WO2023068202A1 - ベーマイト構造体及びその製造方法 - Google Patents

ベーマイト構造体及びその製造方法 Download PDF

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WO2023068202A1
WO2023068202A1 PCT/JP2022/038424 JP2022038424W WO2023068202A1 WO 2023068202 A1 WO2023068202 A1 WO 2023068202A1 JP 2022038424 W JP2022038424 W JP 2022038424W WO 2023068202 A1 WO2023068202 A1 WO 2023068202A1
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Prior art keywords
boehmite
particles
hydraulic alumina
boehmite structure
inorganic oxide
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PCT/JP2022/038424
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English (en)
French (fr)
Japanese (ja)
Inventor
直樹 栗副
亮介 澤
夏希 佐藤
達郎 吉岡
徹 関野
知代 後藤
成訓 趙
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Panasonic Intellectual Property Management Co Ltd
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Panasonic Intellectual Property Management Co Ltd
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Priority to JP2023554655A priority Critical patent/JP7724463B2/ja
Priority to US18/700,746 priority patent/US20240417330A1/en
Priority to CN202280070214.9A priority patent/CN118215645A/zh
Priority to EP22883506.2A priority patent/EP4421051B1/en
Publication of WO2023068202A1 publication Critical patent/WO2023068202A1/ja
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Definitions

  • the present invention relates to a boehmite structure and its manufacturing method.
  • Boehmite is an aluminum oxide hydroxide represented by the AlOOH composition formula. Boehmite is insoluble in water and hardly reacts with acids and alkalis at room temperature, so it has high chemical stability. Furthermore, boehmite has a high dehydration temperature of around 500° C., so it has excellent heat resistance. Boehmite powder having such properties is used as a resin additive, a catalyst raw material, an abrasive, and the like.
  • Boehmite has a specific gravity of about 3.07. Therefore, it is desired to develop a structure using boehmite that is lightweight and has excellent chemical stability and heat resistance.
  • Patent Document 1 discloses that a porous boehmite compact can be obtained by subjecting a mixture of aluminum hydroxide, a reaction accelerator and water to hydrothermal treatment at 140°C to less than 350°C.
  • the porous boehmite molded body has an intergrowth structure of plate-like or needle-like boehmite crystals, which are connected to form continuous pores, a porosity of 65% or more, and a bending strength.
  • JIS R1601 is 400 N/cm 2 or more.
  • Patent Literature 1 hydroxides of sodium and calcium are used as reaction accelerators, so these remain as impurities in the resulting structure. Therefore, in the production method of Patent Document 1, there is a problem that it is difficult to obtain a molded article that retains the original properties of boehmite. Furthermore, Patent Document 1 describes that the bending strength of the obtained compact is about 1600 N/cm 2 (16 MPa) at maximum. However, when the molded body is used as a plate member, for example, a higher strength is required.
  • An object of the present invention is to provide a boehmite structure having high strength and a method for producing the boehmite structure.
  • the boehmite structure according to the first aspect of the present invention includes a plurality of boehmite particles, and adjacent boehmite particles are bound together.
  • the boehmite structure has a boehmite crystallite size of 10 nm or less and a porosity of 15% or less.
  • a method for producing a boehmite structure according to a second aspect of the present invention includes a mixing step of obtaining a mixture by mixing mechanochemically treated hydraulic alumina with a solvent containing water, and and a pressurizing and heating step of pressurizing and heating under conditions of 10 to 600 MPa and a temperature of 50 to 300°C.
  • FIG. 1 is a cross-sectional view schematically showing an example of a boehmite structure according to this embodiment.
  • FIG. 2 is a cross-sectional view schematically showing another example of the boehmite structure according to this embodiment.
  • FIG. 3 is a diagram showing the bending strength and Vickers hardness of the test samples of Example 1-1 and Comparative Example 1-1, and the results of observing the surfaces of the test samples with a scanning electron microscope (SEM). .
  • FIG. 4 shows the X-ray diffraction patterns of the test samples of Examples 2-1 and 2-2 and Comparative Example 2-1, and the ICSD registered boehmite (AlOOH) and nordstrand (Al(OH) 3 ) X-ray diffraction patterns.
  • FIG. 5(a) is a diagram showing a backscattered electron image at position 1 in test sample 1 of Example 3-1.
  • FIG. 5B is a diagram showing binarized data of the backscattered electron image at position 1 in test sample 1 of Example 3-1.
  • FIG. 6(a) is a diagram showing a backscattered electron image at position 2 in test sample 1 of Example 3-1.
  • FIG. 6B is a diagram showing binarized data of the backscattered electron image at position 2 in test sample 1 of Example 3-1.
  • FIG. 7(a) is a diagram showing a backscattered electron image at position 3 in test sample 1 of Example 3-1.
  • FIG. 7B is a diagram showing binarized data of the backscattered electron image at position 3 in test sample 1 of Example 3-1.
  • FIG. 8(a) is a diagram showing a backscattered electron image at position 1 in test sample 1 of Example 3-2.
  • FIG. 8B is a diagram showing binarized data of the backscattered electron image at position 1 in test sample 1 of Example 3-2.
  • FIG. 9(a) is a diagram showing a backscattered electron image at position 2 in test sample 1 of Example 3-2.
  • FIG. 9B is a diagram showing binarized data of the backscattered electron image at position 2 in test sample 1 of Example 3-2.
  • FIG. 10(a) is a diagram showing a backscattered electron image at position 3 in test sample 1 of Example 3-2.
  • FIG. 10B is a diagram showing binarized data of the backscattered electron image at position 3 in test sample 1 of Example 3-2.
  • FIG. 11(a) is a diagram showing a backscattered electron image at position 1 in test sample 1 of Example 3-3.
  • FIG. 11B is a diagram showing binarized data of the backscattered electron image at position 1 in test sample 1 of Example 3-3.
  • FIG. 12(a) is a backscattered electron image at position 2 in test sample 1 of Example 3-3.
  • FIG. 12B is a diagram showing binarized data of the backscattered electron image at position 2 in test sample 1 of Example 3-3.
  • FIG. 13(a) is a diagram showing a backscattered electron image at position 3 in test sample 1 of Example 3-3.
  • FIG. 13B is a diagram showing binarized data of the backscattered electron image at position 3 in test sample 1 of Example 3-3.
  • FIG. 14 is a photograph showing the results of observing the particles of hydraulic alumina of Example 4-1 and Comparative Example 4-1 at magnifications of 500 and 3000 times.
  • FIG. 15 is a graph showing the results of infrared spectroscopic analysis for the hydraulic alumina of Example 4-1 and Comparative Example 4-1.
  • FIG. 16 is a diagram showing the bending strength and Vickers hardness of the test samples of Example 5-1 and Comparative Example 5-1, and the results of observing the cross section and raw material powder of the test samples with a scanning electron microscope. .
  • FIG. 17 is a diagram showing the bending strength and Vickers hardness of the test samples of Examples 6-1 and 6-2, and the results of observing the cross section of the test samples with a scanning electron microscope.
  • FIG. 18 is a diagram showing the result of observing the cross section of the test sample of Example 6-1 with a scanning electron microscope.
  • a boehmite structure according to the present embodiment and a method for manufacturing the boehmite structure will be described below with reference to the drawings. Note that the dimensional ratios in the drawings are exaggerated for convenience of explanation, and may differ from the actual ratios.
  • the boehmite structure 1 of this embodiment includes a plurality of boehmite particles 2, as shown in FIG. Adjacent boehmite particles 2 are bonded to each other to form a boehmite structure 1 in which the boehmite particles 2 are combined. Furthermore, pores 3 are present between adjacent boehmite particles 2 .
  • the boehmite particles 2 may be particles composed only of a boehmite phase, or particles composed of a mixed phase of boehmite and aluminum oxide or aluminum hydroxide other than boehmite.
  • the boehmite particles 2 may be particles in which a boehmite phase and a gibbsite (Al(OH) 3 ) phase are mixed.
  • the average particle diameter of the boehmite particles 2 constituting the boehmite structure 1 is not particularly limited, it is preferably 300 nm or more and 20 ⁇ m or less, more preferably 300 nm or more and 10 ⁇ m or less, and particularly 300 nm or more and 5 ⁇ m or less. preferable.
  • the average particle diameter of the boehmite particles 2 is within this range, the crystallites of boehmite contained in the boehmite structure 1 become small, so that the strength of the boehmite structure 1 can be increased.
  • the ratio of the pores 3 existing inside the boehmite structure 1 is 15% or less, as will be described later.
  • the value of "average particle size” is measured using an observation means such as a scanning electron microscope (SEM) or a transmission electron microscope (TEM), and several to several tens of fields of view. A value calculated as an average value of the particle diameters of the particles observed inside is adopted.
  • the shape of the boehmite particles 2 is not particularly limited, but can be spherical, for example.
  • the boehmite particles 2 may be whisker-like (needle-like) particles or scale-like particles. Since the whisker-like particles or the scale-like particles are more contactable with other particles than the spherical particles, the strength of the boehmite structure 1 as a whole can be increased.
  • the boehmite structure 1 of this embodiment is composed of a particle group of boehmite particles 2 . That is, the boehmite structure 1 is composed of a plurality of boehmite particles 2 mainly composed of boehmite, and the boehmite structures 1 are formed by bonding the boehmite particles 2 to each other. At this time, the boehmite particles 2 may be in a state of point contact, or may be in a surface contact state in which the particle surfaces of the boehmite particles 2 are in contact with each other.
  • adjacent boehmite particles 2 are bonded via at least one of aluminum oxide and hydroxide.
  • the boehmite particles 2 are not bound by an organic binder made of an organic compound, nor are they bound by an inorganic binder made of an inorganic compound other than oxides and hydroxides of aluminum. That is, as will be described later, the boehmite structure 1 can be formed by heating while pressurizing a mixture of mechanochemically treated hydraulic alumina and water. Therefore, since the boehmite structure 1 does not contain impurities derived from the reaction accelerator, it is possible to maintain the original properties of boehmite.
  • the boehmite structure 1 has at least a boehmite phase composed of boehmite (AlOOH), but may have a crystal phase other than the boehmite phase.
  • Crystal phases other than the boehmite phase possessed by the boehmite structure 1 include a gibbsite phase composed of aluminum hydroxide (Al(OH) 3 ) and a ⁇ -alumina phase composed of alumina oxide (Al 2 O 3 ). can.
  • Al(OH) 3 aluminum hydroxide
  • Al 2 O 3 ⁇ -alumina phase composed of alumina oxide
  • the boehmite structure 1 is mainly composed of the boehmite phase.
  • boehmite is lightweight and has high chemical stability and heat resistance. You can get 1 body.
  • the abundance of the boehmite phase is preferably 50% by mass or more, more preferably 60% by mass or more, and even more preferably 70% by mass or more.
  • the ratio of the boehmite phase in the boehmite structure 1 can be obtained by measuring the X-ray diffraction pattern of the boehmite structure 1 by the X-ray diffraction method and then performing Rietveld analysis.
  • the boehmite structure 1 may have a gibbsite phase made of aluminum hydroxide (Al(OH) 3 ) in addition to the boehmite phase.
  • Al(OH) 3 aluminum hydroxide
  • the boehmite structure 1 may be heated to dehydrate the gibbsite phase. That is, by heating the boehmite structure 1, a dehydration reaction occurs and the crystal structure changes from the gibbsite phase to the boehmite phase.
  • the heating conditions for the boehmite structure 1 are not particularly limited as long as the dehydration reaction of the gibbsite phase occurs.
  • the boehmite structure 1 it is also preferable to heat the raw material hydraulic alumina to reduce the abundance of gibbsite in the hydraulic alumina. Specifically, it is also preferable to use hydraulic alumina in which gibbsite is reduced by heating hydraulic alumina to, for example, 300° C. or higher. By using such a hydraulic alumina with reduced gibbsite as a raw material, it is possible to reduce the abundance of the gibbsite phase in the boehmite structure 1 and increase the chemical stability of the boehmite structure 1.
  • the boehmite structure 1 can also be formed by heating a mixture of hydraulic alumina with reduced gibbsite and water while pressurizing it, as will be described later.
  • the crystallite size of boehmite is 10 nm or less. As the crystallite size of the boehmite contained in the boehmite structure 1 becomes smaller, the bending strength of the obtained boehmite structure 1 is improved, so that the strength of the boehmite structure 1 can be increased. In the boehmite structure 1, the crystallite size of boehmite is more preferably 8 nm or less, more preferably 5 nm or less.
  • the crystallite size of boehmite contained in the boehmite structure 1 is obtained by measuring the diffraction peak of boehmite by a powder X-ray diffraction method, and then using Scherrer's formula from the half width and diffraction angle (Bragg angle of diffracted X-rays) of the diffraction peak. can be obtained using Specifically, powder X-ray diffraction measurement is performed on the boehmite structure 1 after pulverizing the boehmite structure 1 . Then, the crystallite size can be determined from the half-value width and the diffraction angle of the diffraction peak of boehmite in the boehmite structure 1 by using Scherrer's formula (1).
  • the cross section of the boehmite structure 1 preferably has a porosity of 15% or less. That is, when observing the cross section of the boehmite structure 1, the average value of the ratio of pores per unit area is preferably 15% or less. When the porosity is 15% or less, the rate of bonding between the boehmite particles 2 increases, so the boehmite structure 1 becomes denser and stronger. Therefore, the durability of the boehmite structure 1 can be improved. Further, when the porosity is 15% or less, cracks are suppressed from occurring in the boehmite structure 1 starting from the pores 3, so that the bending strength of the boehmite structure 1 can be increased. .
  • the cross-sectional porosity of the boehmite structure 1 is preferably 10% or less, more preferably 5% or less, and even more preferably 3% or less. The smaller the porosity in the cross section of the boehmite structure 1, the more the cracks starting from the pores 3 are suppressed, so the strength of the boehmite structure 1 can be increased.
  • the porosity can be obtained as follows. First, the cross section of the boehmite structure 1 is observed to identify the boehmite particles 2 and the pores 3 . Then, the unit area and the area of the pores 3 in the unit area are measured to obtain the ratio of the pores 3 per unit area. After obtaining such a ratio of pores 3 per unit area at a plurality of locations, the average value of the ratio of pores 3 per unit area is taken as the porosity.
  • an optical microscope, scanning electron microscope (SEM), or transmission electron microscope (TEM) can be used. Also, the unit area and the area of the pores 3 in the unit area may be measured by binarizing the image observed with a microscope.
  • the size of the pores 3 existing inside the boehmite structure 1 is not particularly limited, but is preferably as small as possible. Since the pores 3 are small in size, cracks originating from the pores 3 are suppressed, so that the strength of the boehmite structure 1 can be increased and the durability of the boehmite structure 1 can be improved.
  • the size of the pores 3 of the boehmite structure 1 is preferably 5 ⁇ m or less, more preferably 1 ⁇ m or less, and even more preferably 100 nm or less.
  • the size of the pores 3 existing inside the boehmite structure 1 can be obtained by observing the cross section of the boehmite structure 1 with a microscope, similarly to the porosity described above.
  • the boehmite structure 1 may have a structure in which the boehmite particles 2 are bonded to each other, the boehmite crystallite size is 10 nm or less, and the porosity is 15% or less. Therefore, the shape of the boehmite structure 1 is not particularly limited as long as it has such a structure.
  • the shape of the boehmite structure 1 can be plate-like, film-like, rectangular, block-like, rod-like, or spherical, for example.
  • the thickness t is not particularly limited, but can be, for example, 50 ⁇ m or more.
  • the boehmite structure 1 of this embodiment is formed by a pressure heating method, as described later. Therefore, the boehmite structure 1 having a large thickness can be easily obtained.
  • the thickness t of the boehmite structure 1 can be 1 mm or more, and can be 1 cm or more. Although the upper limit of the thickness t of the boehmite structure 1 is not particularly limited, it can be set to 50 cm, for example.
  • the boehmite structure 1 has a high mechanical strength because the crystallite size and porosity of boehmite are within a predetermined range. Therefore, the boehmite structure 1 preferably has a bending strength of 50 MPa or more as measured in accordance with Japanese Industrial Standard JIS T6526:2018 (dental ceramic material). The bending strength of the boehmite structure 1 is measured by a biaxial bending test of JIS T6526. When the bending strength of the boehmite structure 1 is 50 MPa or more, the mechanical strength is excellent, so the machinability is enhanced. Therefore, the boehmite structure 1 can be easily used, for example, for building members that require high mechanical strength and workability.
  • the bending strength of the boehmite structure 1 is more preferably 80 MPa or more, more preferably 100 MPa or more. Although the upper limit of the bending strength of the boehmite structure 1 is not particularly limited, it can be set to 300 MPa, for example.
  • the plurality of boehmite particles 2 are not bound by an organic binder made of an organic compound, and are bound by an inorganic binder made of an inorganic compound other than aluminum oxides and hydroxides.
  • the content of elements other than aluminum is preferably 5% by mass or less, more preferably 3% by mass or less, and 1% by mass or less. is more preferred. Since the boehmite structure 1 hardly contains impurities such as sodium and calcium, it is possible to retain the original characteristics of boehmite.
  • the boehmite structure 1 of the present embodiment includes a plurality of boehmite particles 2, and adjacent boehmite particles 2 are bound together.
  • the boehmite structure 1 has a boehmite crystallite size of 10 nm or less and a porosity of 15% or less.
  • the boehmite crystallite size is 10 nm or less and the porosity is 15% or less, so that the boehmite particles 2 are closely and firmly bonded to each other.
  • the boehmite structure 1 has improved mechanical strength, and thus can have high durability.
  • the plurality of boehmite particles 2 are bonded without using an organic binder and an inorganic binder composed of an inorganic compound other than aluminum oxides and hydroxides. Furthermore, the boehmite structure 1 is mainly composed of the boehmite phase. Therefore, the boehmite structure 1 is lightweight and has excellent chemical stability.
  • the boehmite structure 1 can be obtained by mixing mechanochemically treated hydraulic alumina with a solvent containing water, and then heating under pressure.
  • Hydraulic alumina is a hydrate produced by heat-treating aluminum hydroxide and contains ⁇ -alumina. Such hydraulic alumina has the property of bonding and hardening through hydration reactions.
  • the pressurized heating method the hydration reaction of the hydraulic alumina progresses and the hydraulic alumina bonds with each other, and the crystal structure changes to boehmite, so that the boehmite structure 1 can be obtained.
  • the hydraulic alumina powder is mechanochemically treated, and coarse particles of the hydraulic alumina are pulverized into fine particles.
  • the specific surface area of the hydraulic alumina increases, thereby promoting the hydration reaction between the hydraulic alumina and the water-containing solvent.
  • mechanochemically treating the hydraulic alumina particles the number of hydroxy groups on the surface of the hydraulic alumina particles increases, and the reactivity with the solvent increases. As a result, the particles of the hydraulic alumina are more likely to bond with each other, making it possible to obtain the boehmite structure 1 with high strength.
  • the mechanochemical treatment of the hydraulic alumina powder is not particularly limited as long as it is a method of pulverizing coarse particles of hydraulic alumina into fine particles.
  • the mechanochemical treatment is preferably pulverization treatment using at least one selected from the group consisting of ball mills, bead mills and vibration mills.
  • the mechanochemical treatment is preferably pulverization treatment using a planetary ball mill.
  • a planetary ball mill is a ball mill that pulverizes hydraulic alumina by rotating a pot containing hydraulic alumina and hard balls (media) and rotating (orbiting) a stage on which the pot is placed.
  • Such a planetary ball mill exerts a stronger centrifugal force by rotating and revolving in the opposite direction in addition to the collision between the hard balls and the wall of the pot. can be done.
  • the hard balls (media) used in the mechanochemical treatment are not particularly limited, and those made of ceramics, resin or metal can be used.
  • the pot used in the mechanochemical treatment is not particularly limited, and a pot made of ceramics, resin or metal can be used. Ceramic hard balls and pots made of zirconia, alumina, agate or silicon nitride can be used. From the viewpoint of efficiently pulverizing the hydraulic alumina, the hard balls and the pot are preferably made of ceramics.
  • the mechanochemical treatment of hydraulic alumina powder may be wet, dry, or a combination of wet and dry. However, from the viewpoint of efficiently pulverizing the hydraulic alumina, the mechanochemical treatment is preferably wet.
  • the solvent used for wet pulverization must be one that does not readily react with hydraulic alumina.
  • an organic solvent As a solvent for wet pulverization, alcohol is preferably used, and ethanol is more preferably used. Since ethanol hardly reacts with hydraulic alumina and can be easily removed after pulverization, it can be suitably used as a solvent for wet pulverization.
  • the average particle size of the mechanochemically treated hydraulic alumina powder is not particularly limited, it is preferably 0.1 ⁇ m to 5 ⁇ m, more preferably 0.5 ⁇ m to 3 ⁇ m.
  • the particle size of the hydraulic alumina is within this range, the hydration reaction between the hydraulic alumina and the water-containing solvent is facilitated, and thus the bonding between the hydraulic alumina particles is promoted.
  • the boehmite crystallite size in the boehmite structure 1 is 10 nm or less, the strength of the boehmite structure 1 can be further improved.
  • the average particle size of the hydraulic alumina powder can be measured using an observation means such as a scanning electron microscope (SEM) or a transmission electron microscope (TEM).
  • the solvent containing water is preferably pure water or ion-exchanged water.
  • the solvent containing water may contain an acidic substance or an alkaline substance in addition to water.
  • the solvent containing water may contain water as a main component, and may contain, for example, an organic solvent (for example, alcohol).
  • the amount of solvent added to the hydraulic alumina is preferably an amount that allows the hydration reaction of the hydraulic alumina to proceed sufficiently.
  • the amount of solvent to be added is preferably 20 to 200% by mass, more preferably 50 to 150% by mass, relative to the hydraulic alumina.
  • the interior of the mold is filled with a mixture obtained by mixing hydraulic alumina and a solvent containing water.
  • the mold may be heated as necessary.
  • the inside of the mold becomes a high pressure state.
  • the hydraulic alumina is highly packed, and the hydraulic alumina particles are bonded to each other to increase the density.
  • the hydraulic alumina undergoes a hydration reaction to form boehmite and aluminum hydroxide on the surface of the hydraulic alumina particles.
  • boehmite structure 1 in which a plurality of boehmite particles 2 are bonded together via at least one of aluminum oxide and aluminum hydroxide.
  • the conditions for heating and pressurizing the mixture obtained by mixing the hydraulic alumina and the water-containing solvent are not particularly limited as long as the conditions allow the reaction between the hydraulic alumina and the solvent to proceed.
  • the temperature when heating the mixture obtained by mixing the hydraulic alumina and the water-containing solvent is more preferably 80 to 250°C, more preferably 100 to 200°C.
  • the pressure when pressurizing the mixture obtained by mixing the hydraulic alumina and the water-containing solvent is more preferably 50 to 600 MPa, further preferably 200 to 600 MPa.
  • boehmite structure As a method of forming a boehmite structure, a method of pressing only boehmite powder is conceivable. However, even if boehmite powder is put into a mold and pressurized at room temperature, the particles of boehmite are unlikely to react with each other, and it is difficult to firmly bond the particles together. As a result, the green compact obtained has many pores and is insufficient in mechanical strength.
  • the sintering method has been conventionally known as a method for manufacturing inorganic members made of ceramics.
  • the sintering method is a method of obtaining a sintered body by heating an aggregate of solid powder made of an inorganic substance at a temperature lower than the melting point. Therefore, as a method of forming a boehmite structure, a method of pressing only boehmite powder to form a green compact and then firing at 500° C. is also conceivable.
  • the dehydration reaction of boehmite proceeds and the crystal structure changes from boehmite to ⁇ -alumina. Since ⁇ -alumina has a specific gravity of about 3.98, a lightweight structure cannot be obtained.
  • the boehmite particles are difficult to sinter, so the resulting structure has many pores and insufficient mechanical strength. .
  • a method of pressing only boehmite powder to form a green compact and then firing it at 1400°C is also conceivable.
  • a green compact of boehmite powder is fired at 1400° C.
  • the boehmite powders are sintered together to form a structure.
  • the boehmite green compact is fired at 1400° C.
  • the dehydration reaction of boehmite progresses and the crystal structure changes from boehmite to ⁇ -alumina.
  • densification is hindered by the generation of pores due to dehydration, and ⁇ -alumina has a specific gravity of about 3.98.
  • the mixture obtained by mixing the hydraulic alumina and the solvent containing water is heated and pressurized. A good structure can be obtained.
  • the method for producing the boehmite structure 1 of the present embodiment includes a mixing step of obtaining a mixture by mixing mechanochemically treated hydraulic alumina with a solvent containing water, and pressurizing and and a pressure heating step of heating.
  • the mixture is preferably heated and pressurized at a temperature of 50 to 300° C. and a pressure of 10 to 600 MPa.
  • the boehmite structure 1 is formed under such low temperature conditions, so the resulting structure is mainly composed of the boehmite phase. Therefore, it is possible to obtain the boehmite structure 1 which is lightweight, has excellent chemical stability, and has a reduced amount of impurities by a simple method.
  • the mechanochemically treated hydraulic alumina is used, so that the crystallite size of boehmite in the boehmite structure 1 can be reduced to 10 nm or less. Further, by using the mechanochemically treated hydraulic alumina, the hydration reaction between the hydraulic alumina and the water-containing solvent is promoted, and the particles of the hydraulic alumina are easily bonded to each other. Therefore, a high-strength boehmite structure 1 can be obtained.
  • the boehmite structure 1A of the second embodiment includes a plurality of boehmite particles 2, and adjacent boehmite particles 2 are bonded to each other as in the first embodiment.
  • the boehmite structure 1A further contains inorganic oxide particles 4 in addition to the boehmite particles 2, and the inorganic oxide particles 4 are highly dispersed inside the boehmite structure 1A.
  • the boehmite structure 1A of the present embodiment is a molded body that includes a plurality of boehmite particles 2 and a plurality of inorganic oxide particles 4, and is formed by bonding at least the boehmite particles 2 to each other.
  • the inorganic oxide particles 4 act as an aggregate, so that the strength of the boehmite structure 1A can be increased.
  • the average particle size and shape of the boehmite particles 2 can be the same as in the first embodiment.
  • the boehmite structure 1A may have a gibbsite phase made of aluminum hydroxide (Al(OH) 3 ). Less is better.
  • the boehmite crystallite size is preferably 10 nm or less, more preferably 8 nm or less, and even more preferably 5 nm or less.
  • the boehmite structure 1A is present at least in one place between the adjacent boehmite particles 2, between the adjacent inorganic oxide particles 4, and between the boehmite particles 2 and the inorganic oxide particles 4. , stomata 3 are present.
  • the size of the pores 3 of the boehmite structure 1A is preferably 5 ⁇ m or less, more preferably 1 ⁇ m or less, and even more preferably 100 nm or less.
  • the porosity in the cross section of the boehmite structure 1A is also preferably 15% or less, more preferably 10% or less, and further preferably 5% or less, as in the first embodiment. 3% or less is particularly preferable.
  • the boehmite structure 1A contains the inorganic oxide particles 4 in addition to the boehmite particles 2.
  • the inorganic oxide particles 4 often have a plurality of hydroxyl groups on the surface of the particles. Therefore, as will be described later, when a mixture of hydraulic alumina and inorganic oxide particles is heated under pressure to form the boehmite structure 1A, the boehmite particles 2 and the inorganic oxide particles 4 are bonded by dehydration condensation. easier. As a result, the boehmite particles 2 and the inorganic oxide particles 4 are strongly bonded, so that the strength of the boehmite structure 1A can be increased.
  • the inorganic oxide particles 4 consist of an oxide of at least one metal element selected from the group consisting of alkali metals, alkaline earth metals, transition metals, base metals and semi-metals.
  • alkaline earth metals include beryllium and magnesium in addition to calcium, strontium, barium and radium.
  • Base metals include aluminum, zinc, gallium, cadmium, indium, tin, mercury, thallium, lead, bismuth and polonium.
  • Metalloids include boron, silicon, germanium, arsenic, antimony and tellurium.
  • the inorganic oxide particles 4 are alumina (Al 2 O 3 ), zirconia (ZrO 2 ), mullite (3Al 2 O 3 .2SiO 2 ), zircon (ZrSiO 4 ), cordierite (2MgO.2Al 2 O 3.5SiO 2 ), forsterite (2MgO ⁇ SiO 2 ), yttria (Y 2 O 3 ), steatite (MgO ⁇ SiO 2 ), silica (quartz glass, SiO 2 ), titanium oxide (TiO 2 ), copper oxide (CuO) and Particles made of at least one selected from the group consisting of iron oxide (Fe 2 O 3 ) can be used.
  • the boehmite structure 1A may contain inorganic carbide particles instead of the inorganic oxide particles 4. Moreover, the boehmite structure 1A may contain inorganic carbide particles in addition to the inorganic oxide particles 4 . Since the inorganic carbide particles also act as an aggregate, the inclusion of the inorganic carbide particles makes it possible to increase the strength of the boehmite structure 1A.
  • the inorganic carbide particles particles made of carbide of at least one metal element selected from the group consisting of alkali metals, alkaline earth metals, transition metals, base metals and semi-metals can be used. Particles made of silicon carbide (SiC) can also be used as the inorganic carbide particles.
  • the inorganic oxide particles 4 preferably contain silicon. Moreover, the inorganic oxide particles 4 preferably contain silica (SiO 2 ). When the inorganic oxide particles 4 contain a silica component, hydroxy groups are likely to occur on the surfaces of the particles. As a result, the boehmite particles 2 and the inorganic oxide particles 4 are more likely to bond with each other through dehydration condensation, so that the strength of the boehmite structure 1A can be further increased.
  • Inorganic oxide particles containing silica include mullite (3Al 2 O 3.2SiO 2 ), zircon (ZrSiO 4 ), cordierite ( 2MgO.2Al 2 O 3.5SiO 2 ), and forsterite (2MgO.SiO 2 ) . , steatite (MgO.SiO 2 ) and quartz glass (SiO 2 ).
  • the average particle size of the inorganic oxide particles 4 is preferably 5 ⁇ m or less. Since the smaller the particle diameter of the inorganic oxide particles 4, the larger the specific surface area, the contact sites between the boehmite particles 2 and the inorganic oxide particles 4 can be increased, and the bonding sites can be increased. As a result, it becomes possible to further increase the strength of the boehmite structure 1A.
  • the average particle size of the inorganic oxide particles 4 is more preferably 3 ⁇ m or less, and further preferably 1 ⁇ m or less. The average particle size of the inorganic oxide particles 4 can be measured using observation means such as a scanning electron microscope (SEM) or a transmission electron microscope (TEM), as described above.
  • the inorganic oxide particles 4 may have an average particle diameter of 0.1 mm to 10 cm.
  • the inorganic oxide particles 4 having a relatively large particle diameter it is possible to improve the hardness of the boehmite structure 1A.
  • the hardness of the boehmite structure 1A itself can be improved due to the inorganic oxide particles 4. becomes possible.
  • the inorganic oxide particles 4 preferably have a Vickers hardness of 10 GPa or less.
  • the boehmite structure 1A can be produced by mixing mechanochemically treated hydraulic alumina particles and inorganic oxide particles with a solvent containing water, and then heating the mixture under pressure.
  • the Vickers hardness of the inorganic oxide particles is low, when the mixture of the hydraulic alumina particles, the inorganic oxide particles and the solvent is pressurized, the inorganic oxide particles are crushed by the pressure in the mixture. As a result, the crushed inorganic oxide particles enter the voids in the mixture, resulting in close packing of the hydraulic alumina and inorganic oxide particles.
  • the close-packed hydraulic alumina and the inorganic oxide particles adhere to each other, so that the boehmite structure 1A having high strength can be obtained.
  • a value measured according to JIS R1610 (hardness test method for fine ceramics) for the material forming the inorganic oxide particles 4 is adopted.
  • the inorganic oxide particles 4 preferably have an elastic modulus (Young's modulus) of 320 GPa or less.
  • Young's modulus Young's modulus
  • the inorganic oxide particles 4 can bend in the mixture. Therefore, when the pressure reduction operation is performed after the hydraulic alumina and the inorganic oxide particles 4 are adhered to form the boehmite structure 1A by the heating and pressurizing step, the inorganic oxide particles are originally removed inside the boehmite structure 1A. can maintain its shape.
  • the elastic modulus (Young's modulus) of the inorganic oxide particles 4 a value measured according to JIS R1602 (test method for elastic modulus of fine ceramics) for the material forming the inorganic oxide particles 4 is adopted.
  • Table 1 shows typical Vickers hardness values of alumina, zirconia, mullite, zircon, cordierite, forsterite, and silica (quartz glass) that can be constituent materials of the inorganic oxide particles 4 .
  • Table 1 also shows representative values of bending strength, thermal expansion coefficient and specific gravity of these inorganic oxides.
  • Table 1 also shows typical values of Vickers hardness, bending strength, coefficient of thermal expansion and specific gravity of boehmite.
  • Table 2 shows representative values of elastic modulus (Young's modulus) of alumina, mullite, zirconia, yttria, forsterite, cordierite, steatite, and silica.
  • the boehmite phase is preferably an amorphous crystal. That is, when the cross section of the boehmite structure 1A is observed with a microscope, it is preferable that the boehmite phase has a large number of irregularities on the surface and that the shape of the boehmite phase is not uniform. Also, the boehmite phase preferably does not have a faceted surface, that is, a flat surface. Since the boehmite phase is an amorphous crystal, the contact area between the boehmite particles 2 (boehmite phase) and the inorganic oxide particles 4 is increased, so that the bonding strength between them can be increased.
  • the inorganic oxide particles 4 may have a particle shape and may have a faceted surface, that is, a flat surface on the particle surface. Since the inorganic oxide particles 4 are spherical particles having facet surfaces, the dispersibility of the inorganic oxide particles 4 increases during molding, so that the inorganic oxide particles 4 are dispersed substantially uniformly in the boehmite structure 1A. be able to. As a result, variations in the strength and hardness of the boehmite structure 1A can be suppressed.
  • the inorganic oxide particles 4 have facet surfaces, there is a possibility that the pinning effect of suppressing the crystal growth of the hydraulic alumina can be exhibited during the molding of the boehmite structure 1A. As a result, cracking of the boehmite particles 2 can be suppressed, and the strength of the boehmite structure 1A can be further increased.
  • the inorganic oxide particles 4 have a particle shape, and may have an irregular shape without facets. Since the inorganic oxide particles 4 are amorphous particles, the number of locations where they are entangled with the amorphous boehmite particles 2 increases. As a result, the shear strength between the inorganic oxide particles 4 and the boehmite particles 2 increases, so that the strength of the entire boehmite structure 1A can be further improved.
  • the content ratio of the boehmite particles 2 and the inorganic oxide particles 4 in the boehmite structure 1A is not particularly limited. That is, in the boehmite structure 1A, the content of the inorganic oxide particles 4 should be decreased in order to improve the properties of the boehmite. Further, for example, when the strength of the boehmite structure 1A is desired to be increased, the content of the inorganic oxide particles 4 may be increased. Therefore, in the boehmite structure 1A, the volume ratio of the inorganic oxide particles 4 can be 10 to 90% by volume, can be 20 to 70% by volume, and can also be 25 to 60% by volume. .
  • the shape of the boehmite structure 1A can be, for example, plate-like, film-like, rectangular, block-like, rod-like, or spherical like the first embodiment.
  • the thickness t is not particularly limited, but can be, for example, 50 ⁇ m or more.
  • the thickness t of the boehmite structure 1A can be 1 mm or more, and can be 1 cm or more.
  • the upper limit of the thickness t of the boehmite structure 1A is not particularly limited, it can be set to 50 cm, for example.
  • the boehmite structure 1A has high mechanical strength because the plurality of boehmite particles 2 are strongly bonded to each other and the boehmite crystallite size is 10 nm or less. Therefore, the boehmite structure 1A also preferably has a bending strength of 50 MPa or more as measured according to JIS T6526:2018.
  • the bending strength of the boehmite structure 1A is more preferably 80 MPa or more, more preferably 100 MPa or more.
  • the upper limit of the bending strength of the boehmite structure 1A is not particularly limited, it can be set to 300 MPa, for example.
  • the boehmite structure 1A of the present embodiment includes multiple boehmite particles 2 and multiple inorganic oxide particles 4, and the adjacent boehmite particles 2 are bonded.
  • the boehmite structure 1A has a boehmite crystallite size of 10 nm or less and a porosity of 15% or less.
  • the boehmite crystallite size is 10 nm or less and the porosity is 15% or less, so that the boehmite particles 2 and the inorganic oxide particles 4 adhere densely and firmly. .
  • the boehmite structure 1A has improved mechanical strength, and thus can have high durability.
  • the boehmite structure 1A has the inorganic oxide particles 4 as aggregate dispersed therein, it is possible to further increase the strength.
  • the boehmite structure 1A can be obtained by a pressure heating method as in the first embodiment. That is, the boehmite structure 1A can be obtained by mixing the mechanochemically treated hydraulic alumina and inorganic oxide particles with a solvent containing water, and then pressurizing and heating the mixture. By using such a pressurized heating method, the hydration reaction of the hydraulic alumina proceeds in a state in which the hydraulic alumina and the inorganic oxide particles are mixed. Then, the crystal structure changes to boehmite while the hydraulic alumina bonds to each other. As a result, a boehmite structure 1A including the boehmite particles 2 and the inorganic oxide particles 4 and in which adjacent boehmite particles 2 are bonded can be obtained.
  • the hydraulic alumina powder is mechanochemically treated.
  • the mechanochemical treatment for hydraulic alumina can be performed in the same manner as in the first embodiment.
  • the average particle size of the mechanochemically treated hydraulic alumina powder is not particularly limited, but is preferably 0.1 ⁇ m to 5 ⁇ m, more preferably 0.5 ⁇ m to 3 ⁇ m.
  • the mechanochemical treatment for inorganic oxide particles can be performed in the same manner as the mechanochemical treatment for hydraulic alumina. That is, the mechanochemical treatment is preferably pulverization treatment using at least one selected from the group consisting of ball mills, bead mills and vibration mills. Among these, the mechanochemical treatment is preferably pulverization treatment using a planetary ball mill.
  • the mechanochemical treatment of the powder of inorganic oxide particles may be a wet process, a dry process, or a combination of the wet process and the dry process. If the inorganic oxide particles are difficult to react with water, water may be used as a solvent for wet pulverization.
  • the average particle size of the mechanochemically treated inorganic oxide particles is not particularly limited, but is preferably 0.1 ⁇ m to 5 ⁇ m, more preferably 0.5 ⁇ m to 3 ⁇ m.
  • the mechanochemically treated inorganic oxide particles and the hydraulic alumina have the same average particle size, the inorganic oxide particles and the hydraulic alumina are easily mixed uniformly. Therefore, it is possible to promote the adhesion between the inorganic oxide particles and the hydraulic alumina, and further increase the strength of the boehmite structure 1A.
  • the average particle size of the powder of inorganic oxide particles can be measured using observation means such as a scanning electron microscope (SEM) or a transmission electron microscope (TEM).
  • the mechanochemical treatment for hydraulic alumina and the mechanochemical treatment for inorganic oxide particles may be performed separately or together. That is, the hydraulic alumina and the inorganic oxide particles may be separately mechanochemically treated and then mixed. Moreover, after putting hydraulic alumina and inorganic oxide particles into one pot, the mechanochemical treatment may be performed collectively. However, since it is preferable to uniformly mix the hydraulic alumina and the inorganic oxide particles, it is preferable to subject them to mechanochemical treatment collectively.
  • the mechanochemically treated hydraulic alumina powder and inorganic oxide particle powder are mixed with a solvent containing water to prepare a mixture.
  • the solvent containing water is preferably pure water or ion-exchanged water.
  • the solvent containing water may contain an acidic substance or an alkaline substance other than water, and may contain an organic solvent.
  • the amount of solvent added to the mixture of hydraulic alumina and inorganic oxide particles is preferably an amount that allows the hydration reaction of hydraulic alumina to proceed sufficiently.
  • the amount of solvent to be added is preferably 20 to 200% by mass, more preferably 50 to 150% by mass, relative to the hydraulic alumina.
  • the inside of the mold is filled with a mixture obtained by mixing hydraulic alumina and inorganic oxide particles with a solvent containing water.
  • the mold may be heated as necessary.
  • the inside of the mold becomes a high pressure state.
  • the hydraulic alumina and the inorganic oxide particles are highly packed, and the hydraulic alumina particles are bonded to each other.
  • the dehydration reaction proceeds by heating, so that the boehmite particles 2 are bonded to each other.
  • the dehydration condensation reaction with the boehmite particles 2 proceeds, so that the boehmite particles 2 and the inorganic oxide particles 4 bond to each other.
  • the boehmite structure 1A in which the boehmite particles 2 are bonded to each other and the inorganic oxide particles 4 are dispersed can be obtained by removing the compact from the inside of the mold.
  • the mixture obtained by mixing hydraulic alumina and inorganic oxide particles with a solvent containing water is heated to 50 to 300 ° C. and at a pressure of 10 to 600 MPa. Pressurization is preferred.
  • the temperature at which the mixture is heated is more preferably 80 to 250°C, more preferably 100 to 200°C.
  • the pressure when pressurizing the mixture is more preferably 50 to 600 MPa, further preferably 200 to 600 MPa.
  • the method for producing the boehmite structure 1A of the present embodiment includes a mixing step of obtaining a mixture by mixing mechanochemically treated hydraulic alumina and inorganic oxide particles with a solvent containing water; and a pressurizing and heating step of pressurizing and heating the mixture.
  • the mixture is preferably heated and pressurized at a temperature of 50 to 300° C. and a pressure of 10 to 600 MPa.
  • hydraulic alumina and inorganic oxide particles that have been mechanochemically treated are used. Therefore, the crystallite size of boehmite in the boehmite structure 1A can be set to 10 nm or less, and the inorganic oxide particles acting as an aggregate can be highly dispersed. Therefore, a high-strength boehmite structure 1A can be obtained.
  • Example 1 (Preparation of test sample) ⁇ Example 1-1> First, as hydraulic alumina, hydraulic alumina BK-112 manufactured by Sumitomo Chemical Co., Ltd. was prepared. The hydraulic alumina has a median particle size of 16 ⁇ m. As a result of analyzing the hydraulic alumina powder by a powder X-ray diffraction method, it was found to be a mixture of boehmite and gibbsite (aluminum hydroxide). The hydraulic alumina also contained ⁇ -alumina.
  • the hydraulic alumina was mechanochemically treated using a planetary ball mill. Specifically, first, hydraulic alumina, ethanol as a solvent, and hard balls (media) were put into a pot made of resin.
  • the pot used was made of polyamide and had a capacity of 250 mL.
  • the media used were made of zirconia and had a diameter of ⁇ 3 mm.
  • the pot containing the hydraulic alumina, solvent and hard balls was treated with a planetary ball mill to pulverize the hydraulic alumina.
  • a planetary ball mill a planetary ball mill, Classicline P-5 manufactured by Fritsch was used.
  • the rotation speed of the pot was 200 rpm, and the treatment time was 3 hours.
  • a mechanochemically treated hydraulic alumina was obtained by removing the solvent after the mixture of hydraulic alumina and solvent was taken out of the pot.
  • ion-exchanged water is weighed so as to be 80% by mass with respect to the mechanochemically treated hydraulic alumina, and then the hydraulic alumina and ion-exchanged water are mixed using an agate mortar and pestle. A mixture was thus obtained. Next, the obtained mixture was put into the inside of a cylindrical molding die ( ⁇ 10) having an internal space. Then, the mixture was heated and pressurized under conditions of 400 MPa, 180° C., and 20 minutes to obtain a test sample of Example 1-1.
  • ⁇ Comparative Example 1-1 First, as hydraulic alumina, hydraulic alumina BK-112 manufactured by Sumitomo Chemical Co., Ltd. was prepared. Next, ion-exchanged water is weighed so as to be 80% by mass with respect to hydraulic alumina, and then the hydraulic alumina and ion-exchanged water are mixed using an agate mortar and pestle to obtain a mixture. got Next, the obtained mixture was put into the inside of a cylindrical molding die ( ⁇ 10) having an internal space. Then, the mixture was heated and pressurized under conditions of 400 MPa, 180° C., and 20 minutes to obtain a test sample of Comparative Example 1-1. In other words, the test sample of Comparative Example 1-1 is a sample in which the hydraulic alumina is not mechanochemically treated.
  • the bending strength of the test samples of Example 1-1 and Comparative Example 1-1 was measured according to JIS T6526. As a result, as shown in FIG. 3, the bending strength (maximum value of stress) of the test sample of Example 1-1 was 83.2 MPa. In contrast, the bending strength of the test sample of Comparative Example 1-1 was 51.4 MPa.
  • the Vickers hardness of the test samples of Example 1-1 and Comparative Example 1-1 was measured according to JIS R1610. As a result, as shown in FIG. 3, the Vickers hardness of the test sample of Example 1-1 was 2.48 GPa. In contrast, the Vickers hardness of the test sample of Comparative Example 1-1 was 1.87 GPa.
  • Example 1-1 The surfaces of the test samples of Example 1-1 and Comparative Example 1-1 were observed using a scanning electron microscope. As a result, as shown in FIG. 3, the test sample of Comparative Example 1-1 contained a large number of coarse particles as indicated by symbol A. In contrast, it can be seen that the test sample of Example 1-1 does not contain coarse particles. In other words, it can be seen that the test sample of Example 1-1 has finer and more uniform particles than Comparative Example 1-1.
  • Example 2 (Preparation of test sample) ⁇ Example 2-1>
  • hydraulic alumina hydraulic alumina BK-112 manufactured by Sumitomo Chemical Co., Ltd. was prepared.
  • the hydraulic alumina was mechanochemically treated using a planetary ball mill. Specifically, first, hydraulic alumina, ethanol as a solvent, and hard balls (media) were put into a pot made of resin.
  • the pot used was made of polyamide and had a capacity of 250 mL.
  • the media used were made of zirconia and had a diameter of ⁇ 3 mm.
  • the pot containing the hydraulic alumina, solvent and hard balls was treated with a planetary ball mill to pulverize the hydraulic alumina.
  • the same planetary ball mill as in Example 1-1 was used.
  • the rotation speed of the pot was 200 rpm, and the treatment time was 1 hour.
  • a mechanochemically treated hydraulic alumina was obtained by removing the solvent after taking out the mixture of hydraulic alumina and solvent from the pot.
  • ion-exchanged water is weighed so as to be 80% by mass with respect to the mechanochemically treated hydraulic alumina, and then the hydraulic alumina and ion-exchanged water are mixed using an agate mortar and pestle. A mixture was thus obtained. Next, the obtained mixture was put into the inside of a cylindrical molding die ( ⁇ 10) having an internal space. Then, the mixture was heated and pressurized under conditions of 400 MPa, 180° C., and 20 minutes to obtain a test sample of Example 2-1.
  • Example 2-2 A test sample of Example 2-2 was obtained in the same manner as in Example 2-1 except that in the planetary ball mill treatment, a zirconia pot was used and the treatment time was set to 3 hours.
  • Comparative Example 2-1 A test sample prepared in the same manner as in Comparative Example 1-1 was used as a test sample in Comparative Example 2-1.
  • Example 2-1 and 2-2 and Comparative Example 2-1 were subjected to powder X-ray diffraction measurement using an X-ray diffractometer to determine the crystallite size. Specifically, after pulverizing each test sample, powder X-ray diffraction measurement using Cu-K ⁇ rays was performed. Then, the crystallite size was determined using Scherrer's formula (1) from the half-value width and the diffraction angle of the diffraction peak of boehmite in each test sample.
  • FIG. 4 shows the X-ray diffraction pattern of each test sample.
  • FIG. 4 also shows the X-ray diffraction patterns of ICSD registered boehmite (AlOOH) and nordstrand (Al(OH) 3 ).
  • the crystallite size of boehmite in the test sample of Example 2-1 using the resin pot was 6.8 nm.
  • the crystallite size of boehmite in the test sample of Example 2-2 using a ceramic spot was 3.4 nm.
  • the crystallite size of boehmite in the test sample of Comparative Example 2-1 which was not mechanochemically treated, was 10.3 nm.
  • Example 3 (Preparation of test sample) ⁇ Example 3-1> First, as hydraulic alumina, hydraulic alumina BK-112 manufactured by Sumitomo Chemical Co., Ltd. was prepared. Next, the hydraulic alumina was mechanochemically treated using a planetary ball mill. Specifically, first, hydraulic alumina, ethanol as a solvent, and hard balls (media) were put into a pot made of zirconia. The pot used had a capacity of 250 mL. The media used were made of zirconia and had a diameter of ⁇ 3 mm.
  • the pot containing the hydraulic alumina, solvent and hard balls was treated with a planetary ball mill to pulverize the hydraulic alumina.
  • the same planetary ball mill as in Example 1-1 was used.
  • the rotation speed of the pot was 250 rpm, and the treatment time was 3 hours.
  • a mechanochemically treated hydraulic alumina was obtained by removing the solvent after taking out the mixture of hydraulic alumina and solvent from the pot.
  • ion-exchanged water is weighed so as to be 80% by mass with respect to the mechanochemically treated hydraulic alumina, and then the hydraulic alumina and ion-exchanged water are mixed using an agate mortar and pestle. A mixture was thus obtained. Next, the obtained mixture was put into the inside of a cylindrical molding die ( ⁇ 10) having an internal space. Then, the mixture was heated and pressurized under conditions of 400 MPa, 180° C., and 20 minutes to obtain a test sample of Example 3-1.
  • Example 3-2 In the planetary ball mill treatment, the test of Example 3-2 was performed in the same manner as in Example 3-1 except that a pot made of polyamide was used, the rotation speed of the pot was 200 rpm, and the treatment time was 3 hours. Got a sample.
  • Example 3-3 In the planetary ball mill treatment, the test of Example 3-3 was performed in the same manner as in Example 3-1 except that a pot made of polyamide was used, the rotation speed of the pot was 200 rpm, and the treatment time was 1 hour. Got a sample.
  • Table 3 summarizes the material of the pot, the rotation speed of the pot in the planetary ball mill, and the processing time of the planetary ball mill in Examples 3-1 to 3-3.
  • the pore portions were clarified by binarizing the SEM images of the three fields of view. Images obtained by binarizing the backscattered electron images of FIGS. 5(a), 6(a) and 7(a) are shown in FIGS. 5(b), 6(b) and 7(b), respectively. Then, the area ratio of the pore portion was calculated from the binarized image, and the average value was taken as the porosity. Specifically, from FIG. 5(b), the area ratio of the pore portion at position 1 was 0.255%. From FIG. 6(b), the area ratio of the pore portion at position 2 was 0.585%. From FIG. 7(b), the area ratio of the pore portion at position 3 was 0.249%. Therefore, the porosity of the test sample of Example 3-1 was 0.36%, which is the average area ratio of the pore portions at positions 1-3.
  • the porosity of the test samples of Examples 3-2 and 3-3 was determined in the same manner as the test sample of Example 3-1.
  • Backscattered electron images obtained by observing three locations (positions 1 to 3) of the cross section of the test sample of Example 3-2 are shown in FIGS. 8(a), 9(a) and 10(a). shown.
  • the binarized images of the backscattered electron images of FIGS. 8(a), 9(a) and 10(a) are shown in FIGS. 8(b), 9(b) and 10(b) respectively. show.
  • Backscattered electron images obtained by observing three locations (positions 1 to 3) in the cross section of the test sample of Example 3-3 are shown in FIGS. 11(a), 12(a) and 13(a). shown.
  • 11(a), 12(a) and 13(a) are binarized and shown in FIGS. 11(b), 12(b) and 13(b), respectively.
  • Table 3 summarizes the porosities of the test samples of Examples 3-1, 3-2
  • Example 1 From Example 1, it can be seen that the use of mechanochemically treated hydraulic alumina improves the bending strength and Vickers hardness of the test sample. Furthermore, it can be seen that the use of mechanochemically treated hydraulic alumina makes the particles constituting the test sample finer and uniformly dispersed.
  • Example 2 From Example 2, it can be seen that the test sample obtained by mixing hydraulic alumina with water and heating and pressurizing has a structure mainly composed of boehmite, since a boehmite peak is observed. In addition, it can be seen that the test sample using the mechanochemically treated hydraulic alumina has a boehmite crystallite size of 10 nm or less.
  • Example 3 From Example 3, it can be seen that the test sample made of mechanochemically treated hydraulic alumina has a porosity of less than 1%. Thus, it can be seen that a boehmite structure having a boehmite crystallite size of 10 nm or less and a porosity of 15% or less has high bending strength.
  • Example 4 (Preparation of test sample) ⁇ Example 4-1> The mechanochemically treated hydraulic alumina prepared in Example 1-1 was used as the hydraulic alumina of this example.
  • the coarse particles of the hydraulic alumina are pulverized into fine particles, and the specific surface area is improved, so that the reactivity between the hydraulic alumina and water is increased. I understand.
  • Infrared spectroscopic analysis Infrared spectroscopic analysis was performed on the hydraulic alumina of Example 4-1 and Comparative Example 4-1. Specifically, the infrared absorption spectrum of the surface of the hydraulic alumina of each example was measured by the total reflection measurement method (ATR method). FIG. 15 shows the measurement results.
  • the mechanochemically treated hydraulic alumina of Example 4-1 was observed to have an absorption peak due to a hydroxy group (OH group).
  • the hydraulic alumina of Comparative Example 4-1 which was not mechanochemically treated, did not show any absorption peak due to hydroxyl groups (OH groups).
  • the mechanochemically treated hydraulic alumina has hydroxy groups on the particle surfaces, and thus is considered to have improved reactivity with water.
  • Example 5 (Preparation of test sample) ⁇ Example 5-1> First, as hydraulic alumina, hydraulic alumina BK-112 manufactured by Sumitomo Chemical Co., Ltd. was prepared. Furthermore, as zircon (ZrSiO 4 ), zirconium silicate MZ-50B manufactured by Daiichi Kigenso Kagaku Kogyo Co., Ltd. was prepared.
  • hydraulic alumina and zircon were weighed, and the hydraulic alumina and zircon were mechanochemically treated using a planetary ball mill. Specifically, first, hydraulic alumina, zircon, ethanol as a solvent, and hard balls (media) were put into a pot made of resin.
  • the pot used was made of polyamide and had a capacity of 250 mL.
  • the media used were made of zirconia and had a diameter of ⁇ 3 mm.
  • the pot containing the hydraulic alumina, zircon, solvent and hard balls was treated with a planetary ball mill to pulverize the hydraulic alumina and zircon.
  • the same planetary ball mill as in Example 1-1 was used.
  • the rotation speed of the pot was 200 rpm, and the treatment time was 3 hours.
  • the mixture of hydraulic alumina, zircon and solvent was taken out from the pot and then the solvent was removed to obtain a mechanochemically treated mixture of hydraulic alumina and zircon.
  • the mixture of hydraulic alumina and zircon and the ion-exchanged water are mixed using an agate mortar and pestle. A mixture was obtained. The resulting mixture was then put into a cylindrical molding die ( ⁇ 10) having an internal space. Then, the mixture was heated and pressurized under conditions of 400 MPa, 180° C., and 20 minutes to obtain a test sample of Example 5-1.
  • Example 5-1 First, the same hydraulic alumina and zircon as in Example 5-1 were prepared, and 50% by volume of each of the hydraulic alumina and zircon were weighed. Next, ion-exchanged water is weighed so as to be 80% by mass with respect to the hydraulic alumina, and then the hydraulic alumina, zircon, and ion-exchanged water are mixed using an agate mortar and pestle. , to obtain a mixture. The resulting mixture was then put into a cylindrical molding die ( ⁇ 10) having an internal space. Then, the mixture was heated and pressurized under conditions of 400 MPa, 180° C., and 20 minutes to obtain a test sample of Comparative Example 5-1. In other words, the test sample of Comparative Example 5-1 is a sample in which hydraulic alumina and zircon are not mechanochemically treated.
  • the bending strength of the test samples of Example 5-1 and Comparative Example 5-1 was measured according to JIS T6526. As a result, as shown in FIG. 16, the bending strength of the test sample of Example 5-1 was 102.1 MPa. In contrast, the bending strength of the test sample of Comparative Example 5-1 was 34.1 MPa.
  • the Vickers hardness of the test samples of Example 5-1 and Comparative Example 5-1 was measured according to JIS R1610. As a result, as shown in FIG. 16, the Vickers hardness of the test sample of Example 5-1 was 3.0 GPa. In contrast, the Vickers hardness of the test sample of Comparative Example 5-1 was 1.8 GPa.
  • FIG. 16 also shows a scanning electron micrograph of a mixture of hydraulic alumina and zircon before being subjected to pressure and heat treatment. From FIG. 16, it can be seen that the mixture of hydraulic alumina and zircon of Comparative Example 5-1 contains many coarse particles. In contrast, the mixture of hydraulic alumina and zircon of Example 5-1 does not contain coarse particles as a result of the mechanochemical treatment to refine the particles.
  • the mechanochemical treatment pulverizes hydraulic alumina and zircon and mixes them almost uniformly, so boehmite and zircon firmly adhere to each other in the resulting test sample. Therefore, it can be seen that the test sample has good results in both bending strength and Vickers hardness. Further, from FIGS. 3 and 16, it is possible to further increase the bending strength and Vickers hardness of the resulting test sample by including zircon as the inorganic oxide particles.
  • Example 6 (Preparation of test sample) ⁇ Example 6-1> First, as hydraulic alumina, hydraulic alumina BK-112 manufactured by Sumitomo Chemical Co., Ltd. was prepared. Further, as alumina (Al 2 O 3 ), Advanced Alumina AA-03 manufactured by Sumitomo Chemical Co., Ltd. was prepared. The advanced alumina AA-03 is a single crystal particle of ⁇ -alumina having a shape close to a polyhedral sphere, and has a median particle size of 0.40 ⁇ m.
  • hydraulic alumina and alumina powder were mechanochemically treated using a planetary ball mill.
  • hydraulic alumina, alumina powder, ethanol as a solvent, and hard balls (media) were put into a pot made of resin.
  • the pot used was made of polyamide and had a capacity of 250 mL.
  • the media used were made of zirconia and had a diameter of ⁇ 3 mm.
  • the pot containing the hydraulic alumina, alumina powder, solvent and hard balls was treated with a planetary ball mill to pulverize the hydraulic alumina.
  • the same planetary ball mill as in Example 1-1 was used.
  • the rotation speed of the pot was 250 rpm, and the treatment time was 3 hours.
  • the mixture of hydraulic alumina, alumina powder and solvent was taken out from the pot and the solvent was removed to obtain a mechanochemically treated mixture of hydraulic alumina and alumina powder.
  • ion-exchanged water is weighed so as to be 80% by mass with respect to hydraulic alumina, and then the mixture of hydraulic alumina and alumina powder and ion-exchanged water are mixed using an agate mortar and pestle. A mixture was thus obtained. The resulting mixture was then put into a cylindrical molding die ( ⁇ 10) having an internal space. Then, the mixture was heated and pressurized under conditions of 400 MPa, 180° C., and 20 minutes to obtain a test sample of Example 6-1.
  • Example 6-2 A test sample of Example 6-2 was prepared in the same manner as in Example 6-1, except that cordierite (2MgO ⁇ 2Al 2 O 3 ⁇ 5SiO 2 ) was used instead of alumina (Advanced Alumina AA-03). Obtained.
  • cordierite As the cordierite, SS-200 (average particle size 7.5 ⁇ m) manufactured by Marusu Yakuyaku Co., Ltd. was used.
  • the bending strength of the test samples of Examples 6-1 and 6-2 was measured according to JIS T6526. As a result, as shown in FIG. 17, the bending strength of the test sample of Example 6-1 was 103.2 MPa. Also, the bending strength of the test sample of Example 6-2 was 90.7 MPa.
  • the Vickers hardness of the test samples of Examples 6-1 and 6-2 was measured according to JIS R1610. As a result, as shown in FIG. 17, the Vickers hardness of the test sample of Example 6-1 was 2.6 GPa. Also, the Vickers hardness of the test sample of Example 6-2 was 1.9 GPa.
  • FIG. 18 shows the result of observing the cross section of the test sample of Example 6-1 with a scanning electron microscope. From FIG. 18, it can be seen that in the test sample, the boehmite particles 2 composed of the boehmite phase are amorphous crystals. In other words, it can be seen that the boehmite particles 2 have a large number of irregularities on the surface and are not uniform in shape. On the other hand, the inorganic oxide particles 4 made of ⁇ -alumina have a particle shape and facets on the particle surfaces.

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