(12) United States Patent
`Kishi et al.
`
`(10) Patent N0.:
`(45) Date of Patent:
`
`US 6,932,925 B2
`Aug. 23, 2005
`
`US006932925B2
`
`(54) METHOD OF MANUFACTURING A SUPER
`LIGHTWEIGHT CERAMIC FOAM
`
`(75) Inventors: Kazushi Kishi, Saga-ken (JP); Eiji
`Tani, Saga-ken (JP); Eishi Maeda,
`Saga-ken (JP)
`
`(73) Assignee: National Institute of Advanced
`Industrial Science and Technology,
`Tokyo (JP)
`
`( * ) Notice:
`
`Subject to any disclaimer, the term of this
`patent is extended or adjusted under 35
`U.S.C. 154(b) by 41 days.
`
`(21) Appl. No.: 10/677,338
`(22) Filed:
`Oct. 3, 2003
`
`(65)
`
`(30)
`
`Prior Publication Data
`
`US 2004/0077480 A1 Apr. 22, 2004
`Foreign Application Priority Data
`
`Oct. 18, 2002
`
`(JP) ..................................... .. 2002-303707
`
`(51) Int. Cl.7 .............................................. .. B29C 44/00
`(52) US. Cl. .......................................... .. 264/43; 264/50
`(58) Field of Search .......................... .. 264/43, 621, 50,
`264/42
`
`(56)
`
`References Cited
`
`U.S. PATENT DOCUMENTS
`
`3,935,060 A *
`6,602,449 B1 *
`
`1/1976 Blome et al. ............. .. 162/152
`8/2003 Grader et al. ............... .. 264/43
`
`* cited by examiner
`
`Primary Examiner—Steven P. Grif?n
`Assistant Examiner—Carmen Lyles-Irving
`(74) Attorney, Agent, or Firm—Sughrue Mion, PLLC
`(57)
`ABSTRACT
`
`A super-lightweight ceramic foam With a cellular structure
`effectively reinforced by ceramic short ?bers, Which has a
`density of 0.2 g/cm3 or less and a suf?cient strength. The
`ceramic foam is prepared by evenly dispersing ceramic short
`?bers throughout a nonaqueous solvent through the use of
`the reactivity of metal alkoXide With the surface of the
`ceramic short ?bers, adding into the nonaqueous solvent an
`aqueous slurry containing ceramic poWder dispersed therein,
`alloWing the evenly dispersed ceramic ?bers to move into an
`aqueous phase separately from a nonaqueous solvent phase
`so as to obtain an aqueous slurry containing the ceramic
`?bers evenly dispersed therein, and foaming and ?ring the
`aqueous slurry.
`
`8 Claims, No Drawings
`
`R.J. Reynolds Vapor
`IPR2016-01268
`R.J. Reynolds Vapor v. Fontem
`Exhibit 1031-00001
`
`

`

`US 6,932,925 B2
`
`1
`METHOD OF MANUFACTURING A SUPER
`LIGHTWEIGHT CERAMIC FOAM
`
`CROSS-REFERENCE TO RELATED
`APPLICATION
`
`This application is based upon and claims the bene?t of
`priority from Japanese Patent Application No. 2002-303707,
`?led Oct. 18, 2002, the entire contents of Which are incor
`porated herein by reference.
`
`10
`
`FIELD OF THE INVENTION
`
`The present invention relates to a super-lightWeight
`ceramic foam Which is reinforced by ceramic short ?bers
`evenly dispersed therein. The present invention also relates
`to a method of producing a super-lightWeight ceramic foam
`by use of an aqueous slurry containing ceramic short ?bers,
`Wherein the ceramic short ?bers are evenly dispersed therein
`and are not entangled With each other or agglomerated.
`
`15
`
`BACKGROUND OF THE INVENTION
`The folloWing primary methods of producing super
`lightWeight ceramic foams are knoWn in the art.
`Impregnating a polyurethane foam having continuous
`cells With a slurry containing, among other things, ceramic
`poWder and an organic binder, drying and heating the
`impregnated foam to remove the organic component
`therefrom, and sintering the foam.
`Mixing a foamable polyurethane material With a slurry
`containing, among other things, ceramic poWder and an
`organic binder, foaming the mixture, solidifying the foam,
`heating the solidi?ed foam to remove the organic component
`therefrom, and sintering the foam.
`Adding a surfactant into a dispersion medium containing
`ceramic poWder and a hydrophobic resin binder to emulsify
`the hydrophobic resin binder therein, foaming the emulsion,
`solidifying the foam, heating the solidi?ed foam to remove
`the organic component therefrom, and sintering the foam.
`Adding a ?ller, such as plastic beads, into a slurry,
`Wherein the ?ller is to be thermally removed in a subsequent
`?ring process in order to form cells, drying the slurry, and
`?ring the dried body to produce a material having a foam
`like structure.
`Also, the present inventors have previously proposed a
`method of producing a lightWeight ceramic material, com
`prising adding a given amount of inorganic poWer into a
`diluted aluminum-hydroxide sol solution serving as a binder,
`foaming the solution, drying the foam, and ?ring the foam,
`as described in Japanese Patent Laid-Opening Publication
`No. 2002-114584, Which is incorporated herein by reference
`in its entirety.
`In the above-described methods 1—4 of producing ceramic
`foams, a large amount of organic matter is commonly added
`as a binder or ?ller. Thus, methods 1—4 inevitably involve a
`problem of cracks and/or fractures possibly caused by gases
`generated in the process of thermally removing the organic
`matter in advance of sintering the ceramic poWder, or the
`difference in thermal expansion betWeen the organic and
`ceramic phases. In particular, a lightWeight ceramic foam is
`formed having a cellular structure With a thin cell Wall
`having poor strength, and thus the above-described adverse
`effect leads to more serious defects, such as deteriorated
`strength or poWdering due to micro-cracks caused in the
`sintering process. While this problem may be solved by
`providing enhanced strength in the cellular structure without
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`2
`increasing the amount of the binder, the cell Wall of the
`cellular structure inevitably becomes thicker, resulting in
`loWered porosity and increased density in a ceramic foam to
`be obtained.
`A lightWeight ceramic foam produced through the above
`described method using a diluted aluminum-hydroxide sol
`solution also has a loW-strength cellular structure, and
`further involves a problem of limited uses due to poWdering
`caused by scratching or scraping the ceramic foam.
`Thus, When a ceramic foam is produced With a higher
`porosity to facilitate reduction in the Weight thereof, the
`strength of its cellular structure is reduced accordingly and
`must be compensated for Without an increase in the density
`of the ceramic foam. In this connection, the inventors are not
`aWare of any attempt to disperse ceramic short ?bers in a
`ceramic foam to achieve the reinforcement of its cellular
`structure.
`Monolithic ceramics reinforced by ceramic short ?bers
`dispersed therein are knoWn. In a process of producing such
`monolithic ceramics, the ceramic short ?bers are added into
`a raW material slurry directly or after having been miXed
`With a dispersion medium containing any suitable type of
`surfactant, and the slurry is simply stirred using a mechani
`cal blender, such as a ball mill or attritor mill, to facilitate
`dispersion of the ceramic short ?bers throughout the slurry.
`HoWever, the ceramic short ?bers generally become
`entangled With each other and agglomerate, and the above
`described dispersion method does not alloW such ceramic
`short ?bers to be evenly dispersed throughout the slurry.
`Particularly in the process of dispersing ceramic short ?bers
`in a lightWeight ceramic foam, agglomerates of short ?bers
`cause a critical defect by damaging the thin cell Wall of the
`foam’s cellular structure. In addition, if the slurry is stirred
`in the blender for a long time, the ?bers Will be inevitably
`damaged by media balls in the blender. The intended pur
`pose of dispersing ceramic short ?bers in the ceramic matriX
`is to reinforce the cellular structure or provide a higher
`toughness to the cellular structure by utiliZing the toughness
`of the ceramic short ?ber. If the ?ber itself is damaged in the
`dispersion process, the eXpected effect Will be signi?cantly
`deteriorated.
`
`SUMMARY OF THE INVENTION
`In vieW of the above problems, it is therefore an object of
`the present invention to provide a super-lightWeight ceramic
`foam capable of achieving a previously unattainable high
`porosity and a suf?cient strength based on a cellular struc
`ture reinforced by ceramic short ?bers.
`It is another object of the present invention to provide a
`method of producing a super-lightWeight ceramic foam,
`capable of overcoming the previously unsolved problems in
`conventional processes of dispersing ceramic short ?bers,
`and providing an improved super-lightWeight ceramic foam
`reinforced by ceramic short ?bers evenly dispersed therein.
`More speci?cally, as disclosed in Japanese Patent No.
`1332466, Which is incorporated herein by reference in its
`entirety, the inventors veri?ed that When ceramic poWder is
`miXed With a solvent having, among other things, aluminum
`alkoXide dissolved therein, a reaction layer betWeen the
`aluminum alkoXide and the ceramic poWder is formed on the
`surface of the ceramic poWder to alloW the ceramic poWder
`to be evenly dispersed throughout the solvent, and the
`evenly dispersed ceramic poWder can serve as a ceramics
`raW material in a sintering process to provide drastically
`improved properties in the resulting sintered body.
`Through subsequent research, it Was found that the above
`described interaction With metal alkoXide is also signi?
`
`R.J. Reynolds Vapor Exhibit 1031-00002
`
`

`

`US 6,932,925 B2
`
`3
`cantly exhibited by ceramic short ?bers. It Was also found
`that When a large amount of an aqueous solution or an
`aqueous slurry containing ceramic powder is added to a
`slurry of ceramic short ?bers evenly dispersed in a nonpolar
`solvent having metal alkoxide dissolved therein, the entire
`ceramic short ?bers evenly dispersed in the nonpolar solvent
`are transferred to an aqueous phase, and a limpid nonpolar
`solvent is left on the aqueous phase. This supernatant
`nonaqueous phase can be removed to obtain an aqueous
`solution or aqueous slurry containing ceramic short ?bers
`evenly dispersed therein, and the aqueous solution or aque
`ous slurry can be used as a raW material capable of providing
`a super-lightWeight ceramic foam having a high-strength
`cellular structure and excellent properties.
`In order to achieve the objects of the invention, there is
`provided a super-lightWeight ceramic foam having a cellular
`structure formed by foaming one of an aqueous slurry
`containing ceramic poWder and ceramic short ?bers dis
`persed evenly throughout, and an aqueous slurry containing
`ceramic short ?bers dispersed evenly throughout an aqueous
`solution having a component serving as a raW material of
`ceramic poWder dissolved therein, and ?ring the foamed
`slurry. The ceramic short ?bers are evenly dispersed
`throughout the foam’s cellular structure to effectively rein
`force the cellular structure, and the ceramic foam has a
`density of 0.2 g/cm3 or less.
`In the above-described ceramic foam, each of the ceramic
`short ?bers may have a length 1.5 or more times greater than
`the diameter of each cell in the cellular structure. The length
`of the ceramic short ?bers is such that it alloWs them to be
`evenly dispersed in the foam’s cellular structure.
`The present invention also provides a method of produc
`ing a super-lightWeight ceramic foam. The method com
`prises the steps of adding ceramic short ?bers into a non
`aqueous solvent containing metal alkoxide dissolved
`therein, dispersing the ceramic short ?bers in the nonaque
`ous solvent, adding one of an aqueous slurry containing
`ceramic poWder, and an aqueous solution containing a
`component serving as a raW material of ceramic poWder
`dissolved therein, into the nonaqueous solvent, stirring the
`obtained mixture, alloWing the mixture to separate into an
`aqueous phase and an nonaqueous phase, removing the
`supernatant nonaqueous phase to obtain an aqueous slurry
`containing the ceramic short ?bers dispersed therein, adding
`a foaming agent into the slurry, foaming the slurry under
`mechanical stirring, ?lling and drying the foamed slurry in
`a mold to form a molded body, and ?ring the molded body.
`In the above-described method, the ceramic short ?bers
`may be added into the nonaqueous solvent in the range of 5
`to 95 Weight % relative to the ceramic material contained in
`the aqueous slurry or the aqueous solution.
`In the above-described method, the aqueous slurry or the
`aqueous solution may include mixed thereWith or dissolved
`therein a substance serving as a sintering aid and/or a
`particle groWth inhibitor.
`According to the present invention, ceramic short ?bers
`can effectively reinforce the cellular structure of a ceramic
`foam having an inherently loW strength to provide a super
`lightWeight ceramic foam With a previously unattainable
`high porosity and a suf?cient strength. Further, the method
`of the present invention alloWs ceramic short ?bers to be
`evenly dispersed throughout the cellular structure of a
`ceramic foam to provide an improved super-lightWeight
`ceramic foam having excellent properties.
`Other features and advantages of the present invention
`Will be apparent from the detailed description.
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`4
`DESCRIPTION OF THE PREFERRED
`EMBODIMENT
`
`The present invention Will noW be described in detail in
`conjunction With speci?c examples.
`For the purpose of reinforcing a ceramic foam With
`ceramic short ?bers, each of the ceramic short ?bers must
`have a length 1.5 or more times greater than the diameter of
`each cell in a cellular structure formed by foaming an
`aqueous solution or an aqueous slurry containing the
`ceramic ?bers dispersed therein. If the length of a ceramic
`?ber is less than the diameter of the cell, the ?ber cannot be
`arranged in such a manner that it serves as a bridge betWeen
`a plurality of cells, and thus the cellular structure cannot be
`reinforced. If the ceramic ?bers are too long, they cannot be
`evenly dispersed throughout the cellular structure. Acellular
`structure formed by a method according to the present
`invention described herein beloW has cells With a diameter
`of 200 to 500 pm. In this case, a ceramic short ?ber to be
`used therein preferably has a length of 0.5 to 5 mm.
`In a super-lightWeight ceramic foam of the present
`invention, each ceramic short ?ber is attached to a plurality
`of cells, and a plurality of such cells are assembled together
`to form a cellular structure. Thus, the cellular structure can
`be effectively reinforced by the ceramic short ?bers to alloW
`a ceramic foam to be increased in porosity or reduced in
`Weight While maintaining excellent properties.
`In the method of the present invention, for the purpose of
`dispersing the aforementioned ceramic short ?bers in a
`ceramic foam, the ceramic short ?bers are ?rst added into a
`hydrophobic organic solvent containing a small amount of
`metal alkoxide dissolved therein. The metal alkoxide to be
`dissolved in the solvent is preferably in the range of about
`0.1 to 20 Weight parts, more preferably 0.5 to 10 Weight
`parts, relative to 100 Weight parts of the ceramic short ?bers
`to be added in the solvent. While the ceramic short ?bers
`may be added in any amount such that they can be
`adequately dispersed throughout the organic solvent, it is
`desired to determine the amount in consideration of the
`amount of aqueous solution or aqueous slurry to be subse
`quently added into the metal alkoxide solution, as described
`later.
`In the organic solvent added With the ceramic short ?bers,
`the metal alkoxide reacts With a hydroxyl group on the
`surface of the ceramic short ?bers, as shoWn in the folloWing
`formula (1), to form a reaction layer, and an alkyl group of
`the metal alkoxide acts to facilitate dispersion of the ceramic
`short ?bers throughout the organic solvent.
`
`(ceramics)-OH+M(OR),,—>(ceramics)—O—M(OR),,,1+ROH
`
`(1)
`
`Thus, the ceramic short ?bers can be evenly dispersed
`throughout the solvent using a mechanical stirrer or by
`ultrasonic-irradiation from an ultrasonic stirrer, Without any
`dif?culties.
`After the ceramic short ?bers are suf?ciently dispersed
`throughout the organic solvent, a large amount of aqueous
`solution or aqueous slurry is added to the solvent, and the
`mixture is stirred. As a result of the addition of the aqueous
`solution or aqueous slurry, the alkyl group of the metal
`alkoxide is hydrolyZed and changed to a hydroxyl group, as
`shoWn in the folloWing formula (2), and consequently the
`ceramic short ?bers lose their lipophilic property. Thus, the
`ceramic short ?bers quickly move to the aqueous phase, and
`the mixture separates into an aqueous solution phase con
`taining the ceramic short ?bers dispersed therein, and an
`organic solvent phase.
`
`R.J. Reynolds Vapor Exhibit 1031-00003
`
`

`

`US 6,932,925 B2
`
`5
`
`Then, the separated supernatant organic solvent phase is
`removed through a decantation-process or the like, to obtain
`an aqueous solution or aqueous slurry containing the
`ceramic short ?bers dispersed therein.
`In the above-described process, if Water, ie the aqueous
`solution or aqueous slurry, is added in an insuf?cient
`amount, the metal alkoxide Will be condensed on the surface
`of the ceramic short ?bers, as shoWn in the folloWing
`formula (3), and thus the ceramic short ?bers Will be
`undesirably aggregated.
`
`Thus, it is desirable to add the aqueous solution or
`aqueous slurry in an amount that causes no aggregation of
`the ceramic short ?bers. While the desired amount varies
`according to the amount or type of the ceramic short ?bers,
`if the organic solvent contains 10 Weight part or more of the
`ceramic short ?bers relative to 100 Weight part of the organic
`solvent, the volume of the aqueous solution or aqueous
`slurry should be at least equal to or greater than one-fourth
`of that of the organic solvent.
`Preferably, a component serving as a peptiZer or promot
`ing peptiZation is contained in the aqueous solution or
`aqueous slurry to be added into the nonaqueous solvent
`containing the ceramic short ?bers dispersed therein, to
`facilitate dispersion of the ceramic short ?bers in the aque
`ous phase. The component promoting peptiZation may be an
`acid, a base or a polyacrylic ammonium generally used as a
`peptiZer. On the other hand, any component that causes
`ceramic short ?bers to aggregate is preferably not contained
`in the aqueous solution or aqueous slurry. For subsequent
`molding and ?ring processes, a salt serving as a sintering aid
`and/or a particle groWth inhibitor may be dissolved in the
`aqueous solution or aqueous slurry to provide a ceramic
`foam having a more even structure.
`The present invention is not limited to a speci?c metal
`alkoxide. Any suitable metal alkoxide capable of being
`dissolved in a hydrophobic organic solvent and being
`formed as a ceramic martial, such as oxide, nitride or
`carbide, by itself through a reaction in the subsequent heat
`treatment. Among the metal alkoxides ful?lling such
`requirements, one may be selected depending on the com
`position of the intended ceramic foam, or a plurality of metal
`alkoxides may be used in combination depending on the
`composition of the intended ceramic foam.
`The present invention utiliZes the reaction betWeen the
`hydroxyl group on the surface of the ceramic short ?bers and
`the metal alkoxide to facilitate dispersion of the ceramic
`short ?bers throughout the solvent. Thus, a ceramic short
`?ber to be used in the present invention must have a
`hydroxyl group for reacting With the metal alkoxide.
`HoWever, all ceramic short ?bers, except for those having a
`coated surface, can be used in the present invention because
`the uncoated surface of a ceramic short ?ber is oxidiZed or
`hydrolyZed by Water vapor in the atmosphere and thus has
`many hydroxyl groups thereon. Even if a ceramic short ?ber
`has a surface With a coating formed using a siZing agent or
`the like, it can be used by removing such a coating in
`advance through scrubbing or calcination. Any inorganic
`?ber, such as glass ?ber and carbon ?ber, having a surface
`capable of reacting With the metal alkoxide may also be
`used.
`In the present invention, the inorganic poWder to be used
`in the aqueous slurry may include, but is not limited to,
`
`6
`alumina, mullite, Zirconia, silicon nitride, silicon carbide and
`any other material generally used as refractory ceramics.
`TWo or more kinds of the poWders may be used in combi
`nation. Further, a substance serving as a sintering aid and/or
`particle groWth inhibitor for the poWder, such as yttria or
`magnesia, may be used in combination thereWith. The
`substance serving as a sintering aid and/or particle groWth
`inhibitor may be dissolved in the form of a salt thereof and
`added into the slurry. Inorganic poWder having an exces
`sively large particle siZe can be precipitated by its oWn
`Weight, and inorganic poWder having an excessively ?ne
`particle siZe can increase the viscosity of the aqueous slurry
`due to the increased speci?c surface area of the poWder.
`Thus, the inorganic poWder preferably has an average par
`ticle siZe in the range of about 0.2 to 5 pm. Further, tWo or
`more kinds of the poWders different in particle siZe may be
`used in combination.
`In the present invention, the aqueous solution containing
`a component serving as a raW material of ceramic poWder
`may be an aluminum-hydroxide sol solution, a silica sol
`solution, a titanium-hydroxide sol solution, or mixtures
`thereof. Additionally, a hydroxide or salt of a component
`serving as a sintering aid and/or particle groWth inhibitor
`may be dissolved in the above solution. If the aqueous
`solution contains only a salt or only a hydroxide Which
`gelates in a drying process and loses its function as a binder,
`it should be added With a binder to be burnt in a ?ring
`process.
`A foaming agent to be used in the present invention may
`include, but is not limited to, commonly used saponin and
`any other suitable surfactants. By Way of exception, a
`surfactant containing sodium and an organic material are
`undesirable because they cause deterioration in the heat
`resistance of a sintered ceramic foam.
`The present invention may be applied to a method of
`producing large-siZe super-lightweight ceramic foams hav
`ing different shapes, in Which a plurality of calcinated
`preforms of foamed slurry are prepared and then jointed to
`each other using a foamed slurry prepared in the same Way,
`as proposed by the inventors in Japanese Patent Application
`No. 2002-088250, Which is incorporated herein by reference
`in its entirety.
`The present invention is noW illustrated, but not limited,
`by the folloWing Examples.
`EXAMPLE 1
`20 g of alumina short ?bers having an average length of
`1 mm Were added, While stirring, into a solution consisting
`of 200 ml of n-hexane and 0.5 g of aluminum isopropoxide
`dissolved therein, and the alumina short ?bers Were dis
`persed throughout the solution using an ultrasonic cleaner.
`In parallel, 12 g of aluminum iso-propoxide Was added to
`150 ml of boiling distilled Water, and hydrolyZed under
`stirring. A White solution obtained by cooling the solution
`containing the hydrolysate Was added With dilute hydrochlo
`ric acid under stirring to adjust its pH value at 2, and then
`peptiZed under continuous stirring for 4 hours to prepare a
`limpid aluminum-hydroxide sol solution. This solution Was
`added With 60 g of alumina poWder having an average
`particle siZe of 0.2 pm, and 0.4 g of Mg (NO3)2~6 H2O as an
`MgO source serving as a particle groWth inhibitor for
`alumina, and these Were stirred together With silicon nitride
`balls for 20 hours to prepare an aqueous slurry of alumina.
`This aqueous slurry Was quickly added into the above
`n-hexane solution containing the alumina short ?bers dis
`persed therein, under stirring. After stirring for about 5
`minutes, the mixture Was left statically and alloWed to
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`R.J. Reynolds Vapor Exhibit 1031-00004
`
`

`

`US 6,932,925 B2
`
`7
`separate into a nonaqueous phase and an aqueous phase. The
`supernatant limpid nonaqueous phase Was promptly
`removed through a decantation process. After the removal of
`the nonaqueous phase, the aqueous phase Was heated under
`stirring for some time to vaporiZe and remove a small
`amount of remaining hexane therein so as to obtain 100 ml
`of concentrated aqueous slurry containing the alumina short
`?bers dispersed therein. This slurry Was added With 10 ml of
`20% saponin solution, and foamed using a domestic bubble
`machine to tenfold the volume thereof. The meringue-like
`bubbles or foams Were ?lled and dried in a mold made of a
`paperboard having a siZe of 8 cm><8 cm><4 cm and an inner
`surface applied With paradichlorobenZene to form a molded
`body. The obtained molded body Was sintered at 1,350° C.
`under atmospheric air for 1 hour to obtain an alumina foam.
`The alumina foam had a bulk density of 0.11 g/cm3, and
`a suf?cient strength capable of Withstanding a pressure
`applied thereto by ?ngers Without breakage.
`
`EXAMPLE 2
`
`20 g of alumina short ?bers having an average length of
`1 mm Were added, While stirring, into a solution consisting
`of 200 ml of n-hexane and 0.5 g of aluminum isopropoxide
`dissolved therein, and the alumina short ?bers Were dis
`persed throughout the solution using an ultrasonic cleaner.
`In parallel, 8 g of aluminum iso-propoxide Was added to 150
`ml of boiling distilled Water, and hydrolyZed under stirring,
`and an aluminum-hydroxide sol solution Was prepared in the
`same Way as that in Example 1. This solution Was added
`With 50 g of alumina poWder having an average particle siZe
`of 0.2 um, and 0.3 g of Mg (NO3)2.6 H2O as an MgO source
`serving as a particle groWth inhibitor for alumina, and an
`aqueous slurry of alumina Was prepared in the same Way as
`that in Example 1. Then, in the same Way as that in Example
`1, a molded body of ceramic foam having a siZe of 8 cm><8
`cm><4 cm Was obtained. The obtained molded body Was
`sintered at 1,450° C. under atmospheric air for 1 hour to
`obtain an alumina foam. The alumina foam had a bulk
`density of 0.08 g/cm3, and a sufficient strength capable of
`Withstanding a pressure applied thereto by ?ngers Without
`breakage.
`
`EXAMPLE 3
`
`10 g of alumina short ?bers having an average length of
`1 mm Were added, While stirring, into a solution consisting
`of 150 ml of n-hexane and 0.5 g of aluminum iso-propoxide
`dissolved therein, and the alumina short ?bers Were dis
`persed throughout the solution using an ultrasonic cleaner.
`In parallel, 16 g of aluminum iso-propoxide Was added to
`100 ml of boiling distilled Water, and hydrolyZed under
`stirring. After the completion of hydrolysis, the solution Was
`heated and evaporated to about 50 ml, and then cooled. The
`obtained solution Was added With dilute hydrochloric acid
`under stirring to adjust its pH value at 2, and then peptiZed
`under continuous stirring for 4 hours. This solution Was then
`added With 0.1 g of Mg (NO3)2.6 H2O to prepare a limpid
`aluminum-hydroxide sol solution. This aluminum
`hydroxide sol solution Was added into the above n-hexane
`solution, and then a molded body of ceramic foam having a
`siZe of 8 cm><8 cm><2 cm Was obtained in the same Way as
`that in Example 1. The obtained molded body Was sintered
`at 1,650° C. under atmospheric air for 1 hour to obtain an
`alumina foam. The alumina foam had a bulk density of 0.04
`g/cm3.
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`8
`Although the present invention has been described in
`speci?c features and/or methodological steps, it is to be
`understood that the invention de?ned in the appended claims
`is not necessarily limited to the speci?c features or steps
`described. Rather, the speci?c features and steps are dis
`closed as exemplary forms of implementing the claimed
`invention.
`What is claimed is:
`1. A method of producing a super-lightWeight ceramic
`foam, comprising the steps of:
`
`adding ceramic short ?bers into a nonaqueous solvent
`containing a metal alkoxide dissolved therein;
`dispersing said ceramic short ?bers in said nonaqucous
`solvent;
`adding one of an aqueous slurry containing ceramic
`poWder, and an aqueous solution containing a compo
`nent serving as a raW material of ceramic poWder
`dissolved therein, into said nonaqueous solvent;
`stirring the mixture;
`alloWing said mixture to separate into an aqueous phase
`and an nonaqueous phase;
`removing said nonaqueous phase to obtain an aqueous
`slurry containing said ceramic short ?bers dispersed
`therein;
`adding a foaming agent into said slurry;
`foaming said slurry under mechanical stirring;
`?lling and drying said foamed slurry in a mold to form a
`molded body; and
`?ring said molded body.
`2. The method as claimed in claim 1, Wherein said
`ceramic short ?bers are added into said nonaqueous solvent
`in the range of 5 to 95 Weight % relative to the ceramic
`poWder in said aqueous slurry or the raW material of ceramic
`poWder dissolved in said aqueous solution.
`3. The method as claimed in claim 1 or 2, Wherein said
`aqueous slurry or said aqueous solution includes mixed
`thereWith or dissolved therein a substance serving as a
`sintering aid and/or a particle groWth inhibitor.
`4. The method as claimed in claim 1, Wherein said metal
`alkoxide is dissolved in said nonaqueous solvent in a range
`of 0.1 to 20 Weight parts per 100 Weight parts of said ceramic
`short ?bers dispersed in said nonaqucous solvent.
`5. The method as claimed in claim 4, Wherein said metal
`alkoxide is dissolved in said nonaqueous solvent in a range
`of 0.5 to 10 Weight parts per 100 Weight parts of said ceramic
`short ?bers dispersed in said nonaqueous solvent.
`6. The method as claimed in claim 1, Wherein said
`ceramic short ?bers are dispersed in said nonaqueous sol
`vent in a range of 10 Weight parts or more per 100 Weight
`parts of said nonaqueous solvent, and the volume of said
`aqueous slurry or aqueous solution added to said nonaque
`ous solvent is at least 25% of the volume of said nonaqueous
`solvent.
`7. The method as claimed in claim 1, Wherein said
`aqueous slurry or aqueous solution further contains a pep
`tiZer.
`8. The method as claimed in claim 7, Wherein said
`peptiZer is selected from the group consisting of an acid, a
`base, and a polyacrylic ammonium.
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`R.J. Reynolds Vapor Exhibit 1031-00005
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