Inorganic Structure and Method for Producing the Same

Abstract

This inorganic structure (1) comprises a plurality of inorganic particles (2) and a joining portion (3) which covers the surfaces of each of the plurality of inorganic particles (2) and joins together each of the plurality of inorganic particles (2). The joining portion (3) contains: an amorphous compound which includes oxygen, one or more metal elements and at least one of aluminium and titanium; and a plurality of microparticles (4) with an average particle size of 100 nm or less. The average particle size of the plurality of inorganic particles (2) is 1 μm or more, and the volume percentage of the plurality of inorganic particles (2) is 30% or more.

Description

Technical Field

[0001] The present invention relates to an inorganic structure and a method for manufacturing the same.

Background Art

[0002] As a method for manufacturing an inorganic structure made of ceramics, a sintering method is known. 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.

[0003] In Patent Document 1, WO 3 , TiO 2 or a solid solution thereof, and glass powder particles containing a crystal having photocatalytic properties are disclosed. Further, it is disclosed that a solidified molded product having an arbitrary shape can be obtained by sintering the glass powder particles. And it is described that such a solidified molded product is useful as a photocatalytic functional material having excellent photocatalytic properties.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

[0005] However, since the sintering method requires heating solid powder at a high temperature, there is a problem that energy consumption during manufacturing is large and cost is high. Further, when only solid powder is simply compacted under low-temperature conditions, the solid powders do not sufficiently bond to each other, so that there are many pores in the obtained molded body and the mechanical strength is insufficient.

[0006] The present invention has been made in view of such problems of the prior art. And an object of the present invention is to provide an inorganic structure that can be produced by a simple method and further has high denseness, and a method for manufacturing the inorganic structure.

[0007] In order to solve the above problems, the inorganic structure according to the first aspect of the present invention includes a plurality of inorganic particles and a bonding portion that covers the surface of each of the plurality of inorganic particles and bonds each of the plurality of inorganic particles. The bonding portion contains an amorphous compound containing at least one of aluminum and titanium and oxygen and one or more metal elements, and a plurality of fine particles having an average particle diameter of 100 nm or less. The average particle diameter of the plurality of inorganic particles is 1 μm or more, and the volume ratio of the plurality of inorganic particles is 30% or more.

[0008] The method for manufacturing an inorganic structure according to the second aspect of the present invention includes a step of obtaining a mixture by mixing a plurality of inorganic particles having an average particle diameter of 1 μm or more, at least one oxide selected from the group consisting of aluminum oxide, titanium oxide, and a composite oxide of aluminum and titanium, a plurality of fine particles having an average particle diameter of 100 nm or less, and an aqueous solution containing a metal element. The above method includes a step of pressurizing and heating the mixture under conditions where the pressure is 10 to 600 MPa and the temperature is 50 to 300 °C. The volume ratio of the plurality of inorganic particles in the mixture is 30% or more.

Brief Description of the Drawings

[0009]

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Mode for Carrying Out the Invention

[0010] Hereinafter, the inorganic structure according to the present embodiment and the method for manufacturing the inorganic structure will be described in detail with reference to the drawings. Note that the dimensional ratios in the drawings are exaggerated for convenience of explanation and may be different from the actual ratios.

[0011] [Inorganic Structure] As shown in FIG. 1, the inorganic structure 1 of the present embodiment includes a plurality of inorganic particles 2 and a bonding portion 3. Then, adjacent inorganic particles 2 are bonded to each other via the bonding portion 3, thereby forming an inorganic structure 1 in which a plurality of inorganic particles 2 are aggregated.

[0012] The inorganic particles 2 are composed of an inorganic substance, and the inorganic substance contains at least one metal element selected from the group consisting of an alkali metal, an alkaline earth metal, a transition metal, a base metal, and a metalloid. In this specification, alkaline earth metals include beryllium and magnesium in addition to calcium, strontium, barium, and radium. Transition metals include, for example, scandium, titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, yttrium, zirconium, niobium, molybdenum, ruthenium, rhodium, palladium, silver, tungsten, platinum, and gold. Base metals include aluminum, zinc, gallium, cadmium, indium, tin, mercury, thallium, lead, bismuth, and polonium. Metalloids include boron, silicon, germanium, arsenic, antimony, and tellurium. Among these, it is preferable that the inorganic substance contains aluminum. As will be described later, the inorganic particles 2 containing the above metal elements are easily bonded via the bonding portion 3 by a pressure heating method.

[0013] The inorganic substance constituting the inorganic particles 2 is preferably at least one selected from the group consisting of, for example, oxides, nitrides, hydroxides, oxyhydroxides, sulfides, borides, carbides, and halides of the above metal elements. The above-mentioned oxides of the metal elements may include phosphates, silicates, aluminates, and borates in addition to compounds in which only oxygen is bonded to the metal elements. Further, the inorganic substance constituting the inorganic particles 2 may be a composite anion compound containing the above metal element. A composite anion compound is a substance containing a plurality of anions in a single compound, and examples thereof include oxyfluorides, oxychlorides, and oxynitrides. The inorganic substance constituting the inorganic particles 2 is preferably an oxide or nitride of the above metal element. Such an inorganic substance has high stability against oxygen and water vapor in the atmosphere, and thus an inorganic structure 1 excellent in chemical stability and reliability can be obtained.

[0014] The inorganic substance constituting the inorganic particles 2 is particularly preferably an oxide. By including the oxide of the above metal element in the inorganic substance, an inorganic structure 1 with higher durability can be obtained compared to fluorides and nitrides. The oxide of the metal element is preferably a compound in which only oxygen is bonded to the metal element. Specific examples of the inorganic substance constituting the inorganic particles 2 include aluminum oxide. Specific examples of the inorganic particles 2 include alumina particles. Since aluminum oxide has high acid resistance and alkali resistance, an inorganic structure 1 having high durability can be obtained even under acidic or alkaline conditions.

[0015] The inorganic particles 2 are composed of simple metal oxides or composite metal oxides. It is preferable that the metal element contained in the simple metal oxide is one kind, and the metal elements contained in the composite metal oxide are two or more kinds. By the inorganic particles 2 containing the simple metal oxide or composite metal oxide of the above metal element, the obtained inorganic structure 1 becomes a stable and excellent ceramics in various properties. In addition, it is preferable that the inorganic particles 2 contain a simple metal oxide or composite metal oxide as a main component. Specifically, it is preferable that the inorganic particles 2 contain 80 mol% or more of a simple metal oxide or composite metal oxide, more preferably 90 mol% or more, and still more preferably 95 mol% or more.

[0016] Each of the plurality of inorganic particles 2 is preferably crystalline. That is, the inorganic particles 2 contain the above-mentioned inorganic substance, and it is preferable that the inorganic substance is crystalline. By the inorganic particles 2 containing a crystalline inorganic substance, an inorganic structure 1 with high durability can be obtained as compared with the case of containing an amorphous inorganic substance. Note that the inorganic particles 2 may be single crystal particles or polycrystalline particles.

[0017] The average particle diameter of the plurality of inorganic particles 2 is 1 μm or more. When the average particle diameter of the inorganic particles 2 is within this range, the inorganic particles 2 are firmly bonded to each other, and the strength of the inorganic structure 1 can be increased. In addition, when the average particle diameter of the inorganic particles 2 is within this range, as will be described later, the ratio of pores existing inside the inorganic structure 1 becomes 20% or less, so that the strength of the inorganic structure 1 can be increased. The average particle diameter of the inorganic particles 2 is preferably 5 μm or more, more preferably 10 μm or more. Further, the average particle diameter of the plurality of inorganic particles 2 is preferably 50 μm or less, more preferably 30 μm or less, still more preferably 25 μm or less, and particularly preferably 20 μm or less. In addition, in this specification, as the value of the "average particle diameter", unless otherwise specified, a value calculated as the average value of the particle diameters of the particles observed in several to several tens of fields of view using observation means such as a scanning electron microscope (SEM) or a transmission electron microscope (TEM) is adopted.

[0018] The shape of the inorganic particles 2 is not particularly limited, and for example, it can be spherical. Further, the inorganic particles 2 may be whisker-shaped (needle-shaped) particles or flake-shaped particles. Since whisker-shaped particles or flake-shaped particles have higher contact properties with other particles and the joint portion 3 compared to spherical particles, it is possible to increase the strength of the entire inorganic structure 1.

[0019] The joint portion 3 binds each of the plurality of inorganic particles 2. By binding adjacent inorganic particles 2 via the joint portion 3, the inorganic particles 2 are three-dimensionally bound to each other, so that a bulk body with high mechanical strength can be obtained. The joint portion 3 preferably directly contacts the inorganic particles 2. Further, the joint portion 3 covers at least a part of the surface of each of the plurality of inorganic particles 2. The joint portion 3 preferably covers the entire surface of each of the plurality of inorganic particles 2. Thereby, since the inorganic particles 2 and the joint portion 3 are firmly bound, an inorganic structure 1 excellent in density and mechanical strength can be obtained.

[0020] The joint portion 3 contains a plurality of fine particles 4 having an average particle diameter of 100 nm or less. Since the joint portion 3 contains such a plurality of fine particles 4, a dense structure is formed, so that it is possible to increase the strength of the inorganic structure 1. Note that the average particle diameter of the fine particles 4 may be 80 nm or less, may be 50 nm or less, or may be 30 nm or less. Further, the average particle diameter of the fine particles 4 may be 1 nm or more, may be 5 nm or more, or may be 10 nm or more. As described above, the average particle diameter of the plurality of fine particles 4 can be measured using a scanning electron microscope (SEM) or a transmission electron microscope (TEM).

[0021] The fine particles 4 may contain at least one oxide selected from the group consisting of aluminum oxide, titanium oxide, and a composite oxide of aluminum and titanium. Since these oxides have high acid resistance and alkali resistance, an inorganic structure 1 with high durability can be obtained even under acidic or alkaline conditions. The oxide contained in the fine particles 4 may be a crystalline compound or an amorphous compound. From the viewpoint of suppressing the generation of cracks starting from the gaps between the inorganic particles 2 and the bonding portion 3, it is preferable that the fine particles 4 contain aluminum oxide.

[0022] Each of the plurality of fine particles 4 is preferably crystalline. That is, the fine particles 4 preferably contain the above-mentioned inorganic substances and are further crystalline particles. Since the inorganic particles 2 are crystalline particles, an inorganic structure 1 with high durability can be obtained as compared with the case of amorphous particles. Note that the fine particles 4 may be single crystal particles or polycrystalline particles. The fine particles 4 may contain at least one of the crystals of γ-alumina and η-alumina. Further, the fine particles 4 may contain at least one of the crystals of rutile-type titanium dioxide and anatase-type titanium dioxide.

[0023] The bonding portion 3 contains an amorphous compound containing at least one of aluminum and titanium and oxygen and one or more metal elements. The metal element contained in the bonding portion 3 is a metal element other than aluminum and titanium, and is, for example, at least one selected from the group consisting of alkaline earth metals, transition metals, base metals, and metalloids. The metal element contained in the bonding portion 3 may be zirconium.

[0024] Each of the plurality of fine particles 4 and the bonding portion 3 preferably contains the same metal element. For example, when the fine particles 4 contain aluminum, the bonding portion 3 preferably contains an amorphous compound containing aluminum. Further, when the fine particles 4 contain titanium, the bonding portion 3 preferably contains an amorphous compound containing titanium. When the fine particles 4 contain aluminum and titanium, the bonding portion 3 preferably contains an amorphous compound containing aluminum and titanium.

[0025] It is preferable that the joint portion 3 substantially does not contain an alkali metal element, B, V, Te, P, Bi, Pb, and Zn. Further, it is preferable that the joint portion 3 substantially does not contain Ca, Sr, and Ba. In this specification, "the joint portion substantially does not contain an alkali metal element, B, V, Te, P, Bi, Pb, and Zn" means that the joint portion 3 is not intentionally made to contain an alkali metal element, B, V, Te, P, Bi, Pb, and Zn. Therefore, when an alkali metal element, B, V, Te, P, Bi, Pb, and Zn are mixed as inevitable impurities into the joint portion 3, the condition that "the joint portion substantially does not contain an alkali metal element, B, V, Te, P, Bi, Pb, and Zn" is satisfied. Similarly, in this specification, "the joint portion substantially does not contain Ca, Sr, and Ba" means that the joint portion 3 is not intentionally made to contain Ca, Sr, and Ba. Therefore, when Ca, Sr, and Ba are mixed as inevitable impurities into the joint portion 3, the condition that "the joint portion substantially does not contain Ca, Sr, and Ba" is satisfied.

[0026] In the inorganic structure 1, the volume ratio of the plurality of inorganic particles 2 is 30% or more. In this case, the obtained inorganic structure 1 becomes a structure in which the characteristics of the inorganic particles 2 can be easily utilized. Specifically, when the inorganic particles 2 contain an inorganic compound having a low thermal conductivity, the heat insulation property of the entire inorganic structure 1 can be improved. Conversely, when the inorganic particles 2 contain an inorganic compound having a high thermal conductivity, the thermal conductivity of the entire inorganic structure 1 can be improved. It is preferable that the volume ratio of the inorganic particles 2 is larger than the volume ratio of the joint portion 3. Further, in the inorganic structure 1, it is more preferable that the volume ratio of the plurality of inorganic particles 2 is 50% or more.

[0027] Pores may be present inside the joint portion 3 and at least one location between the joint portion 3 and the inorganic particles 2. The porosity in the cross-section of the inorganic structure 1 is preferably 20% or less. That is, when observing the cross-section of the inorganic structure 1, the average value of the ratio of pores per unit area is preferably 20% or less. When the porosity is 20% or less, the ratio of the inorganic particles 2 being bonded by the joint portion 3 increases, so that the inorganic structure 1 becomes dense and the strength increases. Therefore, it becomes possible to improve the machinability of the inorganic structure 1. Further, when the porosity is 20% or less, the occurrence of cracks in the inorganic structure 1 starting from the pores is suppressed, so that the bending strength of the inorganic structure 1 can be increased. In addition, the porosity in the cross-section of the inorganic structure 1 is preferably 10% or less, more preferably 8% or less, and even more preferably 5% or less. The smaller the porosity in the cross-section of the inorganic structure 1, the more the cracks starting from the pores are suppressed, so that the strength of the inorganic structure 1 can be increased.

[0028] In this specification, the porosity can be determined as follows. First, observe the cross-section of the inorganic structure 1 to distinguish the inorganic particles 2, the joint portion 3, and the pores. Then, measure the unit area and the area of the pores in the unit area, obtain the ratio of the pores per unit area, and use that value as the porosity. It is more preferable to obtain the average value of the ratio of the pores per unit area at a plurality of locations with respect to the cross-section of the inorganic structure 1 and use the average value as the porosity. When observing the cross-section of the inorganic structure 1, an optical microscope, a scanning electron microscope (SEM), or a transmission electron microscope (TEM) can be used. Also, the unit area and the area of the pores in the unit area may be measured by binarizing the image observed with the microscope.

[0029] The size of the pores present inside the inorganic structure 1 is not particularly limited, but is preferably as small as possible. Small pore sizes suppress cracks originating from the pores, which makes it possible to increase the strength of the inorganic structure 1 and improve the machinability of the inorganic structure 1. The size of the pores in the inorganic structure 1 is preferably 5 μm or less, more preferably 1 μm or less, and even more preferably 100 nm or less. The size of the pores present inside the inorganic structure 1 can be determined by observing a cross section of the inorganic structure 1 with a microscope, similar to the above-mentioned porosity.

[0030] The inorganic structure 1 may have a structure in which the inorganic particles 2 are bonded to each other via the bonding portion 3. Therefore, as long as the inorganic structure 1 has such a structure, its shape is not limited. The shape of the inorganic structure 1 can be, for example, a plate-like, film-like, rectangular, block-like, rod-like, or spherical shape. In addition, when the inorganic structure 1 is a plate-like or film-like structure, its thickness is not particularly limited, but can be, for example, 100 μm or more. The inorganic structure 1 of this embodiment is formed by a pressurized heating method as described later. Therefore, an inorganic structure 1 having a large thickness can be easily obtained. The thickness of the inorganic structure 1 can be 500 μm or more, 1 mm or more, or 1 cm or more. The upper limit of the thickness of the inorganic structure 1 is not particularly limited, but can be, for example, 50 cm.

[0031] In the inorganic structure 1, the inorganic particles 2 are bonded to each other at the bonding parts 3, and are not bonded by an organic binder containing an organic compound, and are not bonded by any inorganic binder other than the bonding parts 3. Therefore, the inorganic structure 1 is a structure that retains the properties of the inorganic particles 2 and the bonding parts 3. For example, when the inorganic particles 2 and the bonding parts 3 contain an inorganic material having high thermal conductivity, the obtained inorganic structure 1 is also a structure with excellent thermal conductivity. Furthermore, when the inorganic particles 2 and the bonding parts 3 contain an inorganic material having high electrical insulation, the obtained inorganic structure 1 is also a structure with excellent electrical insulation.

[0032] As described above, the inorganic structure 1 of the present embodiment includes a plurality of inorganic particles 2 and a bonding portion 3 that covers the surface of each of the plurality of inorganic particles 2 and bonds each of the plurality of inorganic particles 2. The bonding portion 3 contains an amorphous compound containing at least one of aluminum and titanium, oxygen, and one or more metal elements, and a plurality of fine particles 4 having an average particle diameter of 100 nm or less. The average particle diameter of the plurality of inorganic particles 2 is 1 μm or more. The volume ratio of the plurality of inorganic particles 2 is 30% or more. In the inorganic structure 1, the plurality of inorganic particles 2 are bonded via a highly dense bonding portion 3. Therefore, an inorganic structure 1 excellent in density and mechanical strength can be obtained.

[0033] Note that, as shown in FIG. 1, the inorganic structure 1 of the present embodiment can be a structure in which only the inorganic particles 2 are bonded via the bonding portion 3. However, as will be described later, since the inorganic structure 1 can be obtained by pressurizing while heating at 50 to 300°C, a member having low heat resistance can be added to the inorganic structure 1. Specifically, the inorganic structure 1 may contain an organic substance or resin particles in addition to the inorganic particles 2 and the bonding portion 3. Further, it is not limited to a member having low heat resistance such as an organic substance, and the inorganic structure 1 may contain particles containing an inorganic compound other than the inorganic particles 2 and the bonding portion 3.

[0034] [Manufacturing Method of Inorganic Structure] Next, a manufacturing method of the inorganic structure 1 will be described. As shown in FIG. 2, the manufacturing method of the inorganic structure 1 includes a step of obtaining a mixture by mixing a plurality of inorganic particles 11, a plurality of fine particles 12, and an aqueous solution 13 containing a metal element, and a step of pressurizing and heating the mixture.

[0035] Specifically, first, a powder of inorganic particles 11, a powder of fine particles 12, and an aqueous solution 13 containing a metal element are mixed to prepare a mixture. The inorganic particles 11 may be composed of the same inorganic substance as the above-described inorganic particles 2. The average particle diameter of the plurality of inorganic particles 11 can adopt the same average particle diameter as the above-described plurality of inorganic particles 2 and is 1 μm or more. Further, the volume ratio of the plurality of inorganic particles 11 in the mixture is 30% or more, and preferably 50% or more.

[0036] The fine particles 12 contain at least one oxide selected from the group consisting of aluminum oxide, titanium oxide, and a composite oxide of aluminum and titanium. The average particle diameter of the plurality of fine particles can adopt the same average particle diameter as the above-described fine particles 4 and is 100 nm or less. Specifically, the fine particles 12 contain at least one selected from the group consisting of aluminum oxide particles, titanium oxide particles, and composite oxide particles of aluminum and titanium. Alumina particles are particles containing aluminum oxide. Titania particles are particles containing titanium oxide. Composite oxide particles of aluminum and titanium are particles containing a composite oxide of aluminum and titanium.

[0037] The fine particles 12 are preferably fume-like particles. That is, the aluminum oxide particles are preferably fumed alumina. Fumed alumina is particles produced by the combustion hydrolysis of aluminum trichloride. Also, the titanium oxide particles are preferably fumed titania. Fumed titania is particles produced by the combustion hydrolysis of titanium tetrachloride. Further, the composite oxide particles of aluminum and titanium are preferably fumed aluminum-titanium composite oxide. Fumed aluminum-titanium composite oxide is particles produced by the combustion hydrolysis of aluminum trichloride and titanium tetrachloride. The fume-like particles form bulky secondary particles by aggregation and agglomeration of primary particles. The fume-like particles have an average particle diameter of the primary particles of, for example, about 5 nm to 50 nm. Therefore, the fume-like particles have high reactivity with the aqueous solution 13 and can easily form an amorphous compound containing at least one of aluminum and titanium and oxygen and a metal element.

[0038] The aqueous solution 13 containing a metal element is an aqueous solution containing the metal element contained in the joint portion 3 as ions. The metal element contained in the aqueous solution 13 is preferably at least one selected from the group consisting of alkaline earth metals, transition metals, base metals, and metalloids as described above. Note that the solvent for dissolving the metal element is preferably pure water or ion-exchanged water. Note that the solvent may contain an acidic substance or an alkaline substance in addition to water, or may contain an organic solvent (for example, alcohol).

[0039] Specifically, when producing the inorganic structure 1 in which the bonding portion 3 contains an amorphous compound containing aluminum, oxygen, and zirconium, aluminum oxide particles can be used as the fine particles 12, and an aqueous solution of zirconium oxyacetate can be used as the aqueous solution 13. Further, when producing the inorganic structure 1 in which the bonding portion 3 contains an amorphous compound containing titanium, oxygen, and zirconium, titanium oxide particles can be used as the fine particles 12, and an aqueous solution of zirconium oxyacetate can be used as the aqueous solution 13. Further, when producing the inorganic structure 1 in which the bonding portion 3 contains an amorphous compound containing aluminum, titanium, oxygen, and zirconium, composite oxide particles of aluminum and titanium can be used as the fine particles 12, and an aqueous solution of zirconium oxyacetate can be used as the aqueous solution 13. Further, when producing the inorganic structure 1 in which the bonding portion 3 contains an amorphous compound containing aluminum, titanium, oxygen, and zirconium, aluminum oxide particles and titanium oxide particles can be used as the fine particles 12, and an aqueous solution of zirconium oxyacetate can be used as the aqueous solution 13.

[0040] Next, as shown in FIG. 2, a mixture obtained by mixing the inorganic particles 11, the fine particles 12, and the aqueous solution 13 is filled into the mold 14. After filling the mixture into the mold 14, the mold 14 is heated as necessary. Then, by applying pressure to the mixture inside the mold 14, the inside of the mold 14 becomes a high-pressure state. At this time, since the reactivity of the fine particles 12 is high, the fine particles 12 and the aqueous solution 13 react. Then, by taking out the molded body from the inside of the mold 14, the inorganic structure 1 in which a plurality of inorganic particles 2 are bonded via the bonding portion 3 can be obtained.

[0041] The heating and pressurizing conditions of the mixture formed by mixing the inorganic particles 11, the fine particles 12, and the aqueous solution 13 are not particularly limited as long as the reaction between the fine particles 12 and the aqueous solution 13 proceeds. For example, it is preferable to pressurize the above mixture at a pressure of 10 to 600 MPa while heating the mixture to 50 to 300°C. Note that the temperature when heating the above mixture is more preferably 80 to 250°C, and even more preferably 100 to 200°C. Also, the pressure when pressurizing the above mixture is more preferably 50 to 600 MPa, and even more preferably 200 to 600 MPa. The pressurization time is preferably 1 minute to 360 minutes, and more preferably 10 minutes to 240 minutes.

[0042] Through the above heating and pressurizing process, a part of the fine particles 12 reacts with the aqueous solution 13, and a bonding part 3 containing an amorphous compound containing at least one of aluminum and titanium and oxygen and one or more metal elements is formed. And the bonding part 3 covers the surface of each of the plurality of inorganic particles 2 and bonds each of the plurality of inorganic particles 2. Also, a part of the fine particles 12 does not react with the aqueous solution 13 and remains as the fine particles 4. Therefore, the bonding part 3 contains a plurality of fine particles with an average particle diameter of 100 nm or less.

[0043] Also, since the average particle diameter of the fine particles 12 is at the nano level, they are filled in the gaps between the inorganic particles 11 without any gaps. Therefore, the obtained bonding part 3 has a dense structure and can firmly bond the inorganic particles 11 to each other.

[0044] Here, as a method for forming an aggregate of inorganic particles, a method of pressing only the powder of inorganic particles can be considered. However, even if the powder of inorganic particles is put into a mold and pressurized at room temperature, it is difficult for the particles of inorganic particles to react with each other, and it is difficult to firmly bond the particles to each other. Therefore, many pores exist in the obtained compacted powder, and the mechanical strength is insufficient.

[0045] In addition, as a method for forming aggregates of inorganic particles, a method of pressing only the powder of inorganic particles to form a compact and then sintering at a high temperature (for example, 1700 °C or higher) can be considered. However, even when the compact of inorganic particles is sintered at a high temperature, many pores exist in the resulting structure, and the mechanical strength is insufficient. Further, when sintering inorganic particles at a high temperature, precise temperature control is required, which increases the manufacturing cost.

[0046] On the other hand, in the manufacturing method of the present embodiment, since the mixture formed by mixing the inorganic particles 11, the fine particles 12, and the aqueous solution 13 is pressurized while being heated, a dense and strong structure can be obtained. Further, since the manufacturing method of the present embodiment can be obtained by pressurizing while heating at 50 to 300 °C, precise temperature control is not required, and the manufacturing cost can be reduced.

[0047] Thus, the manufacturing method of the inorganic structure 1 of the present embodiment includes a step of obtaining a mixture by mixing a plurality of inorganic particles 11, a plurality of fine particles 12, and an aqueous solution 13 containing a metal element. The manufacturing method further includes a step of pressurizing and heating the mixture under conditions where the pressure is 10 to 600 MPa and the temperature is 50 to 300 °C. The average particle diameter of the plurality of inorganic particles 11 is 1 μm or more. The plurality of fine particles 12 include at least one oxide selected from the group consisting of aluminum oxide, titanium oxide, and a composite oxide of aluminum and titanium, and the average particle diameter is 100 nm or less. The volume ratio of the plurality of inorganic particles 11 in the mixture is 30% or more. Therefore, the manufacturing method of the present embodiment can produce the inorganic structure 1 with high density by a simple method.

[0048] [Member provided with inorganic structure] Next, the member provided with the inorganic structure 1 will be described. As described above, the inorganic structure 1 can be a plate shape with a large thickness, and since it is denser, it also has excellent chemical stability. Further, the inorganic structure 1 has high mechanical strength and can be cut in the same manner as a general ceramic member, and its surface can also be processed. Therefore, the inorganic structure 1 can be suitably used as a building member. The building member is not particularly limited, and examples thereof include exterior wall materials (siding), roofing materials, etc. Further, as building members, road materials and outer groove materials can also be mentioned.

[0049] The inorganic structure 1 can also be suitably used as a member for electronic devices. Examples of members for electronic devices include structural materials, heat-resistant members, insulating members, heat-radiating members, heat-insulating members, sealing materials, circuit boards, optical members, etc.

Examples

[0050] Hereinafter, the present embodiment will be described in more detail with reference to examples and reference examples, but the present embodiment is not limited to these examples.

[0051] [Preparation of test samples] (Example 1) First, powders of first alumina particles with an average particle diameter of about 20 μm (Advanced Alumina AA-18 manufactured by Sumitomo Chemical Co., Ltd.) were prepared. Also, powders of second alumina particles with an average particle diameter of about 15 nm (fumed alumina, AEROXIDE (registered trademark) Alu C manufactured by Nippon Aerosil Co., Ltd.) were prepared. Next, 0.2 g of the first alumina powder and 0.2 g of the second alumina powder were mixed using an agate mortar and an agate pestle, and acetone was added for mixing to obtain a mixed powder. In the mixed powder, the volume ratio (vol%) of the first alumina powder to the second alumina powder was 50:50.

[0052] Also, zirconium oxyacetate powder (ZrO(CH 3 COO) 2, 4 g of zirconium oxyacetate (manufactured by Mitsuwa Chemical Co., Ltd.) was dissolved in 6 ml of ion-exchanged water to obtain a 40% aqueous zirconium oxyacetate solution.

[0053] Next, the total amount of the mixed powder was put into the inside of a cylindrical mold for molding (Φ10) having an internal space. Further, 100 μl of the aqueous zirconium oxyacetate solution was added to the inside of the mold for molding and mixed with a plastic spatula.

[0054] Then, the mixed powder containing the aqueous zirconium oxyacetate solution was heated and pressurized under the conditions of 200 °C, 400 MPa, and 60 minutes. In this way, the test sample of the present example in a columnar shape was obtained.

[0055] (Reference Example 1) First, 0.3 g of the same second alumina powder as in Example 1 was put into the inside of a cylindrical mold for molding (Φ10) having an internal space. Further, 300 μl of the aqueous zirconium oxyacetate solution prepared in Example 1 was added to the inside of the mold for molding and mixed with a plastic spatula.

[0056] Then, the second alumina powder containing the aqueous zirconium oxyacetate solution was heated and pressurized under the conditions of 200 °C, 400 MPa, and 60 minutes to obtain a test sample containing no first alumina particles.

[0057] (Reference Example 2) A test sample was prepared in the same manner as in Reference Example 1, except that the mixed powder containing the aqueous zirconium oxyacetate solution was heated and pressurized under the conditions of 200 °C, 400 MPa, and 240 minutes.

[0058] [Evaluation of Test Samples] For the test samples prepared as described above, structural observation, elemental analysis, crystal structure analysis, pore observation, and porosity measurement were performed.

[0059] (Structural Observation) The cross-section of the columnar test sample produced in Example 1 after being cut was observed using a scanning electron microscope (SEM). The observation surface of the test sample was sputtered with gold. In FIG. 3, an SEM image of the test sample of Example 1 magnified 500 times is shown. In FIG. 4, an SEM image of the test sample of Example 1 magnified 2000 times is shown. Also, for reference, in FIG. 5, an SEM image of the second alumina powder magnified 2000 times is shown. In FIG. 6, an SEM image of the second alumina powder magnified 10000 times is shown. In FIG. 7, an SEM image of the test sample of Reference Example 1 magnified 2000 times is shown. In FIG. 8, an SEM image of the test sample of Reference Example 1 magnified 10000 times is shown.

[0060] In the test sample of Reference Example 1 shown in FIGS. 7 and 8, it can be seen that the fine particles 4 derived from the second alumina powder shown in FIGS. 5 and 6 are bonded to each other. From this, in the test sample of Example 1 shown in FIGS. 3 and 4, it can be understood that the bonding part 3 covers the surface of each of the first alumina particles (a plurality of inorganic particles 2) and bonds each of the first alumina particles.

[0061] (Elemental analysis) The cross-section of the columnar test sample produced in Example 1 after being cut was observed using an energy dispersive X-ray analyzer (EDX). In FIG. 9, the EDX spectrum of the part where particles exist in the test sample of Example 1 is shown. In FIG. 10, the EDX spectrum of the part where the particles are bonded in the test sample of Example 1 is shown. In FIG. 11, the result of the mapping analysis in the test sample of Example 1 is shown.

[0062] From the EDX spectrum in Fig. 9 and the results of the mapping analysis in Fig. 11, it was confirmed that the part where the particles exist contains aluminum (Al) and oxygen (O), and thus it is derived from the first alumina particles (inorganic particles 2) of the raw material. Also, from the EDX spectrum in Fig. 10 and the results of the mapping analysis in Fig. 11, the part binding the particles (bonding part 3) contains aluminum (Al), zirconium (Zr), and oxygen (O), and Al, Zr, and O are uniformly dispersed. From this, it is suggested that an Al-Zr-O-based compound generated by the reaction of the second alumina particles (fine particles 4) of the raw material with an aqueous zirconium oxyacetate solution exists. Although a trace amount of carbon (C) exists in the bonding part 3, this is considered to be an organic residue derived from the aqueous zirconium oxyacetate solution of the raw material.

[0063] (Crystal Structure Analysis) Using a powder X-ray diffraction (XRD) apparatus, a powder obtained by pulverizing the test sample of Reference Example 2 was measured to obtain an XRD pattern. Fig. 12 shows the XRD patterns of the second alumina powder (fumed alumina) as the raw material, the XRD pattern of the test sample of Reference Example 2, and the XRD patterns of γ-alumina and η-alumina registered in the ICSD.

[0064] As shown in Fig. 12, peaks similar to those of the second alumina powder as the raw material were confirmed in the XRD pattern of the test sample of Reference Example 2. These peaks coincide with the peaks included in the XRD patterns of α-alumina and η-alumina. From these results, it is considered that the bonding part 3 contains crystals of α-alumina and η-alumina derived from the second alumina particles as the raw material, and at least a part of the second alumina particles remains as fine particles 4 with an average particle diameter of 100 nm or less without reacting.

[0065] In addition, the test sample of Reference Example 1 with a pressure application time of 60 minutes was also measured, and an XRD pattern similar to that of the test sample of Reference Example 2 with a pressure application time of 240 minutes was obtained. From this, it is considered that even if the pressure application time is increased from 60 minutes to 240 minutes, the crystal phase does not change significantly and the fine particles 4 remain.

[0066] In addition, no peak derived from zirconium is observed in the XRD pattern of the test sample of Reference Example 2. Although the test sample of Reference Example 2 does not contain the first alumina powder, since the first alumina powder contains aluminum oxide in the same manner as the second alumina powder, it is expected that the test sample of Example 1 will also obtain an XRD pattern similar to that of Reference Example 2. Therefore, it is considered that the joint portion 3 of the test sample of Example 1 contains an amorphous compound containing Zr and fine particles 4.

[0067] From the results of the elemental analysis described above, it was confirmed that the joint portion 3 contains aluminum, oxygen, and zirconium. And from the results of the crystal structure analysis, no peak derived from zirconium was observed in the XRD pattern of the test sample of Reference Example 2. From these results, it is considered that the joint portion 3 contains an amorphous compound containing aluminum, oxygen, and zirconium.

[0068] (Observation of pores) First, cross-section polishing (CP processing) was performed on the cross-section of the columnar test sample of Example 1. Next, using a scanning electron microscope (SEM), SEM images of the cross-section of the test sample were observed at magnifications of 2000 times, 5000 times, 10000 times, and 50000 times. Figures 13, 14, 15, and 16 show SEM images of the cross-section of the test sample of Example 1 magnified 2000 times, 5000 times, 10000 times, and 50000 times, respectively.

[0069] From the SEM images of Figures 13 to 16, voids were present between the inorganic particles 2 and the joint portion 3 in the test sample of Example 1, and cracks starting from these voids were observed. However, it was confirmed that the test sample of Example 1 has a dense structure with few macropores and does not have as many pores as those found in conventional compacted powders obtained by pressing only inorganic particle powders.

[0070] (Measurement of porosity) First, cross-section polishing (CP processing) was performed on the cross-section of the test sample of Example 1, which is cylindrical. Next, using a scanning electron microscope (SEM), the cross-section of the test sample was observed at a magnification of 2000 times to obtain an SEM image. The SEM image obtained by observing the cross-section of the test sample is shown in FIG. 17. Next, the obtained SEM image was binarized to clarify the pore portion. Then, the area ratio of the pore portion was calculated from the binarized image to obtain the porosity. The binarized image of the SEM image in FIG. 17 is shown in FIG. 18. Note that the black portion in the binarized image is the pore.

[0071] As a result of calculating the porosity from the binarized image in FIG. 18, the porosity was 4.3%. In addition, the porosity was calculated in the same manner as above at two locations different from FIG. 18. As a result, the average value of the porosity at three locations was 3.2%, and a very small porosity value was obtained.

[0072] [Preparation of Test Sample] (Example 2) First, a powder of first alumina particles with an average particle diameter of about 20 μm (Advanced Alumina AA-18 manufactured by Sumitomo Chemical Co., Ltd.) was prepared. Also, a powder of second titania particles with an average particle diameter of about 20 nm (fumed titania, AEROXIDE (registered trademark) TiO 2 P25 manufactured by Nippon Aerosil Co., Ltd.) was prepared. Next, 0.197 g of the above first alumina powder and 0.203 g of the above titania powder were mixed by adding acetone using an agate mortar and an agate pestle to obtain a mixed powder. In the mixed powder, the volume ratio (vol%) of the first alumina powder to the titania powder was 50:50.

[0073] Also, 4 g of zirconium oxyacetate powder (ZrO(CH 3 COO) 2 , manufactured by Mitsuwa Chemical Co., Ltd.) was dissolved in 6 ml of ion-exchanged water to obtain a 40% aqueous zirconium oxyacetate solution.

[0074] Next, the total amount of the mixed powder was put into the inside of a cylindrical molding die (Φ10) having an internal space. Further, 150 μl of an aqueous solution of zirconium oxyacetate was added to the inside of the molding die and mixed with a plastic spatula.

[0075] Then, the mixed powder containing the aqueous solution of zirconium oxyacetate was heated and pressurized under the conditions of 200 °C, 400 MPa, and 30 minutes. In this way, the test sample of the present example in a columnar shape was obtained.

[0076] (Reference Example 3) First, 0.3 g of the same titania powder as in Example 2 was put into the inside of a cylindrical molding die (Φ10) having an internal space. Further, 150 μl of the aqueous solution of zirconium oxyacetate prepared in Example 2 was added to the inside of the molding die and mixed with a plastic spatula.

[0077] Then, the titania powder containing the aqueous solution of zirconium oxyacetate was heated and pressurized under the conditions of 200 °C, 400 MPa, and 30 minutes to obtain a test sample not containing first alumina particles.

[0078] [Evaluation of Test Samples] For the test samples prepared as described above, structural observation, elemental analysis, crystal structure analysis, pore observation, and porosity measurement were performed.

[0079] (Structural Observation) The cross-section of the cylindrical test sample prepared in Example 2 was observed using a scanning electron microscope (SEM). The observation surface of the test sample was subjected to gold sputtering. In Fig. 19, an SEM image of the test sample of Example 2 magnified 500 times is shown. In Fig. 20, an SEM image of the test sample of Example 2 magnified 2000 times is shown. For reference, in Fig. 21, an SEM image of the titania powder magnified 2000 times is shown. In Fig. 22, an SEM image of the titania powder magnified 10000 times is shown. In Fig. 23, an SEM image of the test sample of Reference Example 3 magnified 2000 times is shown. In Fig. 24, an SEM image of the test sample of Reference Example 3 magnified 10000 times is shown.

[0080] In the test samples of Reference Example 3 shown in Figs. 23 and 24, it can be seen that the fine particles 4 derived from the titania powder shown in Figs. 21 and 22 are bonded to each other. From this, it can be understood that in the test samples of Example 2 shown in Figs. 19 and 20, the bonding portion 3 covers the surface of each of the first alumina particles (a plurality of inorganic particles 2) and bonds each of the first alumina particles.

[0081] (Elemental analysis) The cross-section of the cylindrical test sample prepared in Example 2 was observed using an energy dispersive X-ray analyzer (EDX). In Fig. 25, the EDX spectrum of the portion where particles exist in the test sample of Example 2 is shown. In Fig. 26, the EDX spectrum of the portion bonding the particles in the test sample of Example 2 is shown. In Fig. 27, the result of the mapping analysis in the test sample of Example 2 is shown.

[0082] From the EDX spectrum of Fig. 25 and the results of the mapping analysis of Fig. 27, since the part where the particles are present contains aluminum (Al) and oxygen (O), it was confirmed that it is derived from the first alumina particles (inorganic particles 2) of the raw material. Also, from the EDX spectrum of Fig. 26 and the results of the mapping analysis of Fig. 27, the part binding the particles (binding part 3) contains titanium (Ti), zirconium (Zr), and oxygen (O), and Ti, Zr, and O are uniformly dispersed. From this, it is suggested that a Ti-Zr-O-based compound generated by the reaction of the second titania particles (fine particles 4) of the raw material and the zirconium oxyacetate aqueous solution exists. Although a trace amount of C is present in the binding part 3, this is considered to be an organic residue derived from the zirconium oxyacetate aqueous solution of the raw material.

[0083] (Crystal Structure Analysis) Using a powder X-ray diffraction (XRD) apparatus, a powder obtained by pulverizing the test sample of Reference Example 3 was measured to obtain an XRD pattern. In Fig. 28, the XRD pattern of the titania powder (fumed titania) as the raw material, the XRD pattern of the test sample of Reference Example 3, and the rutile-type TiO registered in the ICSD 2 and the XRD pattern of anatase-type TiO 2 are shown.

[0084] As shown in Fig. 28, peaks similar to those of the titania powder as the raw material were confirmed in the XRD pattern of the test sample of Reference Example 3. These peaks match the peaks included in the XRD patterns of rutile-type TiO 2 and anatase-type TiO 2 . From these results, it is considered that the binding part 3 contains crystals of rutile-type TiO 2 and anatase-type TiO 2 derived from the second titania particles as the raw material, and at least a part of the second titania particles remains as fine particles 4 with an average particle diameter of 100 nm or less without reacting.

[0085] In addition, in the XRD pattern of the test sample of Reference Example 3, no peak derived from zirconium was observed. Also, from the results of the elemental analysis described above, it was confirmed that the joint portion 3 hardly contained aluminum. From these results, it is considered that the joint portion 3 contains an amorphous compound containing titanium, oxygen, and zirconium.

[0086] (Observation of pores) First, cross-section polisher processing (CP processing) was performed on the cross-section of the columnar test sample of Example 2. Next, using a scanning electron microscope (SEM), SEM images of the cross-section of the test sample were observed at magnifications of 2000 times, 5000 times, 10000 times, and 50000 times. FIGS. 29, 30, 31, and 32 show SEM images of the cross-section of the test sample of Example 2 magnified 2000 times, 5000 times, 10000 times, and 50000 times, respectively.

[0087] From the SEM images of FIGS. 29 to 32, voids were observed between the inorganic particles 2 and the joint portion 3 in the test sample of Example 2. However, it was confirmed that the test sample of Example 2 did not have as many pores as those in a conventional compact obtained by pressing only the powder of the inorganic particles, and had a dense structure with few macropores. Also, the test sample of Example 2 had fewer cracks starting from the voids between the inorganic particles 2 and the joint portion 3 as seen in the test sample of Example 1.

[0088] (Measurement of porosity) First, cross-section polisher processing (CP processing) was performed on the cross-section of the columnar test sample of Example 2. Next, using a scanning electron microscope (SEM), an SEM image of the cross-section of the test sample was observed at a magnification of 2000 times. The SEM image obtained by observing the cross-section of the test sample is shown in FIG. 33. Next, the obtained SEM image was binarized to clarify the pore portion. FIG. 34 shows the binarized image of the SEM image of FIG. 33. Then, the area ratio of the pore portion was calculated from the binarized image to obtain the porosity. Note that the black portion in the binarized image is the pore.

[0089] As a result of calculating the porosity from the binarized image of Fig. 34, the porosity was 1.1%. In addition, the porosity was calculated in the same manner as above for two locations different from Fig. 34. As a result, the average value of the porosity at three locations was 1.7%, and a very small porosity value was obtained.

[0090] In Example 1, fumed alumina was used as the fine particles 4, and in Example 2, fumed titania was used as the fine particles 4 to produce the inorganic structure 1. However, even when fumed aluminum-titanium composite oxide is used as the fine particles 4, it is considered that the same inorganic structure 1 as fumed alumina and fumed titania can be obtained.

[0091] The entire contents of Japanese Patent Application No. 2021-021639 (filing date: February 15, 2021) are incorporated herein by reference.

[0092] As described above, although this embodiment has been described, this embodiment is not limited to these, and various modifications are possible within the scope of the gist of this embodiment.

Industrial Applicability

[0093] According to the present disclosure, it is possible to provide an inorganic structure that can be produced by a simple method and has higher density, and a method for manufacturing the inorganic structure.

Explanation of Reference Numerals

[0094] 1 Inorganic structure 2 Inorganic particles 3 Bonding part 4 Fine particles 11 Inorganic particles 12 Fine particles 13 Aqueous solution containing a metal element

Claims

1. A plurality of inorganic particles, a bonding portion that covers the surface of each of the plurality of inorganic particles and bonds each of the plurality of inorganic particles, and comprising, the bonding portion contains an amorphous compound containing at least one of aluminum and titanium, oxygen, and one or more metal elements, and at least one oxide selected from the group consisting of aluminum oxide, titanium oxide, and a composite oxide of aluminum and titanium, and contains a plurality of fine particles having an average particle diameter of 100 nm or less, the average particle diameter of the plurality of inorganic particles is 1 μm or more, the volume ratio of the plurality of inorganic particles is 30% or more, the metal element contains zirconium, an inorganic structure having a porosity of 20% or less.

2. The inorganic structure according to claim 1, wherein the bonding portion substantially does not contain an alkali metal element, B, V, Te, P, Bi, Pb, and Zn.

3. The inorganic structure according to claim 1 or 2, wherein the bonding portion substantially does not contain Ca, Sr, and Ba.

4. The inorganic structure according to any one of claims 1 to 3, wherein the volume ratio of the plurality of inorganic particles is 50% or more.

5. The inorganic structure according to any one of claims 1 to 4, wherein each of the plurality of inorganic particles is crystalline.

6. The inorganic structure according to any one of claims 1 to 5, having a thickness of 100 μm or more.

7. A step of obtaining a mixture by mixing a plurality of inorganic particles having an average particle diameter of 1 μm or more, at least one oxide selected from the group consisting of aluminum oxide, titanium oxide, and a composite oxide of aluminum and titanium, a plurality of fine particles having an average particle diameter of 100 nm or less, and an aqueous solution containing a metal element; a step of pressurizing and heating the mixture under conditions where the pressure is 10 to 600 MPa and the temperature is 50 to 300 °C; and comprising, the volume ratio of the plurality of inorganic particles in the mixture is 30% or more, a method for producing an inorganic structure, wherein the metal element contains zirconium.

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