Method for producing silicon carbide porous body and silicon carbide porous body

Abstract

Provided is a method for producing a silicon carbide porous body that can suppress an increase in the alkali metal element concentration in the silicon carbide porous body due to scattering and adhesion / solid solution of alkali metal elements during kiln use, and can suppress a decrease in catalytic performance. [Solution] The method for producing a silicon carbide porous body includes a step of adding an alkaline earth metal element or a compound containing an alkaline earth metal element, metallic silicon, and an organic binder to a silicon carbide particle raw material, and mixing and kneading them to obtain a puddle (step S1); a step of molding the puddle into a predetermined shape to obtain a molded body (step S2); a step of calcining the molded body to remove the organic binder in the molded body (step S3); a step of firing the molded body in a non-oxidizing atmosphere after calcining the molded body; and a step of oxidizing the molded body in an oxidizing atmosphere after firing the molded body (step S5).

Description

[Technical Field]

[0001] The present invention relates to a method for producing a silicon carbide porous body and a silicon carbide porous body. [Background technology]

[0002] For example, as disclosed in Patent Documents 1 and 2 below, a silicon carbide porous body is used as a catalyst support.

[0003] Patent Document 1 discloses "a silicon carbide porous body containing silicon carbide particles as aggregate and metallic silicon, and characterized by having an oxide phase containing Si, Al, and alkaline earth metals." Patent Document 1 explains that the presence of an oxide phase containing Si, Al, and alkaline earth metals suppresses oxidative decomposition of silicon carbide and metallic silicon even when exposed to high temperatures in a low-oxygen atmosphere, such as when used as a diesel particulate filter (DPF).

[0004] Patent Document 2 discloses a silicon carbide porous body having a sodium content of 0 to 0.12 mass% calculated as Na2O. Patent Document 2 explains that when the amount of alkali metal added to the raw materials for the silicon carbide porous body is increased, the alkali metal promotes the formation of the α-cristobalite phase in the oxide film, which increases thermal expansion due to the α-to-β phase transition of α-cristobalite and reduces thermal shock resistance. However, it explains that by controlling the sodium content as described above, it is possible to suppress the promotion of the formation of the α-cristobalite phase in the oxide film. It also explains that one possible method for controlling the sodium content in the silicon carbide porous body is to reduce the sodium contained in the raw materials. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] International Publication No. 03 / 082770 [Patent Document 2] Japanese Patent Application Publication No. 2019-178053 Summary of the Invention [Problem to be solved by the invention]

[0006] When the silicon carbide porous body described above is used as a catalyst support, a catalyst slurry is poured into the silicon carbide porous body, and after the excess catalyst slurry is removed, the silicon carbide porous body and catalyst slurry are dried and fired. Because the catalyst slurry contains various acids such as nitric acid and acetic acid, if the alkali metal elements in the silicon carbide porous body dissolve in the acid of the catalyst slurry, the alkali metal elements will be incorporated into the catalyst, raising concerns that the catalytic performance will be reduced due to the reducing action and active site blocking action of the alkali metal elements.

[0007] Conventionally, the content of alkali metal elements in silicon carbide porous bodies has been controlled by limiting the amount of alkali metal elements in the raw materials, as in Patent Document 2. Despite this, a new phenomenon has been discovered in which alkali metal elements that have accumulated in the firing jig during oxidation treatment are dispersed during the kiln and adhere to / dissolve in the silicon carbide porous body, thereby increasing the alkali metal element concentration in the silicon carbide porous body.

[0008] The present invention has been made to solve the above-mentioned problems, and one of its objects is to provide a method for producing a silicon carbide-based porous body that can suppress an increase in the alkali metal element concentration in the silicon carbide-based porous body due to scattering and adhesion / solid solution of the alkali metal element during kiln use, thereby suppressing a decrease in catalytic performance. Another object of the present invention is to provide a silicon carbide-based porous body that can suppress a decrease in catalytic performance. [Means for solving the problem]

[0009] As a result of extensive investigations, the present inventors have discovered the following new findings. Specifically, they have found that adding an alkaline earth metal element or a compound containing an alkaline earth metal element to the raw materials for a silicon carbide porous body, obtaining a molded body, calcining the molded body, and then sintering the molded body in a non-oxidizing atmosphere and then oxidizing it in an oxidizing atmosphere can incorporate an alkaline earth metal element into the oxide film. They have also found that incorporating an alkaline earth metal element into the oxide film can suppress an increase in the alkali metal element concentration in the silicon carbide porous body due to alkali metal element dispersion during kiln processing. This is thought to be because adding a certain amount of alkaline earth metal to the raw materials and dissolving the alkaline earth metal into the oxide film eliminates the possibility of alkali metal element dissolving in the oxide film later, thereby suppressing an increase in the alkali metal element concentration in the silicon carbide porous body due to alkali metal element dispersion and adhesion / dissolution during kiln processing. The present invention was completed based on these findings.

[0010] [1] In one embodiment, the present invention relates to a method for producing a silicon carbide porous body, the method comprising the steps of: adding an alkaline earth metal element or a compound containing the alkaline earth metal element, metallic silicon, and an organic binder to a silicon carbide particle raw material, and mixing and kneading the mixture to obtain a puddle; forming the puddle into a predetermined shape to obtain a molded body; calcining the molded body to remove the organic binder from the molded body; calcining the molded body in a non-oxidizing atmosphere after calcining; and oxidizing the molded body in an oxidizing atmosphere after calcining the molded body.

[0011] [2] The present invention may relate to the method for producing a silicon carbide-based porous body according to the first aspect, wherein a Plosser mixer is used for the mixing.

[0012] [3] The present invention may relate to the method for producing a silicon carbide-based porous body according to the first or second aspect, wherein, during the mixing, the alkaline earth metal element or the compound containing the alkaline earth metal element is made into a slurry and added to the silicon carbide particle raw material.

[0013] [4] The present invention may relate to the method for producing a silicon carbide-based porous body according to any one of items 1 to 3, wherein the oxidation treatment is carried out in the range of 1150 to 1350°C.

[0014] [5] The present invention may relate to the method for producing a silicon carbide-based porous body according to any one of items 1 to 4, wherein the alkaline earth metal element is magnesium, calcium or strontium.

[0015] [6] In one embodiment, the present invention relates to a silicon carbide-based porous body comprising silicon carbide particles and metallic silicon as aggregates, and an oxide film formed on the surfaces of the silicon carbide particles and the metallic silicon, wherein the oxide film contains an alkaline earth metal element and silicon dioxide.

[0016] [7] The present invention may relate to the silicon carbide porous body according to item 6, wherein the alkaline earth metal element is magnesium, calcium or strontium.

[0017] [8] The present invention may relate to the silicon carbide-based porous body according to item 6 or 7, wherein the alkaline earth metal element is 0.1% by mass or more and 5% by mass or less when the total of the silicon carbide particles and metallic silicon is 100% by mass.

[0018] [9] The present invention may relate to the silicon carbide-based porous body according to any one of items 6 to 8, wherein the oxide film has a thickness of 0.1 μm or more.

[0019]

[10] The present invention may relate to the silicon carbide-based porous body according to any one of items 6 to 9, wherein the proportion of alkali metal elements present in the oxide film measured by EPMA is less than 1 mass% of the total amount of elements detected by EPMA.

[0020]

[11] The present invention may relate to the silicon carbide porous body according to item 10, wherein the alkali metal element is sodium and / or potassium. [Effects of the Invention]

[0021] According to one embodiment of the method for producing a silicon carbide-based porous body of the present invention, an increase in the alkali metal element concentration in the silicon carbide-based porous body due to scattering and adhesion / dissolution of the alkali metal element during kiln use can be suppressed, and a decrease in catalytic performance can be suppressed. Furthermore, according to one embodiment of the silicon carbide-based porous body of the present invention, a decrease in catalytic performance can be suppressed. [Brief explanation of the drawings]

[0022] [Figure 1] 1 is a flowchart showing a method for producing a silicon carbide-based porous body according to an embodiment of the present invention. [Figure 2] FIG. 2 is an explanatory view schematically showing a silicon carbide-based porous body produced by the production method of FIG. 1. [Figure 3] 1 is an example of an SEM image used to measure the thickness of an oxide film in an example. [Figure 4] 1 is an example of an EPMA image used to measure the thickness of an oxide film in an example. DETAILED DESCRIPTION OF THE INVENTION

[0023] Hereinafter, embodiments of the present invention will be described with reference to the drawings. The present invention is not limited to each embodiment, and the components can be modified and embodied without departing from the spirit of the present invention. Furthermore, various inventions can be formed by appropriately combining multiple components disclosed in each embodiment. For example, some components may be omitted from all the components shown in the embodiments. Furthermore, components of different embodiments may be appropriately combined.

[0024] (Method for manufacturing silicon carbide porous body) FIG. 1 is a flow chart showing a method for producing a silicon carbide-based porous body 1 according to an embodiment of the present invention, and FIG. 2 is an explanatory diagram schematically showing a silicon carbide-based porous body 1 produced by the production method of FIG.

[0025] The manufacturing method of the silicon carbide-based porous body 1 of this embodiment is a method for manufacturing the silicon carbide-based porous body 1. As shown in FIG. 2, the silicon carbide-based porous body 1 includes silicon carbide particles 10 and metallic silicon 11 as aggregates, and oxide films 12 formed on the surfaces of the silicon carbide particles 10 and metallic silicon 11. Although not limited thereto, the silicon carbide-based porous body 1 can form a honeycomb structure. More specifically, the silicon carbide-based porous body 1 can form the outer peripheral wall of the honeycomb structure, and partition walls that define a plurality of cells that form flow paths between a first end face and a second end face of the honeycomb structure inside the outer peripheral wall. The silicon carbide-based porous body 1 can be used as a catalyst carrier.

[0026] As shown in FIG. 1, the method for producing the silicon carbide porous body 1 of this embodiment includes a step of obtaining a clay (step S1), a step of obtaining a molded body (step S2), a step of removing the organic binder (step S3), a step of firing (step S4), and a step of oxidizing (step S5).

[0027] In the step of obtaining a clay (step S1), an alkaline earth metal element or a compound containing an alkaline earth metal element, metallic silicon (Si), and an organic binder are added to a silicon carbide particle raw material, and then mixed and kneaded to obtain a clay.

[0028] The alkaline earth metal element added to the silicon carbide particle raw material may be magnesium (Mg), calcium (Ca), or strontium (Sr). Examples of the compound containing an alkaline earth metal element added to the silicon carbide particle raw material include compounds that are oxidized or decomposed during calcination or sintering to become at least one alkaline earth metal monoxide selected from the group consisting of magnesium oxide (MgO), calcium oxide (CaO), and strontium oxide (SrO), such as strontium carbonate (SrCO) and calcium acetate (Ca(CHCOO)).

[0029] Metallic silicon (Si) may contain trace amounts of impurities such as Fe, Al, and Ca, but it may be used as is, or may be purified by chemical treatment such as chemical washing.

[0030] Examples of organic binders include methyl cellulose, hydroxypropyl methyl cellulose, hydroxyethyl cellulose, carboxymethyl cellulose, and polyvinyl alcohol. It is particularly preferable to use methyl cellulose and hydroxypropyl methyl cellulose in combination. The organic binders may be used singly or in combination of two or more.

[0031] The silicon carbide particle raw material may contain trace amounts of impurities such as Fe, Al, and Ca, but may be used as is or may be purified by chemical treatment such as chemical washing.

[0032] Although various mixers can be used for mixing, it is preferable to use a Plosser mixer (e.g., a Lödige mixer). A Plosser mixer has a shovel blade and a multi-stage chopper blade. The Plosser mixer can effectively break down agglomerates of the raw material powder.

[0033] During mixing, it is preferable to add the alkaline earth metal element or the compound containing an alkaline earth metal element in a slurry form to the silicon carbide particle raw material. By adding the alkaline earth metal element or the compound containing an alkaline earth metal element in a slurry form, the alkaline earth metal element or the compound containing an alkaline earth metal element can be uniformly mixed with the silicon carbide particle raw material. As a method for making the alkaline earth metal element or the compound containing an alkaline earth metal element into a slurry form, various mixers can be used, but it is particularly preferable to use an emulsifying disperser.

[0034] In the step of obtaining a molded body (step S2), the clay is molded into a predetermined shape to obtain a molded body. When the silicon carbide porous body 1 constitutes a honeycomb structure as described above, a honeycomb molded body (an unfired honeycomb structure) is obtained in the step of obtaining a molded body.

[0035] In the step of removing the organic binder (step S3), the compact is calcined to remove the organic binder from the compact. The calcination of the compact may be performed in an electric furnace or a gas combustion furnace, and the calcination of the compact is preferably performed in an air atmosphere.

[0036] In the firing step (step S4), the compact is pre-fired and then fired in a non-oxidizing atmosphere. An electric furnace may be used for firing the compact, and the firing of the compact is performed in an atmosphere with an oxygen partial pressure of 10 -4 It is preferable to carry out the process under conditions of 1000 kJ / cm 2 atm or less.

[0037] In the oxidation treatment step (step S5), the compact is sintered and then oxidized in an oxidizing atmosphere. This oxidation treatment forms an oxide film 12 (FIG. 2). The oxidation treatment is preferably carried out in the range of 1150 to 1350°C. The thickness of the oxide film can be controlled by the temperature of the oxidation treatment, and by setting the temperature in the range of 1150 to 1350°C, it is possible to obtain the oxide film thickness necessary to ensure the desired material properties. An electric furnace or a gas combustion furnace may be used for the oxidation treatment, and the time for the oxidation treatment may be in the range of 1 to 20 hours.

[0038] When the silicon carbide porous body 1 described above is used as a catalyst support, a catalyst slurry is poured into the silicon carbide porous body 1, and after removing excess catalyst slurry, the silicon carbide porous body 1 and catalyst slurry are dried and fired. Such pouring of the catalyst slurry is performed after the oxidation treatment step (step S5). Because the catalyst slurry contains various acids such as nitric acid and acetic acid, if the alkali metal elements in the silicon carbide porous body 1 dissolve in the acids of the catalyst slurry, the alkali metal elements will be incorporated into the catalyst, raising concerns that the catalytic performance will be reduced due to the reducing action and active site blocking action of the alkali metal elements.

[0039] Although the content of alkali metal elements in the silicon carbide porous body 1 is controlled by limiting the amount of alkali metal elements in the raw materials, there is a phenomenon in which alkali metal elements that have accumulated in the firing jig during the oxidation treatment are dispersed during the kiln and adhere to / dissolve in the silicon carbide porous body 1, resulting in an increase in the concentration of alkali metal elements in the silicon carbide porous body 1.

[0040] As described above, in the manufacturing method of this embodiment, an alkaline earth metal element or a compound containing an alkaline earth metal element is added to the raw materials for silicon carbide porous body 1 to obtain a compact, which is then calcined and subsequently fired in a non-oxidizing atmosphere and oxidized in an oxidizing atmosphere, thereby allowing the alkaline earth metal element to be contained in oxide film 12. Furthermore, by including an alkaline earth metal element in oxide film 12, it is possible to suppress an increase in the alkali metal element concentration in silicon carbide porous body 1 due to the scattering and adhesion / solid solution of the alkali metal element during kiln processing. This is thought to be because adding a certain amount or more of alkaline earth metal to the raw materials and dissolving the alkaline earth metal in oxide film 12 eliminates the possibility of the alkali metal element being solid-dissolved in oxide film 12 later, thereby suppressing an increase in the alkali metal element concentration in silicon carbide porous body 1 due to the scattering of the alkali metal element during kiln processing. That is, according to the manufacturing method of this embodiment, an increase in the alkali metal element concentration in the silicon carbide porous body 1 due to scattering and adhesion / dissolution of the alkali metal element during kiln passing can be suppressed, and a decrease in catalytic performance can be suppressed.

[0041] (Silicon carbide porous body) 2, silicon carbide-based porous body 1 includes silicon carbide particles 10 and metallic silicon 11 as aggregates, and oxide films 12 formed on the surfaces of silicon carbide particles 10 and metallic silicon 11. In silicon carbide-based porous body 1 of this embodiment, oxide film 12 contains an alkaline earth metal element and silicon dioxide. By including these elements in oxide film 12, it is possible to suppress a decrease in catalytic performance.

[0042] The silicon carbide porous body 1 is inspected with an EPMA (Electron Probe Micro Analyzer) to distinguish between silicon carbide particles 10, metallic silicon 11, and oxide film 12. In the EPMA observation image, the areas where silicon and carbon are detected are silicon carbide particles 10, the areas where only silicon is detected are metallic silicon 11, and the areas where silicon and oxygen are detected are oxide film 12. For this distinction, the acceleration voltage is 15 kV and the Au coating is 100 angstroms thick. Similar measurements and detections can also be performed by element mapping using EDS (Energy Dispersive X-ray Spectroscopy).

[0043] The oxide film 12 covers the aggregates (silicon carbide particles 10 and metallic silicon 11) and is located within approximately 5 μm of the interface of the aggregates along the normal. The "oxide phase" in Patent Document 1 is formed in the form of particles between the aggregates. Generally, the "oxide phase" does not cover the aggregates but exists on the surface between the aggregates. Therefore, it should be noted that the "oxide phase" in Patent Document 1 does not correspond to the oxide film 12 in this specification. It should also be noted that the molded body in Patent Document 1 was not subjected to an oxidation treatment, and therefore the invention according to Patent Document 1 does not produce a film corresponding to the oxide film 12 in this specification. While the oxide film 12 in this specification contains silicon dioxide (SiO2) and an alkaline earth metal, the oxide phase in Patent Document 1 further contains aluminum oxide (Al2O3) in addition to silicon dioxide (SiO2) and an alkaline earth metal.

[0044] The alkaline earth metal element contained in the oxide film 12 may be magnesium (Mg), calcium (Ca), or strontium (Sr).

[0045] When the total of the silicon carbide particles 10 and metallic silicon 11 is taken as 100% by mass, the alkaline earth metal element content is preferably 0.1% by mass or more and 5% by mass or less. When the alkaline earth metal element content is 0.1% by mass or more, there is no room for the alkali metal element to form a solid solution in the silicon carbide porous body 1, and absorption of the alkali metal element can be suppressed. On the other hand, when the alkaline earth metal element content is 5% by mass or less, the form of an oxide film can be maintained. The contents of the silicon carbide particles 10, metallic silicon 11, and alkaline earth metal element are measured by X-ray fluorescence analysis using the glass bead method and powder X-ray diffraction.

[0046] The thickness of the oxide film 12 is preferably 0.1 μm or more. By setting the thickness to such a value, oxidation resistance can be improved. The thickness of the oxide film 12 is defined as the distance along the normal from the interface between the aggregates (silicon carbide particles 10 and metallic silicon 11). As mentioned above, the upper limit of the thickness of the oxide film 12 is 5 μm. The thickness of the oxide film 12 is the average value of five arbitrary locations.

[0047] The silicon dioxide of the oxide film 12 may have at least one of the following structures: cristobalite, quartz, and amorphous. The structure of the oxide film 12 is determined by powder X-ray diffraction.

[0048] When the oxide film 12 is measured by EPMA, the proportion of alkali metal elements present is preferably less than 1 mass% of the total amount of elements detected by the EPMA. This is because, while a smaller proportion is better for suppressing deterioration of the catalyst component, the detection accuracy must also be taken into consideration. The alkali metal elements may be sodium and / or potassium. The EPMA can be, for example, the "FE-EPMA JXA-8500F" manufactured by JEOL Ltd. When determining the proportion of alkali metal elements present, the acceleration voltage is 15 kV, the probe current is 0.1 μA, the magnification is 1000x, the pixel size is 300 × 300, the pixel size is X = 0.34 μm, Y = 0.34 μm, and the measurement time per pixel is 30 msec.

[0049] Although the preferred embodiments of the present invention have been described in detail above with reference to the accompanying drawings, the present invention is not limited to these examples. It is clear that a person skilled in the art to which the present invention pertains can conceive of various modifications and alterations within the scope of the technical ideas set forth in the claims, and it is understood that these also naturally fall within the technical scope of the present invention. [Example]

[0050] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

[0051] [Manufacturing honeycomb segments] Silicon carbide (SiC) powder and metallic silicon (Si) powder were mixed in a mass ratio of 80:20, 2.5 mass% aluminum oxide (Al2O3) powder, strontium oxide (SrO) powder (a compound containing alkaline earth metal elements), and calcium oxide powder (CaO) (a compound containing alkaline earth metal elements) in the mass ratios shown in Table 1 corresponding to the test number. To this was added 10 mass% pore-forming material (starch), 6 mass% organic binder (hydroxypropyl methylcellulose), and surfactant (oleic acid ester), and an appropriate amount of water was then added to obtain a clay.

[0052] This clay was extruded through a predetermined die and dried to obtain a rectangular parallelepiped honeycomb formed body having an outer peripheral sidewall and partition walls that defined a plurality of cells extending from the first bottom surface to the second bottom surface. Plugging portions were formed at one end of each cell of this rectangular parallelepiped honeycomb formed body so that both bottom surfaces presented a checkerboard pattern. That is, the plugging portions were formed so that adjacent cells were plugged at their opposite ends. The plugging portions were made of the same material as the columnar honeycomb formed body. After the plugging portions were formed and dried, the columnar honeycomb formed body was degreased in an air atmosphere at approximately 450°C and then fired in an Ar atmosphere (non-oxidizing atmosphere) at approximately 1450°C to bond the SiC particles in the formed body with Si. Further, an oxidation treatment was performed under the conditions listed in Table 1 to obtain a rectangular parallelepiped honeycomb structure segment with the following specifications.

[0053] Bottom shape: 35mm square Total length: 152mm Average thickness of partition wall: 0.305 mm Cell cross-sectional shape: square Cell density: 44 cells / cm 2 Average thickness of outer wall: 0.5 mm

[0054] [Composition analysis] The resulting honeycomb structure segments were subjected to compositional analysis using X-ray fluorescence and inert gas fusion. One-cm square specimens were mirror-polished and subjected to SEM and EPMA analysis to measure the oxide film thickness and the composition of Na in the oxide film (measurement of the amount of Na in the oxide film). Figure 3 shows an example of an SEM image used for oxide film thickness measurement, and Figure 4 shows an example of an EPMA image used for oxide film thickness measurement. In the SEM image, the oxide film can be seen as different colors on the surfaces of the SiC and Si particles, allowing for magnification and measurement of the oxide film thickness. In the EPMA image, elemental mapping of O (oxygen) allows for more clear distinction and measurement of the oxide film. The thickness of the oxide film 12 was calculated as the average value of five randomly selected locations. In the examples shown in Figures 3 and 4, the oxide film thickness is approximately 2 μm.

[0055] [Table 1]

[0056] In Examples 1 to 4, a compound containing an alkaline earth metal element was added to silicon carbide particle raw material, and the mixture was mixed and kneaded to obtain a puddle, whereas in Comparative Examples 1 and 2, no compound containing an alkaline earth metal element was added. Compared to Comparative Examples 1 and 2, the oxide films in Examples 1 to 4 contained less Na (alkali metal element). These results demonstrate that by adding a compound containing an alkaline earth metal element to silicon carbide particle raw material, and then mixing and kneading the mixture to obtain a puddle, it is possible to suppress an increase in the alkali metal element concentration in the silicon carbide porous body due to the scattering and adhesion / solid solution of the alkali metal element during kiln use.

[0057] [Analysis of oxidation catalyst and SCR catalyst purification performance] The obtained honeycomb structure segment was coated with approximately 150 g / L of an oxidation catalyst and an SCR catalyst, respectively, and the purification performance was evaluated by the following method.

[0058] The purification performance of the oxidation catalyst was measured by cutting a cylindrical test piece with a diameter of 25.4 mm and a length of 50 mm from a honeycomb structure segment, loading the oxidation catalyst on it, and then flowing a model gas (HC: 300 ppm, O2: 10%, remaining N2) through the test piece at an SV value (space velocity) of 6000 (1 / h), and measuring the purification rate at an ambient temperature of 350°C.

[0059] The purification performance of the SCR catalyst was measured by cutting a cylindrical test specimen with a diameter of 25.4 mm and a length of 50 mm from a honeycomb structure segment, loading the SCR catalyst on it, and then flowing a model gas (NH3: 300 ppm, NO: 300 ppm, H2O: 5%, CO2: 8%, O2: 10%, remaining N2) at SV8000 (1 / h) and measuring the purification rate at an ambient temperature of 400°C.

[0060] The measurement results of these purification rates are shown in Table 2.

[0061] [Table 2]

[0062] Compared with Comparative Examples 1 and 2, improvements in purification rate were observed for all catalysts in Examples 1 to 4. These results demonstrate that, as described above, the deterioration of catalytic performance can be suppressed by suppressing the increase in the alkali metal element concentration in the silicon carbide porous body due to the scattering and adhesion / solid solution of alkali metal elements during kiln use. [Explanation of symbols]

[0063] 1: Silicon carbide porous material 10: Silicon carbide particles 11: Metallic silicon 12: Oxide film

Claims

1. a step of adding an alkaline earth metal element or a compound containing the alkaline earth metal element, metallic silicon, and an organic binder to a silicon carbide particle raw material, and mixing and kneading the mixture to obtain a clay; A step of forming the clay into a predetermined shape to obtain a molded body; a step of calcining the compact to remove the organic binder from the compact; a step of calcining the compact and then firing the compact in a non-oxidizing atmosphere; a step of subjecting the compact to an oxidation treatment in an oxidizing atmosphere after the compact is subjected to main firing; Including, A method for producing a silicon carbide porous body.

2. A proshare mixer is used for the mixing. A method for producing the silicon carbide porous body according to claim 1.

3. During the mixing, the alkaline earth metal element or the compound containing the alkaline earth metal element is added to the silicon carbide particle raw material in the form of a slurry. A method for producing the silicon carbide porous body according to claim 1 or 2.

4. The oxidation treatment is carried out in the range of 1150 to 1350°C. A method for producing the silicon carbide porous body according to claim 1 or 2.

5. The alkaline earth metal element is magnesium, calcium or strontium; A method for producing the silicon carbide porous body according to claim 1 or 2.

6. A silicon carbide porous body comprising silicon carbide particles and metallic silicon as aggregates, and an oxide film formed on the surfaces of the silicon carbide particles and the metallic silicon so as to cover the silicon carbide particles and the metallic silicon, The oxide film contains an alkaline earth metal element and silicon dioxide. Silicon carbide porous material.

7. The alkaline earth metal element is magnesium, calcium or strontium; The silicon carbide porous body according to claim 6 .

8. When the total amount of the silicon carbide particles and metallic silicon is 100 mass%, the alkaline earth metal element is 0.1 mass% or more and 5 mass% or less. The silicon carbide porous body according to claim 6 or 7.

9. The thickness of the oxide film is 0.1 μm or more. The silicon carbide porous body according to claim 6 or 7.

10. the content of alkali metal elements in the oxide film measured by EPMA is less than 1 mass % of the total amount of elements detected by EPMA; The silicon carbide porous body according to claim 6 or 7.

11. The alkali metal element is sodium and / or potassium. The silicon carbide porous body according to claim 10.

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