WO2021068139A1 - Particules d'alumine et procédé de production de particules d'alumine - Google Patents

Particules d'alumine et procédé de production de particules d'alumine Download PDF

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WO2021068139A1
WO2021068139A1 PCT/CN2019/110211 CN2019110211W WO2021068139A1 WO 2021068139 A1 WO2021068139 A1 WO 2021068139A1 CN 2019110211 W CN2019110211 W CN 2019110211W WO 2021068139 A1 WO2021068139 A1 WO 2021068139A1
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compound
alumina particles
alumina
silicon
potassium
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PCT/CN2019/110211
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Shaowei YANG
Masamichi Hayashi
Shingo Takada
Jianjun Yuan
Cheng Liu
Wei Zhao
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Dic Corporation
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Priority to JP2022520965A priority Critical patent/JP7388548B2/ja
Priority to CN201980101198.3A priority patent/CN114555718B/zh
Priority to PCT/CN2019/110211 priority patent/WO2021068139A1/fr
Publication of WO2021068139A1 publication Critical patent/WO2021068139A1/fr

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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
    • C01F7/021—After-treatment of oxides or hydroxides
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01G—COMPOUNDS CONTAINING METALS NOT COVERED BY SUBCLASSES C01D OR C01F
    • C01G39/00—Compounds of molybdenum
    • C01G39/006—Compounds containing, besides molybdenum, two or more other elements, with the exception of oxygen or hydrogen
    • C—CHEMISTRY; METALLURGY
    • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09C—TREATMENT OF INORGANIC MATERIALS, OTHER THAN FIBROUS FILLERS, TO ENHANCE THEIR PIGMENTING OR FILLING PROPERTIES ; PREPARATION OF CARBON BLACK  ; PREPARATION OF INORGANIC MATERIALS WHICH ARE NO SINGLE CHEMICAL COMPOUNDS AND WHICH ARE MAINLY USED AS PIGMENTS OR FILLERS
    • C09C1/00—Treatment of specific inorganic materials other than fibrous fillers; Preparation of carbon black
    • C09C1/40—Compounds of aluminium
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2002/00—Crystal-structural characteristics
    • C01P2002/80—Crystal-structural characteristics defined by measured data other than those specified in group C01P2002/70
    • C01P2002/85—Crystal-structural characteristics defined by measured data other than those specified in group C01P2002/70 by XPS, EDX or EDAX data
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2004/00—Particle morphology
    • C01P2004/20—Particle morphology extending in two dimensions, e.g. plate-like
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2004/00—Particle morphology
    • C01P2004/30—Particle morphology extending in three dimensions
    • C01P2004/45—Aggregated particles or particles with an intergrown morphology
    • 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
    • C01P2004/61—Micrometer sized, i.e. from 1-100 micrometer
    • 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
    • C01P2006/20—Powder free flowing behaviour
    • 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
    • C01P2006/21—Attrition-index or crushing strength of granulates
    • 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

Definitions

  • inorganic fillers include boron nitride fillers and alumina fillers. Different inorganic fillers are used for different purposes and applications.
  • Alumina has excellent technical characteristics, such as high hardness, high mechanical strength, and high maximum operating temperature for oxidizing atmospheres, and in addition, alumina is relatively inexpensive. As such, alumina is a highly desirable material compared with boron nitride and the like.
  • alumina products have various types of structures, which are derived from different production methods. Examples of the structures include spherical, acicular, and planar. In general, for practical use, plate-shaped alumina particles present a problem in that as the aspect ratio increases, the flowability of the powder decreases because of an increased surface area and an increased bulk density.
  • PTL 2 discloses particles formed of planar assemblies of microparticles of a crystalline alumina composite oxide, which are assemblies in which microparticles of a whisker-form alumina composite oxide, such as boehmite, are aggregated in a planar form.
  • the assemblies have a card-house structure.
  • the planar assemblies of microparticles of a crystalline alumina composite oxide are characterized in that the microparticles of a whisker-form alumina composite oxide have an average length ranging from 2 to 100 nm and an average diameter ranging from 1 to 20 nm, and the assemblies of the microparticles of the composite oxide have an average particle diameter ranging from 30 to 300 nm and an average thickness ranging from 2 to 50 nm. That is, the particles themselves, which are formed of card-house-structured assemblies of microparticles, are very small, submicron-scale alumina composite oxide particles.
  • PTL 1 it is possible to provide a polymer composition having excellent transparency and which imparts wear resistance to plastics and rubber, improve the strength and non-flammable properties thereof, and increase the surface frictional coefficient thereof.
  • PTL 1 does not suggest that such twinning alumina particles exhibit excellent powder flowability.
  • PTL 2 also does not suggest that the particles described above, which are formed of card-house-structured assemblies of microparticles of a composite oxide, exhibit excellent powder flowability.
  • the particles there are possibilities such as the following, for example: when added as a filler to a binder and a solvent, the viscosity of the slurry may excessively increase, which may result in a decrease in workability; and moreover, as a result of an increase in interfaces, a disadvantage may arise in forming an efficient conductive path, and consequently inherent functions of alumina, which has excellent thermal conductivity, may be impaired.
  • the present invention has been made in view of the above circumstances, and an object of the present invention is to provide alumina particles having excellent flowability.
  • the present invention provides alumina particles having a specified shape and, therefore, having excellent flowability.
  • Fig. 1 is a schematic diagram of a twinning alumina particle.
  • Fig. 2 is a schematic diagram of an alumina particle having a card-house structure that includes at least three planar alumina flakes adhered to one another.
  • Fig. 3 is an SEM image of alumina particles having a card-house structure. The alumina particles were obtained in an example.
  • Alumina particles and a method for producing the alumina particles according to embodiments of the present invention will be described in detail below.
  • Alumina particles of the present invention includes particles having the following features: 1) the particles have a card-house structure that includes at least three planar alumina flakes adhered to one another; 2) the particles have an average particle diameter of 1 to 1000 ⁇ m; and 3) the particles contain potassium.
  • the alumina particles having a card-house structure that includes at least three planar alumina flakes adhered to one another, having an average particle diameter of 1 to 1000 ⁇ m, and containing potassium may be simply referred to as "alumina particles" .
  • planar is meant to include the following shapes, for example: a hexahedral plate shape in a three-dimensional view, which is, two-dimensionally, in a projection plane, a typical quadrilateral shape having four corners (quadrilateral plate shape) ; and a polygonal shape having five or more corners in a two-dimensional projection plane (hereinafter this shape may be referred to as a "polygonal plate shape” .
  • the morphology of the alumina particles can be examined with a scanning electron microscope (SEM) .
  • SEM scanning electron microscope
  • the term "card-house structure" refers to, for example, a structure in which planar particles are disposed in a complex manner without being oriented in a particular direction.
  • the card-house structure is a structure that includes at least three planar alumina flakes and in which the planar alumina flakes are adhered to one another.
  • the structure may be a structure in which at least three planar alumina flakes intersect one another at at least two locations to form an assembly, and surfaces of planar alumina flakes intersecting one another are oriented in a disorderly manner (see Figs. 2 and 3) .
  • planar alumina flakes may intersect one another at any locations of the planar alumina flakes.
  • the phrase "oriented in a disorderly manner" refers to a state in which each of the surfaces intersecting one another may be oriented in any direction in the X axis, Y axis, and Z axis without limitation and in which the angle at which the surfaces intersect one another may be any angle. Details of the planar alumina flakes will be described later.
  • the number of planar alumina flakes to be included in one alumina particle be, for example, 3 to 10000. Specifically, the number is preferably 10 to 5000 and particularly preferably 15 to 3000.
  • planar alumina flakes The intersecting of planar alumina flakes occurs when at least three planar alumina flakes interact with one another, for example, in the process of crystallization in a calcination step, and are adhered to one another, thereby forming an assembly. As a result, in some cases, it may appear that the planar alumina flakes intersect one another in a penetrating manner. When planar alumina flakes are firmly adhered to one another, the strength of the card-house structure increases.
  • intersecting means that at least two surfaces cross one another at a location, and there are no limitations on the position, diameter, area, and the like of the surfaces intersecting one another. Furthermore, the number of the directions of the surfaces, with the intersecting location being the reference point, may be three or may be four or more.
  • planar alumina flakes themselves which are included in the card-house structure, may have any size in terms of length, width, and thickness.
  • the size of the planar alumina flakes included may be a plurality of sizes.
  • the planar alumina flakes may be alumina flakes having a quadrilateral plate shape or alumina flakes having a polygonal plate shape.
  • alumina flakes having a quadrilateral plate shape or alumina flakes having a polygonal plate shape may exist, or both of the two types may exist, with the ratio between the two types not being limited.
  • the alumina particles may have one or more different structures, in addition to the card-house structure. Some of the planar alumina flakes may be included in the different structure in any manner provided that the effect of improving flowability, which is a primary object, is not impaired. Examples of the different structure include the following: a structure including two planar alumina flakes intersecting each other and having a shape, such as a generally X shape, a generally T shape, or a generally L shape (the generally X-shaped particle is sometimes referred to as a twinning alumina particle. See Fig. 1) ; and a structure including one planar alumina flake.
  • the proportion of alumina particles including planar alumina flakes in the different structure be as small as possible. It is preferable that the proportion of the particles having a card-house structure that includes at least three planar alumina flakes adhered to one another be greater than or equal to 80%on a weight basis or on a number basis. The proportion is more preferably greater than or equal to 90%and even more preferably greater than or equal to 95%.
  • the proportions of alumina particles including two planar alumina flakes and alumina particles including one planar alumina flake can be readily adjusted by performing a typical size classification operation, such as sieving or air classification. With a method for producing alumina particles using a flux method, which will be described later, substantially all the alumina particles produced can be particles having a card-house structure.
  • the alumina particles of the present invention have a very high crushing strength and therefore do not easily collapse even when an external stress is applied. As such, in cases where the alumina particles are mixed with a binder and a solvent, it is unlikely that a flow failure due to anisotropy of alumina particles themselves will occur. As a result, inherent capabilities of the alumina particles can be sufficiently exploited, and, even in a case where the alumina particles are mixed with plate-shaped alumina particles and used, the plate-shaped alumina particles, which tend to be oriented in a longitudinal direction, can be caused to be present in random directions. Consequently, inherent characteristics of alumina, such as thermal conductivity and mechanical strength, can be exhibited not only in a longitudinal direction but also in a thickness direction.
  • the alumina particles of the present invention have excellent powder flowability and therefore enhance the discharge performance of the supply machine used for mechanical transportation, such as a hopper or a feeder, for application of the alumina particles to use as industrial products.
  • the alumina particles of the present invention include voids in the interior because of the distinctive structure and therefore have a bulk density that is not significantly different from that of plate-shaped alumina particles.
  • the alumina particles of the present invention have a high sphericity and, as described above, have a high crushing strength and therefore does not easily collapse, and consequently, presumably, the effect of facilitating transportation as a result of rolling of the alumina particles is increased.
  • the alumina particles used in the present invention have a card-house structure.
  • the card-house structure is as described above. It is preferable that the alumina particles be alumina particles having a card-house structure in which the planar alumina flakes have a quadrilateral plate shape and are disposed such that a planar face portion and an edge face portion are in contact with each other and edge face portions are in contact with each other. It is more preferable that the alumina particles be alumina particles having a card-house structure in which the planar alumina flakes have a polygonal plate shape and are disposed such that a planar face portion and an edge face portion are in contact with each other and edge face portions are in contact with each other.
  • the alumina particles of the present invention are aluminum oxide particles, and the crystal form is not particularly limited.
  • the aluminum oxide may be a transition alumina having any of a variety of crystalline forms, such as ⁇ , ⁇ , ⁇ , and ⁇ , or may be a transition alumina including alumina hydrate.
  • the crystal form basically be an ⁇ crystalline form.
  • the degree of ⁇ crystallization of the alumina particles of the present invention can be determined by conducting an XRD measurement.
  • the degree of ⁇ crystallization is determined from the intensity ratio between peak intensities, which can be obtained as follows.
  • a Rint-Ultima wide-angle X-ray diffractometer (manufactured by Rigaku Corporation) is used.
  • a prepared sample is placed ona measurement sample holder and then placed in the diffractometer.
  • a measurement is conducted under conditions ofa Cu-K ⁇ ray, 40 kV-30 mA, a scan speed of 1.0°/min, and a scan range of 5 to 80°.
  • the degree of ⁇ crystallization varies depending on calcination conditions and the raw materials used, for example.
  • Alumina particles having high crushing strength and high flowability have a degree of ⁇ crystallization of greater than or equal to 90%. More preferably, the degree of ⁇ crystallization is greater than or equal to 95%.
  • the sample to be used for the measurement may be the alumina particles or the planar alumina flakes, which can be obtained by disassembling the card-house structure by performing a mechanical process.
  • the average particle diameter of the alumina particles having a card-house structure that includes at least three planar alumina flakes adhered to one another may be any diameter within a range in which the structure can be formed.
  • the average particle diameter is preferably greater than or equal to 1 ⁇ m, more preferably greater than or equal to 3 ⁇ m, and even more preferably greater than or equal to 10 ⁇ m. If the size is too large, appearance defects may occur due to exposure of the card-house structure in various applications, such as in a thermally conductive filler and a high-brightness pigment.
  • the average particle diameter is preferably less than or equal to 1000 ⁇ m, more preferably less than or equal to 300 ⁇ m, and even more preferably less than or equal to 100 ⁇ m.
  • the average particle diameter may be 1 ⁇ m or greater and 1000 ⁇ m or less, may be 3 ⁇ m or greater and 300 ⁇ m or less, or may be 10 ⁇ m or greater and 100 ⁇ m or less.
  • the average particle diameter of the alumina particles is a volume-based median diameter d50, which is calculated from a volume-based cumulative particle size distribution measured using a dry laser diffraction particle size distribution analyzer.
  • the maximum particle diameter of the alumina particles is greater than the upper limit mentioned above, in cases where the alumina particles are used by being mixed with a solvent and a binder, which forms a matrix, there is a possibility that, in some cases, depending on the form of the final application, some of the alumina particles may protrude above the surface of the binder layer, which leads to appearance defects. Thus, maximum particle diameters greater than the upper limit are not preferable.
  • the planar alumina flakes have a polygonal plate shape and have an aspect ratio of 2 to 500.
  • the aspect ratio is a ratio of a particle diameter of the planar alumina flakes to a thickness of the planar alumina flakes.
  • the card-house structure can be formed advantageously in a state in which characteristics unique to the planar alumina flakes are retained, and therefore such an aspect ratio is preferable.
  • the aspect ratio is 500 or less, the average particle diameter of the alumina particles can be easily adjusted, and in addition, a decrease in mechanical strength and appearance defects that may occur due to exposure of the card-house structure in various applications, such as in a thermally conductive filler and a high-brightness pigment, can be suppressed. Accordingly, such an aspect ratio is preferable.
  • the aspect ratio is more preferably 5 to 300, more preferably 7 to 100, and particularly preferably 7 to 50.
  • the aspect ratio is 7 to 100, the planar alumina flakes exhibit excellent thermal properties and excellent optical properties, such as in terms of brightness, and the resulting alumina particles having a card-house structure have high flowability. Accordingly, such an aspect ratio is preferable for practical use.
  • the value of the average particle diameter of the planar alumina flakes is a value obtained by measuring the particle diameters of randomly selected 100 planar alumina flakes, from images obtained by using a scanning electron microscope (SEM) , and calculating the average.
  • the average particle diameter of the planar alumina flake is determined by, for example, using the following method: an alumina particle is observed with an SEM, and the maximum length of a planar alumina flake positioned in a middle of the alumina particle is measured. Another method that may be used is as follows: the alumina particles are subjected to an air classification operation, and the maximum length of a flake resulting from the operation is measured using an SEM.
  • Still another method that may be used is as follows: under conditions that do not cause breakage of the planar alumina flakes themselves, the card-house structure is disassembled by performing a mechanical process to obtain a flake, and the maximum length of the flake is measured using an SEM.
  • the potassium may be potassium derived from potassium used in a method for producing alumina particles. The method will be described later. Utilizing potassium enables a highly efficient production of alumina particles having excellent flowability in the later-described method for producing alumina particles.
  • potassium examples include, but are not limited to, elemental potassium and potassium compounds, such as potassium oxide and partially reduced potassium oxide.
  • the content of the potassium is preferably greater than or equal to 0.05 mass%, more preferably 0.05 to 5 mass%, even more preferably 0.1 to 3 mass%, and particularly preferably 0.1 to 1 mass%, relative to the mass of the alumina particles taken as 100 mass%.
  • Alumina particles having a potassium content within any of the above-mentioned ranges have a card-house structure and have suitable values, such as a suitable value of the average particle diameter. Accordingly, the above-mentioned ranges are preferable. In addition, the above-mentioned ranges are preferable because a higher flowability can be achieved.
  • the XRF analysis is to be performed under the same conditions as the measurement conditions described in Examples, which will be described later, or under comparable conditions under which the same measurement results can be obtained.
  • the alumina particles having a card-house structure that includes at least three planar alumina flakes adhered to one another contain silicon (elemental silicon and/or an inorganic silicon compound) .
  • the silicon be present in or on surfaces of the planar alumina flakes.
  • silicon be present in a localized manner, that is, in or on surfaces, rather than present in inner portions because, for example, affinity for a binder can be effectively improved with a smaller amount of silicon.
  • the approximate amount of the elemental silicon and/or inorganic silicon compound locally present in or on surfaces of the planar alumina flakes containing elemental silicon and/or an inorganic silicon compound can be measured, for example, by analysis using X-ray fluorescence spectroscopy (XRF) and by analysis using X-ray photoelectron spectroscopy (XPS) .
  • XRF X-ray fluorescence spectroscopy
  • XPS X-ray photoelectron spectroscopy
  • X-ray fluorescence spectroscopy is a technique for quantitatively analyzing the bulk composition of a material by detecting fluorescence X-rays produced by X-ray irradiation and measuring wavelengths and intensities.
  • X-ray photoelectron spectroscopy is a technique for analyzing the composition of elements included in the surface of a sample by irradiating the surface of the sample with X-rays and measuring the kinetic energy of photoelectrons emitted from the surface of the sample.
  • [Si] / [Al] % (surface) values mean that, in the planar alumina flakes obtained by inclusion of elemental silicon and/or a silicon compound, the amount of the elemental silicon and/or silicon compound is larger in or on surfaces than in innermost portions of the planar alumina flakes.
  • the XRF analysis can be performed by using, for example, a ZSX100e wavelength dispersive X-ray fluorescence analyzer (manufactured by Rigaku Corporation) .
  • the XPS analysis can be performed by using, for example, a Quantera SXM spectrometer (manufactured by Ulvac-PHI, Inc. ) .
  • a molar ratio [Si] / [Al] determined by XPS analysis which is the ratio of moles of Si to moles of Al, is preferably greater than or equal to 0.001, more preferably greater than or equal to 0.01, and even more preferably greater than or equal to 0.02, and particularly preferably greater than or equal to 0.1.
  • the upper limit of the value of the molar ratio [Si] / [Al] determined by XPS analysis is not particularly limited but may be less than or equal to 0.5, less than or equal to 0.4, or less than or equal to 0.3.
  • the value of the molar ratio [Si] / [Al] determined by XPS analysis which is the ratio of moles of Si to moles of Al, is preferably 0.001 or greater and 0.5 or less, more preferably 0.01 or greater and 0.4 or less, even more preferably 0.02 or greater and 0.3 or less, and particularly preferably 0.1 or greater and 0.3 or less.
  • the molar ratio of moles of Si to moles of Al determined by XPS analysis is within any of the above-mentioned ranges, the alumina particles having a card-house structure that includes planar alumina flakes can be easily obtained, and the resulting alumina particles exhibit excellent flowability and crushing strength. Accordingly, the above-mentioned ranges are preferable. In addition, for example, affinity for binders can be further improved.
  • the XPS analysis is to be performed under the same conditions as the measurement conditions described in Examples, which will be described later, or under comparable conditions under which the same measurement results can be obtained.
  • a molar ratio [Si] / [Al] determined by XRF analysis which is the ratio of moles of Si to moles of Al, is preferably 0.0003 or greater and 0.1 or less, more preferably 0.0005 or greater and 0.08 or less, even more preferably 0.005 or greater and 0.05 or less, and particularly preferably 0.005 or greater and 0.01 or less.
  • the alumina particles having a card-house structure that includes planar alumina flakes can be easily obtained, and the resulting alumina particles exhibit excellent flowability and crushing strength. Accordingly, the above-mentioned ranges are preferable.
  • Silicon included in the alumina particles according to the embodiment corresponds to silicon or a silicon compound used in the production method.
  • the content of the silicon is preferably 0.01 to 8 mass%, more preferably 0.1 to 5 mass%, even more preferably 0.5 to 4 mass%, and particularly preferably 0.5 to 2 mass%, relative to the mass of the alumina particles according to the embodiment taken as 100 mass%.
  • the content of the silicon is within any of the above-mentioned ranges, the alumina particles having a card-house structure that includes planar alumina flakes can be easily obtained, and the resulting alumina particles exhibit excellent flowability and crushing strength. Accordingly, the above-mentioned ranges are preferable.
  • the XRF analysis is to be performed under the same conditions as the measurement conditions described in Examples, which will be described later, or under comparable conditions under which the same measurement results can be obtained.
  • the alumina particles having a card-house structure that includes at least three planar alumina flakes adhered to one another contain molybdenum, in particular.
  • Molybdenum has catalytic functions and optical functions. Furthermore, in the production method, utilizing molybdenum enables production of alumina particles having excellent flowability, as will be described later.
  • molybdenum examples include, but are not limited to, molybdenum metal and molybdenum compounds, such as molybdenum oxide and partially reduced molybdenum oxide.
  • the manner in which the molybdenum is present is not particularly limited.
  • the molybdenum may be present in a manner in which the molybdenum is disposed on surfaces of the planar alumina flakes of the alumina particles having a card-house structure or in a manner in which the molybdenum partially substitutes aluminum in the crystal structure of the alumina. Combinations of these manners are also possible.
  • the content of the molybdenum is preferably less than or equal to 10 mass%, relative to the mass of the alumina particles taken as 100 mass%.
  • the molybdenum content is more preferably 0.01 to 8 mass%and even more preferably 0.1 to 5 mass%, which can be achieved by adjusting the calcination temperature, the calcination time, and/or the conditions for the flux.
  • the content of the molybdenum is less than or equal to 10 mass%, the quality of the ⁇ single crystal of the alumina is improved. Accordingly, such a content is preferable.
  • the XRF analysis is to be performed under the same conditions as the measurement conditions described in Examples, which will be described later, or under comparable conditions under which the same measurement results can be obtained.
  • the alumina particles may contain incidental impurities.
  • the incidental impurities are impurities that are derived from a metal compound used in the production, are present in the raw materials, and/or are incidentally included in the alumina particles in the production process and which are intrinsically unnecessary; however, the incidental impurities are present in trace amounts and therefore do not affect the properties of the alumina particles.
  • incidental impurity examples include, but are not limited to, magnesium, calcium, strontium, barium, scandium, yttrium, lanthanum, cerium, and sodium.
  • incidental impurities may be present alone or two or more of the incidental impurities may be present.
  • additional element examples include, but are not limited to, zinc, manganese, calcium, strontium, and yttrium. These additional elements may be used alone or in a mixture of two or more.
  • the alumina particles may contain an organic compound.
  • the organic compound is present in or on a surface of the alumina particles and has a function of adjusting the surface properties of the alumina particles.
  • the alumina particles when the alumina particles include an organic compound in or on the surface, the alumina particles have improved affinity for resins and therefore can serve a filler function to the maximum extent.
  • organic compound examples include, but are not limited to, organosilanes, alkyl phosphonic acids, and polymers.
  • organosilane examples include alkyl trimethoxysilanes and alkyl trichlorosilanes in which the alkyl group has 1 to 22 carbon atoms, such as methyltrimethoxysilane, dimethyldimethoxysilane, ethyltrimethoxysilane, ethyltriethoxysilane, n-propyltrimethoxysilane, n-propyltriethoxysilane, isopropyltrimethoxysilane, isopropyltriethoxysilane, pentyltrimethoxysilane, and hexyltrimethoxysilane, trimethoxy (3, 3, 3-trifluoropropyl) silane, (tridecafluoro-1, 1, 2, 2-tetrahydrooctyl) trichlorosilane, phenyltrimethoxysilane, phenyltriethoxysilane, p-
  • Examples of the phosphonic acid include methylphosphonic acid, ethylphosphonic acid, propylphosphonic acid, butylphosphonic acid, pentylphosphonic acid, hexylphosphonic acid, heptylphosphonic acid, octylphosphonic acid, decylphosphonic acid, dodecylphosphonic acid, octadecylphosphonic acid, 2-ethylhexylphosphonic acid, cyclohexyl methylphosphonic acid, cyclohexyl ethylphosphonic acid, benzylphosphonic acid, phenylphosphonic acid, and dodecyl benzene phosphonic acid.
  • Suitable examples of the polymer include poly (meth) acrylates.
  • examples of the polymer include polymethyl (meth) acrylate, polyethyl (meth) acrylate, polybutyl (meth) acrylate, polybenzyl (meth) acrylate, polycyclohexyl (meth) acrylate, poly (t-butyl (meth) acrylate) , polyglycidyl (meth) acrylate, and polypentafluoropropyl (meth) acrylate, and further examples include general-purpose polymers, such as polystyrene, polyvinyl chloride, polyvinyl acetate, epoxy resins, polyesters, polyimides, and polycarbonates.
  • One of the organic compounds may be present alone, or two or more of the organic compounds may be present.
  • the manner in which the organic compound is present is not particularly limited.
  • the organic compound may be covalently bonded to the alumina and/or may coat the alumina.
  • the content of the organic compound is preferably less than or equal to 20 mass%and more preferably 10 to 0.01 mass%, relative to the mass of the alumina particles.
  • the content of the organic compound is less than or equal to 20 mass%, the properties derived from the alumina particles can be easily exhibited, and therefore, such a content is preferable.
  • the alumina particles have a high crushing strength.
  • the crushing strength varies depending on the positions where planar alumina flakes intersect one another and the number, area, thickness aspect ratio, and the like of the planar alumina flakes.
  • the required crushing strength varies in various applications. In terms of practical utility, the crushing strength is preferably 1 to 100 MPa, more preferably 20 to 100 MPa, and even more preferably 50 to 100 MPa.
  • the crushing strength of the alumina particles can be measured by using, for example, an NS-A100 model microparticle crushing force measurement instrument (manufactured by Nano Seeds Corporation) or by using, for example, an MCT-510 (manufactured by Shimadzu Corporation) .
  • the difference between the peak value, which is a value at the time of crushing, and the baseline value, which is a value in a state in which no force is applied, is designated as a crushing force F [N]
  • a crushing strength S [Pa] is determined as the average of 10 values calculated according to the following equation.
  • F is the crushing forth [N]
  • D is the particle diameter [ ⁇ m] .
  • the present inventors know that when the alumina particles having a card-house structure that includes at least three planar alumina flakes adhered to one another contain elemental silicon and/or an inorganic silicon compound in an appropriate amount, the above-described crushing strength is high compared with alumina particles that contain no silicon or inorganic silicon compound.
  • the content of the elemental silicon and/or inorganic silicon compound affects the magnitude of the crushing strength.
  • the flowability and the crushing strength of the particles can be increased with an appropriate increase in the content.
  • particular production conditions can be employed to increase the crushing strength.
  • the crushing strength can be adjusted with production conditions. For example, the crushing strength of the alumina particles can be increased by increasing the calcination temperature.
  • a powder of the alumina particles of the present invention has excellent powder flowability compared with plate-shaped alumina particles and twinning alumina particles. This is because the alumina particles themselves included in the powder have a distinctive structure and a specific average particle diameter.
  • the shape of a largest enclosing surface of the alumina particles which is defined as follows, be spherical or generally spherical. In an alumina particle having one unit of a card-house structure, assuming that all the planar alumina flakes included in the particle are enclosed by a surface in a manner in which the planar alumina flakes are wrapped, the largest possible surface on a volume basis is the largest enclosing surface. Furthermore, as necessary, a lubricant, microparticulate silica, and/or the like may be added to improve flowability.
  • the powder flowability of the card-house-structured alumina particles can be determined by, for example, measuring the angle of repose as specified in JIS R 9301-2-2. It is preferable that the value of the angle of repose be less than or equal to 50° in terms of reducing the probability of problems associated with a feeder, a hopper, or the like in mechanical transportation. Examples of the problem include hopper bridging, a feed-neck phenomenon, non-uniform supply, and a decrease in the discharge rate. It is more preferable that the angle of repose be less than or equal to 40°
  • the present invention relates to alumina particles that have a card-house structure including at least three planar alumina flakes adhered to one another, have an average particle diameter of 1 to 1000 ⁇ m, and contain potassium.
  • the card-house structure in which planar alumina flakes are adhered to one another is more suitably as follows: the at least three planar alumina flakes intersect one another at at least two locations to form an assembly, and surfaces of planar alumina flakes intersecting one another are oriented in a disorderly manner.
  • Twinning alumina particles known in the art have a highly angular structure because of their shape and therefore cannot easily roll compared with the alumina particles of the present invention. Thus, when used as a filler, twinning alumina particles do not exhibit sufficient flowability. Even if twinning alumina particles had the same card-house structure as the alumina particles of the present invention, the twinning alumina particles have low flowability when the average particle diameter is significantly small. There are no clarified measures for increasing the average particle diameter. In any case, properties for serving as a filler are insufficient. The excellent flowability of the present invention is attributable to a synergistic effect between the card-house structure and the average particle diameter.
  • a powder of the alumina particles having a card-house structure that includes at least three planar alumina flakes adhered to one another has a specific surface area typically within a range of 50 to 0.001 m 2 /g.
  • the specific surface area is preferably within a range of 10 m 2 /g to 0.01 m 2 /g and more preferably within a range of 5.0 m 2 /g to 0.05 m 2 /g.
  • the specific surface area is within any of the above-mentioned ranges, the number of the planar alumina flakes that form the card-house structure is appropriate, inherent functions of alumina can be sufficiently obtained, and, when the alumina particles are slurried, no significant increase in viscosity occurs, and therefore workability is excellent.
  • the specific surface area can be measured by, for example, using the one-point BET method (adsorption gas: nitrogen) specified in JIS Z 8830.
  • the alumina particles have the card-house structure that includes at least three planar alumina flakes adhered to one another, the alumina particles include voids in the interior. If the percentage of voids is small, the shape tends to be non-uniform, and flowability tends to decrease. Accordingly, it is preferable that the void fraction be greater than or equal to 10 vol%. It is more preferable that the void faction be greater than or equal to 30 vol%. Furthermore, if the percentage of voids is large, the crushing strength of the powder is low. Accordingly, it is preferable that the void fraction be less than or equal to 90 vol%. It is more preferable that the void fraction be less than or equal to 70 vol%.
  • the void fraction can be determined by measurement using, for example, a gas adsorption method according to JIS Z 8831 or the like or using a mercury porosimetry method.
  • the method for producing the alumina particles of the present invention is not limited provided that the alumina particles have a card-house structure, have an average particle diameter of 1 to 1000 ⁇ m, and contain potassium.
  • An example of the method for producing the alumina particles is described in detail below.
  • the average particle diameter, flowability, specific surface area, mechanical strength, and void fraction of the alumina particles, the thickness and aspect ratio of the planar alumina flakes, and the like can be adjusted in a production method described later in detail.
  • the adjustment can be made by selecting the types of the molybdenum compound and the potassium compound, which are used as flux agents, the type of the aluminum compound, the average particle diameter of the aluminum compound, the purity of the aluminum compound, the proportion of the silicon or silicon compound used, the types of one or more additional shape control agents, the proportion of the additional shape control agent used, the co-existence state of the silicon or silicon compound and the aluminum compound, and the co-existence state of the one or more additional shape control agents and the aluminum compound.
  • any production method may be used to obtain the alumina particles of the present invention provided that the card-house structure that includes at least three planar alumina flakes adhered to one another can be formed, the specific average particle diameter can be obtained, and potassium can be included.
  • the card-house structure which is a distinctive structure, and containing potassium and silicon (elemental silicon and/or an inorganic silicon compound) is to be obtained by using alumina having an existing structure and performing aftertreatments thereon, multiple production steps are necessary, and therefore productivity is iow. Thus, such a method is not preferable.
  • the alumina particles of the present invention be obtained by calcining an aluminum compound in the presence of a molybdenum compound, a potassium compound, elemental silicon and/or a silicon compound, and as necessary, one or more additional shape control agents because, in this case, a higher flowability and a higher dispersibility of the alumina particles can be achieved and a higher productivity can be achieved.
  • a preferable method for producing the alumina particles includes a step (calcination step) of calcining an aluminum compound in the presence of a molybdenum compound, a potassium compound, and silicon or a silicon compound.
  • the calcination step may be a step of calcining a mixture resulting from a step (mixing step) of obtaining a mixture that is to be subjected to the calcination. It is preferable that the mixture further contain a metal compound, which will be described later. It is preferable that the metal compound be a yttrium compound.
  • the organic components are removed as gases in the calcination process. That is, the molybdenum compound reacts with the aluminum compound at a high temperature to form aluminum molybdate, and thereafter, when the aluminum molybdate decomposes to form alumina and molybdenum oxide at a higher temperature, molybdenum is incorporated into the alumina particles. In this manner, the alumina particles can be easily obtained. The molybdenum oxide sublimes, but this can be recovered and reused.
  • This production method is hereinafter referred to as a "flux method" . The flux method will be described in detail later.
  • a shape control agent is used to suppress molybdenum oxide, which is a flux agent, from being selectively adsorbed onto the [113] face, and as a result, a plate-shaped morphology having a hexagonal close-packed crystal structure with the [001] face developed, which is thermodynamically most stable, can be formed.
  • a molybdenum compound as a flux agent makes it possible to easily form alumina particles including molybdenum-containing planar alumina flakes and having a high degree of ⁇ crystallization, specifically a degree of ⁇ crystallization of greater than or equal to 90%.
  • the alumina has a high degree of ⁇ crystallization and has a euhedral shape, and consequently, the alumina particles exhibit excellent dispersibility in a matrix and have high mechanical strength and high thermal conductivity.
  • the alumina particles obtained by using the production method described above contain molybdenum in the particles, and as a result, the alumina particles have an isoelectric point, which is associated with the zeta potential, shifted to the acidic side compared with typical alumina and, therefore, have excellent dispersibility. Furthermore, the properties of the molybdenum included in the alumina particles can be utilized to enable the alumina particles to be employed in oxidation reaction catalyst applications and in optical material applications.
  • the method for producing the alumina particles is not particularly limited. However, from the standpoint of suitably controlling, at relatively iow temperatures, the alumina to have a high degree of ⁇ crystallization, it is preferable to employ a production method using a flux method that involves utilization of a molybdenum compound.
  • a preferable method for producing the alumina particles includes a step of calcining an aluminum compound in the presence of a molybdenum compound, a potassium compound, silicon or a silicon compound, and, as necessary, one or more additional shape control agents.
  • the present inventors newly discovered important factors that enable selective production of the alumina particles of the present invention.
  • the important factors include the size of the aluminum compound used as a raw material, the amount of the molybdenum compound used, the amount of the potassium compound used, and the amount of the silicon or silicon compound used.
  • a compound containing molybdenum and potassium that can serve as a flux agent can be produced, for example, in the process of filing in which a molybdenum compound and a potassium compound, which are relatively inexpensive and readily available, are used as raw materials.
  • a molybdenum compound and a potassium compound are used as flux agents, but this example encompasses both the case in which a molybdenum compound and a potassium compound are used as flux agents and the case in which a compound containing molybdenum and potassium is used as a flux agent.
  • the mixing step is a step of mixing together raw materials, such as an aluminum compound, a molybdenum compound, a potassium compound, and silicon or a silicon compound to obtain a mixture. Details of the mixture will be described below.
  • the aluminum compound may be a compound exclusively including an aluminum compound or may be a composite material including an aluminum compound and an organic compound.
  • Suitable examples that may be used include organic-inorganic composite materials obtained by modifying an aluminum compound with an organosilane compound and composite materials of an aluminum compound including a polymer adsorbed thereon.
  • Organic components of the organic compound are removed as gases in the calcination process, and therefore, in the case where a composite material such as those described above is used, the content of the organic compound is not particularly limited. However, from the standpoint of efficiently producing the alumina particles having a card-house structure, the content is preferably less than or equal to 60 mass%and more preferably less than or equal to 30 mass%.
  • the specific surface area of the aluminum compound is not particularly limited. In terms of effective action of the molybdenum compound used as a flux agent, it is preferable that the specific surface area be high. However, aluminum compounds having any specific surface area can be used as a raw material by adjusting the calcination conditions or the amount of the molybdenum compound used.
  • the shape of the alumina particles of the present invention corresponds to the shape of the aluminum compound used as a raw material.
  • Any of various structures, such as spheres, amorphous bodies, structures having an aspect (e.g., wires, fibers, ribbons, and tubes) , and sheets, may be used.
  • a spherical aluminum compound because the resulting alumina particles have a shape close to a spherical shape.
  • the average particle diameter of the alumina particles also basically corresponds to a particle diameter of the aluminum compound used as a raw material.
  • the card-house structure is formed in a manner in which, in the calcination step, primarily within the particles of the raw material aluminum compound, formation of the crystals of the planar alumina flakes and intersecting of at least three adjacent planar alumina flakes progress and adherence occurs. It is presumed that, consequently, the average particle diameter of the resulting alumina particles having a card-house structure primarily corresponds to the average particle diameter of the raw material aluminum particles.
  • the alumina particles of the present invention are alumina particles having an average particle diameter of 1 to 1000 ⁇ m.
  • the aluminum compound to be used may be an aluminum compound having a specific average particle diameter, within the range, that is identical or substantially identical with the specified average particle diameter of the alumina particles desired to be produced.
  • the alumina particles having a card-house structure can be obtained in the following manner, for example: in a method for producing alumina particles that includes a step of calcining an aluminum compound in the presence of a molybdenum compound, a potassium compound, silicon or a silicon compound, and, as necessary, an additional shape control agent, planar alumina flakes are formed, and concurrently, crystal faces of at least three planar alumina flakes are caused to come into contact with, intersect, and adhere to one another at two or more locations.
  • the adherence provides a state in which the card-house structure is secured, that is, the card-house structure does not easily break (disassemble) under an external stress, such as pressure.
  • the conditions for the flux and the like for forming the planar alumina flakes affect the crushing strength and the like of the resulting alumina particles having a card-house structure.
  • a method for producing the alumina particles is performed in a manner in which a molybdenum compound and a potassium compound are used as flux agents, silicon or a silicon compound is used as a shape control agent, these are mixed with an aluminum compound, and the mixture is fired, and further, in this method, 1) the aluminum compound used as a raw material has a specified average particle diameter, 2) the amount of the molybdenum compound and the potassium compound used is limited to a specific range, and 3) the amount of the silicon or silicon compound used is limited to a specific range. Consequently, the alumina particles having a card-house structure that includes at least three planar alumina flakes adhered to one another and having an average particle diameter within a specified range can be selectively produced. Thus, the method is preferable.
  • the average particle diameter and the shape of the alumina particles having a card-house structure can be adjusted in a pulverizing step or a size classification step, which will be described later.
  • the molybdenum compound used as a flux has a function of enabling ⁇ crystals of alumina to grow at relatively iow temperatures.
  • the molybdenum compound include, but are not limited to, molybdenum oxide and compounds containing acid group anions in which molybdenum metal is bonded to oxygen (MoO x n- ) .
  • Examples of the compound containing acid group anions include, but are not limited to, molybdic acid, sodium molybdate, potassium molybdate, lithium molybdate, H 3 PMo 12 O 40 , H 3 SiMo 12 O 40 , NH 4 Mo 7 O 12 , and molybdenum disulfide.
  • the molybdenum compound may contain sodium or silicon, and in this case, the molybdenum compound containing sodium or silicon serves both as a flux agent and as a shape control agent.
  • molybdenum oxide is preferable from a cost standpoint.
  • the molybdenum compounds mentioned above may be used alone or in a combination of two or more.
  • using potassium molybdate as a flux agent is equivalent to using a molybdenum compound and a potassium compound as flux agents.
  • the amount of the molybdenum compound used is not particularly limited, but preferably, the molar ratio of moles of elemental molybdenum in the molybdenum compound to moles of elemental aluminum in the aluminum compound (elemental molybdenum/elemental aluminum) is 0.01 to 3.0, more preferably 0.1 to 1.0, and, in terms of suitably advancing the crystal growth with high productivity, even more preferably 0.30 to 0.70.
  • the amount of the molybdenum compound used is within any of the above-mentioned ranges, alumina particles that have a card-house structure in which planar alumina flakes have a high aspect ratio and which, therefore, have excellent dispersibility can be readily obtained.
  • alumina particles contain molybdenum. Based on this fact, the production method with which unknown alumina particles were produced can be identified.
  • the potassium compound examples include, but are not limited to, potassium chloride, potassium chlorite, potassium chlorate, potassium sulfate, potassium hydrogen sulfate, potassium sulfite, potassium bisulfite, potassium nitrate, potassium carbonate, potassium hydrogen carbonate, potassium acetate, potassium oxide, potassium bromide, potassium bromate, potassium hydroxide, potassium silicate, potassium phosphate, potassium hydrogen phosphate, potassium sulfide, potassium hydrogen sulfide, potassium molybdate, and potassium tungstate.
  • the potassium compound includes isomers as with the molybdenum compound.
  • potassium carbonate, potassium hydrogen carbonate, potassium oxide, potassium hydroxide, potassium chloride, potassium sulfate, and potassium molybdate are preferable.
  • Potassium carbonate, potassium hydrogen carbonate, potassium chloride, potassium sulfate, and potassium molybdate are more preferable.
  • the potassium compounds mentioned above may be used alone or in a combination of two or more.
  • potassium molybdate contains molybdenum and therefore can also have functions of the molybdenum compound described above.
  • using potassium molybdate as a flux agent is equivalent to using a molybdenum compound and a potassium compound as flux agents.
  • the potassium compound used as a raw material or the potassium compound that is produced in a reaction during the temperature increase process of the calcination may be a water-soluble potassium compound, such as potassium molybdate.
  • Water-soluble potassium compounds do not vaporize even in calcination temperature ranges and can be readily recovered by washing after calcination, and therefore the amount of the molybdenum compound that is released to the outside of the calcination furnace can be reduced, which results in a significant reduction in the production cost.
  • the molar ratio of moles of elemental molybdenum in the molybdenum compound to moles of elemental potassium in the potassium compound is preferably less than or equal to 5, more preferably 0.01 to 3, and, in terms of further reducing the production cost, even more preferably 0.5 to 1.5.
  • the molar ratio is within any of the above-mentioned ranges, alumina particles having a preferable particle size can be obtained.
  • the alumina particles In the method of the present invention for producing the alumina particles, it is preferable to use silicon or a silicon compound as a shape control agent because the resulting alumina particles have better flowability, for example.
  • the silicon or silicon compound plays an important role for the growth of plate-shaped crystals of alumina in the calcination of the aluminum compound in the presence of the molybdenum compound.
  • Silicon in the silicon compound is selectively adsorbed onto the [113] face of the ⁇ crystal of the alumina, thereby suppressing the molybdenum oxide, which is a flux agent, from being selectively adsorbed onto the [113] face, and as a result, a plate-shaped morphology having a hexagonal close-packed crystal structure with the [001] face developed, which is thermodynamically most stable, can be formed. From this, it is presumed that as the amount of silicon increases, formation of the [001] crystal face is further promoted, and as a result, planar alumina flakes having a small thickness can be obtained.
  • the molybdenum oxide is suppressed from being selectively adsorbed onto the [113] face, and as a result, a plate-shaped morphology having a hexagonal close-packed crystal structure with the [001] face developed, which is thermodynamically most stable, can be formed. From this, it is presumed that as the amount of silicon increases, a hexagonal close-packed crystal structure, which is thermodynamically most stable, develops also at the intersecting locations of planar alumina flakes as well as other locations, and as a result, a strong adherence can be provided. That is, as the amount of silicon is appropriately increased, the crushing strength of the resulting alumina particles having a card-house structure is improved.
  • the silicon or silicon compound is not limited to a particular type, and silicon known in the art, including not only elemental silicon but also silicon compounds, may be used.
  • Specific examples of the silicon or silicon compound include silicon metal (elemental silicon) , artificially synthesized silicon compounds, such as organosilane compounds, silicone resins, microparticulate silica (SiO 2 ) , silica gel, mesoporous silica, SiC, and mullite, and naturally occurring silicon compounds, such as biosilica.
  • organosilane compounds, silicone resins, and microparticulate silica are preferable from the standpoint of uniform combining and mixing with the aluminum compound.
  • the materials mentioned above may be used alone or in a combination of two or more.
  • the silicon compound When the silicon compound is an organosilicon compound, calcination causes the organic components to be removed as gases, and thus, elemental silicon or an inorganic silicon compound is produced and included in the alumina particles.
  • the silicon compound When the silicon compound is an inorganic silicon compound, calcination causes elemental silicon, or, the inorganic silicon compound as it is in the case where the compound does not decompose at high temperatures during calcination, to be included in or on surfaces of the planar alumina flakes in a localized manner. From the above standpoint, it is preferable to use elemental silicon and/or an inorganic silicon compound, which, in a relatively small amount, can increase the content of elemental silicon provided that the comparison is based on the same molecular weight.
  • the shape of the silicon or silicon compound is not particularly limited.
  • any of various structures such as spheres, amorphous bodies, structures having an aspect (e.g., wires, fibers, ribbons, and tubes) , and sheets, may be suitably used.
  • the amount of the silicon or silicon compound used is not particularly limited, but it is preferable to use the silicon or silicon compound in an amount sufficient to enable selective adsorption onto the [113] face of the ⁇ crystal of the alumina.
  • the amount of the silicon or silicon compound added is preferably 0.01 to 10 mass%, more preferably 0.03 to 7 mass%, and even more preferably 0.03 to 3 mass%, relative to the amount of the elemental aluminum in the aluminum compound calculated as mass.
  • the amount of the silicon or the silicon compound used is within any of the above-mentioned ranges, alumina particles in which the planar alumina flakes have a high aspect ratio and which, therefore, have excellent dispersibility can be readily obtained. Accordingly, the above-mentioned ranges are preferable.
  • the amount of the silicon or silicon compound is insufficient, adsorption of the molybdenum oxide, which is used as a flux agent, onto the [113] face cannot be sufficiently suppressed in many cases, and as a result, there is a tendency for the planar alumina flakes to have a iow aspect ratio and to be non-uniform.
  • insufficient amounts of the silicon or silicon compound are not preferable because, in such cases, the resulting alumina particles tend to be polyhedral alumina particles without the card-house structure of the present invention.
  • excessive amounts of the silicon or silicon compound are not preferable because, in such cases, excess silicon forms an oxide alone, and also, crystals other than alumina, such as 3Al 2 O 3 -2SiO 2 , are included in the alumina particles.
  • the silicon or silicon compound may be included in the aluminum compound by being added thereto as described above and/or may be present as an impurity in the aluminum compound.
  • one or more shape control agents other than the silicon or silicon compound may be used as necessary provided that the formation of the planar alumina flakes due to the presence of elemental silicon and/or an inorganic silicon compound is not interfered with.
  • the shape control agent other than the silicon or silicon compound contributes to the growth of plate-shaped crystals of the alumina in the calcination of the aluminum compound in the presence of the molybdenum compound.
  • the existence state of the shape control agent other than the silicon or silicon compound is not particularly limited provided that the shape control agent can be in contact with the aluminum compound.
  • the following may be suitably used: a mixture in which a shape control agent is physically mixed with the aluminum compound; or a composite material in which a shape control agent is present uniformly or locally in or on the surface or in an inner portion of the aluminum compound.
  • the shape control agent other than the silicon or silicon compound may be included in the aluminum compound by being added thereto and/or may be present as an impurity in the aluminum compound.
  • the method for adding the shape control agent other than the silicon or silicon compound is not particularly limited, and examples of the method include dry-blend methods in which a powder is directly added and mixed, blending methods using a mixer, and methods in which the shape control agent is dispersed in a solvent, a monomer, or the like in advance and then added.
  • the elemental sodium and/or sodium compound is not particularly limited and may be sodium and/or a sodium compound known in the art.
  • Specific examples of the elemental sodium and/or sodium compound include sodium carbonate, sodium molybdate, sodium oxide, sodium sulfate, sodium hydroxide, sodium nitrate, sodium chloride, and metallic sodium. Of these, sodium carbonate, sodium molybdate, sodium oxide, and sodium sulfate are preferable from the standpoint of industrial availability and ease of handling.
  • the sodium and/or elemental sodium-containing compounds may be used alone or in a combination of two or more.
  • the shape of the elemental sodium and/or sodium compound is not particularly limited.
  • any of various structures such as spheres, amorphous bodies, structures having an aspect (e.g., wires, fibers, ribbons, and tubes) , and sheets, may be suitably used.
  • the amount of the elemental sodium and/or sodium compound used is not particularly limited, but preferably, the amount, calculated as sodium metal, is 0.0001 to 2 moles and more preferably 0.001 to 1 moles, relative to 1 mole of aluminum metal in the aluminum compound.
  • the amount of the sodium and/or sodium compound used is within any of the above-mentioned ranges, alumina particles in which the planar alumina flakes have a high aspect ratio and which, therefore, have excellent dispersibility can be readily obtained. Accordingly, the above-mentioned ranges are preferable.
  • the metal compound can have a function of promoting the growth of crystals of the alumina as will be described later.
  • the metal compound may be used for the calcination as desired. Note that the metal compound has a function of promoting the growth of crystals of ⁇ -alumina but is not a requirement for production of the alumina particles of the present invention.
  • the metal compound is not particularly limited, but it is preferable to include at least one selected from the group consisting of Group II metal compounds and Group III metal compounds.
  • Group II metal compound examples include magnesium compounds, calcium compounds, strontium compounds, and barium compounds.
  • Examples of the Group III metal compound include scandium compounds, yttrium compounds, lanthanum compounds, and cerium compounds.
  • metal compound is meant to include oxides, hydroxides, carbonates, and chlorides of elemental metal.
  • yttrium compounds include yttrium oxide (Y 2 O 3 ) , yttrium hydroxide, and yttrium carbonate.
  • the metal compound be an oxide of elemental metal.
  • the metal compound includes isomers.
  • the metal compound is preferably a Period 3 metal compound, a Period 4 metal compound, a Period 5 metal compound, or a Period 6 metal compound, more preferably a Period 4 metal compound or a Period 5 metal compound, and even more preferably a Period 5 metal compound.
  • the metal compound is preferably at least one of magnesium compounds, calcium compounds, yttrium compounds, and lanthanum compounds, more preferably, magnesium compounds, calcium compound, and yttrium compounds, and particularly preferably, yttrium compounds.
  • the amount of the metal compound added is preferably 0.02 to 20 mass%and more preferably 0.1 to 20 mass%, relative to the amount of the elemental aluminum in the aluminum compound calculated as mass.
  • the amount of the metal compound added is greater than or equal to 0.02 mass%, the growth of crystals of the ⁇ -alumina containing molybdenum can suitably proceed. Accordingly, such a content is preferable.
  • the amount of the metal compound added is less than or equal to 20 mass%, alumina particles having a iow content of metal-compound-derived impurities can be obtained. Accordingly, such a content is preferable.
  • the crystal growth proceeds more suitably in the calcination step, and consequently, ⁇ -alumina and a water-soluble yttrium compound are formed.
  • the water-soluble yttrium compound tends to be localized in or on the surface of the ⁇ -alumina, that is, the alumina particles.
  • the yttrium compound can be removed from the alumina particles by washing using water, alkaline water, warmed water, warmed alkaline water, or the like.
  • the amounts of the aluminum compound, the molybdenum compound, the potassium compound, and the silicon or silicon compound used are not particularly limited.
  • the calcination may be performed using a mixture 1) or 2) described below.
  • the amount of a compound containing elemental molybdenum and elemental potassium or the amount of a molybdenum compound containing elemental molybdenum plus a potassium compound containing elemental potassium is calculated as oxide, specifically as potassium molybdate (Mo 2 K 2 O 7 ) , and the total amount of all the raw materials, calculated as oxides, is taken as 100 mass%.
  • the alumina particles having a card-house structure can be produced more efficiently.
  • one common phenomenon that occurs when the mixture 1) or 2) is fired is as follows: at an initial stage of the crystal growth, the crystal growth progresses in a state in which the original shape of the aluminum compound used as a raw material is at least partially retained. Accordingly, it is believed that each of the planar alumina flakes are formed, each based on a portion of the aluminum compound used as a raw material, and consequently, the card-house structure that includes at least three planar alumina flakes and in which the planar alumina flakes are adhered to one another is formed.
  • the silicon or silicon compound containing elemental silicon is used in an amount greater than 0.3 mass% calculated as SiO 2 , that is, the proportion thereof is relatively high, loss of shape of the raw material aluminum compound is suppressed, and, therefore, the shape of the aluminum compound used as a raw material can be retained.
  • the molybdenum compound and the potassium compound are used in an amount less than or equal to 30 mass%calculated as Mo 2 K 2 O 7 , that is, the proportion thereof is relatively low, loss of shape of the raw material aluminum compound is suppressed, and, therefore, the shape of the aluminum compound used as a raw material can be retained.
  • the amount of the molybdenum compound plus the potassium compound, calculated as Mo 2 K 2 O 7 , relative to the total amount of all the raw materials calculated as oxides taken as 100 mass% is preferably greater than or equal to 50 mass%, more preferably 50 mass%or greater and 80 mass%or less, even more preferably 55 mass%or greater and 75 mass%or less, and particularly preferably 60 mass%or greater and 70 mass%or less.
  • the amount of the silicon or silicon compound containing elemental silicon calculated as SiO 2 , relative to the total amount of all the raw materials calculated as oxides taken as 100 mass%, is preferably greater than 0.3 mass%, more preferably greater than 0.3 mass%and 5 mass%or less, and even more preferably 0.4 mass%or greater and 3 mass%or less.
  • the amount of each of the raw materials in the mixture relative to the total amount of all the raw materials calculated as oxides taken as 100 mass% be as follows.
  • the amount of the aluminum compound, calculated as Al 2 O 3 , relative to the total amount of all the raw materials calculated as oxides taken as 100 mass% is preferably greater than or equal to 50 mass%, more preferably 50 mass%or greater and 96 mass%or less, even more preferably 60 mass%or greater and 95 mass%or less, and particularly preferably 70 mass%or greater and 90 mass%or less.
  • the amount of the molybdenum compound plus the potassium compound, calculated as Mo 2 K 2 O 7 , relative to the total amount of all the raw materials calculated as oxides taken as 100 mass% is preferably less than or equal to 30 mass%, more preferably 2 mass%or greater and 30 mass%or less, even more preferably 3 mass%or greater and 25 mass%or less, and particularly preferably 4 mass%or greater and 10 mass%or less.
  • the amount of the silicon or silicon compound containing elemental silicon calculated as SiO 2 , relative to the total amount of all the raw materials calculated as oxides taken as 100 mass%, is preferably greater than or equal to 0.01 mass%, more preferably greater than 0.01 mass%and 5 mass%or less, even more preferably 0.05 mass%or greater and 3 mass%or less, and particularly preferably 0.15 mass%or greater and 3 mass%or less.
  • the amount of the yttrium compound used is not particularly limited, but it is preferable that the yttrium compound be present in an amount less than or equal to 5 mass%calculated as Y 2 O 3 relative to the total amount of all the raw materials calculated as oxides taken as 100 mass%. It is more preferable that the yttrium compound be present in an amount of 0.01 mass%or greater and 3 mass%or less calculated as Y 2 O 3 relative to the total amount of all the raw materials calculated as oxides taken as 100 mass%.
  • the yttrium compound be present in an amount of 0.1 mass%or greater and 1 mass%or less calculated as Y 2 O 3 relative to the total amount of all the raw materials calculated as oxides taken as 100 mass%.
  • the presence of elemental silicon and/or an inorganic silicon compound localized in and near the surface of the alumina particles that result from calcination is an important factor in that, for example, the elemental silicon and/or inorganic silicon compound significantly change the condition of the surface of the alumina, which intrinsically lacks active sites and, therefore, by themselves, enable excellent characteristics of alumina to be exhibited to the maximum extent, and in addition, the elemental silicon and/or inorganic silicon compound can impart even better surface conditions by being combined with a surface treatment agent in a reaction that occurs with the active sites serving as starting points.
  • the alumina particles of the present invention are obtained by calcining an aluminum compound in the presence of a molybdenum compound, a potassium compound, and a shape control agent.
  • this production method is referred to as a flux method. It is presumed that, according to the flux method, the formation of the planar alumina flakes and the formation of the card-house structure, which is associated with the adherence of at least three of the planar alumina flakes, proceed in parallel.
  • the concentration of the flux decreases, that is, the effect of the flux of decreasing the melting point of the solute is reduced, and thus, the evaporation of the flux serves as a driving force to cause crystals of the solute to grow (flux evaporation method) .
  • Another preferable method is to grow crystals in a fluxing agent that is in a liquid phase. Growth of crystals of a solute can be also caused by cooling the solute and a flux that are in liquid phases (slow cooling method) .
  • the flux method has advantages such as the following: crystals can be grown at temperatures much lower than the melting point; crystal structures can be controlled precisely; and polyhedral crystals having a euhedral shape can be formed.
  • alumina particles In the production of alumina particles by using a flux method in which a molybdenum compound is used as flux, although the mechanism is not necessarily clear, it is speculated that the mechanism is as follows, for example. Specifically, when an aluminum compound is fired in the presence of a molybdenum compound, aluminum molybdate is first formed. From the aluminum molybdate, crystals of alumina grow at temperatures lower than the melting point of alumina, as will be appreciated from the description above. Further, for example, when the flux is evaporated, the aluminum molybdate decomposes and crystals grow, and consequently, the alumina particles can be obtained. That is, the molybdenum compound serves as flux, and, via aluminum molybdate, which is an intermediate product, the alumina particles are produced.
  • a potassium compound and silicon or a silicon compound may also be used, and in this case, the alumina particles having a card-house structure that includes at least three planar alumina flakes can be readily produced. More specifically, in the case where the molybdenum compound and the potassium compound are used in combination, a reaction between the molybdenum compound and the potassium compound first occurs, and accordingly potassium molybdate is formed. Concurrently, the molybdenum compound reacts with the aluminum compound to form aluminum molybdate.
  • the aluminum molybdate decomposes in the presence of the potassium molybdate, and the crystal growth progresses in the presence of the silicon or silicon compound, and as a result, the alumina particles having a card-house structure that includes at least three planar alumina flakes can be obtained. That is, in the case where the alumina particles are produced via aluminum molybdate, which is an intermediate product, the presence of potassium molybdate enables the production of the alumina particles having a card-house structure that includes at least three planar alumina flakes.
  • the potassium or potassium compound forms potassium molybdate, which serves as a fluxing agent.
  • the presence of the metal compound enables the production of alumina particles having higher flowability for at least one of the following reasons: excessive formation of crystal nuclei of alumina is prevented or suppressed; diffusion of the aluminum compound, which is necessary for the growth of crystals of alumina, is promoted, in other words, excessive formation of crystal nuclei is prevented; and a function of increasing the rate at which the aluminum compound diffuses is exhibited, thereby enabling a more precise control of the direction in which crystals of alumina grow, which in turn facilitates control of the shape, for example, control for exhibiting the shape of the precursor.
  • the mechanism described above is merely a speculated mechanism, and therefore, in cases where effects of the present invention are produced by a mechanism different from the mechanism described above, such cases are also included in the technical scope of the present invention.
  • Suitable methods for producing the alumina particles of the present invention can be implemented at high temperatures higher than, for example, 2000°C, but even when the method is implemented at a temperature much lower than the melting point of ⁇ -alumina, for example, at lower than or equal to 1600°C, alumina particles that have a high degree of ⁇ crystallization and which includes high-aspect-ratio planar alumina flakes can be formed.
  • alumina particles that have a degree of ⁇ crystallization of greater than or equal to 90%and in which the planar alumina flakes have a high aspect ratio can be formed conveniently, at iow cost, and efficiently.
  • Calcination with a maximum temperature of 920 to 1500°C is more preferable, and calcination with a maximum temperature of 950 to 1400°C is most preferable.
  • the ⁇ crystallization of the intersecting locations of the planar alumina flakes is improved similarly to other locations, and therefore alumina particles having a card-house structure that have excellent mechanical strength can be obtained.
  • the time period for increasing the temperature to a predetermined maximum temperature be within a range of 15 minutes to 10 hours, and the holding time at the calcination maximum temperature be within a range of 5 minutes to 30 hours.
  • the calcination holding time be approximately 10 minutes to 15 hours.
  • the ⁇ crystallization of the intersecting locations of the planar alumina flakes is improved similarly to other locations, and therefore alumina particles having a card-house structure that have excellent crushing strength can be obtained.
  • the atmosphere for the calcination is not particularly limited provided that the effects of the present invention can be produced.
  • oxygen-containing atmospheres such as air atmospheres and oxygen atmospheres
  • inert atmospheres such as nitrogen atmospheres and argon atmospheres are preferable, and, when cost is taken into consideration, air atmospheres are more preferable.
  • the apparatus for performing the calcination is also not necessarily limited, and a so-called calcination furnace may be used. It is preferable that the calcination furnace be formed of a material that does not react with sublimed molybdenum oxide, and it is further preferable that a gas-tight furnace be used to efficiently utilize the molybdenum oxide. Examples of calcination furnaces that may be used for the calcination include tunnel furnaces, roller hearth furnaces, rotary kilns, and muffle furnaces.
  • the suitable production method described above enables selective production of alumina particles having a card-house structure that includes at least three planar alumina flakes adhered to one another and having an average particle diameter of 1 to 1000 ⁇ m. Further, the method facilitates production of a powder in which the alumina particles are present in an amount greater than or equal to 60%, on a number basis, relative to the total number of particles. In the production method, selecting relatively more suitable conditions for production is preferable because, in this case, production of a powder such as the following is facilitated.
  • the powder is such that the alumina particles particularly have a card-house structure in which the at least three planar alumina flakes intersect one another at at least two locations to form an assembly, with surfaces of planar alumina flakes intersecting one another being oriented in a disorderly manner, and the alumina particles are present in the powder in an amount greater than or equal to 80%, on a number basis, relative to the total number of particles.
  • the production method of the present invention may include a cooling step.
  • the cooling step is a step of cooling alumina in which the crystals are grown as a result of the calcination step. More specifically, the cooling step may be a step of cooling a composition including the alumina and a fluxing agent that is in a liquid phase, which result from the calcination step.
  • the cooling rate is not particularly limited, but preferably, the cooling rate is 1 to l000°C/hour, more preferably 5 to 500°C/hour, and even more preferably 50 to 100°C/hour.
  • the cooling rate is greater than or equal to l°C/hour, the production time can be shortened. Accordingly, such cooling rates are preferable.
  • the cooling rate is less than or equal to 1000°C/hour, the occurrence of cracking in the calcination vessel due to heat shock is reduced, which results in a long period of use of the calcination vessel. Accordingly, such a cooling rate is preferable.
  • the method for the cooling is not particularly limited and may be natural cooling or cooling using a cooling device.
  • the production method of the present invention may include an aftertreatment step.
  • the aftertreatment step is a step of removing the fluxing agent.
  • the aftertreatment step may be performed after the calcination step described above, after the cooling step described above, or after the calcination step and after the cooling step. As necessary, the aftertreatment step may be performed repeatedly, two or more times.
  • Examples of methods for the aftertreatment include washing and high-temperature treatment. These may be performed in combination.
  • the method for the washing is not particularly limited. Washing using water, an aqueous solution of ammonia, an aqueous solution of sodium hydroxide, or an acidic aqueous solution may be employed to remove the flux agent.
  • the concentration and the amount of the water, aqueous solution of ammonia, aqueous solution of sodium hydroxide, or acidic aqueous solution to be used, the portion to be washed, the washing time, and the like may be appropriately changed to control the molybdenum content.
  • the method for the high-temperature treatment may be a method in which a temperature is increased to a temperature higher than or equal to the sublimation point or the boiling point of the flux.
  • the particle diameter of the fired product falls outside of the range suitable for the present invention. Accordingly, as necessary, the alumina particles may be pulverized to conform to the particle diameter range suitable for the present invention.
  • the method for the pulverizing of the fired product is not particularly limited. Any known pulverizing method using a ball mill, jaw crusher, jet mill, disc mill, SpectroMill, grinder, mixer mill, or the like may be employed.
  • the alumina particles be subjected to a size classification process.
  • the purposes of the size classification include adjusting the average particle diameter to improve the flowability of the powder and suppressing a viscosity increase that may occur when added to a binder for forming a matrix.
  • the size classification may be wet classification or dry classification, but, from the standpoint of productivity, dry classification is preferable.
  • the dry classification include classification using a sieve, air classification, in which classification is performed by using the difference between the centrifugal force and the fluid drag, and the like. From the standpoint of classification accuracy, air classification is preferable, and the air classification may be performed by using a classifier, such as an air sifter that utilizes a Coanda effect, a swirling airflow type classifier, a forced vortex centrifugal classifier, or a semi-free vortex centrifugal classifier.
  • a classifier such as an air sifter that utilizes a Coanda effect, a swirling airflow type classifier, a forced vortex centrifugal classifier, or a semi-free vortex centrifugal classifier.
  • the pulverizing step and the size classification step may be performed at stages where the steps are necessary, for example, before and/or after an organic compound layer formation step, which will be described later.
  • the average particle diameter of the resulting alumina particles can be adjusted.
  • the average particle diameter of the alumina particles is closely related to the angle of repose thereof.
  • the average particle diameter of the alumina particles can be changed (the angle of repose can be changed indirectly) by selecting particular conditions for the classification or the like, thereby adjusting the flowability of the alumina particles.
  • alumina particles having large average particle diameters may be screened out by size classification or the like to obtain alumina particles having a card-house structure that have a smaller average particle diameter and which therefore have higher flowability than known alumina particles provided that the comparison is made between alumina particles having the same average particle diameter.
  • the above-described method for producing the alumina particles may further include a step of forming an organic compound layer on surfaces of the planar alumina flakes.
  • the organic compound layer forming step may be performed as necessary at a temperature at which the organic compound does not decompose typically after the calcination step or after the aftertreatment step.
  • the method for forming an organic compound layer on surfaces of the planar alumina flakes of the alumina particles is not particularly limited, and any known method may be appropriately employed.
  • the method may be a method in which a solution or a dispersion containing an organic compound is brought into contact with the molybdenum-containing alumina particles and dried.
  • the alumina particles having a card-house structure of the present invention contain elemental silicon and/or an inorganic silicon compound, a surface modification effect, such as that described above, can be expected as compared with cases in which elemental silicon and/or an inorganic silicon compound are absent.
  • the alumina particles containing elemental silicon and/or an inorganic silicon compound may be reacted with an organosilane compound, and the reaction product may be used.
  • alumina particles having a card-house structure that are reaction products of the alumina particles and an organosilane compound are preferable.
  • a reason for this is that, based on the reaction between the organosilane compound and the elemental silicon and/or inorganic silicon compound localized in or on surfaces of the planar alumina flakes, which form the alumina particles, affinity for matrices can be improved.
  • organosilane compound examples include alkyl trimethoxysilanes and alkyl trichlorosilanes in which the alkyl group has 1 to 22 carbon atoms, such as methyltrimethoxysilane, dimethyldimethoxysilane, ethyltrimethoxysilane, ethyltriethoxysilane, n-propyltrimethoxysilane, n-propyltriethoxysilane, isopropyltrimethoxysilane, isopropyltriethoxysilane, pentyltrimethoxysilane, and hexyltrimethoxysilane, trimethoxy (3, 3, 3-trifluoropropyl) silane, (tridecafluoro-1, 1, 2, 2-tetrahydrooctyl) trichlorosilane, phenyltrimethoxysilane, phenyltriethoxysilane, p
  • the organosilane compound be covalently bound to at least part of or the entirety of the elemental silicon and/or inorganic silicon compound present in or on surfaces of the planar alumina flakes of the alumina particles. Not only part of the alumina but also the entirety thereof may be coated with the reaction product.
  • immersion coating or chemical vapor deposition (CVD) may be employed as a method for providing the organosilane compound to the surface of the alumina.
  • the amount of the organosilane compound used is preferably less than or equal to 20 mass%and more preferably 10 to 0.01 mass%, on an elemental silicon basis, relative to the mass of the elemental silicon or inorganic silicon compound present in or on surfaces of the planar alumina flakes of the alumina particles.
  • the amount of the organosilane compound used is less than or equal to 20 mass%, the properties derived from the alumina particles can be easily exhibited, and therefore such an amount is preferable.
  • the reaction between the alumina particles containing elemental silicon and/or an inorganic silicon compound and the organosilane compound may be carried out by using a known filler surface modification method.
  • a dry method such as a spraying method using a fluid nozzle, a stirring method using a shear force, a ball mill method, or a mixer method, may be employed, or a wet method, such as a method using an aqueous system or an organic solvent system, may be employed.
  • a shear force it is desirable that the process be performed in a manner in which the alumina particles used in the present invention do not break apart.
  • the system temperature for the dry method or the drying temperature after a treatment using the wet method is appropriately determined in accordance with the type of organosilane compound while ensuring that the temperature is within a range in which the organosilane compound does not thermally decompose.
  • the temperature is desirably 80 to 150°C.
  • the method for producing the alumina particles which includes using a molybdenum compound as an essential fluxing agent, and using silicon or a silicon compound as a shape control agent, and mixing these with an aluminum compound and calcining the mixture, in the case where a molybdenum compound and a potassium compound are used as fluxing agents or in the case where a compound containing molybdenum and potassium is used as a fluxing agent, in contrast to a case where a molybdenum compound such as molybdenum trioxide is exclusively used, the following can be achieved.
  • the fluxing agent is prevented from being released out of the system, thereby reducing a degradation of the calcination operation environment, and in addition, in many cases, the compound containing molybdenum and potassium present in the mixture of the alumina particles and the fluxing agent particles, which results from the cooling step, is highly water soluble, and, therefore, greater amounts of molybdenum can be removed more easily from the alumina.
  • the amount of the fluxing agent used is greater than or equal to 2 mass%, calculated as Mo 2 K 2 O 7 .
  • transition alumina transition alumina primarily containing ⁇ -alumina, here and hereinafter
  • silicon dioxide manufactured by Kanto Chemical Co., Inc.
  • molybdenum trioxide manufactured by Taiyo Koko Co., Ltd.
  • 51 g of potassium carbonate manufactured by Kanto Chemical Co., Inc.
  • yttrium oxide manufactured by Kanto Chemical Co., Inc.
  • the resulting mixture was placed in a crucible, which was heated in a ceramic electric furnace at 5°C/min to 1000°C and then held at 1000°C for 24 hours. In this manner, calcination was performed. Subsequently, the crucible was cooled at 5°C/min to room temperature and was then taken out. Thus, 224 g of a light blue powder was obtained.
  • Amount added to Al 2 O 3 represents the amount of the silicon compound added relative to the amount of the elemental aluminum in the aluminum compound calculated as mass.
  • Amount added to Al 2 O 3 represents the amount of the yttrium compound added relative to the amount of the elemental aluminum in the aluminum compound calculated as mass.
  • Powders were produced in a manner similar to that for Example 1 except that the amounts of the transition alumina, molybdenum trioxide, potassium carbonate, silicon dioxide, and yttrium oxide, which were used in Example 1, were changed as shown in Table 1. SEM observation confirmed that substantially all (95%or more) , ona number basis, of the alumina particles present in each of the powders obtained in Examples 2 to 5 were particles having a card-house structure.
  • a mixture was obtained by mixing together 122 gof aluminum hydroxide (manufactured by Kanto Chemical Co., Inc. ) , 0.8 g of silicon dioxide (manufactured by Kanto Chemical Co., Inc. ) , 108 gof molybdenum trioxide (manufactured by Taiyo Koko Co., Ltd. ) , 51 gof potassium carbonate (manufactured by Kanto Chemical Co., Inc. ) , and 0.4 g of yttrium oxide (manufactured by Kanto Chemical Co., Inc. ) in a mortar.
  • the resulting mixture was placed in a crucible, which was heated in a ceramic electric furnace at 5°C/min to 1000°C and then held at 1000°C for 24 hours. In this manner, calcination was performed. Subsequently, the crucible was cooled at 5°C/min to room temperature and was then taken out. Thus, 223 gof a light blue powder was obtained.
  • a mixture was obtained by mixing together 77.0 g of aluminum hydroxide (manufactured by Nippon Light Metal Company, Ltd., average particle diameter of 10 ⁇ m) , 0.1 g of silicon dioxide (manufactured by Kanto Chemical Co., Inc., special grade) , and 50.0 g of molybdenum trioxide (manufactured by Taiyo Koko Co., Ltd. ) in a mortar.
  • the resulting mixture was placed in a crucible, which was heated in a ceramic electric furnace at 5°C/min to 1100°C and then held at 1100°C for 24 hours. In this manner, calcination was performed.
  • the crucible was cooled at 5°C/min to room temperature and was then taken out.
  • 52 g of a light blue powder was obtained.
  • the resulting powder was pulverized in a mortar until the particles could be passed through a 106- ⁇ m sieve.
  • 52.0 g of the obtained light blue powder was dispersed in 150 mL of 0.5%ammonia water, and the dispersion was stirred at room temperature (25 to 30°C) for 0.5 hours. Thereafter, filtration was performed to remove ammonia water, which was followed by water washing and drying to remove molybdenum remaining in or on the surface of the particles.
  • 51 g of a blue powder was obtained.
  • the prepared sample was secured to a sample support stage with double-sided tape and was then observed with a VE-9800 surface observation device (manufactured by Keyence Corporation) .
  • a VE-9800 surface observation device manufactured by Keyence Corporation
  • particles in which a card-house structure was observed are indicated as "With” a card-house structure
  • particles in which no card-house structure was observed are indicated as “Without” a card-house structure.
  • X-ray source monochromatic AlK ⁇ ; beam diameter, 100 ⁇ m ; and output, 25 W
  • Cis 284.8 eV
  • the amount of Si in the surface layer of the alumina particles was determined as a molar ratio [Si] / [Al] determined by the results of the XPS analysis.
  • XRF X-ray fluorescence
  • the amount of Si in the interior of the alumina particles was determined as a molar ratio [Si] / [Al] determined by the results of the XRF analysis.
  • the amount of potassium was determined as the amount determined by the results of the XRF analysis, which was calculated as potassium oxide (mass%) , relative to the mass of the alumina particles taken as 100 mass%.
  • the amount of silicon was determined as the amount determined by the results of the XRF analysis, which was calculated as silicon dioxide (mass%) , relative to the mass of the alumina particles taken as 100 mass%.
  • the amount of molybdenum was determined as the amount determined by the results of the XRF analysis, which was calculated as molybdenum trioxide (mass%) , relative to the mass of the alumina particles taken as 100 mass%.
  • the prepared sample was measured by using a HELOS (H3355) and a RODOS (both manufactured by Japan Laser Corporation) , which are a dry laser diffraction particle size distribution analyzer and a dry dispenser, under conditions including a dispersion pressure of 0.3 MPa and a suction pressure of 90 hPa.
  • the average particle diameter d50 ( ⁇ m) was determined from a volume-based cumulative particle size distribution.
  • a crushing force F [N] of the prepared sample was determined by using an NS-A100 model microparticle crushing force measurement instrument (manufactured by Nano Seeds Corporation) .
  • the crushing force F [N] corresponds to the difference between the peak value, which is a value at the time of crushing, and the baseline value, which is a value in a state in which no force is applied.
  • a crushing strength S [Pa] was calculated according to the following equation. The values shown in Table 2 are the average of ten values. Crushing strengths of 50 MPa or greater were rated as "A” , 20 MPa or greater and less than 50 MPa as "B” , and less than 20 MPa as "C” .
  • the prepared sample was placed on a measurement sample holder having a depth of 0.5 mm and leveled off under a given load.
  • the sample holder was placed in a Rint-Ultima wide-angle X-ray diffractometer (manufactured by Rigaku Corporation) , and a measurement was conducted under the following conditions: Cu-K ⁇ ray; 40 kV-30 mA; scan speed, 1°/min; and scan range, 5 to 80°.
  • the degree of ⁇ crystallization was determined from the ratio between the maximum peak height of ⁇ -alumina and the maximum peak height of transition alumina.
  • Fig. 3 is an SEM image of the alumina particles of Example 1.
  • the alumina particles of Examples 1 to 6 had a card-house structure, and the alumina particles of Comparative Example 1 were plate-shaped alumina particles without a card-house structure.
  • a feature of Examples 4 and 5 regarding the amounts can be distinguished from a feature of Examples 1 to 3 and 6 regarding the amounts.
  • the alumina particles having a card-house structure were produced efficiently because the component corresponding to a fluxing agent (Mo 2 K 2 O 7 or MoO 3 in Table 2) was used in an amount less than or equal to 30 mass%.
  • a fluxing agent Mo 2 K 2 O 7 or MoO 3 in Table 2
  • alumina particles of Examples 1 to 6 it was confirmed that substantially 100%of the particles had a card-house structure. That is, of all the alumina particles for which the shape was checked, which are taken as 100%, 95 %or greater of the particles, on a number basis, were observed to have a card-house structure. This is a significantly good result compared with percentages that can be achieved with other methods for producing alumina particles having a card-house structure. It is believed that the result was achieved efficiently because the component corresponding to a fluxing agent (Mo 2 K 2 O 7 in Table 2) was used in a relatively large amount, and the production method including a cooling step (slow cooling method) was employed. Presumably, with the production method, the fluxing agent acted like a spacer, and accordingly the crystals grew in a state in which the particles are relatively spaced apart from one another, and as a result, the efficiency for card-house structure formation was significantly improved.
  • a fluxing agent Mo 2 K 2 O 7 in Table 2
  • alumina particles having excellent flowability are provided.

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Abstract

L'invention concerne des particules d'alumine comprennent une structure de logement de carte qui comprend au moins trois flocons d'alumine plans, les flocons d'alumine plans étant collés l'un à l'autre, les particules d'alumine ayant un diamètre moyen de particule de 1 à 1000 µm et contenant du potassium.
PCT/CN2019/110211 2019-10-09 2019-10-09 Particules d'alumine et procédé de production de particules d'alumine WO2021068139A1 (fr)

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