Classifications

• • 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

Definitions

• Patent Document 2 reports that titanium oxide is used as a crystallization control agent, and sintered at a temperature of 1100°C or higher in the presence of sulfate, a high-temperature flux, to produce flaky aluminum oxide containing titanium oxide with an average particle size of 5 to 60 ⁇ m, a thickness of 1 ⁇ m or less, and an aspect ratio of 20 or more.
• Patent Document 4 reports that by using zinc oxide and tin oxide as crystallization control agents and firing at a temperature of 1200°C in the presence of a sulfate, a high-temperature flux, plate-like ⁇ -alumina particles containing zinc oxide and tin oxide with an average particle thickness of 0.5 ⁇ m or less, an average particle diameter of 30 ⁇ m or more, and an aspect ratio of 100 or more are produced.
• Patent Document 5 reports that by using zirconium oxide as a crystallization control agent and firing at a temperature of 1150°C in the presence of sulfate, a high-temperature flux, plate-like ⁇ -alumina particles with an average thickness of 0.1 to 1 ⁇ m, an average diameter of 5 to 25 ⁇ m, and an aspect ratio of 25 to 250 are produced.
• the present invention was made in consideration of the above circumstances, and aims to provide plate-shaped alumina particles that can be produced at a lower firing temperature than conventional methods, and a method for producing the plate-shaped alumina particles.
• the element (A) exists in a so-called doped state, in which the trivalent aluminum element is replaced by the element (A) in the corundum structure of the plate-like alumina particles.
• the valence of the element (A) is doped by adding the tetravalent titanium element so as to keep the charge of the entire crystal neutral, so it is presumed that the element (A) exists as a divalent element.
• the titanium element is preferably derived from titanium oxide from the viewpoints of availability and ease of synthesis.
• the alumina particles By utilizing molybdenum and a shape control agent in the production of the plate-like alumina particles, the alumina particles have a high alpha crystal rate and are idiomorphic, which allows for excellent dispersibility, mechanical strength, and high thermal conductivity.
• the plate-like alumina particles have, for example, a density of 3.70 g/cm 3 or more and 4.10 g/cm 3 or less, preferably a density of 3.72 g/cm 3 or more and 4.10 g/cm 3 or less, and more preferably a density of 3.80 g/cm 3 or more and 4.10 g/cm 3 or less.
• the density can be measured by pretreating the plate-like alumina particles at 300° C. for 3 hours, and then using a dry automatic density meter Accupyc II1330 manufactured by Micromeritics, at a measurement temperature of 25° C. and helium as a carrier gas.
• the "alumina" contained in the plate-like alumina particles is aluminum oxide, and may be transition alumina of various crystal forms such as ⁇ , ⁇ , ⁇ , ⁇ , etc., or may contain alumina hydrate in the transition alumina, but is basically preferably in the ⁇ crystal form ( ⁇ type) in terms of superior mechanical strength or thermal conductivity.
• the ⁇ crystal form is a dense crystal structure of alumina, and is advantageous in improving the mechanical strength or thermal conductivity of the plate-like alumina.
• the ⁇ -crystallinity ratio is preferably as close to 100% as possible, since the inherent properties of the ⁇ -crystal form are more easily exhibited.
• the ⁇ -crystallinity ratio of the plate-like alumina particles is, for example, 90% or more, preferably 95% or more, and more preferably 99% or more.
• the platelet alumina particles according to the embodiment may contain silicon (Si).
• the silicon may be derived from silicon or a silicon compound that can be used as a shape control agent. By utilizing these, it is possible to produce plate-like alumina particles having excellent luster in the production method described below.
• the plate-like alumina particles according to the embodiment may contain silicon.
• the plate-like alumina particles according to the embodiment may contain silicon in a surface layer.
• the term "surface layer” refers to a region within 10 nm from the surface of the plate-like alumina particle according to the embodiment. This distance corresponds to the detection depth of the XPS used for measurement in the examples.
• the plate-like alumina particles may have silicon unevenly distributed on the surface.
• distributed unevenly on the surface refers to a state in which the mass of silicon per unit volume in the surface layer is greater than the mass of silicon per unit volume outside the surface layer. The fact that silicon is unevenly distributed on the surface layer can be determined by comparing the results of a surface analysis by XPS and an overall analysis by XRF.
• the silicon contained in the plate-like alumina particles may be silicon alone or silicon in a silicon compound.
• the plate-like alumina particles may contain at least one selected from the group consisting of mullite, Si, SiO 2 , SiO, and aluminum silicate produced by reacting with alumina as silicon or a silicon compound, and may contain the above-mentioned substance in the surface layer. Mullite will be described later.
• the plate-like alumina particles can detect Si by XRF analysis.
• the plate-like alumina particles have a molar ratio of Si to Al [Si]/[Al] obtained by XRF analysis of, for example, 0.04 or less, preferably 0.035 or less, and more preferably 0.02 or less.
• the value of the molar ratio [Si]/[Al] is not particularly limited, but is, for example, 0.003 or more, preferably 0.004 or more, and more preferably 0.005 or more.
• the molar ratio [Si]/[Al] of Si to Al obtained by XRF analysis of the plate-like alumina particles is, for example, 0.003 to 0.04, preferably 0.004 to 0.035, and more preferably 0.005 to 0.02.
• the plate-like alumina particles having the molar ratio [Si]/[Al] obtained by the XRF analysis within the above range satisfy the above average particle size, thickness, and aspect ratio values, have better brilliance, and have a good plate-like shape.
• deposits are less likely to adhere to the surface of the plate-like alumina particles, and are excellent in quality.
• the deposits are considered to be SiO2 particles, and are considered to be generated due to excess Si when the generation of mullite on the surface layer of the plate-like alumina particles becomes saturated.
• the plate-like alumina particles may contain silicon corresponding to the silicon or silicon compound containing elemental silicon used in the production method thereof.
• the silicon content relative to 100 mass% of the plate-like alumina particles, calculated as silicon dioxide, is preferably 10 mass% or less, more preferably 0.1 to 10 mass%, and even more preferably 0.1 to 5 mass%.
• the silicon content is within the above range, the above average particle size, thickness, and aspect ratio values are satisfied, the brilliance is more favorable, and the plate-like shape is well formed.
• deposits that appear to be SiO2 particles are less likely to adhere to the surface of the plate-like alumina particles, resulting in excellent quality.
• the plate-like alumina particles of the embodiment may contain mullite. It is presumed that the inclusion of mullite in the surface layer of the plate-like alumina particles improves the selectivity of the inorganic material constituting the inorganic coating portion, and allows the inorganic coating portion to be efficiently formed on the plate-like alumina particles. Mullite is contained in the surface layer of the plate-like alumina particles, and thus a significant reduction in wear of the equipment is achieved.
• the "mullite” that may be contained in the surface layer of the plate-like alumina particles is a composite oxide of Al and Si and is expressed as AlXSiYOz, but there is no particular limit to the values of x, y, and z.
• a more preferred range is Al2Si1O5 to Al6Si2O13 .
• the XRD peak intensity confirmed in the examples described below is that containing Al2.85Si1O6.3 , Al3Si1O6.5 , Al3.67Si1O7.5 , Al4Si1O8 , or Al6Si2O13 .
• the plate- like alumina particles may contain at least one compound selected from the group consisting of Al2.85Si1O6.3 , Al3Si1O6.5 , Al3.67Si1O7.5 , Al4Si1O8 , and Al6Si2O13 in the surface layer.
• the "surface layer” refers to within 10 nm from the surface of the plate - like alumina particles.
• the plate-like alumina particles preferably have mullite unevenly distributed in the surface layer.
• "unevenly distributed in the surface layer” refers to a state in which the mass of mullite per unit volume in the surface layer is greater than the mass of mullite per unit volume in the area other than the surface layer.
• the mullite of the surface layer may form a mullite layer, or may be a mixture of mullite and alumina.
• the interface between the mullite and alumina of the surface layer may be in a state where the mullite and alumina are in physical contact with each other, or the mullite and alumina may form a chemical bond such as Si-O-Al.
• the plate-like alumina particles of the embodiment may contain molybdenum.
• the plate-like alumina particles preferably contain molybdenum in their surface layers.
• the molybdenum may be derived from a molybdenum compound used as a fluxing agent in the method for producing alumina particles described below.
• the particle size and the above-mentioned values for average particle size, thickness, and aspect ratio are satisfied, and the brilliance of the resulting alumina particles tends to be even better.
• the use of molybdenum promotes the formation of mullite, making it possible to produce plate-like alumina particles with a high aspect ratio and excellent dispersibility.
• the properties of the molybdenum contained in the plate-like alumina particles may enable their application as oxidation reaction catalysts and optical materials.
• molybdenum oxide is preferred, and molybdenum trioxide is particularly preferred.
• Molybdenum oxide has extremely high acidity and reacts in a gaseous state at temperatures of 800° C. or higher, and therefore reacts particularly easily with aluminum oxide as a fluxing agent, making it suitable for suppressing the remaining of unreacted raw materials and transition alumina, etc.
• the molybdenum compound may be contained in the platelet alumina particles in any of its possible polymorphic forms or in combination, and may be contained in the platelet alumina particles as ⁇ -MoO 3 , ⁇ -MoO 3 , MoO 2 , MoO, molybdenum cluster structures, and the like.
• molybdenum is contained in a form in which it is attached to the surface of the plate-like alumina particles, or in a form in which it is substituted for part of the aluminum in the crystal structure of the alumina, or it may be a combination of these.
• compound (A) is preferably at least one compound selected from the group consisting of iron hydroxide, iron oxide, iron oxyhydroxide, nickel oxide, copper oxide, chromium oxide, cobalt oxide, zinc oxide, scandium oxide, and ruthenium oxide, more preferably at least one compound selected from the group consisting of iron hydroxide, iron oxide, iron oxyhydroxide, nickel oxide, chromium oxide, cobalt oxide, and zinc oxide, and particularly preferably at least one compound selected from the group consisting of iron oxide, iron hydroxide, iron oxyhydroxide, nickel oxide, and chromium oxide.
• the material may be left to cool naturally or may be cooled using a cooling device.
• the method for producing plate-like alumina particles according to the embodiment may include a post-treatment step.
• the post-treatment step is a post-treatment step for the plate-like alumina particles, and is a step of removing a fluxing agent.
• the post-treatment step may be performed after the above-mentioned firing step, after the above-mentioned cooling step, or after the firing step and the cooling step.
• the post-treatment step may be repeated two or more times as necessary.
• Post-treatment methods include washing and high-temperature treatment, which can be combined.
• the cleaning method is not particularly limited, but it can be removed by washing with water, an aqueous ammonia solution, an aqueous sodium hydroxide solution, or an acidic aqueous solution.
• the molybdenum content can be controlled by appropriately changing the concentration and amount of water, ammonia water solution, sodium hydroxide solution, and acidic solution used, as well as the cleaning area and cleaning time.
• Another high-temperature treatment method is to raise the temperature above the sublimation or boiling point of the flux.
• the plate-like alumina particles may aggregate and may not satisfy the particle size range suitable for the present invention. Therefore, the plate-like alumina particles may be pulverized as necessary to satisfy the particle size range suitable for the present invention.
• the method for pulverizing the fired product is not particularly limited, and any conventionally known pulverizing method such as a ball mill, a jaw crusher, a jet mill, a disk mill, a spectromill, a grinder, or a mixer mill can be used.
• the plate-like alumina particles are preferably classified to adjust the average particle size, improve the powder flowability, or suppress the increase in viscosity when mixed with a binder to form a matrix.
• Classification refers to an operation of classifying particles into groups based on their size. The classification may be either wet or dry, but from the viewpoint of productivity, dry classification is preferred.
• the plate-like alumina particles of the embodiment, or the plate-like alumina particles obtained by the manufacturing method of the embodiment are preferably those with little or no agglomeration, as they are more likely to exhibit their inherent properties, are easier to handle, and have better dispersibility when dispersed in a dispersion medium.
• the manufacturing method of plate-like alumina particles if particles with little or no agglomeration can be obtained without performing the above-mentioned crushing and classification steps, there is no need to perform the above steps, and plate-like alumina having the desired excellent properties can be manufactured with high productivity, which is preferable.
• Example 1 10 g of aluminum hydroxide (manufactured by Nippon Light Metals Co., Ltd., average particle size 1.2 ⁇ m), 1 g of molybdenum trioxide (manufactured by Nippon Inorganic Chemical Industry Co., Ltd.), 0.05 g of silicon dioxide (manufactured by Tosoh Silica Corporation), 0.0115 g of iron oxide hydroxide (manufactured by Kanto Chemical Co., Ltd.), and 0.0103 g of titanium oxide (manufactured by Nippon Aerosil Co., Ltd.) were weighed into a plastic bag and mixed by shaking by hand for 5 minutes to obtain a mixture.
• aluminum hydroxide manufactured by Nippon Light Metals Co., Ltd., average particle size 1.2 ⁇ m
• molybdenum trioxide manufactured by Nippon Inorganic Chemical Industry Co., Ltd.
• silicon dioxide manufactured by Tosoh Silica Corporation
• iron oxide hydroxide manufactured by Kanto Chemical Co., Ltd
• the resulting mixture was placed in a crucible, heated to 1000 ° C. at 5 ° C./min in a ceramic electric furnace, and held at 1000 ° C. for 10 hours for firing. After that, the temperature was lowered to room temperature at 5 ° C./min, and the crucible was removed to obtain a silvery white powder.
• the obtained silvery white powder was then dispersed in 300 mL of 0.25% aqueous ammonia, and the dispersion was stirred at room temperature (25-30°C) for 2 hours, then passed through a 106 ⁇ m sieve, filtered to remove the aqueous ammonia, and washed with water and dried to remove molybdenum remaining on the particle surface, obtaining a silvery white powder.
• Examples 2 to 10 Plate-like alumina particles were obtained in the same manner as in Example 1, except that the raw material composition shown in Table 1 was used. The results are shown in Tables 2 and 3.
• aluminum hydroxide manufactured by Nippon Light Metals Co., Ltd., average particle size 1.2 ⁇ m
• molybdenum trioxide manufactured by Nippon Inorganic Chemical Industry Co., Ltd.
• silicon dioxide manufactured by Tosoh Silica Corporation

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Citations (6)

• 2024
  • 2024-12-11 WO PCT/JP2024/043890 patent/WO2025142499A1/ja active Pending
  • 2024-12-11 JP JP2025515322A patent/JP7736220B1/ja active Active

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