WO2000024676A1 - Procede de decomposition moleculaire pour la synthese de poudres ceramiques et metalliques de grosseur nanometrique - Google Patents

Procede de decomposition moleculaire pour la synthese de poudres ceramiques et metalliques de grosseur nanometrique Download PDF

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WO2000024676A1
WO2000024676A1 PCT/US1999/024052 US9924052W WO0024676A1 WO 2000024676 A1 WO2000024676 A1 WO 2000024676A1 US 9924052 W US9924052 W US 9924052W WO 0024676 A1 WO0024676 A1 WO 0024676A1
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precursor
constituent
soluble
solvent
nanosize
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PCT/US1999/024052
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WO2000024676A9 (fr
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Anil Vasudeo Virkar
Sanjeevani Vidyadhar Bhide
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University Of Utah
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Priority to US09/830,399 priority Critical patent/US6803027B1/en
Application filed by University Of Utah filed Critical University Of Utah
Priority to JP2000578252A priority patent/JP2002528369A/ja
Priority to AU18076/00A priority patent/AU758256B2/en
Publication of WO2000024676A1 publication Critical patent/WO2000024676A1/fr
Publication of WO2000024676A9 publication Critical patent/WO2000024676A9/fr
Priority to US10/960,433 priority patent/US7311754B2/en

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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
    • C01F17/00—Compounds of rare earth metals
    • C01F17/20—Compounds containing only rare earth metals as the metal element
    • C01F17/206—Compounds containing only rare earth metals as the metal element oxide or hydroxide being the only anion
    • C01F17/224—Oxides or hydroxides of lanthanides
    • C01F17/235—Cerium oxides or hydroxides
    • 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
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
    • B22F1/00—Metallic powder; Treatment of metallic powder, e.g. to facilitate working or to improve properties
    • B22F1/05—Metallic powder characterised by the size or surface area of the particles
    • B22F1/054—Nanosized particles
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
    • B22F9/00—Making metallic powder or suspensions thereof
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    • C01B13/00—Oxygen; Ozone; Oxides or hydroxides in general
    • C01B13/14—Methods for preparing oxides or hydroxides in general
    • 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
    • C01F17/00—Compounds of rare earth metals
    • C01F17/20—Compounds containing only rare earth metals as the metal element
    • C01F17/206—Compounds containing only rare earth metals as the metal element oxide or hydroxide being the only anion
    • C01F17/241—Compounds containing only rare earth metals as the metal element oxide or hydroxide being the only anion containing two or more rare earth metals, e.g. NdPrO3 or LaNdPrO3
    • 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
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01G—COMPOUNDS CONTAINING METALS NOT COVERED BY SUBCLASSES C01D OR C01F
    • C01G23/00—Compounds of titanium
    • C01G23/04—Oxides; Hydroxides
    • C01G23/047—Titanium dioxide
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01G—COMPOUNDS CONTAINING METALS NOT COVERED BY SUBCLASSES C01D OR C01F
    • C01G23/00—Compounds of titanium
    • C01G23/04—Oxides; Hydroxides
    • C01G23/047—Titanium dioxide
    • C01G23/053—Producing by wet processes, e.g. hydrolysing titanium salts
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01G—COMPOUNDS CONTAINING METALS NOT COVERED BY SUBCLASSES C01D OR C01F
    • C01G25/00—Compounds of zirconium
    • C01G25/02—Oxides
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    • C01G—COMPOUNDS CONTAINING METALS NOT COVERED BY SUBCLASSES C01D OR C01F
    • C01G31/00—Compounds of vanadium
    • C01G31/02—Oxides
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    • C01G37/00—Compounds of chromium
    • C01G37/02—Oxides or hydrates thereof
    • C—CHEMISTRY; METALLURGY
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    • C01G—COMPOUNDS CONTAINING METALS NOT COVERED BY SUBCLASSES C01D OR C01F
    • C01G37/00—Compounds of chromium
    • C01G37/02—Oxides or hydrates thereof
    • C01G37/033—Chromium trioxide; Chromic acid
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    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2002/00—Crystal-structural characteristics
    • C01P2002/30—Three-dimensional structures
    • C01P2002/34—Three-dimensional structures perovskite-type (ABO3)
    • C—CHEMISTRY; METALLURGY
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    • C01P2002/50—Solid solutions
    • C01P2002/52—Solid solutions containing elements as dopants
    • C—CHEMISTRY; METALLURGY
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    • C01P2002/00—Crystal-structural characteristics
    • C01P2002/70—Crystal-structural characteristics defined by measured X-ray, neutron or electron diffraction data
    • C01P2002/72—Crystal-structural characteristics defined by measured X-ray, neutron or electron diffraction data by d-values or two theta-values, e.g. as X-ray diagram
    • C—CHEMISTRY; METALLURGY
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    • C01P2004/00—Particle morphology
    • C01P2004/60—Particles characterised by their size
    • C01P2004/64—Nanometer sized, i.e. from 1-100 nanometer

Definitions

  • This invention relates to a process for forming ceramic powders with fine nanosize particles.
  • Nanosize powders are generally considered to be powders having very fine particles in the nanometer range, i.e., less than a few nanometers, e.g., 100 nanometers or less, usually 10 nanometers or less.
  • Nanosize powders have numerous applications such as catalysts, electrocatalysts, catalyst supports, electrodes, active powders for the fabrication of dense bodies, semiconductors for energy storage, photovoltaics, ultrafine magnetic materials for information storage, environmental clean-up as destructive adsorbents, water purification, information storage, and optical computers, to name a few.
  • nanosize (3 to 4 nm) platinum for oxygen reduction in acid electrolytes many metallic powders made by precipitation in aqueous and non-aqueous media for alloy fabrication and for catalysis, nanosize iron oxide catalyst for coal liquefaction, nanosize iron oxide particles for magnetic applications, tetragonal zirconia powder by a hydrothermal treatment at high pressures for structural applications, carbides and nitrides using non-aqueous media, nanosize BaTi ⁇ 3 by a gas-condensation process, etc.
  • Many oxides have potential applications as nanosize powders.
  • Nanocrystalline powders of Ti ⁇ 2, L_2 ⁇ - doped MgO, Ce ⁇ 2, Y-doped Zr ⁇ 2, etc. have been produced by gas-phase condensation. Aerosol spray pyrolysis has been used to synthesize BaFei2 ⁇ i9, Fe2 ⁇ 3 among some other materials. High-energy mechanical milling is used extensively to produce nanostructured materials, especially when large quantities of materials are required.
  • Nanoparticles of a uniform size can in principle be formed by carefully controlling nucleation and growth. Often, a variety of encapsulating methods are necessary to control the size of nanoparticles.
  • an object of the invention to provide method for the formation of nanosize powders that is easy to implement on an industrial scale and in relatively inexpensive when compared to molecular synthesis methods. 5 Another object of the invention is to provide a method in which nanosize powders are formed by a process other than precipitation or deposition from solutions, thus eliminating the possibility of unwanted deposition and growth of the nanosize powders.
  • Another object of the invention is to provide a method which forms nanosize l o powders that have a reduced tendency to agglomerate.
  • Another object of the invention is to provide a method for the formation of nanosize powders that can be applied to forming a variety of powder compositions.
  • the present invention presents an alternative approach for the synthesis of nanosize powders.
  • a precursor inorganic compound is formed from which the unwanted component is leached away so that a fine, nanosize powder is left as a residue.
  • the present invention is
  • the present invention is suitable for making large quantities of nanosize powders of a number of materials.
  • the present invention is a process for forming nanosize powders .
  • the process comprises: forming a precursor ceramic material comprising a fugitive constituent and a non-soluble constituent in a single phase; contacting the precursor material a selective solvent to form a solution of the
  • the precursor sufficiently reactive with the solvent to form the solution of the fugitive constituent in the solvent and the residue of the non-soluble constituent the precursor material and the non-soluble residue sufficiently insoluble in the solvent such that there is insufficient precursor material and non-soluble residue in solution to deposit and precipitate upon the residue of the non-soluble-constituent, the fugitive constituent being sufficiently soluble in the solvent such that the precursor reacts with the solvent to form a solution of the fugitive constituent without precipitation and deposition of fugitive constituent upon the residue of the non-soluble constituent in the form of nanosize particles; removing the selective solvent solution from the residue to form a nanosize powder having the same chemical composition as the non-soluble constituent.
  • the precursor material should be insoluble as the precursor material in the solvent.
  • One of the objects of the present invention is to prevent deposition or precipitation of dissolved materials upon the nanosize particles that are formed from the non-soluble residue freed of the fugitive constituent. Deposition or dissolved precursor material will not only contaminate the residue, but possibly result in particles that are too large.
  • an object is to prevent, as much as possible, deposition of dissolved materials and the resulting growth of existing crystals. Unlike prior-art methods where small crystals are crystallized from solution, it is practical in the present invention to inhibit the crystallization and precipitation process altogether, as crystallization is not required to form initial nanosize crystals. Accordingly, as further illustrated below, a precursor is chosen such that precipitation of any material upon the nanosize particles is essentially avoided.
  • the precursor material is that it be reactive with the solvent. Since the precursor is insoluble, the precursor composition does not dissolve, but it does react to selectively remove the fugitive constituent, leaving a freed non- soluble constituent..
  • the fugitive constituent is sufficiently soluble that it will not precipitate from the solution to contaminate and grow the particles of the non-soluble constitituent.
  • the non-soluble constituent is essentially insoluble to prevent dissolved material dissolving into the solution, there thereafter precipitating upon and growing the nanosize particles of the non-soluble material formed by removal of the fugitive constituent.
  • the invention involves a balance between preventing precursor and non-soluble constituent from forming a solution so that it cannot redeposit and grow crystals, and removing the fugitive constituent, that is sufficiently soluble in the solution that it will not precipitate from the solution to grow crystals.
  • BaCeO 3 does not dissolve in water, but reacts with water to form a solution of the Ba (as Ba(OH) 2 ).
  • NaAlO 2 is soluble in water, and cannot be used as a suitable precursor for the present invention.
  • the precursor should be a single phase material, i.e., where the differentiation between the non-soluble and the fugitive constituents is on a molecular level. Accordingly, the precursor exists as a compound existing is the form of a large molecule, or as an alloy.
  • a precursor material is a mixed oxide with at least two cations, the metal oxide of the first cation being soluble to function as the fugitive constituent, and the oxide of the second being non- soluble to function as the non-soluble constituent.
  • the precursor can exist, for example, as an alloy or an intermetallic compound.
  • the solvent is selected to react with the precursor and have the solubility properties as described above.
  • a preferred solvent is water, but non- aqueous solvents may be required to suppress the solubilities of the non-soluble residue and/or the precursor.
  • the solvent is polar, as the fugitive constituent, which must be solubilized, is often a polar composition.
  • suitable solvents for forming a ceramic nanosize powder are polar liquids that solubilize selected ceramic oxides, which selected oxides in the process of the invention are the fugitive constituents.
  • preferred solvents are water and acids.
  • the selective solvent is typically an acid that reacts with or dissolves the fugitive metal, and not the non-soluble metal.
  • an acid gas such as SO3, N2O5, CO2 or HC1, may be used to react with and remove the fugitive constituent. Any suitable process may be used for forming a precursor is contemplated.
  • the precursor is a mixed ceramic subjecting a powder mixture to a suitable high-temperature treatment is suitable.
  • Precursors for metallic powders are likewise formed by any suitable process to produce a suitable alloy or intermetallic compound, such as alloying methods or powder metallurgy.
  • the solvent is then removed from the remaining non-soluble constituent. With the fugitive constituent removed, the non-soluble constituent assumes the form of nanosize particles.
  • the solvent is removed by conventional methods, including, but not limited to settling, centrifugation, filtering, air drying, or a combination or the above.
  • the solvent may also be removed by replacing it with another liquid, such as replacing at aqueous solvent with an alcohol, and then separating the powder from the replacement liquid. Using a replacement liquid may be desirable to inhibit agglomeration of the powder during drying.
  • the product is chemically the same as the non-soluble constituent.
  • the process of the invention is particularly suitable for synthesizing nanosize powders of AI2O3, Ce ⁇ 2, Zr ⁇ 2, Ti ⁇ 2, V2O5, rare earth (RE) oxide-doped Ce ⁇ 2 and RE- or Y 2 O 3 -doped ZK>2.
  • Figure 1 is a schematic showing a reaction illustrative of the process of the invention
  • Figure 2(a) is an XRD (X-ray diffraction) trace of a single-phase perovskite precursor material (Gd-doped BaCeO3).
  • Figure 2(b) is an XRD trace of the material of Figure 2(a) after boiling in water for two days, showing conversion to nanosize CeO 2 .
  • Figure 2(c) is an XRD trace of a comparative coarse (not nanosize) Ce ⁇ 2 powder.
  • Figure 3(a) is an XRD trace of an as-received, precursor (non-nanosize)
  • Figure 3(b) is an XRD trace of the residue after boiling the NajZrOj of Figure 3(a) in water for 10 minutes.
  • Figure 3(c) is an XRD trace of the residue from the boiling of NajZrOj from Figure 3(c) after heating in air to 100°C for 1.5 hours.
  • Figure 3(d) is an XRD trace of the residue after 1.5 hours in air at 200°C.
  • Figure 3(e) is an XRD trace of the residue after 1.5 hours in air at 300°C.
  • Figure 3(f) is an XRD trace of the residue after 1.5 hours in air at 350°C.
  • Figure 3(g) is an XRD trace of the residue after 1.5 hours in air at 400°C.
  • Figure 3(h) is an XRD trace of the residue after 1.5 hours in air at 500°C.
  • Figure 3(i) is an XRD trace of the residue after 1.5 hours in air at 600°C.
  • the present invention is suitable for the synthesis of many types of powders. Although the following discussion is confined to specific materials, the applicability of the present invention to other powders will be evident to one of ordinary skill in the art. For the purposes of discussion, rare earth (RE)-doped Ce ⁇ 2 and Y2 ⁇ 3 ⁇ doped
  • Zr ⁇ 2 are used as examples.
  • Y2 ⁇ 3-doped Zr ⁇ 2 has many applications such as in oxygen sensors, solid oxide fuel cells, as a constituent in electrodes and in structural ceramics.
  • RE-doped Ce ⁇ 2 has applications in oxygen separation membranes, in fuel cells as well as in catalysis.
  • Respective precursor powders can be synthesized using conventional processing methods.
  • a precursor for the synthesis of nanosize RE2O3 -doped Ce ⁇ 2 by the present invention, a precursor can be BaCe ⁇ . ⁇ )RE x O ⁇ _ ⁇ ) .
  • the precursor is synthesized using BaCO3, RE2O3 and Ce ⁇ 2 in a powder form, mixing reagent powders, and calcining at 1250°C.
  • a similar procedure can be used for other materials such as Y2 ⁇ 3-doped Zr ⁇ 2-
  • SrCe,. x RE x O 3 . 5 precursors for a composition of the final nanosize powder is Ce, . X RE X O 2 . 5 or BaZr,. ⁇ RE x O 3 . ⁇ or BaZr,_ x REXO 3 . ⁇ precursors for a composition of the nanosize powder of Zr,. x RE x O 2.
  • ⁇ RE is a rare earth metal or Y, x is between 0 and about 0.25, and ⁇ is between 0 and about 0.13.
  • Synthesis of the nanosize powders from the precursor involves exposing the precursor to a selective solvent that leaves the desired component.
  • the following approaches can be used be used: (a) A reaction with water.
  • Water is the ideal solvent. Also, in many cases, thermodynamics of the formation of alkali hydroxides or alkaline earth hydroxides are favorable. There are, however, a few potential complications, in particular many elements form hydroxides, and there is the danger of agglomeration during the drying stage. For example, in the synthesis of Zr ⁇ 2 the undesired formation of Zr(OH)4 is possible. However, it has been shown that with Na 2 ZrO 3 as a precursor, a direct reaction with water can be readily effected without the formation of Zr(OH) 4 . The potential for agglomeration can be suppressed by replacing the water with alcohol after solvation.
  • reaction with water is not favorable.
  • reaction of BaZr ⁇ 3 with water to form Zr ⁇ 2 and Ba(OH)2 is not favored.
  • reaction of BaZr ⁇ 3 with HNO3 or N 2 O 5 to form Ba(NO3)2 and Zr ⁇ 2 is favored.
  • Ba(NO3)2 has a reasonable solubility in water.
  • HNO3 as a reactant, the formation of Zr(OH)4 is suppressed. The tendency for agglomeration can be minimized, by either replacing water with an alcohol or other organic liquids of high vapor pressures, or drying under supercritical conditions.
  • Suitable solvents are selected based on the following criteria: (i) the solubility of the reacting gas in the solvent, and (ii) the solubility of the fugitive compound formed; e.g. BaCO3 or BaSO4 in the case of CO 2 or SO 3 .
  • the suspension of the powder is preferably agitated, e.g. by constant stirring, while the gas is bubbled through it.
  • the solvent vapors are also preferably recovered and returned back to the reactor, by using, for example, a water- cooled condenser.
  • the overall reaction mechanism is expected to involve the following steps; (a) The transport of the dissolved reacting gas, e.g., N2O5, CO2 or SO3, (or the respective acids) through the porous layer formed to the interface separating the precursor and the product, (b) Reaction at the interface, and (c) The transport of the dissolved byproduct, e.g., Ba(NO3)2, BaCO3 or BaSO4, from the interface through the porous layer, into the bath.
  • the overall kinetics may be influenced by all three of the factors, and may be dictated by whichever is the slowest step.
  • the solubility of the reacting gas is a function of pressure; the higher the pressure, the higher is the solubility.
  • the advantage of the present invention over the other methods for the synthesis of nanosize powders is that there is negligible tendency for the occurrence of particle growth by either Ostwald ripening or by precipitation. This is because neither the precursor nor the desired product, are soluble in the solvent. For example, neither BaCeO 3 nor CeO 2 is soluble in water; only the leachable Ba(OH) 2 is soluble in water. Since the product is nanosize, it could be argued that its solubility may be higher than bulk materials. It is known, for example, that the solubility of a sparingly soluble species is related to its size by the following equation;
  • C(oo) is the bulk solubility (particle of a large radius)
  • C(r) is the solubility of a particle of radius r
  • ⁇ is the particle-solvent interfacial energy
  • ⁇ is the molecular volume of the particle
  • k B is the Boltzmann constant
  • T is the absolute temperature.
  • the sintering (densification) behavior of nanosize powders synthesized by the present invention is expected to result in densification at lower temperatures, resulting in a finer microstructure.
  • the grain size of sintered bodies made from the nanosize powders should be smaller than those made from conventional ceramic powders. It is well known that very fine-grained ceramics often exhibit interesting properties, such as, for example, superplasticity at elevated temperatures, and high strength at low temperatures.
  • the present invention is also applicable to the synthesis of metallic powders, by the appropriate choice of the metallic precursor and the selective solvent.
  • synthesis of Pd powder can be achieved with precursor of an equimolar alloy of Ba and Pd, which is actually a line compound BaPd.
  • the alloy can be made by arc melting or by powder metallurgy.
  • the powdered alloy is then treated in dilute HC1 to remove the Ba to form nanosize Pd.
  • nanosize powders of a variety of materials are usually made by one or more processes which may be categorized as belonging to molecular synthesis wherein particles are built up by an atom-by-atom or a molecule-by-molecule addition on a particle nucleus.
  • the present invention is based on molecular decomposition wherein unwanted species are chemically leached away thus producing a nanosize powder as a residue, starting with a precursor of a macroscopic size.
  • the method of the present invention should result in nanosize particles of a uniform composition and size.
  • neither the precursor nor the product is soluble in the reaction medium. As a result, particle coarsening is not expected to occur.
  • the starting precursor may be one of the alkaline earth cerates, such as
  • BaCeO3 + H.O ⁇ Ba(OH) 2 + CeO. is - 189.79 kJ/mol. indicating that this reaction is favored.
  • the volume of Ce ⁇ 2 per molecule is -77 A ⁇ and the linear dimension is (cube root of the volume) 4.25 A.
  • the volume per molecule of BaCe ⁇ 3 is -85 A 3 and the linear dimension is 4.4 A.
  • the change in volume for the original BaCeO 3 is ((85 - 77V85) x 100 or 9.4%, or the change in linear dimension is ((4.4 - 4.25)74.4) x 100 or 3.4%.
  • FIG 1 shows a schematic of a particle 11 reacting with H2O to form Ba(OH) 2 .
  • the Ba(OH) 2 formed dissolves into water thus leaving a porous layer 13 of CeO 2 .
  • the volume percent porosity in the layer is expected to be about 9.4%).
  • the fact that BaCe ⁇ 3 readily reacts with water suggests that the porosity is open. This facilitates the transport of the reacting species, H2O here, to the Ce ⁇ 2 (porous)/BaCe ⁇ 3 (dense) interface 15.
  • the reaction continues until all of the BaCe ⁇ 3 17 reacts to form porous Ce ⁇ 2-
  • the formed Ce ⁇ 2 should be fragile and break into a fine, nanosize powder.
  • Gd2 ⁇ 3-doped BaCeO3 powder of composition BaGdo.2Ceo.8 ⁇ (3- ⁇ ) was synthesized using BaCO3, Ce ⁇ 2, and Gd2 ⁇ 3 powders.
  • the powders were mixed in requisite proportions and wet ball-milled for 24 hrs.
  • the well-mixed powder was then dried and calcined at 1450°C for 6 hrs.
  • the calcined powder was then ball-milled and examined by X-ray diffraction (XRD) with CuK ⁇ radiation to ensure the existence of a single-phase perovskite (Figure 2(a)).
  • the starting precursor may be a suitable alkali or alkaline earth zirconate.
  • Na 2 ZrO 3 was used as the precursor. This was simply boiled in water for a few minutes. The reaction is Na 2 ZrO 3 + H 2 O ⁇ ZrO 2 + 2NaOH No thermodynamic data are available. However, preliminary experimental work, results of which are described below, shows that the above reaction is indeed favored.. Powder of Na 2 ZrO 3 was purchased from a commercial vendor. Approximately 10 gms. of the powder was boiled in water for ten minutes. The residue was filtered, washed, and dried. The residue was subsequently examined by X-ray diffraction (XRD) with CuK radiation. The residue was then subjected to a number of thermal treatments. The following are the results of this experiment.
  • XRD X-ray diffraction
  • Figure 3(a) is an XRD trace of the as-received Na ⁇ ZrO j powder. Sharp peaks indicate a relatively coarse (at least a few tenths of a micron or more) particle size. Very tiny peaks at approximately 28 and 31.5 degrees are due to a small amount of monoclinic ZrO 2 that was present in the as-received Na j Z ⁇ powder.
  • Figure 3(b) is an XRD trace of the residue after boiling Na 2 ZrO 3 in water for
  • the trace shows the absence of the original Na 2 ZrO 3 powder.
  • the trace mainly consists of two very broad peaks. These peaks belong to the cubic phase of ZrO 2 . The peaks are very broad and contain more than one peak in each of the peaks. These very broad peaks are indicative of a very fine (nano) particle size.
  • the reaction that occurred is the following: Na 2 ZrO 3 + H 2 O ⁇ ZrO 2 + NaOH
  • Figure 3(c) is an XRD trace of the residue after heating in air to 100°C for 1.5 hours. Note that the trace is similar to that in Figure 3(b).
  • Figure 3(d) is an XRD trace of the residue after 1.5 hours in air at 200°C in air.
  • Figure 3(e) is an XRD trace of the residue after 1.5 hours in air at 300°C.
  • the peaks not only have become sharper but that the initial very broad peaks of the residue have now split into more peaks.
  • a total of 4 broad peaks are apparent, in addition to the two sharp peaks corresponding to the original monoclinic ZrO 2 .
  • the four broad peaks are identified with cubic ZrO 2 .
  • the peaks correspond to (111), (200), (220), and (311) reflections, in increasing diffraction angle.
  • Figure 3(f) is an XRD trace of the residue after 1.5 hours in air at 350°C. The four peaks have become slightly sharper.
  • Figure 3(g) is an XRD trace of the residue after 1.5 hours in air at 400°C. The four peaks have become even sharper.
  • Figure 3(h) is an XRD trace of the residue after 1.5 hours in air at 500°C.
  • Figure 3(i) is an XRD trace of the residue after 1.5 hours in air at 600°C.
  • the corresponding XRD traces in Figures 3(c) to 3(i) show the formation of cubic zirconia as the residue is heated to higher temperatures..
  • ZrO 2 at low temperatures is monoclinic.
  • the formation of a very fine (nanosize) ZrO 2 by the described process leads to the stabilization of cubic ZrO 2 due to surface energy considerations ( ⁇ Cubic ⁇ y Monoc n speak ic where ⁇ denotes surface energy of the respective polymorph).
  • the present experiment showed that: (1) NajZrOj can be used to synthesize nanosize ZrO 2 . (2) The nanosize ZrO 2 formed is of cubic crystal structure.
  • nanosize Ce ⁇ 2 and ZrO 2 can be produced respectively by leaching out BaO from BaCe ⁇ 3, as Ba(OH)2 and Na ⁇ from as NaOH.
  • Various other reacting species can also in principle be used.
  • AI2O3 starting with BaAl2 ⁇ 4 by reacting it with HNO3 by the following reaction.
  • MgTi ⁇ 3 + 2HNO3 ⁇ Mg(NO3)2 + Ti ⁇ 2 + H2O The above reaction is thermodynamically favored at room temperature. Also, Mg(NO.) 2 is water soluble. Preliminary experiments were done wherein MgTi ⁇ 3 was boiled in dilute HNO3 for 11 hours. The reaction went to completion and the resulting Ti ⁇ 2 was indeed nanosize, as judged by XRD peak broadening. The XRD traces are not given here for the sake of brevity.
  • V2O5 which is used as a catalyst in NO x reduction, starting with Na4V2 ⁇ 7.
  • Na2SO4 is highly soluble in many polar liquids including of course water. Also, as long as Na4V2 ⁇ 7 is present, VOSO4 will not form.
  • Table B Some examples of the synthesis of fine ceramic powders by the present invention.
  • Table B shows that the standard free energies of the reactions are all negative suggesting that all of these reactions are thermodynamically favored. Carbonates, sulfates or nitrates of Al, Ti, and Zr are less stable than the corresponding alkaline earth compounds. No thermodynamic data appear to be available for the former.
  • Reactions of the various oxides with CO 2 , N 2 O 5 , and SO 3 to respectively form carbonates, nitrates, and sulfates can in principle be carried out in water or other polar liquids.
  • Ba(NO3)2 is soluble in water, but BaC ⁇ 3 and BaSO4 are essentially insoluble.
  • the prospective solvent to be used must have the following characteristics: (1) It must have a reasonable solubility for the reacting gases, namely, CO2, SO3 or N2O5. (2) It must have a significant solubility for BaCO3, BaSO or Ba(NO3)2- Table C gives a list of possible candidates and their physical properties.
  • the method of the present invention can also be used to synthesize doped powders.
  • the desired powder is Y2 ⁇ 3-doped Zr ⁇ 2 of composition Zr(i- x )Y x O(2- ⁇ then the starting precursor could be BaZr(i_ x )Y x O(3- ⁇ ).
  • the resulting powder should be Zr(i_ x )Y x O(2- ⁇ )-
  • RE-doped Ce ⁇ 2 where RE is a rare earth, namely Ce(i- x )RE x O(2- ⁇ ), which can be made using doped BaCe ⁇ 3, that is, BaCe(i- x )RE x O(3- ⁇ ).
  • nanosize Gd-doped Ce ⁇ 2 was synthesized.
  • the method of the present invention can be used with water as the solvent in many cases.
  • water as the solvent
  • the corresponding aqueous acids namely H2CO3 or H2SO4 or HNO3
  • the choice of the acid being dependent upon the solubility of the leachable compound to be formed, assuming of course that the thermodynamics are favorable.
  • the synthesis of nanosize TiO 2 starting with MgTiO 3 using HNO 3 has been demonstrated.
  • the leachable compound is Na 2 SO 4 as in the formation of V 2 O 5 starting with Na 4 V 2 O 7
  • H 2 SO 4 should be the acid.
  • HNO 3 is the acid of choice.
  • the present invention should also be useful for the synthesis of nanosize metallic powders, provided suitable intermetallic compounds can be used as precursors.
  • suitable intermetallic compounds can be used as precursors.
  • suitable intermetallic compounds There are numerous binary and ternary intermetallic compounds which may be used as precursors.
  • a possible precursor is BaPd which is an intermetallic line compound.
  • the possible approach would consist of first fabricating BaPd by a conventional metallurgical process and then reacting it with an acid, e.g., HC1 acid. It is readily shown that the ⁇ G° for the reaction,
  • BaCl2 + Pd ⁇ Ba + PdC_2 is positive suggesting that the first compound to form will be BaC_2-
  • the BaCl2 formed will dissolve into water thus forming nanosize Pd powder.
  • the so-formed Pd powder should be nanosize and continue to remain nanosize since Pd has a negligible solubility in water.
  • PdCl2 will not form. Note that this process differs from the synthesis of Pd by the reduction of PdC_2.
  • the constituent to be removed e.g., Ba is distributed on a regular, periodic basis, it is anticipated that molecular level cracks or fissures are formed when Ba is removed as Ba(OH) 2 or Ba(NO 3 ) 2 . This should lead to a uniform particle size.
  • the resulting nanosize particles in the present invention are essentially insoluble in the liquid media used, and so are the precursors.
  • growth is not expected unlike conventional chemical synthesis approaches which rely on precursors reacting in solution to form an insoluble product; e.g., the formation of insoluble Fe 3 O 4 from Fe(II) and Fe(III) chlorides in solution. In such cases, growth of particles can readily occur.

Abstract

L'invention concerne un procédé de formation d'une poudre céramique de grosseur nanométrique. Un matériau céramique précurseur est composé d'un constituant fugitif et d'un constituant non soluble en une seule phase. On met le précurseur en contact avec un solvant sélectif (eau, acide, etc) pour former une solution du constituant fugitif dans le solvant et un résidu du constituant non soluble. Le précurseur est suffisamment réactif avec le solvant pour former la solution du constituant fugitif dans le solvant et pour former le résidu non dissous du constituant non soluble. Le matériau précurseur et le résidu non soluble sont suffisamment non insolubles dans le solvant de manière qu'il n'y ait pas assez de matériau précurseur et de résidu non soluble en solution pour former un dépôt et un précipité sur le résidu du constituant non soluble. Le constituant fugitif est suffisamment soluble dans le solvant de manière que le précurseur réagisse avec le solvant pour former la solution du constituant fugitif sans précipitation ni dépôt du constituant fugitif sur le résidu du constituant non soluble sous la forme de particules de grosseur nanométrique. Une fois le constituant fugitif dissous, le solvant sélectif contenant le constituant fugitif est extrait du résidu. Le résidu reste sous la forme d'une poudre de grosseur nanométrique du constituant non soluble.
PCT/US1999/024052 1998-10-26 1999-10-26 Procede de decomposition moleculaire pour la synthese de poudres ceramiques et metalliques de grosseur nanometrique WO2000024676A1 (fr)

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US09/830,399 US6803027B1 (en) 1998-10-26 1998-10-26 Molecular decomposition process for the synthesis of nanosize ceramic and metallic powders
JP2000578252A JP2002528369A (ja) 1998-10-26 1999-10-26 ナノサイズのセラミックおよび金属粉末合成のための分子分解方法
AU18076/00A AU758256B2 (en) 1998-10-26 1999-10-26 A molecular decomposition process for the synthesis of nanosize ceramic and metallic powders
US10/960,433 US7311754B2 (en) 1998-10-26 2004-10-06 Molecular decomposition processes for the synthesis of nanosize metallic powders

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WO2006052280A2 (fr) * 2004-04-30 2006-05-18 Strutt Peter R Pile a combustible en ceramique metastable et procede associe
US7125536B2 (en) 2004-02-06 2006-10-24 Millennium Inorganic Chemicals, Inc. Nano-structured particles with high thermal stability
US8211388B2 (en) 2006-02-16 2012-07-03 Brigham Young University Preparation of uniform nanoparticles of ultra-high purity metal oxides, mixed metal oxides, metals, and metal alloys
US9079164B2 (en) 2012-03-26 2015-07-14 Brigham Young University Single reaction synthesis of texturized catalysts
US9114378B2 (en) 2012-03-26 2015-08-25 Brigham Young University Iron and cobalt based fischer-tropsch pre-catalysts and catalysts

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US9994715B2 (en) * 2016-02-16 2018-06-12 Sila Nanotechnologies Inc. Formation and modifications of ceramic nanowires and their use in functional materials
CN109761261B (zh) * 2019-03-29 2020-07-03 内蒙古大学 粒径形貌可控大比表面积二氧化铈粉体的绿色制备方法

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WO2006024098A1 (fr) * 2004-09-01 2006-03-09 Advanced Nanotechnology Limited Céramique de zircone
US8211388B2 (en) 2006-02-16 2012-07-03 Brigham Young University Preparation of uniform nanoparticles of ultra-high purity metal oxides, mixed metal oxides, metals, and metal alloys
US9079164B2 (en) 2012-03-26 2015-07-14 Brigham Young University Single reaction synthesis of texturized catalysts
US9114378B2 (en) 2012-03-26 2015-08-25 Brigham Young University Iron and cobalt based fischer-tropsch pre-catalysts and catalysts

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