WO2025197973A1 - Alumina porous body, ceramic filter, and method for producing alumina porous body - Google Patents

Abstract

An alumina porous body (1) contains Al₂O₃ and TiO₂. The content of TiO₂ in the alumina porous body (1) is 10-40 mass%. The porosity of the alumina porous body (1) is 10-45%. The alumina porous body (1) has an average pore diameter of 2-12 μm. In the alumina porous body (1), the binding ratio of Al₂O₃ particles (92) to TiO₂ domains (93) is 5% or more. As a result, it is possible to increase the strength of the alumina porous body (1) having a desired porosity and average pore diameter.

Description

Alumina porous body, ceramic filter, and method for manufacturing alumina porous body

The present invention relates to an alumina porous body, a ceramic filter, and a method for producing an alumina porous body.
[Reference to Related Applications]
This application claims the benefit of priority from Japanese Patent Application JP2024-046416, filed on March 22, 2024, the entire disclosure of which is incorporated herein by reference.

Traditionally, filters made of porous ceramics (i.e., ceramic filters) have been used as filters for solid-liquid separation or gas-solid separation to remove solids (e.g., suspended matter) contained in fluids such as liquids and gases. A typical ceramic filter comprises a substrate (i.e., support), which is a porous body in which aggregate particles made of ceramic particles such as alumina are bonded together by a binder phase, and a porous membrane (i.e., filtration membrane) laminated on the surface of the substrate and having an average pore diameter smaller than that of the substrate.

With such ceramic filters, suspended matter contained in the fluid being treated becomes clogged in the pores of the ceramic filter over time, reducing its permeability. For this reason, it is necessary to perform chemical washing or backwashing at regular intervals to remove suspended matter that has clogged the pores.

Chemical washing is a cleaning process that uses a chemical solution suitable for dissolving suspended solids, etc., and is usually carried out to dissolve and remove suspended solids that have accumulated over a long period of time. Examples of such chemical solutions include alkaline solutions such as aqueous sodium hydroxide solutions, or acidic solutions such as aqueous citric acid solutions. Backwashing is a cleaning process that, contrary to normal filtration processes, applies pressure to the fluid flow from the fluid permeation side of the ceramic filter to the supply side of the fluid being treated, removing suspended solids that have clogged the pores and discharging them outside the system. Backwashing is usually carried out to remove suspended solids that have accumulated over a short period of time. Backwashing is carried out between filtration processes, for example, every few minutes to several hours.

In ceramic filters, the strength of the substrate decreases due to the repeated chemical washing and backwashing described above. Specifically, the chemicals used during chemical washing chemically erode the binder phase of the substrate, reducing the bonding strength between the aggregate particles. In addition, backwashing is performed at a higher pressure than during normal filtration processes, which also causes physical erosion of the binder phase. As a result, the strength of the entire substrate and the entire ceramic filter decreases.

In response to this, Japanese Patent Laid-Open No. 2010-228946 (Document 1) proposes that alumina, which has high corrosion resistance against chemical solutions, be used as the main component of the binder phase in an alumina-based porous body used in a ceramic filter. Japanese Patent Laid-Open No. 2010-228948 (Document 2) proposes that titania, which has high corrosion resistance against chemical solutions, be used as the main component of the binder phase in an alumina-based porous body used in a ceramic filter. Furthermore, in Documents 1 and 2, copper oxide (CuO), manganese oxide (MnO ₂ ), or the like is added as a sintering aid during the production of the alumina-based porous body, thereby improving the sinterability of the alumina-based porous body and increasing its strength.

However, the alumina porous bodies described in References 1 and 2 use relatively expensive materials such as copper (Cu) and manganese (Mn) as sintering aids, which increases the manufacturing costs of the alumina porous bodies. There is also a risk that the copper and other materials may contaminate the firing furnace.

On the other hand, if an alumina porous body is produced without using such sintering aids, the strength of the alumina porous body may be reduced. Furthermore, if the amount of raw material for the binder phase is increased or the particle size of the raw material for the aggregate particles is reduced in an attempt to prevent a decrease in the strength of the alumina porous body, the porosity and average pore diameter of the alumina porous body may become excessively small, and the alumina porous body may not meet the performance requirements for use as a substrate for a ceramic filter, etc.

The present invention is directed to an alumina porous body, and aims to increase the strength of an alumina porous body having a desired porosity and average pore diameter.

A first aspect of the invention is an alumina porous body comprising _Al2O3 and _TiO2 . _{The TiO2} content is 10% by mass _or more and 40% by mass or less. The porosity is 10% by mass or more and 45% by mass or less. The average pore diameter is 2 μm or more and 12 μm or less. The bonding ratio between _{the Al2O3} particles and the _TiO2 domains is 5% or more.

According to the present invention, the strength of alumina porous bodies can be increased.

Aspect 2 of the invention is an alumina porous body according to aspect 1, in which the porosity is 20% or more and the average pore diameter is 5 μm or more.

A third aspect of the present invention is the alumina porous body of the first aspect, wherein the total content of Al ₂ O ₃ and TiO ₂ is 100 mass %.

Aspect 4 of the invention is the alumina porous body of aspect 1, further containing Ca. The Ca content in the alumina porous body is 0.1 mass% or more and 1.5 mass% or less, calculated as oxide.

Aspect 5 of the invention is an alumina porous body according to aspect 1 (or any one of aspects 1 to 3), having a bending strength of 15 MPa or more.

Aspect 6 of the invention is an alumina porous body according to aspect 5, in which the body is immersed in an alkaline chemical solution, which is a sodium hydroxide aqueous solution with a pH of 13, at 80°C for 60 hours, followed by washing to remove the alkaline chemical solution and drying. The post-treatment strength, which is the bending strength after the alkaline immersion treatment, and the initial strength, which is the bending strength before the alkaline immersion treatment, have a strength reduction rate, which is the rate at which the post-treatment strength is reduced from the initial strength, of 20% or less.

Aspect 7 of the invention is an alumina porous body according to any one of aspects 1 to 6, which is used as a ceramic filter.

Aspect 8 of the invention is a ceramic filter comprising an alumina porous body according to any one of aspects 1 to 6, and a porous ceramic membrane provided on the surface of the alumina porous body and having an average pore diameter smaller than that of the alumina porous body.

A ninth aspect of the invention is a method for producing an alumina-based porous body, comprising: a) a step of forming a raw material mixture containing Al ₂ O ₃ particles and TiO ₂ particles to obtain a molded body; and b) a step of firing the molded body to obtain an alumina-based porous body.

A tenth aspect of the present invention is the method for producing an alumina porous body according to the ninth aspect, wherein the _TiO2 particles contained in the raw material mixture are coated with aluminum hydroxide.

An eleventh aspect of the invention is the method for producing an alumina-based porous body according to the ninth or tenth aspect, wherein the total content of the Al ₂ O ₃ particles and the TiO ₂ particles in the material constituting the alumina-based porous body in the raw material mixture is 100 mass %.

A twelfth aspect of the invention is the method for producing an alumina porous body according to aspect 9 or 10, wherein the raw material mixture further contains a sintering aid containing Ca. The content of the sintering aid in the material constituting the alumina porous body in the raw material mixture is 0.1% by mass or more and 1.5% by mass or less.

Aspect 13 of the invention is a method for producing an alumina porous body according to aspect 9 or 10, wherein the firing temperature in step b) is 1200°C or higher and 1450°C or lower.

The above and other objects, features, aspects and advantages will become apparent from the following detailed description of the present invention, which proceeds with reference to the accompanying drawings.

1 is a perspective view of an alumina porous body according to one embodiment. 1 is a SEM image showing the microstructure of an alumina porous body. FIG. 2 is a diagram showing the flow of manufacturing an alumina porous body.

FIG. 1 is a perspective view showing an alumina porous body 1 according to one embodiment of the present invention. The alumina porous body 1 shown in FIG. 1 has a substantially cylindrical outer shape. The alumina porous body 1 has a monolithic shape with a plurality of cells 2 (i.e., through holes) penetrating in the longitudinal direction. In the example shown in FIG. 1, the cross section perpendicular to the longitudinal direction of each cell 2 is substantially circular. The alumina porous body 1 is used, for example, as a ceramic filter for solid-liquid separation used in water treatment. Alternatively, the alumina porous body 1 is used as the substrate for such a ceramic filter. The shape of the alumina porous body 1 is not limited to a monolithic shape and may be variously modified, such as a substantially cylindrical shape or a substantially flat plate shape. Furthermore, the use of the alumina porous body 1 is not limited to ceramic filters and ceramic filter substrates and may be variously modified.

The alumina porous body 1 contains alumina (Al ₂ O ₃ ) and titania (TiO ₂ ). The alumina porous body 1 is a porous body whose main component is Al ₂ O ₃ (aluminum oxide). In the alumina porous body 1, Al ₂ O ₃ constitutes aggregate particles, and TiO ₂ (titanium oxide) constitutes a binder phase that bonds the aggregate particles together. Note that the term "porous body whose main component is Al ₂ O ₃ " refers to a porous body in which the proportion of Al ₂ O ₃ in the entire porous body is 50 mass % or more.

The Al ₂ O ₃ content in the alumina porous body 1 is 50 mass% or more and 90 mass% or less. The Al ₂ O ₃ content is preferably 60 mass% or more, and more preferably 70 mass% or more. The Al ₂ O ₃ content is preferably 85 mass% or less, and more preferably 80 mass% or less.

The _TiO2 content in the alumina porous body 1 is 10% by mass or more and 40% by mass or less. The _TiO2 content is preferably 15% by mass or more, and more preferably 20% by mass or more. The _TiO2 content is preferably 35% by mass or less, and more preferably 30% by mass or less.

By setting the _TiO2 content to 10% by mass or more, strong bonding between aggregate particles (i.e., _{Al2O3 particles} ) is achieved, thereby increasing the strength of the alumina porous body 1. Furthermore, by setting the _TiO2 content to 40% by mass or less, it is possible to increase the porosity and average pore diameter (also referred to as average pore diameter) of the alumina porous body 1. As a result, when the alumina porous body 1 is used, for example, in a ceramic filter for solid-liquid separation or as a substrate for the ceramic filter, a sufficient amount of liquid permeation can be obtained.

In the alumina porous body 1, the binder phase that bonds the aggregate particles is not a glass phase, which has low corrosion resistance to alkaline and acidic solutions, but a phase mainly composed of _TiO2 , which has high corrosion resistance. Therefore, the alumina porous body 1 exhibits excellent corrosion resistance to alkaline and acidic solutions, and strength degradation is suppressed even in harsh environments where it is frequently exposed to these solutions. Note that "a binder phase mainly composed of _TiO2 " means a binder phase in which the proportion of _TiO2 in the entire binder phase is 50 mass% or more.

The alumina porous body 1 may contain substances other than Al ₂ O ₃ and TiO _2. However, the alumina porous body 1 does not contain copper (Cu) or Cu compounds, or manganese (Mn) or Mn compounds. In other words, the Cu content and Mn content in the alumina porous body 1 are each 0.00 mass%.

Preferably, the alumina porous body 1 is formed substantially only of _{Al2O3 and TiO2} . In other words, the total content _{of Al2O3} and _TiO2 in the alumina porous body 1 is preferably substantially 100 mass%. In this case, in the alumina porous body 1, the aggregate particles are formed substantially only _{of Al2O3} , and the binder phase is formed only of _TiO2 .

In this specification, "the total content of _Al2O3 and _TiO2 is 100% _by mass" means that the content of substances other than _Al2O3 and _TiO2 in the alumina porous body 1 is less than 0.05% by mass in terms of oxides. For example, the alumina porous body 1 _may contain calcium (Ca) derived from the raw material _{for Al2O3} as an impurity in an amount of about 0.02% by mass in terms of oxides (i.e., assuming that all of the Ca in the alumina porous body 1 is calcium oxide (CaO)). In this case, too, if the alumina porous body 1 does not substantially contain any substances other than Ca as an impurity, or if the total content of impurities including Ca is less than 0.05% by mass in terms of oxides, the total content of _Al2O3 and _TiO2 in the _alumina porous body 1 is considered to be 100% by mass. The alumina porous body 1 does not contain Cu or Mn as impurities.

In this specification, the contents of Al ₂ O ₃ and TiO ₂ are measured by the method for chemical analysis of ceramic raw materials (in accordance with JIS M 8853). The content of Ca in terms of oxide is also measured by the method for chemical analysis of ceramic raw materials (in accordance with JIS M 8853).

Fig. 2 is a scanning electron microscope (SEM) image showing an example of the microstructure of an alumina porous body 1. In the example shown in Fig. 2, the total content of _Al2O3 and _TiO2 in the alumina porous body 1 is ₁₀₀ mass%. The black parts in Fig. 2 are pores 91, the dark gray parts are aggregate particles (i.e., _{Al2O3 particles} ) 92 formed _{by Al2O3} , and the white or light gray parts are binder phases 93 formed by _TiO2 . In the following description, the binder phases 93 are also referred to as " _TiO2 domains 93."

2 , the portion of the outer periphery of an Al ₂ O ₃ particle 92 that is in contact with a TiO ₂ domain 93 is the bonding portion with the TiO ₂ domain 93 in the Al ₂ O ₃ particle 92. Furthermore, the portion of the outer periphery of an Al ₂ O ₃ particle 92 that is not in contact with the TiO ₂ domain 93 is the portion facing the pore in the Al ₂ O ₃ particle 92 (i.e., forming the inner wall of the pore), or the portion in contact with an adjacent Al ₂ O ₃ particle 92.

In the alumina porous body 1, the bonding ratio between the _{Al2O3 particles} 92 and the _TiO2 domains 93 is 5% or more, preferably 12% or more, and more preferably 15% or more. By setting the bonding ratio to 5% or more, strong bonding between the aggregate particles is realized, and the strength of the alumina porous body 1 can be increased.

The bonding ratio is determined as follows. First, an SEM image such as that shown in FIG. 2 is binarized. Next, the entire peripheral edge length (hereinafter also referred to as "particle perimeter") of each _Al2O3 particle ₉₂ is measured in the binarized SEM image. Next, the _TiO2 domains 93 are expanded in the binarized SEM image, and then, for each _Al2O3 particle ₉₂ , the portion of the peripheral edge of the _Al2O3 particle ₉₂ that is in contact with the _TiO2 domain 93 is extracted, and the length of that portion (hereinafter also referred to as "contact length") is measured. In FIG. 2, the peripheral edge of one _Al2O3 particle ₉₂ located slightly to the right of the center of the figure is indicated by a thick black solid line, and the portion of the peripheral edge that is in contact with the _TiO2 domain 93 is indicated by a thick white dashed line that aligns with the thick black solid line. Then, the above-mentioned bonding ratio is obtained by dividing the total contact length of all Al ₂ O ₃ particles 92 in the SEM image by the total particle perimeter of all Al ₂ O ₃ particles 92. The number of Al ₂ O ₃ particles 92 in the SEM image is, for example, 30 to 50.

The bonding ratio of the Al ₂ O ₃ particles 92 to the TiO ₂ domains 93 is preferably 50% or less, and more preferably 40% or less. By setting the bonding ratio to 40% or less, it is possible to increase the porosity and average pore diameter of the alumina porous body 1. As a result, when the alumina porous body 1 is used, for example, in a ceramic filter for solid-liquid separation or as a substrate for the ceramic filter, a sufficient liquid permeation rate can be obtained.

The porosity of the alumina porous body 1 is 10% or more and 45% or less. The porosity is preferably 20% or more, more preferably 25% or more, and even more preferably 30% or more. The porosity is preferably 60% or less, and even more preferably 50% or less. By setting the porosity to 10% or more (preferably 20% or more), a sufficient liquid permeability can be achieved when the alumina porous body 1 is used, for example, as a ceramic filter for solid-liquid separation or as the substrate for such a ceramic filter. Furthermore, by setting the porosity to 45% or less, the strength of the alumina porous body 1 can be increased. In this specification, the porosity of the alumina porous body 1 is measured by the Archimedes method (in accordance with JIS R 1634).

The average pore diameter of the alumina porous body 1 is 2 μm or more and 12 μm or less. The average pore diameter is preferably 5 μm or more, more preferably 5.5 μm or more, and even more preferably 6 μm or more. The average pore diameter is preferably 20 μm or less, and even more preferably 15 μm or less. By making the average pore diameter 2 μm or more (preferably 5 μm or more), a sufficient amount of liquid can be obtained when the alumina porous body 1 is used, for example, in a ceramic filter for solid-liquid separation or as the substrate for such a ceramic filter. Furthermore, by making the average pore diameter 12 μm or less, the strength of the alumina porous body 1 can be increased. Note that, in this specification, the average pore diameter of the alumina porous body 1 is measured by mercury intrusion porosimetry (in accordance with JIS R 1655).

In the alumina porous body 1, the average particle size of the _{Al2O3 particles} is preferably 10 μm or more, and more preferably 20 μm or more. The average particle size of the _{Al2O3 particles} is preferably 80 μm or less, and more preferably 70 μm or less. By setting the average particle size of the _{Al2O3 particles} to 10 μm or more and 80 μm or less, the porosity and average pore diameter of the alumina porous body 1 can be suitably achieved within the above-mentioned ranges.

The average particle size of _{Al2O3 particles} is determined as follows. First, image processing is performed on an SEM image such as that shown in Figure 2 to extract only _Al2O3 particles 92. Next, the area of each _Al2O3 particle ₉₂ is calculated in the processed image, and the diameter (hereinafter also referred to as "particle diameter") of each _Al2O3 particle ₉₂ , assuming that it is circular _, is calculated from the area. Then, the arithmetic average of the particle diameters of a predetermined number of _{Al2O3 particles} 92 is determined as the average particle size of the _{Al2O3 particles} . The predetermined number is, for example, 50 to 200.

The bending strength of the alumina porous body 1 (corresponding to the initial strength described below) is preferably 15 MPa or more, and more preferably 20 MPa or more. By ensuring that the bending strength is 15 MPa or more, breakage of the alumina porous body 1 can be suitably suppressed. Note that in this specification, the bending strength is measured by a bending strength test in accordance with JIS R 1601.

When the alumina porous body 1 is subjected to an alkali immersion treatment, the strength reduction rate is preferably 20% or less, and more preferably 19% or less. The alkali immersion treatment involves immersing the alumina porous body 1 in an alkaline solution (hereinafter also referred to as the "alkaline chemical solution"), which is an aqueous sodium hydroxide (NaOH) solution with a pH of 13, at 80°C for 60 hours, washing the alumina porous body 1 to remove the alkaline chemical solution from the alumina porous body 1, and then drying the alumina porous body 1. The strength reduction rate is the reduction rate of the bending strength of the alumina porous body 1 after one alkali immersion treatment (hereinafter also referred to as the "post-treatment strength") relative to the bending strength of the alumina porous body 1 before the alkali immersion treatment (hereinafter also referred to as the "initial strength"). Specifically, the strength reduction rate can be calculated using the following formula 1.

Strength reduction rate=(initial strength−strength after treatment)/initial strength (Equation 1)
By setting the strength reduction rate to 20% or less, even when the alumina porous body 1 is used, for example, as a ceramic filter for solid-liquid separation that is repeatedly washed with an alkaline chemical solution (i.e., chemical washing) or as the substrate of such a ceramic filter, it is possible to suitably suppress a reduction in strength of the alumina porous body 1 due to chemical washing. Note that, although a strength reduction rate close to 0% is preferable, in reality it is greater than 0%.

Next, an example of a manufacturing flow of the alumina porous body 1 will be described with reference to Fig. _3. Below, a manufacturing method of the above-mentioned alumina porous body 1 in which the total content of _Al2O3 and _TiO2 is substantially 100 mass% will be described. When manufacturing the alumina porous body 1, first, a puddle obtained by kneading the raw material mixture is formed into a predetermined shape (for example, a monolith shape) to obtain a molded body (step S11). The shape of the molded body is not limited to a monolith shape, and various shapes may be used depending on the application.

The raw material mixture contains particles of _Al2O3 and _TiO2 , which are materials that will be fired to form the _alumina porous body 1. In the raw material mixture, the total content of _Al2O3 particles and _TiO2 particles in the materials that form the alumina porous body 1 is substantially 100 mass%. The _{TiO2 particles} may be particles _whose surfaces are coated with aluminum hydroxide (Al(OH) _{3 )} , or may be particles whose surfaces are not coated with aluminum hydroxide.

The average particle size of the Al ₂ O ₃ particles contained in the raw material mixture is, for example, 1 μm to 120 μm. The average particle size of _{the Al 2} O ₃ particles is preferably 5 μm or more, and more preferably 10 μm or more. The average particle size of the Al ₂ O ₃ particles is preferably 100 μm or less, and more preferably 90 μm or less. By making the average particle size of the _{Al 2} O ₃ particles 1 μm or more, the porosity and average pore size of the alumina porous body 1 can be increased. Furthermore, by making the average particle size of the Al ₂ O ₃ particles 120 μm or less, the above-mentioned molded body can be suitably molded.

The Al ₂ O ₃ particles contained in the raw material mixture may be a combination (i.e., a mixture) of multiple types of Al ₂ O ₃ particles with different average particle sizes. In this case, the average particle size of the Al ₂ O ₃ particles after mixing is 1 μm to 120 μm as described above. Furthermore, it is preferable that the average particle size of at least one type of Al ₂ O ₃ particles among the multiple types of Al ₂ O ₃ particles described above is 1 μm to 100 μm.

The average particle size of the _TiO2 particles contained in the raw material mixture is, for example, 0.5 μm to 10 μm. The average particle size of the _TiO2 particles is preferably 0.6 μm or more, and more preferably 0.8 μm or more. Furthermore, the average particle size of the _TiO2 particles is more preferably equal to or smaller than the average particle size of _{the Al2O3} particles contained in the raw material mixture. By setting the average particle size of _{the TiO2} particles to 0.5 μm to 10 μm, it is possible to suppress an increase in the procurement cost of the _TiO2 particles, improve the sinterability of the alumina porous body 1, and increase the strength of the alumina porous body 1.

The average particle diameters of the Al ₂ O ₃ particles and TiO ₂ particles contained in the raw material mixture are volume-based average particle diameters determined from particle size distributions measured by a laser diffraction scattering method in accordance with JIS R 1629.

The raw material mixture contains, in addition to the materials (i.e., _{Al2O3 particles} and _TiO2 particles) that constitute the alumina porous body 1, an organic binder, a dispersant, a surfactant, water, etc. As the organic binder, for example, one or more of methyl cellulose, hydroxypropoxyl cellulose, hydroxyethyl cellulose, carboxymethyl cellulose, polyvinyl alcohol, etc. can be used.

As dispersants and surfactants, for example, one or more of the following can be used: fatty acid salts, alkyl sulfate ester salts, polyoxyethylene alkyl ether sulfate ester salts, alkylbenzene sulfonates, alkylnaphthalene sulfonates, alkyl sulfosuccinates, alkyldiphenyl ether disulfonates, alkyl phosphates, polycarboxylates, polyacrylates, aliphatic quaternary ammonium salts, aliphatic amine salts, polyoxyethylene alkyl ethers, polyoxyethylene alcohol ethers, polyoxyethylene glycerin fatty acid esters, polyoxyethylene sorbitan (or sorbitol) fatty acid esters, polyethylene glycol fatty acid esters, alkyl betaines, amine oxides, cationic cellulose derivatives, etc.

In step S11, as described above, the raw material mixture is kneaded to form a plastic clay, which is then molded into a predetermined shape (e.g., a monolithic shape) to obtain a molded body. The clay is produced, for example, by adding _{Al2O3 particles} , an organic binder, a surfactant, and an appropriate amount of water to a slurry obtained by mixing _TiO2 particles, a dispersant, and water, and then kneading the resulting mixture. The molded body is formed, for example, by extrusion molding.

Once step S11 is completed, the compact is dried and then fired to produce the alumina porous body 1 (step S12). In step S12, the compact is dried using a drying method that uses, for example, microwaves or hot air.

In step S12, the firing temperature for the molded body is preferably 1200°C or higher and 1450°C or lower. The firing temperature is more preferably 1250°C or higher, and even more preferably 1280°C or higher. The firing temperature is more preferably 1330°C or lower, and even more preferably 1300°C or lower. By setting the firing temperature to 1200°C or higher, favorable sintering of the alumina porous body 1 can be achieved. Furthermore, by setting the firing temperature to 1450°C or lower, damage to the alumina porous body 1 during firing can be suppressed. In step S12, the firing time for the molded body is not particularly limited, but is, for example, 0.5 to 10 hours. Furthermore, the firing atmosphere is not particularly limited, but is, for example, air or nitrogen.

In step S12, between the drying and firing of the compact, the compact may be pre-fired to burn and remove organic matter (e.g., organic binders) in the compact. This pre-fire is also called degreasing or de-bindering. The combustion temperature of organic binders is generally around 100°C to 300°C, so the pre-fire temperature is, for example, 200°C to 600°C. The pre-fire time is not particularly limited, but may be, for example, 1 to 10 hours. The pre-fire atmosphere is not particularly limited, but may be, for example, air or nitrogen.

In step S12, heat treatment may be performed after the sintering treatment of the molded body. The heat treatment temperature is preferably 1200°C or higher and 1350°C or lower. It is desirable that the heat treatment temperature does not significantly exceed the sintering treatment temperature of the molded body. By setting the heat treatment temperature to 1200°C or higher, the sinterability of the alumina porous body is improved. Furthermore, by setting the heat treatment temperature to 1350°C or lower, an increase in the amount of shrinkage of the alumina porous body can be suppressed. The heat treatment time is not particularly limited, but is, for example, 5 to 80 hours. Furthermore, the heat treatment atmosphere is not particularly limited, but is, for example, an air atmosphere or a nitrogen atmosphere.

As described above, the alumina porous body 1 shown in Figure 1 is used as a ceramic filter. When the alumina porous body 1 is used alone as a ceramic filter (i.e., without a membrane such as a separation membrane provided on the surface of the alumina porous body 1), the alumina porous body 1 performs the filtering function of the ceramic filter. As described above, the alumina porous body 1 has high initial strength and also high corrosion resistance against alkaline solutions. Therefore, when the alumina porous body 1 is used alone as a ceramic filter, the ceramic filter can maintain sufficient strength for a long period of time even when used in applications where cleaning conditions are more severe than those used for ordinary ceramic filters (for example, removal of solid matter in the pharmaceutical or food industries, etc.).

Furthermore, the alumina porous body 1 may be used as a ceramic filter by providing a porous ceramic membrane on its surface. This ceramic filter comprises the above-mentioned alumina porous body 1 and a porous ceramic membrane provided on the surface of the alumina porous body 1. The average pore diameter of the porous ceramic membrane is smaller than the average pore diameter of the alumina porous body 1. Note that in this specification, the average pore diameter of the porous ceramic membrane is measured by mercury intrusion porosimetry (in accordance with JIS R 1655). In this ceramic filter, the alumina porous body 1 and the porous ceramic membrane perform the filtering function.

As described above, the alumina porous body 1 used as the substrate (i.e., support) for the porous ceramic membrane in a ceramic filter has high initial strength and also high corrosion resistance to alkaline solutions. Therefore, the ceramic filter can maintain sufficient strength over long periods of time, even when used in applications where cleaning conditions are more severe than those used for ordinary ceramic filters (for example, removal of solid matter in the pharmaceutical or food industries).

As described above, the porous ceramic membrane described above is a filtration membrane that performs the filtration function of the ceramic filter. In this case, an intermediate membrane having an average pore diameter smaller than that of the alumina porous body 1 and larger than that of the filtration membrane may be provided between the alumina porous body 1 serving as the substrate and the filtration membrane. In this case, the ends of the alumina porous body 1, intermediate membrane, and filtration membrane are preferably sealed by sealing portions formed to encase the ends. This prevents the fluid to be treated from directly penetrating the alumina porous body 1 and intermediate membrane from the end faces into the interior of the alumina porous body 1 and intermediate membrane without passing through the filtration membrane.

Next, an example of a method for manufacturing the ceramic filter will be described. When manufacturing a ceramic filter, first, approximately 70% by mass of ceramic particles, a dispersant, an organic binder, a surfactant, and water are mixed in a pot mill or the like, and the ceramic particles are crushed to an average particle size of approximately 0.1 μm to 3 μm to prepare a slurry for forming a porous ceramic membrane (hereinafter also referred to as "membrane-forming slurry"). The ceramic particles are, for example, primarily composed of Al ₂ O ₃ particles and TiO ₂ particles.

Next, O-rings are attached to the outer peripheral surface of the monolithic porous alumina body 1 at both longitudinal ends of the alumina porous body 1. The alumina porous body 1 with the O-rings attached is fixed inside a substantially cylindrical flange. This separates the outer peripheral surface of the alumina porous body 1 from the interior of the cell 2.

Next, while the membrane-forming slurry is continuously circulated and supplied into each cell 2 using a liquid feed pump, the outer peripheral surface of the alumina porous body 1 is depressurized using a vacuum pump, creating a pressure difference between the outer peripheral surface and the inside of the cell 2. As a result, the membrane-forming slurry flowing inside the cell 2 is sucked from the outer peripheral surface of the alumina porous body 1 and adheres to the inner peripheral surface of the cell 2, forming a film of ceramic particles on the inner peripheral surface. The alumina porous body 1 is then dried and then fired, for example, at 950°C to 1250°C, to form the above-mentioned ceramic filter.

When forming multiple layers of porous ceramic membranes, the above-mentioned process of forming a membrane using ceramic particles, drying, and firing is repeated multiple times. By gradually decreasing the average particle size of the ceramic particles contained in the membrane-forming slurry with each iteration, a ceramic filter is obtained in which the average pore size gradually decreases toward the porous ceramic membrane (e.g., filtration membrane) located at the surface layer farthest from the substrate. Furthermore, as described above, when sealing portions are provided to enclose the ends of the alumina porous body 1, intermediate membrane, and filtration membrane, sealing portions with significantly low permeability to the treated fluid can be formed, for example, by applying a sealing agent to the ends and their vicinity and then drying or heat-treating them. Examples of sealing agents that can be used include glassy substances, thermoplastic polymers, and thermosetting polymers.

In the above-described method for producing the alumina porous body 1, the total content of _Al2O3 particles and _{TiO2 particles} in the materials constituting the alumina porous body 1 in the raw material mixture is substantially 100% by mass. The materials constituting the alumina porous body 1 do not contain a sintering aid, but may contain a sintering aid. The sintering aid may include, for example, calcium (Ca). The sintering aid may be, for example, calcium carbonate ( _CaCO3 ) particles. The sintering aid may contain elements other than Ca, but does not include Cu or Mn. In the raw material mixture, the content of the sintering aid in the materials constituting the alumina porous body 1 is 0.1% by mass or more and 1.5% by mass or more.

The manufacturing method of the alumina porous body 1 when using a sintering aid is substantially the same as steps S11 and S12 described above. In step S11, for example, when preparing the above-mentioned slurry, the sintering aid is mixed with _TiO2 particles, dispersant, and water. In step S12, the inclusion of the sintering aid in the compact improves the sinterability of _TiO2 , achieving stronger bonding between aggregate particles and further increasing the strength of the alumina porous body 1. In addition, the alumina porous body 1 can be sintered at a relatively low temperature.

In the alumina porous body 1, the Ca in the sintering aid exists in the form of an oxide produced by oxidation during firing, or a complex compound with Ti, etc. The Ca content in the alumina porous body 1 is preferably 0.1 mass% or more and 1.5 mass% or less, calculated as an oxide. The Ca content in terms of oxide is more preferably 0.5 mass% or more, and even more preferably 1.0 mass% or more. The Ca content in terms of oxide is more preferably 5 mass% or less, and even more preferably 3 mass% or less.

By setting the Ca content in terms of oxide to 0.1% by mass or more in the alumina porous body 1, the alumina porous body 1 can effectively function as a sintering agent during sintering. Furthermore, by setting the Ca content in terms of oxide to 1.5% by mass or less, the proportion of the _TiO2 component in the binder phase described above is maintained relatively high, and the binder phase maintains relatively high corrosion resistance to alkaline solutions.

Next, examples and comparative examples of the alumina porous body 1 according to the present invention will be described. Table 1 below shows the conditions for producing the alumina porous bodies 1 of Examples 1 to 26 and the alumina porous bodies of Comparative Examples 1 to 7, and Table 2 shows the properties of the alumina porous bodies 1 of Examples 1 to 26 and the alumina porous bodies of Comparative Examples 1 to 7. Note that the present invention is not limited to the following examples.

In Examples 1 to 26 and Comparative Examples 1 to 7, a slurry was first prepared by mixing _TiO2 particles, a dispersant, and water in a pot mill. In Examples 8 and 9, _CaCO3 particles, a sintering aid, were also added when preparing the slurry. The slurry was then mixed with _{Al2O3 particles} , an organic binder, a surfactant, and water to obtain a raw material mixture, which was then kneaded to obtain a plastic clay. The clay was then extruded and dried to obtain a square plate-shaped compact measuring approximately 25 mm x 50 mm x 5 mm.

The organic binder, dispersant, surfactant, and water contents in the raw material mixture were 6 mass%, 0.09 mass%, 1 mass%, and 17 mass%, respectively. In Examples 8 and 9, when preparing the raw material mixture, the total amount of Al ₂ O ₃ particles and TiO ₂ particles was 100 mass parts, and CaCO ₃ particles were added in the amounts (parts by mass) shown in Table 1.

The compact was then calcined (i.e., degreased) at 450°C and then fired under the firing conditions shown in Table 1 to obtain an alumina porous body 1. In some examples and comparative examples, after the firing treatment, heat treatment was performed under the heat treatment conditions shown in Table 1. Thereafter, for the alumina porous body 1, the initial strength (i.e., bending strength before alkali immersion treatment), post-treatment strength (i.e., bending strength after alkali immersion treatment), strength reduction rate, porosity, average pore diameter, bonding ratio with _TiO2 domains in _Al2O3 particles, _TiO2 content, and Ca content in terms of oxide, etc., shown in _Table 2, were determined by the following method.

Initial strength was measured in accordance with JIS R 1601.

The post-treatment strength was measured in the same manner as for the initial strength after the above-mentioned alkaline immersion treatment was performed once on the alumina porous body 1. In the alkaline immersion treatment, an alkaline solution, which was a sodium hydroxide aqueous solution with a pH of 13, was first stored in a pressure vessel with an inner wall made of Teflon (registered trademark), and the alumina porous body 1 was immersed in the alkaline solution. Next, with the alumina porous body 1 entirely immersed in the alkaline solution, the pressure vessel was sealed and kept at 80°C for 60 hours. Next, the alumina porous body 1 was removed from the alkaline solution and washed, and the alkaline solution was removed from the alumina porous body 1, after which the alumina porous body 1 was dried.

The strength reduction rate was calculated using the above-mentioned formula 1 from the initial strength and post-treatment strength measured as described above.

The porosity was measured by cutting a measurement sample of approximately 25 mm x 10 mm x 5 mm from the alumina porous body 1 using the Archimedes method (in accordance with JIS R 1634).

The average pore diameter was measured by cutting a measurement sample of approximately 8 mm x 10 mm x 5 mm from the alumina porous body 1 and using the mercury intrusion method (in accordance with JIS R 1655).

The bonding ratio between the Al ₂ O ₃ particles and the TiO ₂ domains (hereinafter also simply referred to as "bonding ratio") was determined by the above-mentioned method using an SEM image such as that shown in Figure 2. Specifically, the particle perimeter and contact length of each Al ₂ O ₃ particle 92 in the SEM image were measured, and the bonding ratio was determined by dividing the total contact length of all Al ₂ O ₃ particles 92 in the SEM image by the total particle perimeter of all Al ₂ O ₃ particles 92.

The TiO ₂ content and the Ca content calculated as oxide were measured by the method for chemical analysis of ceramic raw materials (in accordance with JIS M 8853).

In Comparative Example 1, the total content of _{Al2O3 particles} and _TiO2 particles in the raw material mixture was 100 parts by mass, as described above. The content of _{Al2O3 particles} in the raw material mixture was 70 parts by mass, and the content of _TiO2 particles was 30 parts by mass. The _Al2O3 particles in the raw material mixture were a mixture of multiple types of _Al2O3 particles with different average particle sizes. Specifically, the _{Al2O3 particles} in the raw material mixture were a mixture of ₃₀ parts by mass of _{Al2O3 particles} with an average particle size of ₂₇ μm, 30 parts by mass of Al2O3 particles with an average particle size of 15 μm, and 10 parts by mass of _{Al2O3 particles} with an average particle size of 4.6 μm. The average particle size of _{the TiO2 particles} in the raw material mixture was 0.8 μm. The _TiO2 particles with an average particle size of 0.8 μm contained in the raw material mixture were not coated with aluminum hydroxide (the same applies to other Examples and Comparative Examples). The firing temperature and firing time of the compact are 1300° C. and 2 hours, respectively, and the heat treatment temperature and heat treatment time are 1250° C. and 72 hours, respectively.

The alumina porous body of Comparative Example 1 had an initial strength of 55 MPa, a post-treatment strength of 53 MPa, and a strength reduction rate of 3.6%. The porosity was 8%, and the average pore diameter was 1.8 μm. The bonding ratio was 33.8%. The TiO ₂ content was 30 mass%, and the Ca content was 0.0 mass% in oxide equivalent. The alumina porous body of Comparative Example 1 contained approximately 0.02 mass% Ca in oxide equivalent as an impurity derived from the raw material Al ₂ O ₃ particles. The same applies to the other comparative examples and examples. The alumina porous body of Comparative Example 1 had a small porosity of less than 10%, and an average pore diameter of less than 2 μm.

In Comparative Example 2, the conditions for producing an alumina porous body were the same as in Comparative Example 1, except that the contents of _{Al2O3 particles} and _TiO2 particles in the raw material mixture were different. In Comparative Example 2, the contents of _{Al2O3 particles} in the raw material mixture were 65 parts by mass, and the content of _TiO2 particles was 35 parts by mass. The _{Al2O3 particles} in the raw material mixture were a mixture of 27.5 parts by mass of _{Al2O3 particles} with an average particle size of 27 μm, 27.5 parts by mass of _{Al2O3 particles} with an average particle size of 15 μm, and 10 parts by mass of _{Al2O3 particles} with an average particle size of 4.6 μm.

The alumina porous body of Comparative Example 2 had an initial strength of 62 MPa, a post-treatment strength of 59 MPa, and a strength reduction rate of 4.8%. The porosity was 6%, and the average pore diameter was 1.4 μm. The bonding ratio was 37.3%. The _TiO2 content was 35% by mass, and the Ca content, calculated as oxide, was 0.0% by mass. The alumina porous body of Comparative Example 2 had a small porosity of less than 10%, and an average pore diameter of less than 2 μm.

In Example 1, the conditions for producing the alumina porous body 1 were the same as in Comparative Example 1, except that the content and average particle size _{of Al2O3} particles in the raw material mixture and the content of _TiO2 particles were different. In Example 1, the content of _{Al2O3 particles} in the raw material mixture was 80 parts by mass, and the content of _TiO2 particles was 20 parts by mass. _{The Al2O3} particles in the raw material mixture were a mixture of 25 parts by mass of _{Al2O3 particles} with an average particle size of 18 μm, 30 parts by mass of _{Al2O3 particles} with an average particle size of 53 μm, 15 parts by mass of _{Al2O3 particles} with an average particle size of 27 μm, and 10 parts by mass of _Al2O3 particles with an average particle size of 3.9 _μm .

The alumina porous body 1 of Example 1 had an initial strength of 27 MPa, a post-treatment strength of 23 MPa, and a strength reduction rate of 14.8%. The porosity was 33%, and the average pore diameter was 5.9 μm. The bonding ratio was 20.5%. The _TiO2 content was 20% by mass, and the Ca content was 0.0% by mass in terms of oxide. The alumina porous body 1 of Example 1 had an initial strength of 15 MPa or more, a strength reduction rate of 20% or less, a porosity in the range of 20% to 45%, an average pore diameter in the range of 5 μm to 12 μm, a bonding ratio of 5% or more, and a _TiO2 content in the range of 10% to 40% by mass. The same applies to the other examples.

In Example 2, the conditions for producing the alumina porous body 1 were the same as in Example 1, except that the average particle size of the _TiO2 particles in the raw material mixture was different. In Example 2, the average particle size of the _TiO2 particles in the raw material mixture was 0.6 μm. The _TiO2 particles with an average particle size of 0.6 μm contained in the raw material mixture were not coated with aluminum hydroxide (this was also the case in other Examples and Comparative Examples). The alumina porous body 1 of Example 2 had an initial strength of 18 MPa, a post-treatment strength of 15 MPa, and a strength reduction rate of 16.7%. The porosity was 33%, and the average pore diameter was 5.3 μm. The bonding ratio was 12.3%. The _TiO2 content was 20% by mass, and the Ca content, calculated as oxide, was 0.0% by mass.

In Example 3, the conditions for producing the alumina porous body 1 were the same as in Example 1, except that the average particle size of the _TiO2 particles in the raw material mixture was different. In Example 3, the average particle size of the _TiO2 particles in the raw material mixture was 1.4 μm. The _TiO2 particles with an average particle size of 1.4 μm contained in the raw material mixture were coated with aluminum hydroxide (the same applies to other Examples and Comparative Examples). The alumina porous body 1 of Example 3 had an initial strength of 21 MPa, a post-treatment strength of 17 MPa, and a strength reduction rate of 19.0%. The porosity was 32%, and the average pore diameter was 6.7 μm. The bonding ratio was 31.6%. The _TiO2 content was 20% by mass, and the Ca content, calculated as oxide, was 0.0% by mass.

In Example 4, the conditions for producing the alumina porous body 1 were the same as in Example 1, except that the average particle size of the _TiO2 particles in the raw material mixture was different. In Example 4, the average particle size of the _TiO2 particles in the raw material mixture was 0.95 μm. The _TiO2 particles with an average particle size of 0.95 μm contained in the raw material mixture were not coated with aluminum hydroxide (this was also the case in other Examples and Comparative Examples). The alumina porous body 1 of Example 4 had an initial strength of 20 MPa, a post-treatment strength of 18 MPa, and a strength reduction rate of 10.0%. The porosity was 33%, and the average pore diameter was 5.3 μm. The bonding ratio was 13.2%. The _TiO2 content was 20% by mass, and the Ca content, calculated as oxide, was 0.0% by mass.

In Example 5, the conditions for producing the alumina porous body 1 were the same as in Example 3, except that the content and average particle size _{of Al2O3} particles and the content of _TiO2 particles in the raw material mixture were different. In Example 5, the content of _{Al2O3 particles} in the raw material mixture was 60 parts by mass, and the content of _TiO2 particles was 40 parts by mass. The _{Al2O3 particles} in the raw material mixture were a mixture of 30 parts by mass of _{Al2O3 particles} with an average particle size of 18 μm and 30 parts by mass of _{Al2O3 particles} with an average particle size of 27 μm. The average particle size of the _TiO2 particles in the raw material mixture was 1.4 μm.

The alumina porous body 1 of Example 5 had an initial strength of 35 MPa, a post-treatment strength of 32 MPa, and a strength reduction rate of 8.6%. The porosity was 20%, and the average pore diameter was 5.0 μm. The bonding ratio was 35.0%. The _TiO2 content was 40% by mass, and the Ca content, calculated as oxide, was 0.0% by mass.

In Example 6, the conditions for producing the alumina porous body 1 were the same as in Example 3, except for the content and average particle size of the Al ₂ O ₃ particles in the raw material mixture, as well as the firing and heat treatment conditions. In Example 6, the content of Al ₂ O ₃ particles in the raw material mixture was 80 parts by mass, and the content of TiO ₂ particles was 20 parts by mass. The Al ₂ O ₃ particles in the raw material mixture were a mixture of 51.8 parts by mass of Al 2 O ₃ particles with an average particle size of 18 μm, 18.2 parts by mass of Al _{2 O 3} particles with an average particle size of 53 μm, and 10 parts by mass of Al ₂ O ₃ particles with an average particle size of 4.6 μm. The average particle size of the TiO ₂ particles in the raw material mixture was 1.4 μm. The firing temperature and firing time for the compact were 1250°C and 5 hours, respectively. Furthermore, no heat treatment was performed after firing.

The alumina porous body 1 of Example 6 had an initial strength of 15 MPa, a post-treatment strength of 13 MPa, and a strength reduction rate of 13.3%. The porosity was 41%, the average pore diameter was 12.0 μm, and the bonding ratio was 12.0%. The _TiO2 content was 20% by mass, and the Ca content, calculated as oxide, was 0.0% by mass.

In Example 7, the conditions for producing the alumina porous body 1 were the same as in Example 6, except that _CaCO3 particles were added to the raw material mixture as a sintering aid. In Example 7, the content of CaCO3 _particles in the raw material mixture was 0.1 parts by mass. The average particle size of the _CaCO3 raw material particles was 1 μm. The alumina porous body 1 of Example 7 had an initial strength of 19 MPa, a post-treatment strength of 17 MPa, and a strength reduction rate of 10.5%. The porosity was 40%, and the average pore diameter was 11.8 μm. The bonding ratio was 13.6%. The _TiO2 content was 20% by mass, and the Ca content was 0.1% by mass in terms of oxide. Note that no _CaCO3 particles were observed in the SEM image after firing.

In Example 8, the conditions for producing the alumina porous body 1 were the same as in Example 7, except for the content of _CaCO3 particles in the raw material mixture. In Example 8, the content of _CaCO3 particles in the raw material mixture was 1.5 parts by mass. The average particle size of the _CaCO3 raw material particles was 1 μm. The alumina porous body 1 of Example 8 had an initial strength of 22 MPa, a post-treatment strength of 20 MPa, and a strength reduction rate of 9.1%. The porosity was 38%, and the average pore diameter was 10.8 μm. The bonding ratio was 18.8%. The _TiO2 content was 20% by mass, and the Ca content was 1.5% by mass in terms of oxide. Note that no _CaCO3 particles were observed in the SEM image after firing.

In Comparative Example 3, the conditions for producing the alumina porous body were the same as in Example 6, except for the content and average particle size of Al ₂ O ₃ particles in the raw material mixture, the content of TiO ₂ particles, and the firing conditions. In Comparative Example 3, the content of Al ₂ O ₃ particles in the raw material mixture was 75 parts by mass, and the content of TiO ₂ particles was 25 parts by mass. The Al ₂ O ₃ particles in the raw material mixture were a mixture of 25 parts by mass of Al ₂ O ₃ particles with an average particle size of 18 μm, 25 parts by mass of Al ₂ O ₃ particles with an average particle size of 53 μm, 15 parts by mass of Al ₂ O ₃ particles with an average particle size of 27 μm, and 10 parts by mass of Al ₂ O ₃ particles with an average particle size of 3.9 μm. The average particle size of the TiO ₂ particles in the raw material mixture was 1.4 μm. The firing temperature and firing time for the compact were 1250°C and 2 hours, respectively. No heat treatment was performed after firing.

The alumina porous body of Comparative Example 3 had an initial strength of 13 MPa, a post-treatment strength of 11 MPa, and a strength reduction rate of 15.4%. The porosity was 29%, and the average pore diameter was 6.1 μm. The bonding ratio was 25.0%. The _TiO2 content was 25% by mass, and the Ca content, calculated as oxide, was 0.0% by mass. The alumina porous body of Comparative Example 3 had a low initial strength of less than 15 MPa.

In Example 9, the conditions for producing the alumina porous body 1 were the same as those in Comparative Example 3, except for the firing conditions. In Example 9, the firing temperature and firing time for the compact were 1250°C and 5 hours, respectively. The alumina porous body 1 of Example 9 had an initial strength of 19 MPa, a post-treatment strength of 16 MPa, and a strength reduction rate of 15.8%. The porosity was 27%, and the average pore diameter was 5.4 μm. The bonding ratio was 27.5%. The _TiO2 content was 25% by mass, and the Ca content, calculated as oxide, was 0.0% by mass.

In Example 10, the conditions for producing the alumina porous body 1 were the same as those in Comparative Example 3, except for the firing conditions. In Example 10, the firing temperature and firing time for the compact were 1280°C and 2 hours, respectively. The alumina porous body 1 of Example 10 had an initial strength of 23 MPa, a post-treatment strength of 20 MPa, and a strength reduction rate of 13.0%. The porosity was 26%, and the average pore diameter was 5.5 μm. The bonding ratio was 28.9%. The _TiO2 content was 25% by mass, and the Ca content, calculated as oxide, was 0.0% by mass.

In Example 11, the conditions for producing the alumina porous body 1 were the same as those in Example 10, except for the content and average particle size of Al ₂ O ₃ particles, the content and average particle size of TiO ₂ particles in the raw material mixture, and the firing conditions. In Example 11, the content of Al ₂ O ₃ particles in the raw material mixture was 82.2 parts by mass, and the content of TiO ₂ particles was 17.8 parts by mass. The Al ₂ O ₃ particles in the raw material mixture were a mixture of 41.1 parts by mass of Al ₂ O ₃ particles with an average particle size of 18 μm and 41.1 parts by mass of Al ₂ O ₃ particles with an average particle size of 27 μm. The average particle size of the TiO ₂ particles in the raw material mixture was 0.8 μm. The firing temperature and firing time for the compact were 1300°C and 2 hours, respectively.

The alumina porous body 1 of Example 11 had an initial strength of 15 MPa, a post-treatment strength of 12 MPa, and a strength reduction rate of 20%. The porosity was 38%, and the average pore diameter was 5.1 μm. The bonding ratio was 12.6%. The _TiO2 content was 17.8% by mass, and the Ca content, calculated as oxide, was 0.0% by mass.

In Comparative Example 4, the conditions for producing the alumina porous body were the same as in Example 11, except for the different firing conditions. In Comparative Example 4, the firing temperature and firing time for the compact were 1,350°C and 2 hours, respectively. For the alumina porous body 1 of Comparative Example 4, the initial strength was low at 6.0 MPa, so the post-treatment strength was not measured and the strength reduction rate was not calculated. The porosity was 41%, and the average pore diameter was 8.0 μm. The bonding ratio was not measured due to the low initial strength as described above. The _TiO2 content was 17.8% by mass, and the Ca content, calculated as oxide, was 0.0% by mass.

In Comparative Example 5, the conditions for producing the alumina porous body were the same as in Example 11, except for the different firing conditions. In Comparative Example 5, the firing temperature and firing time for the compact were 1400°C and 2 hours, respectively. For the alumina porous body 1 of Comparative Example 5, the initial strength was low at 4.3 MPa, so the post-treatment strength was not measured and the strength reduction rate was not calculated. The porosity was 42% and the average pore diameter was 7.8 μm. The bonding ratio was not measured due to the low initial strength as described above. The _TiO2 content was 17.8% by mass, and the Ca content was 0.0% by mass in terms of oxide.

In Comparative Example 6, the conditions for producing the alumina porous body were the same as in Example 11, except for the different firing conditions. In Comparative Example 6, the firing temperature and firing time for the compact were 1,450°C and 2 hours, respectively. For the alumina porous body 1 of Comparative Example 6, the initial strength was low at 1.8 MPa, so the post-treatment strength was not measured and the strength reduction rate was not calculated. The porosity was 41% and the average pore diameter was 8.3 μm. The bonding ratio was not measured due to the low initial strength as described above. The _TiO2 content was 17.8% by mass, and the Ca content, calculated as oxide, was 0.0% by mass.

In Example 12, the conditions for producing the alumina porous body 1 were the same as in Example 3, except for the firing conditions and heat treatment conditions. In Example 12, the firing temperature and firing time of the compact were 1250°C and 2 hours, respectively. The heat treatment temperature and heat treatment time were also 1250°C and 5 hours, respectively. The alumina porous body 1 of Example 12 had an initial strength of 16 MPa, a post-treatment strength of 13 MPa, and a strength reduction rate of 18.8%. The porosity was 36%, and the average pore diameter was 7.2 μm. The bonding ratio was 13.2%. The _TiO2 content was 20% by mass, and the Ca content, calculated as oxide, was 0.0% by mass.

In Example 13, the conditions for producing the alumina porous body 1 were the same as those in Example 12, except for the heat treatment conditions. In Example 13, the heat treatment temperature and heat treatment time were 1250°C and 10 hours, respectively. The alumina porous body 1 of Example 13 had an initial strength of 17 MPa, a post-treatment strength of 14 MPa, and a strength reduction rate of 17.6%. The porosity was 34%, and the average pore diameter was 7.0 μm. The bonding ratio was 14.3%. The _TiO2 content was 20% by mass, and the Ca content, calculated as oxide, was 0.0% by mass.

In Example 14, the conditions for producing the alumina porous body 1 were the same as in Example 12, except for the heat treatment conditions. In Example 14, the heat treatment temperature and heat treatment time were 1250°C and 20 hours, respectively. The alumina porous body 1 of Example 14 had an initial strength of 18 MPa, a post-treatment strength of 15 MPa, and a strength reduction rate of 16.7%. The porosity was 30%, and the average pore diameter was 6.8 μm. The bonding ratio was 16.5%. The _TiO2 content was 20% by mass, and the Ca content, calculated as oxide, was 0.0% by mass.

In Example 15, the preparation conditions for the alumina porous body 1 were the same as those in Example 12, except for the firing conditions and heat treatment conditions. In Example 15, the firing temperature and firing time for the compact were 1250°C and 5 hours, respectively. Furthermore, no heat treatment was performed after firing. The alumina porous body 1 of Example 15 had an initial strength of 15 MPa, a post-treatment strength of 13 MPa, and a strength reduction rate of 13.3%. Furthermore, the porosity was 37%, and the average pore diameter was 7.5 μm. The bonding ratio was 17.5%. The _TiO2 content was 20% by mass, and the Ca content, calculated as oxide, was 0.0% by mass.

In Example 16, the conditions for producing the alumina porous body 1 were the same as those in Example 15, except for the heat treatment conditions. In Example 16, the heat treatment temperature and time were 1250°C and 5 hours, respectively. The alumina porous body 1 of Example 16 had an initial strength of 17 MPa, a post-treatment strength of 15 MPa, and a strength reduction rate of 11.8%. The porosity was 35%, and the average pore diameter was 7.3 μm. The bonding ratio was 20.4%. The _TiO2 content was 20% by mass, and the Ca content, calculated as oxide, was 0.0% by mass.

In Example 17, the preparation conditions for the alumina porous body 1 were the same as those in Example 16, except for the firing conditions. In Example 17, the firing temperature and firing time for the compact were 1280°C and 2 hours, respectively. The alumina porous body 1 of Example 17 had an initial strength of 19 MPa, a post-treatment strength of 16 MPa, and a strength reduction rate of 15.8%. The porosity was 30%, and the average pore diameter was 6.9 μm. The bonding ratio was 23.1%. The _TiO2 content was 20% by mass, and the Ca content, calculated as oxide, was 0.0% by mass.

In Example 18, the conditions for producing the alumina porous body 1 were the same as those in Example 16, except for the firing conditions. In Example 18, the firing temperature and firing time for the compact were 1300°C and 2 hours, respectively. The alumina porous body 1 of Example 18 had an initial strength of 20 MPa, a post-treatment strength of 18 MPa, and a strength reduction rate of 10.0%. The porosity was 29%, and the average pore diameter was 6.8 μm. The bonding ratio was 25.3%. The _TiO2 content was 20% by mass, and the Ca content, calculated as oxide, was 0.0% by mass.

In Example 19, the conditions for producing the alumina porous body 1 were the same as in Example 18, except for the heat treatment conditions. In Example 19, the heat treatment temperature and heat treatment time were 1,300°C and 5 hours, respectively. The alumina porous body 1 of Example 19 had an initial strength of 23 MPa, a post-treatment strength of 20 MPa, and a strength reduction rate of 13.0%. The porosity was 30%, and the average pore diameter was 6.7 μm. The bonding ratio was 28.7%. The _TiO2 content was 20% by mass, and the Ca content, calculated as oxide, was 0.0% by mass.

In Example 20, the conditions for producing the alumina porous body 1 were the same as in Example 19, except for the heat treatment conditions. In Example 20, the heat treatment temperature and heat treatment time were 1300°C and 10 hours, respectively. The alumina porous body 1 of Example 20 had an initial strength of 25 MPa, a post-treatment strength of 23 MPa, and a strength reduction rate of 8.0%. The porosity was 29%, and the average pore diameter was 6.6 μm. The bonding ratio was 31.8%. The _TiO2 content was 20% by mass, and the Ca content, calculated as oxide, was 0.0% by mass.

In Example 21, the conditions for producing the alumina porous body 1 were the same as in Example 19, except for the heat treatment conditions. In Example 21, the heat treatment temperature and heat treatment time were 1300°C and 20 hours, respectively. The alumina porous body 1 of Example 21 had an initial strength of 29 MPa, a post-treatment strength of 27 MPa, and a strength reduction rate of 6.9%. The porosity was 27%, and the average pore diameter was 6.5 μm. The bonding ratio was 33.5%. The _TiO2 content was 20% by mass, and the Ca content, calculated as oxide, was 0.0% by mass.

In Example 22, the preparation conditions for the alumina porous body 1 were the same as those in Example 11, except for the different firing conditions. In Example 22, the compact was fired at 1450°C for 2 hours, and then at 1280°C for 10 hours. No heat treatment was performed after firing. The alumina porous body 1 of Example 22 had an initial strength of 22 MPa, a post-treatment strength of 20 MPa, and a strength reduction rate of 9.1%. The porosity was 45%, and the average pore diameter was 9.0 μm. The bonding ratio was 35.0%. The _TiO2 content was 17.8% by mass, and the Ca content, calculated as oxide, was 0.0% by mass.

In Comparative Example 7, the conditions for producing the alumina porous body were the same as in Example 22, except for the different firing conditions. In Comparative Example 7, the compact was fired at 1,450°C for 2 hours, and then at 1,250°C for 10 hours. No heat treatment was performed after firing. Since the initial strength of the alumina porous body of Comparative Example 7 was low at 8.0 MPa, the post-treatment strength was not measured, and the strength reduction rate was not calculated. The porosity was 42%, and the average pore diameter was 8.6 μm. The bonding ratio was not measured due to the low initial strength as described above. The _TiO2 content was 17.8% by mass, and the Ca content was 0.0% by mass in terms of oxide.

In Example 23, the conditions for producing the alumina porous body 1 were the same as in Example 1, except that the content and average particle size of the Al ₂ O ₃ particles in the raw material mixture and the content of the TiO ₂ particles in the raw material mixture were different. In Example 23, the content of the Al ₂ O ₃ particles in the raw material mixture was 85 parts by mass, and the content of the TiO ₂ particles in the raw material mixture was 15 parts by mass. The Al ₂ O ₃ particles in the raw material mixture were a mixture of 18.75 parts by mass of Al ₂ O ₃ particles with an average particle size of 47 μm, 37.5 parts by mass of Al ₂ O ₃ particles with an average particle size of 27 μm, 18.75 parts by mass of Al ₂ O ₃ particles with an average particle size of 12 μm, and 10 parts by mass of Al ₂ O ₃ particles with an average particle size of 4.6 μm. The average particle size of the TiO ₂ particles in the raw material mixture was 0.8 μm.

The alumina porous body 1 of Example 23 had an initial strength of 22 MPa, a post-treatment strength of 20 MPa, and a strength reduction rate of 9.1%. The porosity was 33%, and the average pore diameter was 3.8 μm. The bonding ratio was 13.5%. The _TiO2 content was 15% by mass, and the Ca content, calculated as oxide, was 0.0% by mass.

In Example 24, the conditions for producing the alumina porous body 1 were the same as in Example 23, except that the content and average particle size of the Al ₂ O ₃ particles in the raw material mixture were different. In Example 24, the content of Al ₂ O ₃ particles in the raw material mixture was 85 parts by mass, and the content of TiO ₂ particles was 15 parts by mass. The Al ₂ O ₃ particles in the raw material mixture were a mixture of 18.75 parts by mass of Al ₂ O ₃ particles with an average particle size of 53 μm, 37.5 parts by mass of Al ₂ O ₃ particles with an average particle size of 27 μm, 18.75 parts by mass of Al 2 O ₃ particles with an average particle size of 12 μm, and 10 parts by mass of _{Al 2 O 3} particles with an average particle size of 4.6 μm. The average particle size of the TiO ₂ particles in the raw material mixture was 0.8 μm.

The alumina porous body 1 of Example 24 had an initial strength of 27 MPa, a post-treatment strength of 24 MPa, and a strength reduction rate of 11.1%. The porosity was 23%, and the average pore diameter was 3.0 μm. The bonding ratio was 12.8%. The _TiO2 content was 15% by mass, and the Ca content, calculated as oxide, was 0.0% by mass.

In Example 25, the conditions for producing the alumina porous body 1 were the same as in Example 23, except that the content and average particle size of the Al ₂ O ₃ particles in the raw material mixture and the content of the TiO ₂ particles in the raw material mixture were different. In Example 25, the content of the Al ₂ O ₃ particles in the raw material mixture was 90 parts by mass, and the content of the TiO ₂ particles in the raw material mixture was 10 parts by mass. The Al ₂ O ₃ particles in the raw material mixture were a mixture of 40 parts by mass of Al ₂ O ₃ particles with an average particle size of 27 μm, 40 parts by mass of Al ₂ O ₃ particles with an average particle size of 15 μm, and 10 parts by mass of Al ₂ O ₃ particles with an average particle size of 4.6 μm. The average particle size of the TiO ₂ particles in the raw material mixture was 0.8 μm.

The alumina porous body 1 of Example 25 had an initial strength of 29 MPa, a post-treatment strength of 26 MPa, and a strength reduction rate of 10.3%. The porosity was 37%, and the average pore diameter was 3.6 μm. The bonding ratio was 5.8%. The _TiO2 content was 10% by mass, and the Ca content, calculated as oxide, was 0.0% by mass.

In Example 26, the conditions for producing the alumina porous body 1 were the same as in Example 23, except that the content and average particle size of the Al ₂ O ₃ particles in the raw material mixture and the content of the TiO ₂ particles in the raw material mixture were different. In Example 26, the content of the Al ₂ O ₃ particles in the raw material mixture was 75 parts by mass, and the content of the TiO ₂ particles in the raw material mixture was 25 parts by mass. The Al ₂ O ₃ particles in the raw material mixture were a mixture of 32.5 parts by mass of Al ₂ O ₃ particles with an average particle size of 27 μm, 32.5 parts by mass of Al ₂ O ₃ particles with an average particle size of 15 μm, and 10 parts by mass of Al ₂ O ₃ particles with an average particle size of 4.6 μm. The average particle size of the TiO ₂ particles in the raw material mixture was 0.8 μm.

The alumina porous body 1 of Example 26 had an initial strength of 48 MPa, a post-treatment strength of 45 MPa, and a strength reduction rate of 6.3%. The porosity was 15%, and the average pore diameter was 2.0 μm. The bonding ratio was 21.2%. The _TiO2 content was 25% by mass, and the Ca content, calculated as oxide, was 0.0% by mass.

As described above, in the alumina porous bodies 1 of Examples 1 to 26, the porosity, average pore diameter, TiO ₂ content, bonding ratio, initial strength, and strength reduction rate were each within the above-mentioned preferred ranges.

As described above, the alumina porous body 1 according to the present invention contains _Al2O3 and _TiO2 . The _TiO2 content in the alumina porous body 1 is 10% by mass _or more and 40% by mass or less. The porosity of the alumina porous body 1 is 10% by mass or more and 45% by mass or less. The average pore diameter of the alumina porous body 1 is 2 μm or more and 12 μm or less. In the alumina porous body 1, the bonding ratio of the _Al2O3 particles to _{the TiO2} domains is 5% or more. This achieves strong bonding between the aggregate particles (i.e., _{Al2O3 particles} ) in the alumina porous body 1, and prevents the porosity and average pore diameter of the alumina porous body 1 from becoming excessively small. As a result, the strength of the alumina porous body 1 having the desired porosity and average pore diameter can be increased.

As mentioned above, it is preferable that the porosity of the alumina porous body 1 be 20% or more, and that the average pore diameter of the alumina porous body 1 be 5 μm or more. This makes it possible to effectively prevent the porosity and average pore diameter of the alumina porous body 1 from becoming excessively small.

As described above, the total content of Al ₂ O ₃ and TiO ₂ in the alumina porous body 1 is preferably 100 mass %. In this way, by not using a sintering aid (i.e., a material other than Al ₂ O ₃ and TiO ₂ ) when producing the alumina porous body 1, it is possible to reduce the production cost of the alumina porous body 1. In particular, by not using a sintering aid containing Cu and Mn, it is possible to prevent the firing furnace from being contaminated by Cu and Mn.

On the other hand, it is also preferable that the alumina porous body 1 further contains Ca. In this case, the Ca content in the alumina porous body 1 is preferably 0.1 mass % or more and 1.5 mass % or less in terms of oxide. As exemplified in the above-mentioned Examples 7 and 8, by using a sintering aid containing Ca when producing the alumina porous body 1, it is possible to increase the bonding ratio between the Al ₂ O ₃ particles constituting the alumina porous body 1 and the TiO ₂ domains, and as a result, it is possible to increase the initial strength and post-treatment strength of the alumina porous body 1.

As mentioned above, the bending strength (i.e., initial strength) of the alumina porous body 1 is preferably 15 MPa or more. This makes it possible to provide an alumina porous body 1 with high bending strength.

As mentioned above, the strength reduction rate, which is the rate at which the strength of the alumina porous body 1 after treatment is reduced relative to its initial strength, is preferably 20% or less. This makes it possible to suitably suppress reduction in the strength of the alumina porous body 1 due to chemical washing (i.e., cleaning using a chemical solution). Note that the strength after treatment refers to the bending strength of the alumina porous body 1 after undergoing an alkali immersion treatment, which involves immersing the body in an alkaline chemical solution, which is an aqueous sodium hydroxide solution with a pH of 13, at 80°C for 60 hours, followed by washing to remove the alkaline chemical solution and drying. Furthermore, the initial strength refers to the bending strength of the alumina porous body 1 before the alkali immersion treatment.

As mentioned above, the alumina porous body 1 is preferably used as a ceramic filter. This makes it possible to provide a ceramic filter with high initial strength and excellent corrosion resistance against alkaline chemical solutions, and also enables the ceramic filter to achieve a sufficient amount of permeation of the target substance.

Alternatively, the ceramic filter comprises the above-mentioned alumina porous body 1 and a porous ceramic membrane provided on the surface of the alumina porous body 1. The porous ceramic membrane has an average pore diameter smaller than that of the alumina porous body 1. This makes it possible to provide a ceramic filter with high initial strength and excellent corrosion resistance against alkaline chemical solutions, and also enables the ceramic filter to achieve a sufficient amount of permeation of the target substance.

The method for producing an alumina porous body 1 according to the present invention includes a step of forming a raw material mixture containing _{Al2O3 particles} and _TiO2 particles into a molded body (step S11), and a step of firing the molded body to obtain an alumina porous body (step S12). This allows the production of an alumina porous body 1 having a desired porosity, average pore diameter, and high strength.

As described above, the _TiO2 particles contained in the raw material mixture are preferably coated with aluminum hydroxide, which allows for the production of a high-strength alumina porous body 1 having the desired porosity and average pore size.

As described above, it is preferable that the total content of Al ₂ O ₃ particles and TiO ₂ particles in the materials constituting the alumina porous body 1 in the raw material mixture is 100 mass %, which can reduce the production cost of the alumina porous body 1. In particular, by not using a sintering aid containing Cu and Mn, it is possible to prevent the firing furnace from being contaminated by Cu and Mn.

On the other hand, it is also preferable that the raw material mixture further contains a sintering aid containing Ca. In this case, the content of the sintering aid in the material constituting the alumina porous body 1 in the raw material mixture is 0.1 mass % or more and 1.5 mass % or less. This increases the bonding ratio between the TiO2 domains and _{the Al2O3} particles constituting the alumina porous body ₁ , as described above, and as a result, the initial strength and post-treatment strength of the alumina porous body 1 can be increased.

As mentioned above, the firing temperature in step S12 is preferably 1200°C or higher and 1450°C or lower. This makes it possible to achieve optimal sintering of the alumina porous body 1 while suppressing damage to the alumina porous body 1 during firing.

The above-described alumina porous body 1 and method for manufacturing the alumina porous body 1 can be modified in various ways.

For example, the alumina porous body 1 may contain substances other than Al ₂ O ₃ , TiO ₂ and substances derived from the sintering aid.

If a sintering aid containing Ca is used in the production of the alumina porous body 1, the Ca content in the alumina porous body 1, calculated as oxide, may be less than 0.1 mass% or may be greater than 1.5 mass%.

The initial strength of the alumina porous body 1 may be less than 15 MPa.

The above-mentioned strength reduction rate of the alumina porous body 1 may be greater than 20%.

The above-mentioned ceramic filter may be used for various purposes other than as a filter for solid-liquid separation. For example, the ceramic filter may be used as a filter for gas-solid separation.

Furthermore, the alumina porous body 1 does not necessarily have to be used as a substrate for a ceramic filter, but may also be used for a variety of other purposes.

The raw material mixture used to manufacture the alumina porous body 1 may contain substances other than Al ₂ O ₃ particles, TiO ₂ particles, and a sintering aid as materials constituting the alumina porous body 1 .

If a sintering aid is used in the production of the alumina porous body 1, the content of the sintering aid in the materials constituting the alumina porous body 1 in the raw material mixture may be less than 0.1% by mass or more than 1.5% by mass.

In the method for producing the alumina porous body 1, the firing conditions and heat treatment conditions in step S12 may be changed as appropriate. For example, the firing temperature for the compact may be less than 1200°C or higher than 1450°C.

The configurations in the above embodiments and variations may be combined as appropriate as long as they are not mutually inconsistent.

Although the invention has been described in detail, the above description is illustrative and not restrictive. Therefore, numerous modifications and variations are possible without departing from the scope of the invention.

The alumina porous body of the present invention can be suitably used as a substrate for filters used in water treatment.

1 Alumina porous body 92 Al ₂ O ₃ particles 93 TiO ₂ domains

Claims (13)

An alumina porous body,
_Al2O3 , _and
TiO2 , and
Including,
The content of _TiO2 is 10% by mass or more and 40% by mass or less,
The porosity is 10% or more and 45% or less,
The average pore diameter is 2 μm or more and 12 μm or less,
A porous alumina body in which the bonding ratio between Al ₂ O ₃ particles and TiO ₂ domains is 5% or more. The alumina porous body according to claim 1,
The porosity is 20% or more,
An alumina porous body having an average pore diameter of 5 μm or more. The alumina porous body according to claim 1,
An alumina porous body having a total content of Al ₂ O ₃ and TiO ₂ of 100 mass %. The alumina porous body according to claim 1,
Further containing Ca,
The alumina porous body has a Ca content of 0.1 mass % or more and 1.5 mass % or less in terms of oxide. The alumina porous body according to claim 1,
The alumina porous body has a bending strength of 15 MPa or more. The alumina porous body according to claim 5,
The alumina porous body has a post-treatment strength, which is the bending strength after an alkali immersion treatment in which the body is immersed in an alkaline chemical solution, which is a sodium hydroxide aqueous solution with a pH of 13, at 80°C for 60 hours, followed by washing to remove the alkaline chemical solution and drying, and an initial strength, which is the bending strength before the alkali immersion treatment, in which the strength reduction rate, which is the rate of reduction in the post-treatment strength relative to the initial strength, is 20% or less. The alumina porous body according to any one of claims 1 to 6,
A porous alumina material used as a ceramic filter. A ceramic filter,
The alumina porous body according to any one of claims 1 to 6,
a porous ceramic membrane provided on the surface of the alumina porous body and having an average pore diameter smaller than that of the alumina porous body;
A ceramic filter comprising: A method for producing an alumina porous body, comprising:
a) forming a raw material mixture containing Al ₂ O ₃ particles and TiO ₂ particles into a compact;
b) firing the compact to obtain an alumina porous body;
A method for producing an alumina porous body comprising the steps of: The method for producing an alumina porous body according to claim 9,
A method for producing an alumina porous body, wherein the _TiO2 particles contained in the raw material mixture are coated with aluminum hydroxide. The method for producing an alumina porous body according to claim 9 or 10,
A method for producing an alumina porous body, wherein the total content of the Al ₂ O ₃ particles and the TiO ₂ particles in the material constituting the alumina porous body in the raw material mixture is 100 mass %. The method for producing an alumina porous body according to claim 9 or 10,
The raw material mixture further contains a sintering aid containing Ca,
A method for producing an alumina porous body, wherein the content of the sintering aid in the material constituting the alumina porous body in the raw material mixture is 0.1 mass % or more and 1.5 mass % or less. The method for producing an alumina porous body according to claim 9 or 10,
The method for producing an alumina porous body, wherein the firing temperature in step b) is 1200°C or higher and 1450°C or lower.