific literature invariably involve
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`batch casting. Batch casting is defined here as catalyzing one entire volume of sol to induce
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`gelation simultaneously throughout that volume. Gel-forming techniques are well-known to
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`those trained in the art: exampl.es include adjusting the pH and/or temperature of a dilute metal
`
`oxide sol to a point where gelation occms (R. K. Iler, Colloid Chemistry of Silica and Silicates,
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`1954, chapter 6; R. K. Iler, The Chemistty of Silica, 1979, chapter 5, C. J. Brinker and G. W.
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`30
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`Scherer, Sol-Gel Science, 1990, chapters 2 and 3).
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`ASPEN0000906
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`Docket No: 1008-05
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`U.S. Pat. No. 6,068,882 (Ryu) discloses an example of a fiber-reinforced aerogel composite
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`material that can be practiced with the embodiments of the present invention. The preferred
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`aerogel composite precursor materials used in the present invention are those like Clyogel®,
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`Pyrogel®, or Spaceloft™ sold commercially by Aspen Aerogels, Incorporated. U.S. Pat. No.
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`5,306,555 (Ramammthi et al.) discloses an aerogel matrix composite of a bulk aerogel with
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`fibers dispersed within tbe bulk aerogel and a method for preparing the aerogel matrix
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`composite.
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`SUMMARY OF THE INVENTION
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`This invention describes continuous and semi-continuous sol-gel casting methods that are greatly
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`improved over conventional batch sol-gel casting methods for gel sheets, fiber-reinforced
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`flexible gel sheets, and rolls of composite gel materials.
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`More specifically, the invention describes methods for continuously combining a low viscosity
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`solution of a sol and an agent (heat catalyst or chemical catalyst) that induces gel formation and
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`forming a gel sheet on a moving element such as a conveyer belt with edges that defines the
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`volume of the formed gel sheet by dispensing the catalyzed sol at a predetermined rate effective
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`to allow gelation to occuer on the moving element. The sol includes an inorganic, organic or a
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`combination of inorganic/organic hybrid materials. The inorganic materials include zirconia,
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`yttria, hafnia, alumina, titania, ceria, and silica, magnesium oxide, calcium oxide, magnesium
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`fluoride, calcium fluoride, and any combinations of the above. Organic materials include
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`polyacrylates, polyolefins, polystyrenes, polyacrylonitriles, polyurethanes, polyimides,
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`polyfurfural alcohol, phenol furfuryl alcohol, melamine formaldehydes, resorcinol
`
`formaldehydes, cresol formaldehyde, phenol formaldehyde, polyvinyl alcohol dialdehyde,
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`polycyanurates, polyacrylamides, various epoxies, agar, agarose and any combinations of the
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`above. Even more specifically, the methods describe the formation of monolithic gel sheets or
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`fiber-reinforced gel composite having two parts, namely reinforcing fibers and a gel matrix
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`30 wherein the reinforcing fibers are in the form of a lofty fibrous structure (i.e. batting), preferably
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`Docket No: 1008-05
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`based upon either thermoplastic polyester or silica fibers, and more preferably in combination
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`with individual randomly distributed short fibers (microfibers) in a continuous or semi(cid:173)
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`continuous fashion. The fibrous batting or mat material is introduced onto the moving element
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`for combination with the catalyzed sol prior to gelation.
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`Moreover, when a gel matrix is reinforced by a lofty batting material, particularly a continuous
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`non-woven batting comprised of very low denier fibers, the resulting composite material when
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`dried into an aerogel or xerogel product by solvent extraction, maintains similar thermal
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`properties to a monolithic aerogel or xerogel in a much stronger, more durable form. The
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`diameter of the fibers used is in the range of 0. I -10,000 microns. In some cases the fiber batting,
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`crimped fibers can be distributed throughout the gel structure.
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`Even more specifically, the methods describe methods to continuously or semi-continuously
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`form gel composites by introduction of an energy dissipation zone on the moving conveyor
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`apparatus. The gelation of the catalyzed sol can be enhanced by chemical or energy dissipation
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`process. For instance, a controlled flux of electromagnetic (ultraviolet, visible, infrared,
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`microwave), acoustic (ultrasound), or particle radiation can be introduced across the width of a
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`moving sol volume contained by a conveyor belt to induce sufficient cross-linking of the
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`polymers contained within the sol to achieve a gel point. The flux, the point and the area of
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`radiation can be controlled along the conveyance apparatus to achieve an optimized casting rate
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`and desirable gel properties by the time the terminus of the conveyor is reached for a given
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`section of gel. In this fashion, gel properties can be controlled in a novel fashion to a degree not
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`possible with batch casting methods. In addition, another moving element rotating in the
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`opposite direction to the fust moving element can be used to provide the shape of the top portion
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`of the gel sheets.
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`Still more specifically, a roll of gel composite material that is co-wound or corolled with a
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`porous flow layer that facilitates solvent extraction using supercritical fluids processing methods
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`can be formed in a very small footprint using the method of the present invention. This is
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`30
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`accomplished via infusing a predetermined amount of catalyzed sol in a rolled fiber-preform co-
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`Docket No: 1008-05
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`rolled with an impermeable spacer layer, geling the infused roll, followed by un-rolling the gel
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`composite article, removing the impermeable layer, andre-rolling of the incompletely cured
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`body flexible gel composite with a porous spacer layer. The method described in this invention
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`provides great advantage in enhancing the rate of production of gel composite materials in as
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`5
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`small an area as possible.
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`Still more specifically, a method for producing gel sheets in a continuous fashjon is described in
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`which gel sheets are produced by any one of the above mentioned methods and are rolled into a
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`p lurality of layers. This is a novel and effective way of producing gel sheets for efficient drying
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`operations. In another feature, an optional spacer material is co-rolled with the gel sheets. Such a
`spacer material can be permeable or impermeable in nature. Depending on the permeability of
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`the spacer material, one can obtain a favorable flow pattern in a subsequent drying. Spacer
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`material also provides flow paths for subsequent silation (aging) fluids to easily pass through. In
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`the drying they fmther help by proving flow paths that effectively reduce the thickness of the gel
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`15
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`sheet to be extracted in in radial direction.
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`These and still further embodiments of the present invention are described in greater detail
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`below. The advantages of the methods described in this invention for processing monolith and
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`fiber-reinforced composite sheets in a continuous or semi-continuous fashion over previously
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`20
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`described methods are many. For instance, the gel articles can be fashioned continuously or
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`semi-continuously provided all components are fed into the apparatus at the appropriate rate.
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`Thus, Large volumes of material can be fashioned in a smaller production area than with
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`traditional batch casting requiring molds that must be filled and allowed to set for aging prior to
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`solvent exh·action to make aerogel or xerogel materials. Very long continuous sheets offiber-
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`25
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`reinforced, flexible gel material are readily fashioned using the methods oftbis invention
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`because of the combined casting and rolling processing allows a single molding surface to be
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`continuously re-utilized within a small production area. When rolls of gel are cast batchwise
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`followed by roll-to-roll processing to place porous flow layers between layers of gel material, the
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`production footprint is diminished even further, increasing production capacity and potentially
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`lowering production costs relative to flat sheet batch casting.
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`Docket No: 1008-05
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`BRIEF DESCRIPTION OF THE ORA WfNGS
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`FIG. 1 illustrates a method of producing fiber reinforced gel sheets using a counter rotating
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`conveyor belt.
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`FIG. 2 illustrates a method of producing fiber reinforced gel sheets using a single rotating
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`conveyor belt.
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`FIG. 3 illustrates a method of producing fiber reinforced gel sheets using a counter rotating
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`conveyor belt with additional cutting.
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`FIG. 4 illustrates a method of producing fiber reinforced gel sheets using a single rotating
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`conveyor belt with additional cutting.
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`FIG. 5 illustrates the general flow diagram of catalyst-sol mixing prior to casting.
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`FIG. 6 iLLustrates an additional embodiment with dispensing the catalyzed sol to a preformed ro ll
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`including spacer layers.
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`FIG. 7 illustrates an additional embodiment for producing gel sheet by inducing a gelation zone.
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`FIG. 8 illustrates an additional embodiment for producing gel sheets with one or more spacer
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`layers.
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`20
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`25
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`DETAILED DESCRIPTION OF THE INVENTION
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`The invention(s) described herein are directed to producing solvent filled, nanostructured gel
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`monolith and flexible blanket composite sheet materials. These materials give nanoporous
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`30
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`aerogel bodies after all mobile phase solvents are extracted using a hypercritical solvent
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`Docket No: 1008-05
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`extraction (supercritical fluid drying). For instance, the processes described in this invention will
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`offer significantly better production capacities for forming monol.ithic gel sheets or rolled gel
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`composite articles in a form factor that will facilitate removal of solvent in a subsequent
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`supercritical fluids extraction procedure. The frrst method outlines a conveyor-based system that
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`5
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`utilizes delivery of a low viscosity, catalyzed sol mixture at one end and a system to cut and
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`convey formed monolithic (defmed here as polymer or ceramic solid matrix only, no fibers
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`added) sheets of solvent fiJ led gel material into a system for further chemical treatment. The
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`second method describes a conveyor-based system that utilizes delivery of a catalyzed sol
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`mixture of low viscosity at one end and a system to cut and convey solvent-filled, fiber-
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`10
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`reinforced gel composite sheets into a rolling system (with and without a porous separator flow
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`layer) to produce a form factor ready for further treatment prior to supercritical fluid extraction.
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`The third method describes a direct roll-to-roll transfer process between two canisters in which
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`the first hosts a direct "gel in a roll" reaction followed by unrolling and re-rolling the gel with a
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`porous separator flow layer to prepare the form factor for futiher treatment prior to supercritical
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`extraction. The three methods may be used in conjunction with controlled energy delivery
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`methods to facilitate the timing of gelation and the strength of the green bodies formed. Energy
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`in the form of ultrasound, heat, and various forms of radiation can be used to induce gelation
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`from a prepared sol mixture in addition to classical methods of chemical catalysis (such as in a
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`pH change from a stable sol pH to one that facilitates gelation.
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`The matrix materials described in this invention are best derived from sol-gel processing,
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`preferably composed of polymers (inorganic, organic, or inorganic/organic hybtid) that defme a
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`structure with very small pores (on the order of billionths of a meter). Fibrous materials added
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`p rior to the point of polymer gelation reinforce the matrix materials described in this invention.
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`The preferred fiber reinforcement is preferably a lofty fibrous structure (batting or web), but may
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`also include individual randomly oriented short microfibers, and woven or non-woven fibers.
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`More particularly, preferred fiber reinforcements are based upon either organic (e.g.
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`thetmoplastic polyester, high strength carbon, aramid, high strength oriented polyethylene), low(cid:173)
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`temperature inorganic (vatious metal oxide glasses such as E-glass), or refractory (e.g. silica,
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`alumina, aluminum phosphate, aluminosilicate, etc.) fibers. The thickness or diameter of the
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`Docket No: 1008-05
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`fiber used in the embodiments ofthe present invention is in the range ofO.l to 10,000 micron,
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`and preferably in the range of 0. 1 to I 00 micron. In another preferred embodiment
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`nanostructures fibers as small as 0.001 micron are used to reinforce the gel. Typical examples
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`include carbon nanofibers and carbon nanotubes with diameters as small as 0.001 microns.
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`Solvent filled gel sheets combining a ceramic solid (e.g. silica) and a mobile solvent phase (e.g.
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`ethanol) can be formed on a conveyor by continuous injection of a catalyst phase into a sol phase
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`and dispersin g the catalyzed mixture onto a moving conveyor. Such materials will find use in
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`insu lating transparencies, such as double-glazing windows in buildings. Because these gel
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`materials are normally stiff and inflexible when they are composed of a ceramic or cross-linked
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`10
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`polymer matrix material with intercalated solvent (gel solvent) in the absence of fiber
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`reinforcement, these materials need to be handled as molded if they are continuously cast. If the
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`conveyor has molded edges that retain volume, then the gel can be directly cast onto the
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`conveyor surface. If the conveyor has molds placed upon it, then the mold volumes can be
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`continuously filled with freshly catalyzed sol.
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`15
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`Suitable materials for forming inorganic aerogels are oxides of most of the metals that can form
`
`oxides, such as silicon, aluminum, titanium, zirconium, hafnium, yttrium, vanadium, and the
`
`like. Particularly preferred are gels formed primarily from alcohol solutions of hydrolyzed
`
`silicate esters due to their ready availability and low cost (alcogel). Organic aerogels can be
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`20 made from polyacrylates, polystyrenes, polyacrylonitriles, polyurethanes, poly-imides,
`
`polyfurfural alcohol, phenol furfuryl alcohol, melamine formaldehydes, resorcinol
`
`formaldehydes, cresol formaldehyde, phenol formaldehyde, polyvinyl alcohol dialdehyde,
`
`polycyanurates, polyacrylamides, various epoxies, agar, agarose, and the like (see for instance C.
`
`S. Ashley, C. J. Brinker and D. M. Smith, Journal ofNon-Crystalli.ne Solids, volume 285, 2001).
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`25
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`In one prefeiTed embodiment of the methods of this invention, energy dissipation through a
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`portion of the sol volume is utilized in a specific location of a conveyor apparatus utilized for the
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`gel casting. By controlling the area of the catalyzed sol that is exposed to heat or specific flux of
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`radiation (e.g. u ltrasonic, x-ray, electron beam, ultraviolet, visible, infi:ared, microwave, gamma
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`30
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`ray), a gelation phenomenon can be induced at a given point of a conveyor apparatus. It is
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`Docket No: 1008-05
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`advantageous to control the timing of the gelation point with respect to the conveyor speed such
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`that the material bas adequate time to age and strengthen prior to any mechanical manipulation at
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`the terminus of the conveyor apparatus. Although the diffusion of polymer chains and
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`subsequent solid network growth are significantly slowed within the viscous gel structure after
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`5
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`the gelation point, the maintenance of the original gel liquid (mother liquor) for a period of time
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`after gelation is essential to obtaining an aerogel that has the best thermal and mechanical
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`properties. This period of time that the gel "ages" without disturbance is called "syneresis".
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`Syneresis conditions (time, temperature, pH, solid concentration) are important to the aerogel
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`product quality.
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`10
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`Gels are a class of materials formed by entraining a mobile interstitial solvent phase within the
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`pores of a solid structure. The solid structures can be composed of inorganic, organic or
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`inorganic/organic hybrid polymer materials that develop a pore morphology in direct relation to
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`the method of gelation, solvent-polymer interactions, rate of polymerization and cross-Linking,
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`15
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`solid content, catalyst content, temperature and a number of other factors. It is preferred that gel
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`materials are formed from precursor materials, including various fiber-reinforcement materials
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`that lend flexibility to the formed composite, in a continuous or semi-continuous fashion in the
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`form of sheets or rolls of sheets such that the interstitial solvent phase can be readily removed by
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`supercritical fl uids extraction to make an aerogel material. By keeping the solvent phase above
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`20
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`the critical pressure and temperature during the entire, or at minimum the end of the solvent
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`extraction process, strong capillary forces generated by liquid evaporation from very small pores
`
`that cause shrinkage and pore collapse are not realized. Aerogels typically have low bulk
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`densities (about 0.15 glee or less, preferably about 0.03 to 0.3 g/cc), very high smface areas
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`(generally from about 300 to I ,000 m2/g and higher, preferably about 700 to 1000 m2/g), high
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`25
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`porosity (about 90% and greater, preferably greater than about 95%), and relatively large pore
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`volume (about 3 mL/g, preferably about 3.5 mL!g and higher). The combination of these
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`p roperties in an amorphous stmcture gives the lowest thermal conductivity values (9 to 16
`
`mW/m-K at 37° C. and 1 atmosphere of pressure) for any coherent solid material.
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`30
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`The monolithic and composite gel material casting methods described in the present invention
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`Docket No: 1008-05
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`comprise three distinct phases. The first is blending all constituent components (solid precursor,
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`dopants, additives) into a low-viscosity sol that can be dispensed in a continuous fashion. The
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`second involves dispensing the blended sol onto a moving conveyor mold that may also have a
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`synchronized counter-rotating top belt to form a molded upper surface. The second phase may
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`5
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`also include introduction of heat or radiation to the ungelled sol within a defined area of the
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`moving conveyor apparatus to either induce gelation or mod ify the properties of the gel such as
`
`gel modulus, tensile strength, or density. The third phase of the invention process involves gel
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`cutting and conveyance of monolithic gel sheets to a post-processing area or co-rolling a flexible,
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`fi.ber-reinforced gel composite with a flexible, porous flow layer to generate a patticularly
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`10
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`p refen·ed form factor of the material. The formed rolls of gel composite material and flow layer
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`are patticularly amenable to interstitial solvent removal using supercritical processing methods.
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`An example of the preferred gel casting method is shown in FIG. 1, which utilizes a conventional
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`chemically catalyzed sol-gel process in combination with a moving conveyor apparatus with
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`counter-rotating molding capability. The fiber-reinforced, nanoporous gel composite can be
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`15 mechanically rolled, with or without a porous flow layer, as shown in FIG. I. FIG. 2 shows the
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`same process utilizing a moving conveyor belt with only a single molding surface (a
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`continuously rotating bottom belt with molded sides). FIG. 3 shows how monolithic gel sheets,
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`formed from a polymer sol (without added fiber reinforcing structures) can be formed
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`continuously by deposition of a catalyzed sol solution onto a moving conveyor, and FlG. 4
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`20
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`illustrates the same procedure except a counter-rotating conveyor molding strategy is shown. The
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`sols utilized in this invention are mixed and prepared, often by co-mixing with a chemical
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`catalyst, prior to deposition onto the moving conveyor as shown in the block diagram of FIG. 5.
`A related, but alternative embodiment of the invention process is shown in FIG. 6, in which a
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`fiber and separator layer preform roll are infiltrated with a sol, and after initial gelation takes
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`25
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`place, unrolled to separate the gel composite from the impermeable layer and subsequently re(cid:173)
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`rolled with a permeable layer to prepare for further chemical processing.
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`The gel matrix of the preferred precmsor materials for the present invention may be organic,
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`inorganic, or a mixture thereof. Sols can be catalyzed to induce gelation by methods known to
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`30
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`those trained in the att: examples include adjusting the pH and/or temperature of a dilute metal
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`10
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`ASPEN0000914
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`Docket No: 1008-05
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`oxide sol to a point where gelation occurs (The following are incorporated here by reference: R.
`
`K. Iler, Colloid Chemistry of Silica and Silicates, 1954, chapter 6; R. K. Jler, The Chemistry of
`
`Silica, 1979, chapter 5, C. J. Brinker and G. W . Scherer, Sol-Gel Science, 1990, chapters 2 and
`
`3). Suitable materials for forming inorganic aerogels are oxides of most of the metals that can
`
`5
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`form oxides, such as silicon, aluminum, titanium, zirconium, hafnium, yttrium, vanadium, and
`
`the like. Particularly preferred are gels formed primarily from alcohol solutions of hydrolyzed
`
`silicate esters due to their ready availability and low cost (alcogel).
`
`1t is also well known to those trained in the art that organic aerogels can be made from organic
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`10
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`polymer materials including polyacrylates, polystyrenes, polyacrylonitriles, polyurethanes,
`
`polyamides, EPDM and/or polybutadiene rubber solutions, polyimides, polyfurfural alcohol,
`
`phenol furfuryl alcohol, melamine formaldehydes, resorcinol formaldehydes, cresol
`
`formaldehyde, phenol formaldehyde, polyvinyl alcohol dialdehyde, polycyanurates,
`
`polyacrylamides, various epoxies, agar, agarose, and the like (see for instance C. S. Ashley, C. J.
`
`15
`
`Brinker and D. M. Smith, Journal ofNon-Crystalline Solids, volume 285, 2001).
`
`Various forms of electromagnetic, acoustic, or particle radiation sources can be used to induce
`
`gelation of sol precursor materials on the moving conveyor apparatus. The literature contains a
`
`number of examples wherein heat, ultrasonic energy, ultraviolet light, gamma radiation, electron
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`20
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`beam radiation, and the like can be exposed to a sol material to induce gelation. The use of
`
`energy dissipation (heat, acoustic, radiation) into a fixed zone of the conveyor apparatus, such
`
`that a moving sol pool interacts with a controlled energy flux for a fixed period of time is
`
`advantageous to control the properties of the gel as well as the dried aerogel or xerogel materiaL
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`This process is illustrated in FIG. 7.
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`25
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`Generally the principal synthetic route for the fotmation of an inorganic aerogel is the hydrolysis
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`and condensation of an appropriate metal alkoxide. The most suitable metal alkoxides are those
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`having about 1 to 6 carbon atoms, prefer-ably from 1-4 carbon atoms, in each alkyl group.
`
`Specific examples of such compounds include tetraethoxysilane (TEOS), tetramethoxysilane
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`30
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`(TMOS), tetra-n-propoxysilane, aluminum isopropoxide, aluminum sec-butoxide, cerium
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`ASPEN0000915
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`Docket No: 1008-05
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`isopropox-ide, hafnium tert-butoxide, magnesium aluminum isopropoxide, yttrium isopro(cid:173)
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`poxide, titanium isopropoxide, zirconium isopropoxide, and the Like. ln the case of silica
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`precursors, these materials can be partially hydrolyzed and stabilized at Low pH as polymers of
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`polysilicic acid esters such as polydiethoxysiloxane. These materials are commercially available
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`in alcohol solution. Pre-polymerized silica precursors are especially prefened for the processing
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`of gel materials described in this invention. Inducing gelation of metal oxide sols in alcohol
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`solutions i.s referred to as the alcogel process in this disclosure.
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`1t is understood to those trained in the art that gel materials formed using the sol-gel process can
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`be derived from a wide variety of metal oxide or other polymer forming species. It is also well
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`known that sols can be doped with solids (IR opacifiers, sintering retardants, microfibers) that
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`influence the physical and mechanical properties of the gel product. Suitable amounts of such
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`dopants generally range from about 1 to 40% by weight of the finished composite, preferably
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`about 2 to 30% using the casting methods of this invention.
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`Major variables in the inorganic aerogel formation process include the type of alkoxide, solution
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`pH, and alkoxide/alcohollwater ratio. Control of the variables can permit control of the growth
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`and aggregation of the matrix species throughout the transition from the "sol" state to the "gel"
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`state. While properties of the resulting aerogels are strongly affected by the pH of the precursor
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`solution and the molar ratio of the reactants, any pH and any molar ratio that permits the
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`formation of gels may be used in the present invention.
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`Generally, the solvent will be a Lower alcohol, i.e. an alcohol having 1 to 6 carbon atoms,
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`preferably 2 to 4, although other liquids can be used as is known in the art. Examples of other
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`useful liquids include but are not limited to: ethyl acetate, ethyl acetoacetate, acetone,
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`dichloromethane, and the like.
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`For convenience, the alcogel route of forming inorganic silica gels and composites are used
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`below to illustrate how to create the precursors utilized by the invention, though this is not
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`intended to limit the present invention to any specific type of gel. The invention is applicable to
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`Docket No: 1008-05
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`other gel compositions.
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`Altematively, other sol preparation and gel induction methods can be utilized to make a
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`precursor gel atticle using the processing methods of this invention, but the chemical approaches
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`that allow for obtaining the lowest density and/or best thermally insulating articles are prefetTed.
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`For example, a water soluble, basic metal oxide precursor can be neutralized by an aqueous acid
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`in a continuous fashion, deposited onto a moving conveyor belt such as shown in FlGS. 1 aod 2,
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`and induced to make a hydrogel on the moving belt. Sodium silicate has been widely used as a
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`hydrogel precursor. Salt by-products may be removed from the silicic acid precursor by ion-
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`exchange and/or by washing subsequently formed gels with water after formation and
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`mechanical manipulation of the gel.
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`After identification of the gel material to be prepared using the methods of this invention, a
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`suitable metal alkoxide-alcohol solution is prepared. The preparation of aerogel-forming
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`solutions is well known in the art. See, for example, S. J. Teichner et al, Inorganic Oxide
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`Aerogel, Advances in Colloid and Interface Science, Vol. 5, 1976, pp 245-273, and L. D.
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`LeMay, eta!., Low-Density Microcellular Materials, MRS Bulletin, Vol. 15, 1990, p 19. For
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`producing silica gel monoliths and fiber-reinforced containing silica gel composites useful in the
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`manufacture of silica aerogel materials, typically preferred ingredients are tetraethoxysilane
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`(TEOS), water, and ethanol (EtOH). The prefetTed ratio ofTEOS to water is about 0.2-0.5:1 , the
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`prefetTed ratio ofTEOS to EtOH is about 0.02-0.5:1, and the preferred pH is about 2 to 9. The
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`natural pH of a solution of the ingredients is about 5. While any acid may be used to obtain a
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`Lower pH solution, HCL, H2S04 or HF are currently the prefetTed acids. To generate a higher pH,
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`NH40H is the preferred base.
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`For the purposes of this patent, a lofty batting is defined as a fibrous material that shows the
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`p roperties of bulk and some resilience (with or without full bulk recovery). The preferred form is
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`a soft web of this material. The use of a lofty batting reinforcement material minimizes the
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`volume of unsupported aerogel while avoiding substantial degradation of the thermal
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`performance of the aerogel. Batting preferably refers to layers or sheets of a fibrous material,
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`commonly used for lining quilts or for stuffing or packaging or as a blanket of thermal
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`insulation.
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`Batting materials that have some tensile strength are advantageous for inh·oduction to the
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`conveyor casting system, but are not required. Load transfer mechanisms can be utilized in the
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`process to introduce delicate batting materials to the conve