Ceramic body and method of manufacturing same

Abstract

To provide a method for producing a ceramic body having high thermal conductivity, which is made of Si-impregnated SiC.SOLUTION: A method for producing a ceramic body includes: a forming step of forming a forming material containing SiC powders having an average particle size D50 of 15 to 50 μm and SiC powders having an average particle size D50 of 2 to 8 μm in a mass ratio of 3:7 to 7:3 to obtain a formed body; and a firing and impregnating step of firing the formed body and impregnating it with metal Si.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a ceramic body and a method for making the same. [Background technology]

[0002] In recent years, there has been a demand for improved fuel economy in automobiles. In particular, to prevent a decline in fuel economy when the engine is cold, such as when starting the engine, there are hopes for systems that can quickly warm the coolant, engine oil, automatic transmission fluid (ATF), etc., thereby reducing friction loss. There are also hopes for systems that can heat exhaust gas purification catalysts to quickly activate them.

[0003] The above-mentioned systems use heat exchangers that have a honeycomb shape and include a ceramic body (honeycomb structure) made of Si-impregnated SiC (Patent Document 1). The ceramic body is manufactured by degreasing a ceramic molded body containing silicon carbide (hereinafter referred to as "SiC") and then impregnating it with metallic silicon (hereinafter referred to as "Si"). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 6763699 Summary of the Invention [Problem to be solved by the invention]

[0005] In recent years, there has been a demand for increasing the thermal conductivity of ceramic bodies made of Si-impregnated SiC in order to improve the performance of heat exchangers (for example, to improve heat recovery). SiC forms the skeleton of the ceramic body and has a higher thermal conductivity than Si. Therefore, it is believed that the thermal conductivity of the ceramic body can be improved by increasing the proportion of SiC in the ceramic body. However, with conventional methods, it is difficult to stably increase the proportion of SiC in the ceramic body (skeleton), and there is a problem that the thermal conductivity of the ceramic body is not sufficiently improved. Although the ceramic body used in a heat exchanger has been described above as an example, there is also a need for improved thermal conductivity in ceramic bodies used in devices other than heat exchangers.

[0006] The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide a ceramic body made of Si-impregnated SiC and having high thermal conductivity, and a method for producing the same. [Means for solving the problem]

[0007] As a result of extensive research into ceramic bodies made of Si-impregnated SiC, the inventors discovered that the above-mentioned problems can be solved by using a molding material containing two types of SiC powders with predetermined average particle sizes D50 in a predetermined ratio, and thus completed the present invention. That is, the present invention is exemplified as follows.

[0008] [1] SiC powder with an average particle size D50 of 15 to 50 μm and 4 a molding step of molding a molding material containing SiC powder of 3:7 to 7:3 in a mass ratio of 1:1 to 1:3, and SiC powder of 1:1 to 1:8 μm in a mass ratio of 3:7 to 7:3 to obtain a molded body; a firing / impregnation step of firing the molded body and impregnating it with metallic Si; A method for producing a ceramic body having the following structure:

[0009] [2] The method for producing a ceramic body according to [1], wherein the firing and impregnation step is carried out by firing the molded body in a state where the molded body is in contact with metallic Si.

[0010] [3] The method for producing a ceramic body according to [2], wherein the firing is carried out in an inert gas atmosphere or in vacuum at a temperature of 1400 to 1600°C.

[0011] [4] The method for producing a ceramic body according to any one of [1] to [3], wherein the ceramic raw material contained in the molding material is only the SiC powder.

[0012] [5] The method for producing a ceramic body according to any one of [1] to [4], wherein at least one of a drying treatment and a degreasing treatment is performed on the molded body between the molding step and the firing / impregnation step.

[0013] [6] A method for producing a ceramic body according to any one of [1] to [5], wherein the molded body has a honeycomb shape having an outer peripheral wall and a plurality of partition walls arranged inside the outer peripheral wall and defining a plurality of cells extending from a first end face to a second end face, or a hollow honeycomb shape having an inner peripheral wall, an outer peripheral wall, and partition walls arranged between the inner peripheral wall and the outer peripheral wall and defining a plurality of cells extending from a first end face to a second end face.

[0014] [7] A ceramic body for use in a heat exchanger, comprising: a SiC skeleton containing SiC particles having a particle size of 15 to 50 μm and SiC particles having a particle size of 2 to 8 μm in a volume ratio of 3:7 to 7:3; at least a part of the SiC skeleton void The metal Si impregnated part formed in Equipped with 、 Thermal conductivity at 25°C is 140W / mK or more. Ceramic body. [Effects of the Invention]

[0015] According to the present invention, it is possible to provide a ceramic body made of Si-impregnated SiC and having high thermal conductivity, and a method for producing the same. [Brief explanation of the drawings]

[0016] [Figure 1] FIG. 2 is a partially enlarged cross-sectional view of a molded body produced according to a method for producing a ceramic body according to an embodiment of the present invention. [Figure 2] 1 is a cross-sectional view of a honeycomb-shaped molded body taken along a line perpendicular to the cell extension direction. [Figure 3] 1 is a cross-sectional view of a hollow honeycomb-shaped formed body taken along a line perpendicular to the cell extension direction. DETAILED DESCRIPTION OF THE INVENTION

[0017] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. The present invention is not limited to the following embodiments, and it should be understood that modifications and improvements made to the following embodiments based on the ordinary knowledge of those skilled in the art without departing from the spirit of the present invention are also within the scope of the present invention.

[0018] (1) Method for manufacturing ceramic body The method for producing a ceramic body according to an embodiment of the present invention includes a molding step and a firing / impregnation step. These steps will now be described in detail.

[0019] <Forming process> The molding process is a process in which a molding material containing SiC powder with an average particle size D50 of 15 to 50 μm (hereinafter abbreviated as "SiC powder A") and SiC powder with an average particle size D50 of 2 to 8 μm (hereinafter abbreviated as "SiC powder B") in a mass ratio of 3:7 to 7:3 is molded to obtain a molded body. FIG. 1 shows a partially enlarged cross-sectional view of a compact produced under the above conditions. As shown in FIG. 1, by using two types of SiC powders A and B, each having an average particle size D50, in the above-mentioned mass ratio, SiC powder B, which has a smaller average particle size D50, is easily packed between the SiC powder A, which has a larger average particle size D50, in compact 10, thereby increasing the packing density of the SiC powders (SiC powders A and B) that make up compact 10. As a result, the thermal conductivity of the ceramic body obtained by subjecting compact 10 to firing and infiltration processes is improved. On the other hand, if the above conditions are not met, the packing density of the SiC particles that make up the compact cannot be sufficiently increased, and the thermal conductivity of the ceramic body is therefore not sufficiently improved. Here, the "average particle size D50" of the SiC powders A and B used in the molding step refers to the particle size at 50% cumulative value (D50) in the particle size distribution determined by the laser diffraction / scattering method.

[0020] The SiC powder A may be a single type or a combination of two or more types. Specifically, two or more types of SiC powder A having an average particle size D50 in the range of 15 to 50 μm may be used. Similarly, a single type of SiC powder B may be used, or two or more types may be used in combination. Specifically, two or more types of SiC powder B having an average particle size D50 in the range of 2 to 8 μm may be used.

[0021] From the viewpoint of stably ensuring the above effects, the average particle size D50 of the SiC powder A is preferably 20 to 45 μm, and more preferably 25 to 40 μm. Moreover, from the viewpoint of stably ensuring the above-mentioned effects, the average particle size D50 of the SiC powder B is preferably 3 to 7 μm, and more preferably 4 to 6 μm. Furthermore, the mass ratio of SiC powder A to SiC powder B is preferably 4:6 to 6:4, from the viewpoint of stably ensuring the above effects.

[0022] The molding material preferably contains only SiC powders A and B as ceramic raw materials. SiC powders A and B have high thermal conductivity and a thermal expansion coefficient close to that of metallic Si to be impregnated in a process described below, making it possible to obtain a ceramic body with excellent resistance to thermal stress. Here, the ceramic raw material means the raw material that constitutes the skeleton of the ceramic body after the firing and impregnation steps.

[0023] The molding material may contain components known in the art, as needed. Examples of known components include a dispersion medium, a binder, a plasticizer, and a dispersant. The content of these components is not particularly limited as long as it does not impair the effects of the present invention.

[0024] Examples of the dispersion medium include water and a mixed solvent of water and an organic solvent such as alcohol, with water being particularly preferred.

[0025] Examples of binders include organic binders such as methyl cellulose, hydroxypropoxyl cellulose, hydroxyethyl cellulose, carboxymethyl cellulose, and polyvinyl alcohol. In particular, it is preferable to use methyl cellulose and hydroxypropoxyl cellulose in combination. The binder may be a single type, or two or more types may be used in combination.

[0026] Examples of the plasticizer include polyoxyalkylene alkyl ether, polycarboxylic acid polymer, and alkyl phosphate ester.

[0027] The dispersant may be a surfactant such as polyoxyalkylene alkyl ether, ethylene glycol, dextrin, fatty acid soap, polyalcohol, etc. The dispersant may be a single type or a combination of two or more types.

[0028] The molding method is not particularly limited, and known methods such as extrusion molding can be used. In extrusion molding, a molded body of a desired shape can be obtained by selecting a die and a jig of an appropriate shape. For example, when obtaining a honeycomb-shaped molded body, the shape and density of the cells, the number, length and thickness of the partition walls, the shapes and thicknesses of the outer and inner peripheral walls, etc. can be controlled by selecting a die and a jig of an appropriate shape.

[0029] The shape of the molded body obtained by the molding step is not particularly limited, but is preferably a honeycomb shape having an outer peripheral wall and a plurality of partition walls disposed inside the outer peripheral wall to define a plurality of cells extending from the first end face to the second end face, or a hollow honeycomb shape having an inner peripheral wall, an outer peripheral wall, and partition walls disposed between the inner and outer peripheral walls to define a plurality of cells extending from the first end face to the second end face. By using such a shape, for example, when used in a heat exchanger, its performance (e.g., heat recovery ability) can be improved.

[0030] Here, Figure 2 shows a cross-sectional view perpendicular to the cell extension direction of a honeycomb-shaped formed body (honeycomb formed body), and Figure 3 shows a cross-sectional view perpendicular to the cell extension direction of a hollow honeycomb-shaped formed body (hollow honeycomb formed body). As shown in Fig. 2, the honeycomb formed body 100 has an outer peripheral wall 110 and a plurality of partition walls 130 disposed inside the outer peripheral wall 110 and defining a plurality of cells 120 extending from a first end face to a second end face. Also, as shown in Fig. 3, the hollow honeycomb formed body 200 has an inner peripheral wall 140, the outer peripheral wall 110, and partition walls 130 disposed between the inner peripheral wall 140 and the outer peripheral wall 110 and defining a plurality of cells 120 extending from a first end face to a second end face.

[0031] The shapes (external shapes) of the honeycomb formed body 100 and the hollow honeycomb formed body 200 are not particularly limited, and may be, for example, a circular cylinder, an elliptical cylinder, a square prism, or other polygonal prism. That is, the external shapes of the honeycomb formed body 100 and the hollow honeycomb formed body 200 in a cross section perpendicular to the extension direction of the cells 120 may be a circle, an ellipse, a square, or other polygonal shape. Furthermore, the hollow portion of the hollow honeycomb formed body 200 may be the same as or different from the external shape of the hollow honeycomb formed body 200, and may be any of the above-mentioned various shapes. The shape of the cells 120 in a cross section perpendicular to the direction in which the cells 120 extend is not limited to the shape shown in the figure, and may be a circle, an ellipse, a polygon such as a triangle, or the like.

[0032] After the firing and impregnation steps, the honeycomb formed body 100 and the hollow honeycomb formed body 200 preferably have a structure that satisfies the following characteristics: The honeycomb formed body 100 and the hollow honeycomb formed body 200 after the firing and impregnation steps are called honeycomb structures.

[0033] The cell density (i.e., the number of cells 120 per unit area) in the cross section perpendicular to the direction in which the cells 120 of the honeycomb structure extend may be adjusted appropriately depending on the application, etc., but is preferably 4 to 320 cells / cm. 2In a cross section perpendicular to the direction in which the cells 120 extend, the cell density is preferably in the range of 4 cells / cm. 2 By setting the cell density to the above, it is possible to sufficiently secure the strength of the partition walls 130, and in turn the strength and effective GSA (geometric surface area) of the honeycomb structure itself. 2 By satisfying the following conditions, it is possible to prevent an increase in pressure loss when the fluid flows.

[0034] The thickness of the partition walls 130 of the honeycomb structure may be appropriately designed depending on the purpose, but is preferably 50 μm to 2 mm, and more preferably 60 μm to 600 μm. When the thickness of the partition walls 130 is 50 μm or more, the mechanical strength is improved and breakage due to impact or thermal stress can be suppressed. On the other hand, when the thickness of the partition walls 130 is 2 mm or less, the proportion of the cell volume in the honeycomb structure increases, thereby reducing fluid pressure loss and improving the heat exchange rate.

[0035] The thickness of the outer peripheral wall 110 and the inner peripheral wall 140 (if present) of the honeycomb structure may be appropriately designed depending on the purpose, but when used for heat exchange purposes, it is preferably more than 0.3 mm and not more than 10 mm, more preferably 0.5 mm to 5 mm, and even more preferably 1 mm to 3 mm. Furthermore, when used for heat storage purposes, the thickness of the outer peripheral wall 110 may be set to 10 mm or more to increase the heat capacity of the outer peripheral wall 110.

[0036] <Firing and impregnation process> The firing and impregnation step involves firing the compact and impregnating it with metallic Si. The conditions for the calcination / impregnation step are not particularly limited, and the step can be carried out in accordance with a known method. The calcination / impregnation step can be carried out in a single step, or the calcination and impregnation can be carried out in separate steps. Specifically, the calcination step and the impregnation step can be carried out as separate steps.

[0037] The firing and impregnation steps are preferably carried out by firing the compact in a state where it is in contact with metallic silicon. By firing in this state, the molten metallic silicon penetrates into the gaps between the ceramic particles that make up the compact by capillary action, allowing the metallic silicon to be impregnated. Furthermore, this method allows firing and impregnation to be carried out in a single step, thereby reducing manufacturing costs.

[0038] The position where the metal Si is brought into contact with the molded body is not particularly limited, but it is preferable to place the metal Si on the upper surface of the molded body for contact. For example, when the honeycomb molded body 100 and the hollow honeycomb molded body 200 are used as the molded body, the position where the metal Si is brought into contact may be any of the end face (first end face or second end face), the outer peripheral wall 110, or the inner peripheral wall 140 (if present). Furthermore, when the extension direction of the cells 120 is the vertical direction, it is preferable to place the metal Si on the end face (first end face or second end face) located above the honeycomb molded body 100 and the hollow honeycomb molded body 200 for contact. By bringing the metal Si into contact in this manner, gravity makes it easier to impregnate the metal Si.

[0039] The firing is preferably carried out in an inert gas atmosphere or in vacuum at a temperature of 1400 to 1600°C. Firing under these conditions facilitates impregnation of metallic Si. It also prevents insufficient sintering due to oxidation and reduces oxides contained in the molding material. The inert gas atmosphere may be a nitrogen gas atmosphere, a rare gas atmosphere such as argon, or a mixed gas atmosphere thereof. From the viewpoint of stably ensuring the above effects, the firing temperature is preferably 1450 to 1550° C. The firing time is not particularly limited, but is typically 0.25 to 5 hours. The firing furnace used for firing is not particularly limited, but an electric furnace, a gas furnace, or the like can be used.

[0040] <Other processes> Between the molding step and the firing / impregnation step, the molded body may be subjected to at least one of a drying treatment and a degreasing treatment. After the firing / impregnation step, the molded body may be subjected to a surface treatment such as polishing. The drying treatment is not particularly limited, and known methods can be used, such as a microwave dryer, a hot air dryer, a dielectric dryer, a reduced pressure dryer, a vacuum dryer, or a freeze dryer.

[0041] The degreasing treatment is a process for burning and removing components such as binders. The conditions for the degreasing treatment are not particularly limited as long as they are within a range that allows the binders to be burned, and may be set appropriately depending on the type of binder. For example, the degreasing treatment can be performed by heating the compact at 300 to 600°C for 1 to 10 hours.

[0042] (2) Ceramic body A ceramic body according to an embodiment of the present invention is obtained by the above-described method for producing a ceramic body, and includes a SiC skeleton and a metal Si-impregnated portion. The SiC skeleton contains SiC particles with particle sizes of 15 to 50 μm and SiC particles with particle sizes of 2 to 8 μm in a volume ratio of 3:7 to 7:3. By using an SiC skeleton containing two types of SiC particles with predetermined particle sizes in the above volume ratio, the proportion of SiC particles in the ceramic body can be increased, thereby improving the thermal conductivity of the ceramic body.

[0043] Here, the volume ratio of SiC particles with a particle size of 15 to 50 μm to SiC particles with a particle size of 2 to 8 μm in the ceramic body can be determined by observing the cross section of the ceramic body using an SEM. Specifically, in an SEM image of the cross section of the ceramic body, SiC particles with a particle size of 15 to 50 μm are distinguished from SiC particles with a particle size of 2 to 8 μm. In this case, the particle size of the SiC particles is defined as the circle-equivalent diameter. The ratio of the total area of ​​SiC particles with a particle size of 15 to 50 μm to the total area of ​​SiC particles with a particle size of 2 to 8 μm in the ceramic body is defined as the volume ratio of SiC particles with a particle size of 15 to 50 μm to SiC particles with a particle size of 2 to 8 μm in the ceramic body.

[0044] The metal Si-impregnated portion is formed in at least some of the voids in the SiC skeleton, making the ceramic body dense and increasing the thermal conductivity and strength.

[0045] The thermal conductivity of the ceramic body is not particularly limited, but is preferably 140 W / mK or more, more preferably 150 W / mK or more, at 25°C. When the ceramic body is used in a heat exchanger, the heat recovery performance of the heat exchanger can be improved by setting the thermal conductivity of the ceramic body within the above range. The thermal conductivity value means a value measured by the laser flash method (JIS R1611:1997).

[0046] Other characteristics of the ceramic body, such as the material constituting the ceramic body and its shape, are the same as those explained in the method for producing the ceramic body above, and therefore will not be explained here. [Example]

[0047] The present invention will be explained in more detail below with reference to examples, but the present invention is not limited to these examples in any way.

[0048] Examples 1 to 4 Three types of SiC powder with average particle sizes D50 of 35 μm, 25 μm, and 5 μm were prepared. Next, two or three types of these SiC powders were mixed in the mass ratios shown in Table 1, and 28 parts by mass of water and 7 parts by mass of methyl cellulose were further added and mixed for a total of 100 parts by mass of SiC powder to obtain a molding material. This molding material was extrusion-molded to obtain a honeycomb-shaped molded body. The size of the honeycomb molded body was adjusted so that it would become a honeycomb structure with the following shape after the firing and impregnation process. Shape of honeycomb structure in cross section perpendicular to the cell extension direction: circular Cell shape in cross section perpendicular to the cell extension direction: Rectangle Length of cell extension: 100 mm Outer diameter of honeycomb structure in cross section perpendicular to the cell extension direction: 100 mm Cell density: 14 cells / cm 2 Partition thickness: 0.3 mm Outer wall thickness: 1.5 mm

[0049] Next, the honeycomb molded body was placed with the cell extension direction aligned vertically, and metallic Si was placed on the upper end face. After that, the honeycomb structure (ceramic body) was obtained by firing at a temperature of 1500°C in a vacuum.

[0050] (Comparative Examples 1 and 2) A honeycomb structure (ceramic body) was obtained in the same manner as in the above-described Examples, except that SiC powder having an average particle size D50 of 35 μm or SiC powder having an average particle size D50 of 5 μm was used alone.

[0051] The thermal conductivity of the honeycomb structure obtained above was measured at 25°C using the laser flash method (JIS R1611:1997). In the evaluation of thermal conductivity, a thermal conductivity of 150 W / mK or more was represented by ◎, a thermal conductivity of 140 W / mK or more but less than 150 W / mK was represented by ○, and a thermal conductivity of less than 140 W / mK was represented by ×. The results are shown in Table 1.

[0052] [Table 1]

[0053] As shown in Table 1, the honeycomb structures (ceramic bodies) of Examples 1 to 4, which were prepared using SiC powder with an average particle size D50 of 15 to 50 μm and SiC powder with an average particle size D50 of 2 to 8 μm in a mass ratio of 3:7 to 7:3, had higher thermal conductivity than the honeycomb structures (ceramic bodies) of Comparative Examples 1 and 2, which were prepared using a single type of SiC powder.

[0054] As can be seen from the above results, the present invention can provide a ceramic body made of Si-impregnated SiC and having high thermal conductivity, and a method for producing the same. [Explanation of symbols]

[0055] 10 Molded body 100 Honeycomb molded body 110 Peripheral wall 120 cells 130 Bulkhead 140 Inner wall 200 Hollow honeycomb molding

Claims

1. a molding step of molding a molding material containing SiC powder having an average particle size D50 of 15 to 50 μm and SiC powder having an average particle size D50 of 4 to 8 μm in a mass ratio of 3:7 to 7:3 to obtain a molded body; a firing / impregnation step of firing the molded body and impregnating it with metal Si; A method for producing a ceramic body having the following structure:

2. The method for producing a ceramic body according to claim 1 , wherein the firing / impregnation step is carried out by firing the compact in a state where the compact is in contact with metallic Si.

3. The method for producing a ceramic body according to claim 2, wherein the firing is carried out in an inert gas atmosphere or in vacuum at a temperature of 1400 to 1600°C.

4. The method for producing a ceramic body according to any one of claims 1 to 3, wherein the ceramic raw material contained in the molding material is only the SiC powder.

5. The method for producing a ceramic body according to any one of claims 1 to 3, wherein the molded body is subjected to at least one of a drying treatment and a degreasing treatment between the molding step and the firing / impregnation step.

6. The method for producing a ceramic body according to any one of claims 1 to 3, wherein the molded body has a honeycomb shape having an outer peripheral wall and a plurality of partition walls arranged inside the outer peripheral wall and defining a plurality of cells extending from a first end face to a second end face, or a hollow honeycomb shape having an inner peripheral wall, an outer peripheral wall, and partition walls arranged between the inner peripheral wall and the outer peripheral wall and defining a plurality of cells extending from a first end face to a second end face.

7. A ceramic body for use in a heat exchanger, comprising: a SiC skeleton containing SiC particles having a particle size of 15 to 50 μm and SiC particles having a particle size of 2 to 8 μm in a volume ratio of 3:7 to 7:3; a metal Si impregnated portion formed in at least some voids of the SiC skeleton; Equipped with A ceramic body having a thermal conductivity of 140 W / mK or more at 25°C.

Images