Ceramic porous material

Abstract

To provide a functional ceramic porous body capable of performing various functions not only as a structure but also as a component of catalytic bodies, electrodes, and the like.SOLUTION: A ceramic porous body having a three-dimensional mesh structure with continuous pores formed therein is composed of a material whose main constituent is cerium oxide (CeO2).SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present disclosure relates to a ceramic porous body.

Background Art

[0002] Conventionally, various configurations using a porous body as a carrier for a catalyst or the like are known. Among porous bodies, a porous body having a three-dimensional network structure in particular is known as a carrier capable of suppressing a pressure loss. For example, Patent Document 1 discloses a configuration in which a catalyst support layer containing an alkaline earth metal or an alkali metal is formed on an alumina substrate having a three-dimensional network structure. Further, Cited Document 2 discloses a structure in which a catalyst body is adhered to a high-frequency absorber provided with a high-frequency absorption layer on a ceramic porous body having a three-dimensional network structure. Furthermore, Cited Document 3 discloses a configuration in which a porous body having a hydrophilicity enhanced by forming a thin film of a metal oxide such as aluminum oxide or titanium oxide on the surface of a metal porous body composed of nickel (Ni) or the like is used as an electrolysis electrode or the like.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0004] Such a porous body is desired to exhibit various functionalities not only as a structure for simply supporting a catalyst or the like but also as a component such as a catalyst body or an electrode. However, sufficient studies have not been made on such a functional porous body, particularly a functional ceramic porous body.

Means for Solving the Problems

[0005] This disclosure can be implemented in the following forms: (1) According to one embodiment of the present disclosure, a ceramic porous body having a three-dimensional network structure in which interconnected pores are formed is provided. This ceramic porous body is composed of a material whose main component is cerium oxide (CeO2). Because this form of porous ceramic material uses cerium oxide, a functional material, as its main component, it can exhibit performance in various applications such as catalyst supports and electrode substrates that could not be obtained with conventionally known porous ceramic materials having a three-dimensional network structure. (2) In the above-described form of the porous ceramic body, the second component further comprises at least one oxide from aluminum (Al), manganese (Mn), cobalt (Co), and copper (Cu), wherein the second component is a crystal of cerium oxide (CeO2) that constitutes the porous ceramic body. intergranular space They may also be present at the grain boundaries of the crystal. With such a configuration, the strength of the porous ceramic material can be further increased. (3) In the above-described form of the porous ceramic body, the second component may include an oxide of aluminum (Al), and the content of the second component may be 1.0% by mass or more. With such a configuration, the strength of the porous ceramic body can be increased more easily. (4) In the above-described form of the porous ceramic body, at least one of titanium (Ti) and iron (Fe) may be included as a third component. With such a configuration, the strength of the porous ceramic body can be further increased. (5) In the above-described form of porous ceramic body, the bulk density is 0.4 to 3.0 g / cm³ 3 This configuration is also acceptable. With this configuration, it is possible to suppress flow resistance within the porous ceramic material while preventing the porous ceramic material from becoming too strong. (6) In the above-described form of the porous ceramic body, the number of cells in the three-dimensional network structure may be 5 to 50 cells / 25.4 mm. With such a configuration, it is possible to suppress flow resistance inside the porous ceramic body while preventing the porous ceramic body from becoming too strong. This disclosure can be implemented in various forms other than those described above, for example, in the form of a method for manufacturing a porous ceramic body, a hydrogen production apparatus for hydrothermal decomposition using a porous ceramic body as a catalyst support, or an exhaust gas purification apparatus using a porous ceramic body as a catalyst support. [Brief explanation of the drawing]

[0006] [Figure 1] An explanatory diagram showing the appearance of a porous ceramic material. [Figure 2] An explanatory diagram showing the effect of adding a third component to cerium oxide. [Figure 3] An explanatory diagram showing the changes in the XRD chart due to the addition of titanium dioxide. [Figure 4] A flowchart illustrating the manufacturing method of a porous ceramic material. [Figure 5] An explanatory diagram showing the composition and measurement results of each sample. [Figure 6] An explanatory diagram showing the cross-section of sample S1. [Figure 7] An explanatory diagram showing an image of sample S1 observed using SEM-EDS. [Modes for carrying out the invention]

[0007] A. Composition of porous ceramic material: Figure 1 is an explanatory diagram showing the appearance of the ceramic porous body 10 of this embodiment. The ceramic porous body 10 has a three-dimensional network structure in which interconnected pores are formed, and is composed of a material whose main component is cerium oxide (CeO2). In this specification, "main component" of a specific component means that the content of that specific component is 50% by mass or more. The cerium oxide content in the ceramic porous body 10 can be measured, for example, by inductively coupled plasma mass spectrometry (ICP-MS).

[0008] The porous ceramic body 10 may further contain at least one oxide from aluminum (Al), manganese (Mn), cobalt (Co), and copper (Cu) as a second component different from the main component. Such a second component is a crystal of cerium oxide (CeO2) that constitutes the porous ceramic body 10. intergranular space It can exist at the grain boundaries of the crystal. To identify the presence of a second component at the grain boundaries of cerium oxide, the cross-section of the porous ceramic body 10 is mirror-polished, then thermally etched, and the resulting surface is observed with an EDS-equipped scanning electron microscope (SEM-EDS).

[0009] The main component is cerium oxide crystals. intergranular space The presence of the aforementioned second component at the grain boundaries of the ceramic porous body 10 improves the sinterability of the cerium oxide grain boundaries during sintering, thereby increasing the strength of the three-dimensional network structure constituting the ceramic porous body 10. It is desirable that the second component includes aluminum (Al) oxide. The fact that manganese (Mn), cobalt (Co), and copper (Cu) oxides, which are the second component, act as sintering accelerators that improve the sinterability of the cerium oxide grain boundaries is also described, for example, in X. Zhang et al., J. Power Sources 162, 480-485 (2006).

[0010] The content of the second component in the ceramic porous body 10 is desirably 0.1% by mass or more, more desirably 0.5% by mass or more, and even more desirably 1.0% by mass or more. By doing so, it becomes easier to ensure the effect of adding the second component to enhance the sinterability of the ceramic porous body 10. Further, the content of the second component in the ceramic porous body 10 is desirably 20.0% by mass or less, more desirably 17.0% by mass or less, and even more desirably 12.0% by mass or less. By doing so, while ensuring the effect of using cerium oxide as the main component, it becomes easy to appropriately arrange the second component at the grain boundaries of cerium oxide crystals.

[0011] In addition to the second component, or instead of the second component, the ceramic porous body 10 may contain at least one of titanium (Ti) and iron (Fe) as a third component different from the main component and the second component. By adding such a third component, the sinterability of the ceramic porous body 10 can be improved and the strength of the three-dimensional network structure can be enhanced.

[0012] Figure 2 is an explanatory diagram showing the effect of adding titanium (Ti) or iron (Fe), which is a third component, to cerium oxide. Here, the influence of adding a third component to a ceramic having cerium oxide as the main component was confirmed by producing a ceramic formed into a pellet shape. That is, four types of raw material powders were prepared: three types of raw material powders prepared by adding any one of titanium oxide (TiO2), iron oxide (FeO), and calcium oxide (CaO) to cerium oxide powder, and a raw material powder consisting only of cerium oxide. Using each raw material powder, ceramic pellets having cerium oxide as the main component were produced. The mixing amount of each third component in the raw material powder was 1.0% by mass. After each raw material powder was hand-pressed using a mold with a diameter of 10 mm, the ceramic pellets were produced by firing in a temperature range of 1400 to 1600°C. The density of each ceramic pellet was calculated as a ratio to the theoretical density using the specific gravity measured for each ceramic pellet according to the Archimedes method.

[0013] In FIG. 2, the horizontal axis represents the firing temperature, and the vertical axis represents the density of each ceramic pellet. As shown in FIG. 2, by adding titanium (Ti) or iron (Fe), which is the third component, to cerium oxide, a higher density can be obtained even at a lower firing temperature, and it has been confirmed that the sinterability is improved over a wide temperature range in which cerium oxide can be sintered. Since it has the effect of improving the sinterability in this way, it is considered that the strength of the ceramic porous body can be improved by adding the above third component.

[0014] FIG. 3 is an explanatory diagram showing the results of analysis by X-ray diffraction (XRD) for a ceramic pellet obtained by adding 1.0% by mass of titanium oxide described above to cerium oxide and a ceramic pellet composed only of cerium oxide. Here, the results of powder XRD are shown using the powder obtained by pulverizing each of the above ceramic pellets. From FIG. 3, it was confirmed that the peak of cerium oxide shifted due to the addition of titanium oxide. Similar results were obtained for the ceramic pellet to which iron oxide was added (data not shown). Therefore, it is considered that the third component improves the sinterability of the ceramic mainly composed of cerium oxide by solid-solving in the crystal grains of cerium oxide.

[0015] The content of the third component in the porous ceramic body 10 is preferably 0.1% by mass or more, more preferably 0.5% by mass or more, and even more preferably 1.0% by mass or more, when converted to the oxide of the third component. This makes it easier to ensure the effect of adding the third component to improve the sinterability of the porous ceramic body 10. Furthermore, the content of the third component in the porous ceramic body 10 is preferably 35.0% by mass or less, more preferably 30.0% by mass or less, and even more preferably 25.0% by mass or less, when converted to the oxide of the third component. This makes it possible to ensure the effect of using cerium oxide as the main component while suppressing undesirable effects caused by adding the third component, thereby obtaining the effect of improving sinterability.

[0016] The bulk density of the porous ceramic material 10 is 0.4 to 3.0 g / cm³. 3 It is desirable that the bulk density of the porous ceramic body 10 be 0.4 g / cm³. 3 If the density is less than 0.4 g / cm³, the porosity of the ceramic porous body 10 will be high, resulting in insufficient strength, which may make it difficult to maintain the shape of the ceramic porous body 10 and to manufacture the ceramic porous body 10. Specifically, for example, if the entire ceramic porous body 10 is formed from cerium oxide, the bulk density of the ceramic porous body 10 should be 0.4 g / cm³. 3 If the value is less than 3.0 g / cm³, the porosity of the porous ceramic material 10 will exceed 95%. 3 If the value exceeds this range, the porosity of the ceramic porous body 10 decreases, and the effect of increased flow resistance becomes significant; therefore, it is desirable to keep the value within the above range.

[0017] In the porous ceramic body 10, the number of cells in the three-dimensional network structure is preferably 5 to 50 cells / 25.4 mm. Here, the number of cells is the number of bubbles (cells) present on a line segment of unit length (25.4 mm) that is imagined on the cross-section of the porous ceramic body 10. If the number of cells in the porous ceramic body 10 is less than 5 cells / 25.4 mm, the individual bubbles formed in the porous ceramic body 10 become large, resulting in insufficient strength, which may make it difficult to maintain the shape of the porous ceramic body 10 and to manufacture the porous ceramic body 10. On the other hand, if the number of cells in the porous ceramic body 10 exceeds 50 cells / 25.4 mm, the individual bubbles formed in the porous ceramic body 10 become smaller, and the effect of increased flow resistance becomes greater, so it is desirable to keep the number within the above range.

[0018] B. Method for manufacturing porous ceramic materials: Figure 4 is a flowchart illustrating the manufacturing method of the porous ceramic body 10. To manufacture the porous ceramic body 10, first, a raw material powder containing cerium oxide is prepared (step T100). Then, an inorganic binder is added to the raw material powder prepared in step T100 to produce a slurry (step T110).

[0019] When producing a ceramic porous body 10 containing the second or third component described above, the second or third component can be added to the ceramic porous body 10 by preparing a raw material powder containing the second or third component in addition to cerium oxide in step T100. Specifically, when adding the second component, a metal oxide powder which is the second component, or a metal powder or metal compound powder other than an oxide which can become the second component, can be added to the raw material powder. When adding the third component, a metal compound containing the third component, or a metal powder consisting of the third component, can be added to the raw material powder. Furthermore, when producing a ceramic porous body 10 containing the second or third component, at least a portion of the second or third component to be added to the ceramic porous body 10 may be added to the raw material powder as an inorganic binder in step T110.

[0020] The inorganic binder only needs to have enough heat resistance to maintain its function as a binder at the firing temperature in the firing process described later. A glass-based binder can also be used as the inorganic binder, and using a glass-based binder allows for firing at a lower temperature. However, when using a glass-based binder, the heat resistance temperature of the resulting porous ceramic body 10 tends to decrease; therefore, when using the porous ceramic body 10 in a relatively high temperature range, it is desirable to use a metal oxide-based inorganic binder.

[0021] Next, the resin foam is coated using the slurry prepared in step T110 (step T120). The resin foam used in step T120 is a porous body having a mesh structure with three-dimensionally interconnected pores, and is formed from resin material that is burned off in the firing process. For example, polyurethane foam can be used as the resin foam. The number of cells in the three-dimensional mesh structure of the ceramic porous body 10 is determined by the number of cells in the resin foam to be coated with the slurry. Therefore, in step T120, it is desirable to use a resin foam with, for example, 5 to 50 cells / 25.4 mm in the three-dimensional mesh structure, and a resin foam with the desired number of cells should be appropriately selected according to the pore size of the ceramic porous body 10 to be manufactured. In addition, the bulk density of the ceramic porous body 10 can be adjusted by the amount of slurry used to coat the resin foam in step T120.

[0022] Subsequently, the resin foam coated with slurry is fired to burn off the resin foam (step T130) to complete the porous ceramic body 10. The firing temperature in step T130 can be any temperature at which cerium oxide can be sintered, for example, it can be 1400°C or higher.

[0023] As described above, the ceramic porous body 10 of this embodiment, having cerium oxide as its main component, exhibits performance that could not be obtained with conventionally known ceramic porous bodies having a three-dimensional network structure, and can be provided for various applications such as catalyst supports and electrode substrates. Specifically, for example, because the oxidation-reduction potential of cerium oxide is very low at 1.61V and its valence changes easily, it can be used to promote various reactions, and because it has the function of absorbing and releasing oxygen, it is useful as a catalyst support or electrode substrate.

[0024] Cerium oxide has relatively low strength among ceramic materials, making it difficult to form into a three-dimensional network structure. In this embodiment, when coating a resin foam with a slurry mainly composed of cerium oxide, an inorganic binder with a higher heat resistance temperature than commonly used organic binders is used as the binder. As a result, firing at a higher temperature becomes possible, and the material mainly composed of cerium oxide can be sintered well with sufficient strength.

[0025] Furthermore, in the porous ceramic body 10, the strength of the porous ceramic body 10 can be further increased by adding at least one oxide from aluminum (Al), manganese (Mn), cobalt (Co), and copper (Cu) as a second component, in addition to the main component, cerium oxide. Furthermore, in the porous ceramic body 10, the strength of the porous ceramic body 10 can be further increased by adding at least one from titanium (Ti) and iron (Fe) as a third component, in addition to the main component, cerium oxide. [Examples]

[0026] <Preparation of samples with a three-dimensional network structure> Figure 5 is an explanatory diagram showing the compositions of samples S1 to S8 and the measurement results for each sample. As shown below, ceramic porous body samples S1 to S8, which have a three-dimensional network structure and various compositions, were prepared according to the manufacturing method shown in Figure 4, and their strengths were compared. For the ceramic porous bodies of samples S1 to S8, polyurethane foam with similar porosity and average pore diameter was used as the resin foam in step T120.

[0027] [Sample S1] In step T100, cerium oxide (CeO2) powder was prepared as the raw material powder. In step T110, aluminum oxide, the second component, was added by preparing a slurry using an alumina-based binder as the inorganic binder. At this time, the alumina-based binder was added so that the aluminum oxide content in the entire porous ceramic body was 3.5% by mass. To facilitate the coating of the resin foam in step T120, water was added to the slurry as needed to adjust its viscosity. After coating the resin foam with the slurry, it was dried at 60-100°C and fired at 1500°C (step T130) to obtain the porous ceramic body of sample S1.

[0028] [Sample S2] The ceramic porous body of sample S2 was prepared in the same manner as sample S1, except that the amount of alumina-based binder used in process T110 was changed so that the aluminum oxide content in the entire ceramic porous body was 1.0 mass%.

[0029] [Sample S3] The ceramic porous body of Sample S3 was prepared in the same manner as Sample S1, except that the amount of alumina-based binder used in process T110 was changed so that the aluminum oxide content in the entire ceramic porous body was 10.0 mass%.

[0030] [Sample S4] In step T100, iron was added as a third component by adding iron oxide (FeO) to cerium oxide to form a raw material powder. The amount of iron oxide added was set so that the total amount of iron oxide in the constituent materials of the porous ceramic body was 0.5 mass%. In addition, the amount of alumina-based binder used in step T110 was set so that the total amount of aluminum oxide in the porous ceramic body was 3.8 mass%. Sample S4 of the porous ceramic body was prepared under the same conditions as Sample S1, except for the conditions mentioned above.

[0031] [Sample S5] The ceramic porous body of Sample S5 was prepared in the same manner as Sample S4, except that the amount of iron oxide added to the raw material powder in process T100 was changed so that the iron oxide content in the entire ceramic porous body was 1.0 mass%.

[0032] [Sample S6] The ceramic porous body of Sample S6 was prepared in the same manner as Sample S4, except that the amount of iron oxide added to the raw material powder in process T100 was changed so that the iron oxide content in the entire ceramic porous body was 20.0% by mass.

[0033] [Sample S7] In step T100, titanium oxide (TiO2) was added to cerium oxide to form a raw material powder, thereby adding titanium as a third component. The amount of titanium oxide added was such that the total titanium oxide content in the constituent material of the porous ceramic body was 1.0 mass%. Sample S7 of the porous ceramic body was prepared under the same conditions as Sample S4, except for the conditions mentioned above.

[0034] [Sample S8] In process T110, a ceria-based binder was used as the inorganic binder, but the porous ceramic body of sample S8 was fabricated in the same manner as sample S1.

[0035] <Verification of the prepared sample> Figure 5 shows the composition of each sample based on the mixing ratio of the raw materials. However, by measuring the obtained porous ceramic material using inductively coupled plasma mass spectrometry (ICP-MS), it was confirmed that the composition of the porous ceramic material did not deviate from the mixing ratio of the materials (data not shown).

[0036] Figure 6 is an explanatory diagram showing a cross-section of sample S1 as an example. Here, after embedding sample S1 in resin, it was polished and refined, and the cross-section of the sample was photographed using a scanning electron microscope (SEM). As shown in Figure 6, it was confirmed that aluminum (Al) exists at the grain boundaries of cerium oxide in the ceramic porous framework of each sample.

[0037] Figure 7 is an explanatory diagram showing an image obtained by elemental mapping of sample S1 using a scanning electron microscope (SEM-EDS) equipped with an energy-dispersive X-ray spectrometer, as an example. Figures 7(A) to 7(C) show observed images of the same field of view. Figure 7(A) shows the location of cerium (Ce), Figure 7(B) shows the location of aluminum (Al), and Figure 7(C) shows the location of oxygen (O). As shown in Figure 7, aluminum is present where cerium is absent, and oxygen is present where both cerium and aluminum are present. This confirms that both cerium and aluminum exist as oxides. In other words, the second component, aluminum, is a crystal of cerium oxide. intergranular space It was confirmed that it exists as aluminum oxide at the grain boundaries.

[0038] <Measurement of bulk density> The bulk density of each sample was calculated by measuring the external dimensions and weight of each sample.

[0039] <Measuring the number of cells> The number of cells in each sample was determined by setting a line segment of unit length (25.4 mm) at an arbitrary position in the cross-sectional image of each sample after it was embedded in resin, and measuring the number of air bubbles (cells) on this line segment.

[0040] <Measurement of compressive strength> For each sample, a rectangular sample with sides of 30 mm was prepared, and its strength when compressed from the top and bottom surfaces was measured using an autograph. Specifically, the compressive strength was calculated by identifying the stress at which fracture occurred when compressed at a stroke speed of 0.5 mm / min.

[0041] <Evaluation Results> As shown in Figure 5, it was confirmed that sufficient strength could be obtained as a ceramic porous body with a three-dimensional network structure by fabricating a slurry using an inorganic binder (Samples S1-S8). Furthermore, the compressive strength could be further increased by adding aluminum oxide, a second component (comparison of Samples S1-S3 and Sample S8). At this time, it was confirmed that a high effect of improving compressive strength was obtained by setting the content of aluminum oxide, the second component, to 1.0 mass% or more, and that the compressive strength was further improved by setting the content of aluminum oxide to 10.0 mass%. In addition, it was confirmed that the compressive strength was further improved by adding iron (Fe) or titanium (Ti), a third component (Samples S4-S7). At this time, it was confirmed that a high effect of improving compressive strength was obtained by setting the content of iron, the third component, to 0.5 mass% or more when converted to iron oxide, and that the compressive strength was further improved by setting it to 20 mass% when converted to iron oxide.

[0042] This disclosure is not limited to the embodiments described above, and can be implemented in various configurations without departing from its spirit. For example, the technical features in the embodiments corresponding to the technical features in each form described in the summary of the invention can be replaced or combined as appropriate in order to solve some or all of the above-mentioned problems, or to achieve some or all of the above-mentioned effects. Furthermore, if a technical feature is not described as essential in this specification, it can be deleted as appropriate.

[0043] This disclosure can also be implemented in the following forms: [Application Example 1] A porous ceramic body having a three-dimensional network structure in which interconnected pores are formed, It is characterized by being composed of a material whose main component is cerium oxide (CeO2). Ceramic porous material. [Application Example 2] The porous ceramic material described in Application Example 1, further, The second component contains at least one oxide of aluminum (Al), manganese (Mn), cobalt (Co), and copper (Cu). The second component is a crystal of cerium oxide (CeO2) that constitutes the porous ceramic body. intergranular space Characterized by existing at the grain boundaries of the crystal. Ceramic porous material. [Application Example 3] A porous ceramic body as described in Application Example 1 or 2, The second component includes an aluminum (Al) oxide, The second component is characterized in that its content is 1.0% by mass or more. Ceramic porous material. [Application Example 4] A porous ceramic body according to any one of the application examples 1 to 3, further, The third component is characterized by containing at least one of titanium (Ti) and iron (Fe). Ceramic porous material. [Application Example 5] A porous ceramic body according to any one of the application examples 1 to 4, The bulk density is 0.4 to 3.0 g / cm³. 3 It is characterized by being Ceramic porous material. [Application Example 6] A porous ceramic body according to any one of Application Examples 1 to 5, The three-dimensional network structure is characterized by having 5 to 50 cells per 25.4 mm. Ceramic porous material. [Explanation of symbols]

[0044] 10…Ceramic porous material

Claims

1. A porous ceramic body having a three-dimensional network structure in which interconnected pores are formed, The main component is cerium oxide (CeO ２ It is composed of the material, and furthermore, The second component includes at least one oxide of aluminum (Al), manganese (Mn), cobalt (Co), and copper (Cu). The second component is cerium oxide (CeO2), which constitutes the porous ceramic body. ２ ) is characterized by being present at the grain boundaries between the crystal grains. Ceramic porous material.

2. A porous ceramic body according to claim 1, The second component includes an aluminum (Al) oxide, The second component is characterized in that its content is 1.0% by mass or more. Ceramic porous material.

3. A porous ceramic body according to claim 1 or 2, further comprising: The third component is characterized by containing at least one of titanium (Ti) and iron (Fe). Ceramic porous material.

4. A porous ceramic body according to claim 1 or 2, Bulk density is 0.4 to 3.0 g / cm³ ３ It is characterized by being Ceramic porous material.

5. A porous ceramic body according to claim 1 or 2, The three-dimensional network structure is characterized by having 5 to 50 cells per 25.4 mm. Ceramic porous material.

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