US20040198584A1 - Nanoporous ultrafine alpha-alumina powders and freeze drying process of preparing same - Google Patents

Nanoporous ultrafine alpha-alumina powders and freeze drying process of preparing same Download PDF

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US20040198584A1
US20040198584A1 US10/406,060 US40606003A US2004198584A1 US 20040198584 A1 US20040198584 A1 US 20040198584A1 US 40606003 A US40606003 A US 40606003A US 2004198584 A1 US2004198584 A1 US 2004198584A1
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alumina
nanoporous
particles
powder
alumina powder
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Yuhu Wang
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Saint Gobain Ceramics and Plastics Inc
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Saint Gobain Ceramics and Plastics Inc
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Priority to US10/406,060 priority Critical patent/US20040198584A1/en
Assigned to SAINT-GOBAIN CERAMICS & PLASTICS, INC. reassignment SAINT-GOBAIN CERAMICS & PLASTICS, INC. ASSIGNMENT OF ASSIGNORS INTEREST (SEE DOCUMENT FOR DETAILS). Assignors: WANG, YUHU
Priority to AU2004228649A priority patent/AU2004228649B2/en
Priority to NZ542626A priority patent/NZ542626A/en
Priority to BRPI0409138-8A priority patent/BRPI0409138A/pt
Priority to MXPA05010568A priority patent/MXPA05010568A/es
Priority to RU2005130530/15A priority patent/RU2299179C2/ru
Priority to PCT/US2004/010255 priority patent/WO2004089828A2/en
Priority to JP2006509649A priority patent/JP4347884B2/ja
Priority to CA002519420A priority patent/CA2519420C/en
Priority to EP04749696.3A priority patent/EP1608593B1/de
Priority to KR1020057018443A priority patent/KR100726113B1/ko
Priority to CN200480009461XA priority patent/CN1856443B/zh
Assigned to SAINT-GOBAIN CERMICS & PLASTICS, INC. reassignment SAINT-GOBAIN CERMICS & PLASTICS, INC. ASSIGNMENT OF ASSIGNORS INTEREST (SEE DOCUMENT FOR DETAILS). Assignors: WANG, YUHU
Publication of US20040198584A1 publication Critical patent/US20040198584A1/en
Priority to US11/050,135 priority patent/US8080231B2/en
Priority to ZA200507850A priority patent/ZA200507850B/en
Assigned to SAINT-GOBAIN CERAMICS & PLASTICS, INC. reassignment SAINT-GOBAIN CERAMICS & PLASTICS, INC. CORRECTIVE COVERSHEET TO CORRECT THE ASSIGNEE'S ADDRESS PREVIOUSLY RECORDED ON REEL 013938 FRAME 0844. ASSIGNOR(S) HEREBY CONFIRMS THE ASSIGNMENT. Assignors: WANG, YUHU
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    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01F—COMPOUNDS OF THE METALS BERYLLIUM, MAGNESIUM, ALUMINIUM, CALCIUM, STRONTIUM, BARIUM, RADIUM, THORIUM, OR OF THE RARE-EARTH METALS
    • C01F7/00—Compounds of aluminium
    • C01F7/02—Aluminium oxide; Aluminium hydroxide; Aluminates
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B82—NANOTECHNOLOGY
    • B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
    • B82Y30/00—Nanotechnology for materials or surface science, e.g. nanocomposites
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01F—COMPOUNDS OF THE METALS BERYLLIUM, MAGNESIUM, ALUMINIUM, CALCIUM, STRONTIUM, BARIUM, RADIUM, THORIUM, OR OF THE RARE-EARTH METALS
    • C01F7/00—Compounds of aluminium
    • C01F7/02—Aluminium oxide; Aluminium hydroxide; Aluminates
    • C01F7/021—After-treatment of oxides or hydroxides
    • C01F7/023—Grinding, deagglomeration or disintegration
    • C—CHEMISTRY; METALLURGY
    • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
    • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
    • C04B35/00—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products
    • C04B35/01—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on oxide ceramics
    • C04B35/10—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on oxide ceramics based on aluminium oxide
    • C—CHEMISTRY; METALLURGY
    • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09K—MATERIALS FOR MISCELLANEOUS APPLICATIONS, NOT PROVIDED FOR ELSEWHERE
    • C09K3/00—Materials not provided for elsewhere
    • C09K3/14—Anti-slip materials; Abrasives
    • C09K3/1409—Abrasive particles per se
    • C—CHEMISTRY; METALLURGY
    • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09K—MATERIALS FOR MISCELLANEOUS APPLICATIONS, NOT PROVIDED FOR ELSEWHERE
    • C09K3/00—Materials not provided for elsewhere
    • C09K3/14—Anti-slip materials; Abrasives
    • C09K3/1454—Abrasive powders, suspensions and pastes for polishing
    • C09K3/1463—Aqueous liquid suspensions
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B82—NANOTECHNOLOGY
    • B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
    • B82Y40/00—Manufacture or treatment of nanostructures
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2004/00—Particle morphology
    • C01P2004/01—Particle morphology depicted by an image
    • C01P2004/03—Particle morphology depicted by an image obtained by SEM
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2004/00—Particle morphology
    • C01P2004/51—Particles with a specific particle size distribution
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2004/00—Particle morphology
    • C01P2004/60—Particles characterised by their size
    • C01P2004/64—Nanometer sized, i.e. from 1-100 nanometer
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2006/00—Physical properties of inorganic compounds
    • C01P2006/12—Surface area
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2006/00—Physical properties of inorganic compounds
    • C01P2006/16—Pore diameter
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
    • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
    • Y10T428/00—Stock material or miscellaneous articles
    • Y10T428/29—Coated or structually defined flake, particle, cell, strand, strand portion, rod, filament, macroscopic fiber or mass thereof
    • Y10T428/2982—Particulate matter [e.g., sphere, flake, etc.]

Definitions

  • the present invention relates to nanosized ⁇ -alumina particles, nanoporous ⁇ -alumina gels and methods of making same and more particularly to nanosized ⁇ -alumina particles having an average particle size of less than about 100 nm.
  • the present invention also relates to chemical mechanical polishing compositions (CMP) comprising ⁇ -alumina particles of the invention and CMP polishing methods using same.
  • CMP chemical mechanical polishing compositions
  • Ultra-fine alumina (aluminum oxide) powder is one of the most widely used ceramic materials in a variety of industries. Applications of fine alumina powders include use as abrasives for polishing semiconductor and precision optical components, catalyst supports including the support structure in automobile catalytic converters, fillers for polymers, and pigment for painting, and the like.
  • Alumina has over twelve (12) different crystalline phases, each of which has a different lattice structure and physical properties.
  • the most well known and commonly used alumina powders are ⁇ -alumina and ⁇ -alumina.
  • the low temperature phase, ⁇ -alumina is thermodynamically metastable and transforms to the thermodynamically stable phase, ⁇ -alumina, at temperatures in excess of about 1100° C.
  • ⁇ -alumina powder can have very small particle sizes, e.g., particle sizes of less than about 20 nm, and extremely high surface area, e.g., greater than about 300 m 2 /g.
  • ⁇ -alumina can be processed via both vapor and liquid phase processing techniques. Ultrafine ⁇ -alumina having an average particle size of less than 40 nm and a polishing slurry with ⁇ -alumina are commercially available. Ultrafine ⁇ -alumina having an average particle size of less than 40 nm and a polishing slurry with ⁇ -alumina are commercially available.
  • the density of ⁇ -alumina is about 20% higher than the density of ⁇ -alumina and more chemically and mechanically durable than ⁇ -alumina.
  • nanosized ⁇ -alumina particles should be suitable for a greater range of applications than nanosized ⁇ -alumina.
  • the alumina particle size increases drastically such that ⁇ -alumina prepared from ⁇ -alumina normally has a particle size of greater than 100 nm.
  • ⁇ -alumina e.g., ⁇ -alumina particles of less than about 100 nm
  • fine ⁇ -alumina powders having an average particle size of greater than 100 nm can be prepared via a seeded sol-gel process.
  • boehmite is first peptized in acidic aqueous solution, containing nitric acid or acetic acid and then a couple of weight percent of ⁇ -alumina seeds, usually fine ⁇ -alumina particles, are added to the solution during the peptization to allow phase transformation to occur at lower temperature.
  • the sol is oven dried at about 100° C.
  • micron sized granules After crushing to micron sized granules, they are fired at a high temperature, normally over about 1000° C. to the produce of ⁇ -alumina particles. The temperature must be well controlled to prevent particle growth. However, in this process micron sized grains remain intact during the phase transformation process and result in mechanically strong hard grains of ⁇ -alumina after completion of the transformation. To make nanoalumina particles, high mechanical energy is required to crush or break down the grain into primary particles which typically have an average particle size of more than 100 nm. Moreover, the grinding process frequently results in high levels of impurity contamination.
  • U.S. Pat. No. 5,312,791 recites a modified approach to prepare alumina grains and fibers.
  • the starting material is boehmite that is peptized and then dispersed in water to generate an alumina sol.
  • the sol is rapidly cooled in liquid nitrogen or, alternatively slowly cooled by freeze drying. Water is sublimed under vacuum from the sol to form a gel composed of flakes having a thickness of between 1 and 3 ⁇ m.
  • finer alumina powders, flakes, fibers, and grains can be made having micron-sized smallest dimensions.
  • the powders themselves have no porosity, they require high mechanical energy grinding to form smaller particles which introduces high levels of impurities into the ⁇ -alumina product.
  • This invention provides a technique to make stable nanoporous ⁇ -alumina powders and nanosized ⁇ -alumina powders.
  • the invention further provides slurries comprising same which comprise no or very little chemical additives for suspension stability.
  • the slurry of the invention provides a high material removal rates on silicon dioxide (SiO 2 ) and further provides very good surface finishing.
  • the methods of manufacturing the nanoporous ⁇ -alumina powders of the invention comprise seeding an aqueous solution of an alumina precursor with nanosized ⁇ -alumina seed particles, adding a water soluble polymer to make an organic/inorganic sol, freeze drying the sol and firing the dried sol to form a nanoporous ⁇ -alumina powder.
  • Nanosized ⁇ -alumina powders of the invention are prepared by breaking or crushing the nanoporous ⁇ -alumina powders.
  • nanoporous ⁇ -alumina powders which comprises interconnected ⁇ -alumina primary particles having an average particle size of less than about 100 nm and an interpenetrated array of pores or voids.
  • nanoporous ⁇ -alumina powder is intended to include ⁇ -alumina powders composed of porous aggregated particles of ⁇ -alumina, e.g., secondary polycrystalline alumina particles, where each porous particle comprises a plurality of interconnected primary particles having an average particle size of less than 100 nm and a plurality of voids or pores.
  • the size of nanoporous ⁇ -alumina particles are not particularly limited.
  • nanoporous ⁇ -alumina powders of the invention comprise a broad distribution of polycrystalline aggregated particles of between 500 nm and about 100 ⁇ m.
  • the invention further provides a nanosized ⁇ -alumina powder comprising ⁇ -alumina particles having an average particle size of less than about 100 nm and slurries comprising same.
  • the nanosized ⁇ -alumina powders of the invention are typically prepared by milling, crushing or otherwise breaking apart nanoporous ⁇ -alumina powders of the invention to liberate the primary ⁇ -alumina particles of the porous ⁇ -alumina particles.
  • nanosized ⁇ -alumina powders are intended to refer to ⁇ -alumina powders which are composed of ⁇ -alumina particles having an average particle size of less than about 100 nm. More preferably, substantially all of the ⁇ -alumina particles of the nanosized ⁇ -alumina powders of the invention are less than about 100 nm.
  • the invention further provides a process for the production of nanoporous ⁇ -alumina powders which comprises the steps of
  • an inorganic sol comprising at least one alumina precursor and a plurality of ⁇ -alumina seed particles
  • the invention provides a process for the production of a nanosized ⁇ -alumina powder comprising ⁇ -alumina particles having an average particle size of less than about 100 nm, the process comprising the steps of:
  • nanoporous ⁇ -alumina powder comprising interconnected ⁇ -alumina primary particles having an average particle size of less than about 100 nm and an interpenetrated array of pores or voids;
  • the invention further provides polishing methods which include the use of ⁇ -alumina powders and slurries as a polishing agent.
  • the polishing method comprises the steps of:
  • slurry comprising a nanosized ⁇ -alumina powder which comprises ⁇ -alumina particles having an average particle size of less than about 100 nm;
  • FIG. 1 is a scanning electron micrograph of a nanoporous ⁇ -alumina powder of the invention
  • FIG. 2 is another scanning electron micrograph of the nanoporous ⁇ -alumina powder imaged in FIG. 1;
  • FIG. 3 is a micrograph of nanosized ⁇ -alumina particles of the invention prepared by milling a nanoporous ⁇ -alumina powder of the invention.
  • the ⁇ -alumina powders and slurries comprising same provided by the present invention are suitable for use in various applications including, for example, polishing, CMP applications, catalyst support materials, and the like.
  • the nanoporous ⁇ -alumina powders of the present invention are particularly suited for use as catalyst support materials, insulation materials, filtration media and other applications where materials having pores or voids on a nanometer scale are desirable.
  • the nanosized ⁇ -alumina powders and slurries are particularly suited for use in polishing and CMP applications because ⁇ -alumina particles of the invention possess exceptional hardness and have an average particle size of between 10 nm and about 100 nm.
  • the ⁇ -alumina particles of the invention offer high material removal rates with minimal substrate defectivity.
  • the nanosized ⁇ -alumina powders of the invention are suitable for polishing of a variety of hard materials including, but not limited to, sapphire, spinel, silicon, corundum, and other materials having a corundum structure.
  • the nanosized ⁇ -alumina powders may also be used in combination with one or more chemical additives for chemical mechanical polishing application (CMP).
  • CMP chemical mechanical polishing application
  • Preferred substrates for CMP using the nanosized ⁇ -alumina powders of the invention include semiconductor substrates having one or more metal deposited thereon.
  • Preferred metals include platinum, palladium, tantalum, tungsten, copper, silver, gold deposited upon a silicon dioxide substrate.
  • the present invention provides nanoporous ⁇ -alumina powders which are composed of an interconnected array of ⁇ -alumina primary particles having an average particle size of less than about 100 nm and an interpenetrated array of pores or voids. More preferably, the primary ⁇ -alumina particles of the interconnected array have an average size of between about 10-100 nm, between about 20-90 nm, between about 25-80 nm, or between about 30-70 nm.
  • Other preferred nanoporous ⁇ -alumina powders of the invention comprise an interconnected array of ⁇ -alumina primary particles, wherein at least 99% of the ⁇ -alumina primary particles have a size within about a distribution of about 10 run.
  • the interconnected ⁇ -alumina primary particles are connected by necking. That is, ⁇ -alumina primary particles increase in size during the phase transformation thereby causing adjacent particles to fuse.
  • the “neck,” i.e., the area of adjacent particles which have fused is between about 10% and about 90% of the cross-section of the ⁇ -alumina primary particles.
  • the size and shape of the pores or voids of the porous ⁇ -alumina particles present in the nanoporous ⁇ -alumina powders are not particularly limited. In certain preferred embodiments, such as catalyst supports and the like, it may be desirable for the pores or voids to be sufficiently large to permit one or more reactants or products to enter or exit the porous particles. Any pore or void size which permits facile milling or crushing of nanoporous ⁇ -alumina powders are suitable for use in the production of nanosized ⁇ -alumina powders of the invention.
  • Preferred nanoporous ⁇ -alumina powders of the invention comprise porous particles in which the pores or voids have a minimum dimension of between about 20 nm and about 400 nm. More preferably, the minimum dimension of the pores or voids is between about 50 nm and about 300 ⁇ m. In particularly preferred the pores or voids have a minimum dimension of between about 100 nm and about 200 nm.
  • the percent volume of the nanoporous ⁇ -alumina powders which is ⁇ -alumina can be varied depending upon the application.
  • the ⁇ -alumina primary particles account for between 1 and about 75 percent by volume of the nanoporous ⁇ -alumina powders. More preferably the ⁇ -alumina primary particles account for between about 10 to about 75% or between about 10 to about 50% by volume of the nanoporous ⁇ -alumina powders.
  • the architecture and arrangement of the voids and pores in the nanoporous ⁇ -alumina particles are not particularly limited. Although not wishing to be bound by theory, the architecture, size and arrangement of the voids or pores is typically a function of the size and physical properties of the water soluble organic polymer.
  • the interpenetrated array of pores or voids have a columnar or tubular structure. More preferably, the columnar or tubular structure have a diameter of between about 20 nm and about 250 nm or between about 50 nm and about 150 nm.
  • the invention further provides a nanosized ⁇ -alumina powder comprising ⁇ -alumina particles having an average particle size of less than about 100 nm and slurries comprising same.
  • the nanosized ⁇ -alumina powders of the invention are typically prepared by milling, crushing or otherwise breaking apart nanoporous ⁇ -alumina powders of the invention to liberate the primary ⁇ -alumina particles of the porous ⁇ -alumina particles. More preferably, the primary ⁇ -alumina particles of the interconnected array have an average size of between about 10-100 nm, between about 20-90 nm, between about 25-80 nm, or between about 30-70 nm.
  • Other preferred nanoporous ⁇ -alumina powders of the invention comprise an interconnected array of ⁇ -alumina primary particles, wherein at least 99% of the (1-alumina primary particles have a size within about a distribution of about 10 mm.
  • Preferred slurries of the invention comprise one or more nanosized ⁇ -alumina powders of the invention.
  • Preferred nanosized ⁇ -alumina powders include any nanosized ⁇ -alumina powders described herein. More preferred slurries include those slurries in which the ⁇ -alumina particles of the nanosized ⁇ -alumina powder are dispersed in an aqueous mixture.
  • Preferred aqueous mixtures include water, particularly deionized or distilled water, aqueous solutions comprising one or more surfactants, organic acids, or other additives.
  • Preferred additives are chemically inert to ⁇ -alumina under storage or polishing conditions.
  • additives are capable of inhibiting aggregation of ⁇ -alumina particles in an aqueous mixture.
  • Particularly preferred additives to the aqueous mixture include organic acids such as acetic acid, formic acid, lactic acid, glycolic acid, citric acid, oxalic acid, and other carboxylic acids having less than about 6 carbon atoms.
  • slurries of the invention comprise one or more nanosized ⁇ -alumina powders of the present invention. That is, slurries of the invention can comprise a single particle size of ⁇ -alumina or a composite mixture of two or more particles sizes from two or more nanosized ⁇ -alumina powders of the invention having different average particle sizes which when mixed combine to form a mono-modal, bi-modal, or poly-modal particle size distribution. Typically slurries comprising ⁇ -alumina particles having a single average particle size distribution are preferred.
  • Aqueous slurries of the present invention typically have a pH of between about 2 and about 11. In certain preferred applications, slurries having an acidic pH or an alkaline pH are desirable. Thus more preferred aqueous slurries of the invention have a pH of from about 1 or 2 to about 6 or between about 8 and about 10.5.
  • the slurries of the invention are suitable for use in a variety of applications including use as abrasives in polishing or CMP applications, as supports for metal catalysts and the like.
  • any water soluble aluminum compound capable of forming ⁇ -alumina are suitable for use as the ⁇ -alumina precursor.
  • preferred starting materials include boehmite and molecular alumina precursors.
  • the source of boehmite is not particularly relevant so long as the boehmite provides high purity Al(O)OH and may include both naturally occurring or synthetic boehmite.
  • the molecular alumina precursors can be inorganic (Aluminum nitrate, aluminum chloride, aluminum sulfate, and the like) or organic (aluminum alkoxides, aluminum acetate, and the like).
  • Boehmite is a particularly preferred starting material for the processes of the invention.
  • a process for the production of nanoporous ⁇ -alumina powders which comprises the steps of
  • an inorganic sol comprising at least one alumina precursor and a plurality of ⁇ -alumina seed particles
  • any water soluble organic or inorganic coordination complex or salt of aluminum may be suitable for use in the processes of the invention.
  • preferred molecular alumina precursors are selected from aluminum salts comprising one or more anions selected from alkoxides, aryl oxides, carboxylates, halides, sulphate, nitrate, oxalates, and acetoacetonates.
  • Particularly preferred molecular alumina precursors include aluminum alkoxides, carboxylates, halides and nitrates.
  • Preferred aqueous solutions provided or prepared by the processes of the invention comprise water, boehmite and/or a molecular alumina precursor, and ⁇ -alumina seed particles.
  • a molecular alumina precursor is employed, it is sometimes desirable for the aqueous solution to further comprise at least one acid.
  • Preferred acids are selected from the group consisting of nitric acid, sulfuric acid, hydrochloric acid, hydrobromic acid, hydroiodic acid, acetic acid, formic acid, propionic acid and the like.
  • the ⁇ -alumina seed particles have an average particle size of less than about 125 nm, or more preferably less than about 100 nm. Particularly preferred seed particles have an average particle size of between about 30 nm and about 100 nm, between about 40 nm and about 80 nm, or between about 50 nm and about 70 nm.
  • Seed ⁇ -alumina particles are well dispersed in water and then the aluminum compounds are added to the water dispersion of the seed particles. It is desirable to increase the seeding efficacy of the water dispersion.
  • the concentration of the seeds is relatively high to increase the seeding power of the solution, e.g., the ratio of aluminum atoms in the product ⁇ -alumina particles originating in the seed versus the molecular alumina precursor is typically between about 1:3 and about 1:1000 or more preferably between about 1:6 and about 1:20.
  • the seed particles comprise between about 0.1 and about 25 weight percent of the product ⁇ -alumina powder.
  • the concentration of the seeds is about 1-15% or 1-10% by weight of the product ⁇ -alumina.
  • the water soluble organic polymer which is added to the aqueous solution of the alumina precursor and seeds, functions to create a domains of organic material within the sol.
  • the organic-inorganic sol formed from the aqueous mixture comprising ⁇ -alumina seed particles, an ⁇ -alumina precursor, and the water soluble organic polymer had discrete domains which are composed of the precipitated alumina precursor and the seed particles and domains of the solvated organic polymer. Freeze drying of the organic-inorganic sol results in a dried gel having domains of the alumina precursor and seed particles and domains of the organic polymer. Firing of the dried gel pyrolyzes the organic polymer creating voids and transforming the alumina precursor into ⁇ -alumina.
  • the invention contemplates the use of any water soluble organic polymer which burns cleanly at a temperature below the phase transition temperature of alumina and which is capable of forming organic-inorganic sols.
  • Preferred water soluble organic polymers are selected from polyols, sugars, polyalkylene oxides, poly(meth)acrylic acid, poly(meth)acrylates, and mixtures thereof.
  • Particularly preferred water soluble organic polymer include polyvinyl alcohol, polyethylene glycol or a mixture thereof.
  • the processes of the invention comprise a freeze drying step in which the organic-inorganic sol is frozen rapidly and water and other volatiles removed under a reduced atmosphere.
  • the sol is placed in a container with a high surface area to mass to insure rapid cooling and then rapidly frozen by contact with an atmosphere having an ambient temperature of less than 0° C., or more preferably less than ⁇ 20° C., ⁇ 30° C. or ⁇ 40° C.
  • the frozen sol is heated to a temperature of between 0° C. and about 100° C. after exposure to a reduced pressure. More preferably, the frozen sol is heated to a temperature of between about 20° C. and about 80° C. or between about 40° C. and about 80° C.
  • the rate of sublimation is inversely proportional to the pressure in the sublimation vessel and directly proportional to temperature.
  • the present invention provides new processes of preparing nanoporous ⁇ -alumina powders and nanosized ⁇ -alumina powders which comprise firing of a precursor gel at a temperature of less than about 1200° C. More preferably the firing temperature is between about 1000° C. and about 1200° C. or more preferably less than about 1100° C. More preferably, the firing is conducted at a temperature of between about 750° C. and about 1050° C. or more preferably between about 800° C. and about 1000° C. depending upon the molecular alumina precursor. The firing is genrally carried out under ambient atmosphere, i.e., air. However, other atmospheres, including oxygen enriched atmospheres, may be desirable in certain circumstances.
  • ambient atmosphere i.e., air.
  • other atmospheres, including oxygen enriched atmospheres may be desirable in certain circumstances.
  • Preferred processes of the invention provide nanoporous ⁇ -alumina powders which are composed of an interconnected array of ⁇ -alumina primary particles having an average particle size of less than about 100 nm and an interpenetrated array of pores or voids. More preferably, processes of the invention provide nanoporous ⁇ -alumina powders in which the primary ⁇ -alumina particles of the interconnected array have an average size of between about 10-100 nm, between about 20-90 nm, between about 25-80 nm, or between about 30-70 nm. Other preferred processes of the invention provide nanoporous ⁇ -alumina powders in which at least 99% of the ⁇ -alumina primary particles have a size within about a distribution of about 10 nm.
  • Preferred processes of the invention provide nanoporous ⁇ -alumina powders in which the pores or voids have a minimum dimension of between about 20 nm and about 400 mm. More preferably, the processes provide nanoporous powders in which the minimum dimension of the pores or voids is between about 50 nm and about 300 nm, or, more preferably, between about 100 nm and about 200 nm.
  • the processes provide nanoporous ⁇ -alumina powders in which the percent volume ⁇ -alumina based on the total volume of the nanoporous ⁇ -alumina powder can be varied depending upon the application.
  • the processes provide powders in which the ⁇ -alumina primary particles account for between 1 and about 75 percent by volume of the nanoporous ⁇ -alumina powders. More preferably, the processes provide powders in which the ⁇ -alumina primary particles account for between about 10 to about 75% or between about 10 to about 50% by volume of the nanoporous ⁇ -alumina powders (where the volume of the nanoporous ⁇ -alumina powder is the sum of the volume of the ⁇ -alumina primary particles and the volume of the void space).
  • the processes of the invention provide nanoporous ⁇ -alumina powders comprising ⁇ -alumina particles having an interpenetrated array of pores or voids which have a columnar or tubular structure.
  • the columnar or tubular pores have a diameter of between about 20 nm and about 250 nm, or, more preferably, have a diameter of between about 50 nm and about 150 mm.
  • the present invention also provides a process for the production of a nanosized ⁇ -alumina powder comprising ⁇ -alumina particles having an average particle size of less than about 100 nm, the process comprising the steps of:
  • nanoporous ⁇ -alumina powder comprising interconnected ⁇ -alumina primary particles having an average particle size of less than about 100 nm and an interpenetrated array of pores or voids;
  • any nanoporous ⁇ -alumina powder having a primary particle size of less than 100 nm is suitable for use in the process of the invention
  • preferred nanoporous ⁇ -alumina powders are prepared by the processes of the invention.
  • the nanoporous ⁇ -alumina powders of the invention are crushed, milled or otherwise broken up to generate a nanosized ⁇ -alumina powder comprising the primary particles of the nanoporous powder.
  • Any means of breaking the interconnected array of ⁇ -alumina primary particles is suitable for use in the methods of the invention and may include mechanical and ultrasound means. Mechanical breaking means are typically preferred. More preferred processes of the invention include milling the nanoporous particles to break the interconnected array of primary particles.
  • Polycrystalline alpha alumina powder milled with deionized water (DI water) in an attrition miller was used as seeds. 47.6 g of the alumina seeds in slurry (33.5 wt % in solid), was dispersed in 5400 g of DI water in a plastic container. 575 g of nitric acid (7%) was added to the solution, to which 600 g of commercial boehmite powder (Siral-1.5, Condea) was added. The solution was stirred vigorously for two hours in order to peptize the boehmite completely. 200 g of polyvinyl alcohol (PVA, molecular weight 11,000 ⁇ 31,000, J. T. Baker), was first dissolved in 800 g of water to make a 20 wt % PVA solution. The PVA solution was added to the boehmite solution and well mixed using a mixer for one hour.
  • PVA polyvinyl alcohol
  • the solution was divided into stainless steel pans and put into a freeze drier chamber for freeze drying.
  • the solution was first frozen down to ⁇ 45° C. and then subject to sublimation at the temperature of 60° C. under vaccum.
  • the total freeze drying process took ⁇ 72 hours.
  • the as freeze dried material was sponge-like, white colored.
  • the powder was fired in a box furnace at 1190° C. for one hour. After firing, the powder turned to highly fluffy, porous and very easy to ground in a mortal. It was confirmed based on X-ray diffraction and He density measurement, that the material was 98 ⁇ 100% alpha-alumina. SEM shows that the material was nanoporous and honeycomb-structured.
  • the pores are oriented along the direction of the cooling and heating inside the freeze drier, presumably the pores were used as tunnels allowing water to sublimate.
  • the SEM for cross section view of the material showed that the pores are around 150 nm in diameter. See, FIG. 1 and FIG. 2.
  • BET measurement shows that the surface area of the material is 38.5 m2/g.
  • FIG. 3 provides an SEM image of a slurry after milling.
  • the solution was divided into stainless steel pans and put into a freeze drier chamber for freeze drying.
  • the solution was first frozen down to ⁇ 45° C. before the sublimation at temperature of 60° C. under vacuum.
  • the freeze drying were carried out for ⁇ 72 days to allow complete drying.
  • the freeze dried material was sponge-like, white colored.
  • the powder was fired at 1000° C. for 1.5 hours. After firing, the powder turned to highly fluffy, porous. It was confirmed based on X-ray diffraction and He density measurement, that the material was ⁇ 100% alpha-alumina. SEM shows that the material was nanoporous, and had a honeycomb structure.
  • the pores are oriented along the direction of cooling and heating inside the freeze drier, in the similar way as in Example 1.
  • the size of the column is around 150 nm in diameter.
  • this material after firing could be readily crushed and milled in an attrition miller using high purity of alumina as media.

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US10/406,060 US20040198584A1 (en) 2003-04-02 2003-04-02 Nanoporous ultrafine alpha-alumina powders and freeze drying process of preparing same
CN200480009461XA CN1856443B (zh) 2003-04-02 2004-03-31 纳米多孔超细α-氧化铝粉末及其冷冻干燥制备方法
CA002519420A CA2519420C (en) 2003-04-02 2004-03-31 Nanoporous ultrafine alpha-alumina powders and freeze drying process of preparing the same
KR1020057018443A KR100726113B1 (ko) 2003-04-02 2004-03-31 나노다공성 극미세 알파-알루미나 분말 및 이의 동결 건조제조방법
BRPI0409138-8A BRPI0409138A (pt) 2003-04-02 2004-03-31 pós nanoporosos ultrafinos de alfa-alumina e processo de preparação dos mesmos através de secagem dos mesmos através de secagem por congelamento
MXPA05010568A MXPA05010568A (es) 2003-04-02 2004-03-31 Polvos nanoporosos ultrafinos de alfa-alumina y procedimiento de secado por congelamiento para su preparacion.
RU2005130530/15A RU2299179C2 (ru) 2003-04-02 2004-03-31 Нанопористые сверхмелкие порошки из альфа оксида алюминия и способ их приготовления при помощи сублимационной сушки
PCT/US2004/010255 WO2004089828A2 (en) 2003-04-02 2004-03-31 Nanoporous ultrafine alpha-alumina powders and freeze drying process of preparing the same
JP2006509649A JP4347884B2 (ja) 2003-04-02 2004-03-31 ナノサイズα−アルミナ粉末及びそれを含むスラリーの製造方法
AU2004228649A AU2004228649B2 (en) 2003-04-02 2004-03-31 Nanoporous ultrafine alpha-alumina powders and freeze drying process of preparing the same
EP04749696.3A EP1608593B1 (de) 2003-04-02 2004-03-31 Nanoporöses ultrafeines alpha-aluminiumoxidpulver und gefriertrocknungsverfahrens zu dessen herstellung
NZ542626A NZ542626A (en) 2003-04-02 2004-03-31 Nanoporous ultrafine alpha-alumina powders and freeze drying process of preparing the same
US11/050,135 US8080231B2 (en) 2003-04-02 2005-02-02 Process for making nanoporous ultrafine alpha-alumina powder
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US20150250686A1 (en) * 2012-10-01 2015-09-10 Fondazione Istituto Italiano Di Tecnologia Combined material including anodic porous alumina and a polymer matrix, and its use for the dental recondition
US20190262239A1 (en) * 2012-10-01 2019-08-29 Fondazione Istituto Italiano Di Tecnologia Combined material including anodic porous alumina and a polymer matrix, and its use for the dental recondition
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KR100726113B1 (ko) 2007-06-12
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US20050135995A1 (en) 2005-06-23
RU2299179C2 (ru) 2007-05-20

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