Heat storage body and method for manufacturing the same

Abstract

To provide a heat reservoir which includes an antioxidation layer of silicate glass and is configured to inhibit attachment between the heat reservoirs or attachment between the heat reservoir and a cashing.SOLUTION: A heat reservoir is configured with: a spherical base 10 that is a sintered silicon carbide ceramic body; a base with protruding pieces which is a ceramic sintered body and includes a plurality of protruding pieces 20 protruding from a surface of the base 10; and an antioxidation layer 31 of silicate glass which covers a surface of the base with the protruding pieces. Shapes of the plurality of protruding pieces 20 are such irregular shapes that outer shapes of a plurality of end surfaces obtained by cutting by an arbitrary plane orthogonal to an imaginary straight line connecting a centroid of the protruding pieces 20 and a center of the base 10 are approximately polygonal shapes not being similar shapes.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a heat storage body and a method for manufacturing the heat storage body. [Background technology]

[0002] An example of a regenerative heat storage material disposed in a gas flow path for heat exchange with the gas is a regenerative heat storage material disposed in the heat exchange section of a regenerative burner (regenerative burner). Regenerative burners are used in industrial furnaces such as forging furnaces, heat treatment furnaces, melting furnaces, and calcining furnaces. The direction of gas flow is switched at predetermined time intervals so that exhaust gas heated to a high temperature by burner combustion and newly supplied gas for burner combustion are alternately circulated through the heat exchange section. The heat exchange section is filled with a large number of regenerative heat storage materials, and the heat of the exhaust gas is recovered by the regenerative heat materials, and the newly supplied gas is preheated by the recovered heat.

[0003] Solid balls made of alumina have been widely used as heat storage bodies, but there have also been proposals for using honeycomb structures made of ceramics such as alumina, cordierite, and mullite as heat storage bodies.

[0004] The present applicant has also proposed a heat storage medium based on a silicon carbide ceramic sintered body (see Patent Document 1). Silicon carbide is a material with high thermal conductivity among ceramics. Specifically, the thermal conductivities of alumina, cordierite, and mullite are 9 to 30 W / m·K, 0.6 W / m·K, and 1.5 W / m·K, respectively, while the thermal conductivity of silicon carbide is as high as 75 to 130 W / m·K. Therefore, a heat storage medium based on a silicon carbide ceramic sintered body has high heat exchange efficiency.

[0005] In addition, the thermal expansion coefficient of silicon carbide is 4.0 to 4.5 (×10 -6K). Silicon carbide has high thermal conductivity and a small coefficient of thermal expansion, and therefore has excellent thermal shock resistance. Therefore, a heat storage medium based on a silicon carbide ceramic sintered body is suitable as a heat storage medium that is continuously subjected to temperature changes caused by repeated heat storage and heat release.

[0006] However, silicon carbide has the problem of being oxidized when used at high temperatures in an oxygen-containing atmosphere. Therefore, the technology of Patent Document 1 employs a method in which the surface of a substrate, which is a silicon carbide ceramic sintered body, is coated with an anti-oxidation layer of silicate glass. This silicate glass layer prevents contact between the silicon carbide of the substrate and oxygen, effectively suppressing oxidation of the silicon carbide.

[0007] In addition, the applicant's investigations have revealed that the provision of an oxidation prevention layer of silicate-based glass improves thermal shock resistance even more than that of silicon carbide, which already has high thermal shock resistance. This is thought to be because silicate-based glass has the property of softening and plastically deforming at high temperatures, which inhibits crack propagation and also inhibits brittle fracture of the silicon carbide ceramic sintered body.

[0008] However, while the property of silicate glass that softens at high temperatures is advantageous as described above, the softened glass can cause adhesion between heat storage units or between the heat storage unit and the casing. Such adhesion makes it difficult to perform maintenance such as replacing the heat storage unit or removing the heat storage unit from the heat storage unit and cleaning it. Furthermore, if the heat storage unit is a solid ball, the adhesion can clog the gaps that allow gas to pass through, resulting in a problem of reduced heat exchange efficiency. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] Patent No. 5709007 Summary of the Invention [Problem to be solved by the invention]

[0010] Therefore, in view of the above-mentioned circumstances, the present invention aims to provide a heat storage body that has an anti-oxidation layer made of silicate-based glass and that suppresses adhesion between heat storage bodies or between the heat storage body and the casing, and a method for manufacturing such a heat storage body. [Means for solving the problem]

[0011] In order to solve the above problems, the heat storage body according to the present invention is "A spherical substrate made of a silicon carbide ceramic sintered body, and a substrate with protrusions made of a ceramic sintered body and having a plurality of protrusions protruding from the surface of the substrate; an anti-oxidation layer of silicate glass covering the surface of the base body with protrusions; The shape of each of the multiple protrusions is irregular, such that the outer shapes of the multiple end faces cut by any plane perpendicular to the imaginary line connecting the center of gravity of the protrusion and the center of the base are approximately polygonal and not similar to each other.

[0012] Theoretically, the contact between the spheres is point contact, but in the case of conventional heat storage bodies in which the spherical base without protrusions is coated with an antioxidant layer, when the silicate-based glass softens at high temperatures, the oxidation-resistant layer deforms, leading to surface contact. Furthermore, in the case of spherical bases without protrusions, the surface is gently curved toward the contact point, so the softened silicate-based glass tends to flow and gather near the contact point. As a result, the contact area with the silicate-based glass increases on both adjacent heat storage bodies, and after the silicate-based glass cools and solidifies, the heat storage bodies adhere firmly to each other through this. The same applies to adhesion between the heat storage body and the casing.

[0013] In contrast, in the case of the heat storage body of the present invention, protruding pieces protrude from the surface of the base, and the tips of the protruding pieces contact adjacent heat storage bodies or casings. Because the protruding pieces are irregular and have corners, the corners are likely to become contact points. Therefore, even if the silicate-based glass softens, it is unlikely to form surface contact, and even if some surface contact does occur, the degree of contact is low. Furthermore, because the protruding pieces protrude from the surface of the base, even if the softened silicate-based glass flows, it is unlikely to flow toward the tips of the protruding pieces. As a result, an increase in the contact area with the silicate-based glass is suppressed in both adjacent heat storage bodies, or in both adjacent heat storage bodies and casings. Therefore, after the silicate-based glass cools and solidifies, strong adhesion between the heat storage bodies or between the heat storage body and casing is suppressed.

[0014] Furthermore, since the heat storage body has a plurality of protrusions, the surface area is larger than that of a heat storage body without protrusions, and the heat exchange efficiency is also improved.

[0015] In addition to the above configuration, the heat storage body according to the present invention has the following features: "The protruding piece is a silicon carbide ceramic sintered body, the ratio of the maximum length of each of the plurality of protrusions to the diameter of the base is 5% to 18%; The ratio of the total mass of the plurality of protruding pieces to the mass of the base body may be 5% to 40%.

[0016] During heat exchange, the heat storage medium repeatedly rises in temperature due to heat storage and falls in temperature due to heat release. Therefore, if the thermal expansion coefficients of the protruding pieces and the base differ significantly, there is a risk that the difference in thermal expansion coefficients will cause the protruding pieces to detach from the base during repeated temperature rises and falls. In contrast, in this configuration, the protruding pieces are made of sintered silicon carbide ceramics and have the same thermal expansion coefficient as the base, which is also a sintered silicon carbide ceramics, effectively preventing the protruding pieces from detaching from the base.

[0017] Furthermore, by setting the ratio of the maximum length of the outer shape of each of the multiple protrusion pieces to the diameter of the base (hereinafter sometimes referred to as the "protrusion piece size ratio to the base") to 5% to 18%, and the ratio of the total mass of the multiple protrusion pieces to the mass of the base (hereinafter sometimes referred to as the "protrusion piece mass ratio") to 5% to 40%, it is possible to prevent the heat storage bodies from firmly adhering to each other or to the heat storage body and the casing when the heat storage body is placed under high temperatures, as will be described in detail later.

[0018] In addition to the above configuration, the heat storage body according to the present invention has the following features: It is possible for the ratio of the total mass of the plurality of protruding pieces to the mass of the base to be 37% to 40%.

[0019] By setting the mass ratio of the protruding pieces to 37% to 40%, as will be described in detail later, it is possible to more effectively prevent the heat storage bodies from firmly adhering to each other or to the heat storage body and the casing.

[0020] Next, the method for manufacturing a heat storage body according to the present invention is as follows: "Ceramic sintered body is crushed into crushed pieces with corners, a plurality of the crushed pieces are attached to a surface of a spherically molded body made of silicon carbide ceramic raw material, with each piece being partially embedded; the compact having the plurality of pulverized pieces attached to its surface is fired to form the compact into a base of a silicon carbide ceramic sintered body, and the pulverized pieces into protruding pieces integrated with the base; The surface of the base and the surfaces of the plurality of protruding pieces are coated with an antioxidant containing silicon dioxide, and the silicon dioxide is then melted by heating and then cooled to turn the antioxidant into an antioxidant layer of silicate glass.

[0021] This is the configuration of the method for manufacturing the heat storage body having the above configuration. [Effects of the Invention]

[0022] As described above, according to the present invention, it is possible to provide a heat storage body that has an anti-oxidation layer made of silicate-based glass and that suppresses adhesion between heat storage bodies or between the heat storage body and the casing, and a method for manufacturing the heat storage body. [Brief explanation of the drawings]

[0023] [Figure 1] FIG. 2 is a front view of the heat storage medium according to the embodiment of the present invention. [Figure 2] 2A is an end view of the base body with protrusions that is the base of the heat storage body of FIG. 1, cut along a line corresponding to the line AA, and FIG. 2B is an end view of the cut portion along the line AA. [Figure 3] 10(a) to 10(e) are diagrams illustrating that the protruding pieces have an irregular shape. DETAILED DESCRIPTION OF THE INVENTION

[0024] A heat storage body 1 according to a specific embodiment of the present invention and a method for manufacturing the same will be described below. As shown in Figures 1 and 2, the heat storage body 1 of this embodiment comprises a spherical base body 10 which is a silicon carbide ceramic sintered body, a plurality of protruding pieces 20 which are ceramic sintered bodies and protrude from the surface of the base body 10, and an antioxidant layer 31 made of silicate glass which covers the surface of the base body 10 and the surfaces of the plurality of protruding pieces 20. Note that the thickness of the antioxidant layer 31 is exaggerated in Figure 2(b).

[0025] The manufacturing method of the heat storage body 1 having such a configuration includes a crushed piece manufacturing process for manufacturing crushed pieces, a molded body manufacturing process for manufacturing a molded body that is the basis of the base body 10, an integration process for manufacturing a base body with protrusions 30 in which protrusions 20 protrude from the surface of the base body 10 from the molded body and crushed pieces, and an oxidation prevention layer forming process for coating the surface of the base body with protrusions 30 with an oxidation prevention layer 31 of silicate glass.

[0026] The crushed piece production process is a process of roughly crushing a plate-shaped or block-shaped ceramic sintered body. By roughly crushing the ceramic sintered body, a large number of irregularly shaped crushed pieces with sharp corners are formed. Two arbitrary points are set on the outer surface of each crushed piece, and the distance between the two points is R. The maximum value of the distance R, Rmax, is the maximum length of the crushed piece. Crushing is performed so that the maximum length Rmax of each of the many crushed pieces falls within a predetermined range. Alternatively, the crushed piece production process can include a classification process in which, after crushing the ceramic sintered body, the maximum length Rmax of each crushed piece is made uniform within a predetermined range by sieving or the like.

[0027] The ceramic sintered body to be used as the pulverized pieces may be a non-oxide ceramic sintered body such as a silicon carbide ceramic sintered body or a silicon nitride ceramic sintered body, or an oxide ceramic sintered body such as an alumina ceramic sintered body, a zirconia ceramic sintered body, a magnesia ceramic sintered body, a mullite ceramic sintered body, a cordierite ceramic sintered body or an aluminum titanate ceramic sintered body. If the pulverized pieces are produced from a silicon carbide ceramic sintered body, the thermal expansion coefficient of the silicon carbide ceramic sintered body constituting the base 10 in the heat storage body 1 is equal to the thermal expansion coefficient of the protruding pieces 20, which is desirable because the protruding pieces 20 are less likely to detach from the base 10 when the heat storage body 1 is repeatedly heated and cooled.

[0028] In the compact manufacturing process, spherical (solid) compacts are manufactured from raw materials that will become silicon carbide ceramic sintered bodies when fired. For example, raw material powder is mixed with a liquid medium such as water along with additives such as a binder and a surfactant to form a kneaded mixture, which is then molded into a spherical shape. For example, the kneaded mixture is extruded through a circular mold and cut in a direction perpendicular to the extrusion direction to form a cylindrical compact with a height close to the diameter of the circular mold, and then the particles are sized in a spheroidizing machine to form a spherical compact.

[0029] Here, the "raw material that will become a silicon carbide ceramic sintered body upon firing" can be a raw material made of silicon carbide powder. Alternatively, a reactive firing raw material that produces silicon carbide upon heating can be used, and sintered while reacting to produce silicon carbide (reactive sintering).

[0030] The reactive sintering raw material can be a mixed raw material obtained by mixing silicon carbide powder as an aggregate with a silicon source and a carbon source for producing silicon carbide. The silicon carbide powder as an aggregate can be 65% to 95% by mass of the mixed raw material. If the proportion of silicon carbide powder as an aggregate is less than 65% by mass, the strength of the resulting sintered body is likely to be low. On the other hand, if it is more than 95% by mass, the resulting molded body is likely to be difficult to sinter. It is more preferable that the proportion of silicon carbide powder as an aggregate in the mixed raw material is 75% to 85% by mass, as this balances the above-mentioned opposing effects.

[0031] Regarding the silicon source and carbon source for producing silicon carbide, when the molar ratio of silicon to carbon (Si / C) is 1, silicon carbide is produced stoichiometrically in the right amount, but it is preferable to set the Si / C to 0.5 to 1.5. If the Si / C is less than 0.5, there will be too much residual carbon, which may cause coarse pores and inhibit the grain growth of the produced silicon carbide. On the other hand, if the Si / C is greater than 1.5, the amount of produced silicon carbide will be small, and reaction sintering will likely be insufficient. A Si / C of 0.8 to 1.2 is more preferable, as it minimizes the excess or deficiency of silicon and carbon. Silicon nitride and silicon (so-called metallic silicon) can be used as the silicon source, and graphite, coal, coke, charcoal, etc. can be used as the carbon source.

[0032] The integration process includes an attachment process in which a large number of crushed pieces are attached to the surface of a spherical molded body, and a firing and fixing process in which the molded body with the crushed pieces attached is fired to form a base 30 with protrusions 20 protruding from the surface of the spherical base 10.

[0033] In the adhesion process, a large number of pulverized pieces are attached to the surface of the spherically shaped compact, with a portion of each piece embedded. For example, a predetermined amount of pulverized pieces are introduced into a spheroidizing machine that rolls the spherical compacts, and the pieces are rolled together. As a result, a portion of each pulverized piece is embedded in the surface of the spherical compact, and the remaining portion of each pulverized piece protrudes from the surface of the spherical compact. In this process, spraying a small amount of liquid such as water onto the spherical compact makes it easier for some of the pulverized pieces to penetrate into the surface of the compact, making it easier for the pulverized pieces to adhere to the compact.

[0034] In the firing and bonding step, the compact with the pulverized pieces attached is fired in a non-oxidizing atmosphere. Through this firing, the spherical compact becomes a base 10 made of a silicon carbide ceramic sintered body, and the pulverized pieces become protruding pieces 20 fixed to the base 10 while protruding from the surface of the base 10, resulting in a base 30 with protruding pieces as a whole. The firing temperature can be 1800°C to 2300°C. If the firing is reactive firing, a firing temperature lower than 1800°C may result in insufficient reactive sintering, while a firing temperature higher than 2350°C may result in sublimation of the silicon carbide. The "non-oxidizing atmosphere" used for firing can be an inert gas atmosphere such as argon or helium, a nitrogen gas atmosphere, a mixed gas atmosphere of these, or a vacuum atmosphere.

[0035] The integration process may include a drying process carried out after the adhering process and before the firing / fixing process. In this drying process, the compact with the pulverized pieces attached is dried. This drying process can be carried out by blowing air in a temperature and humidity controlled chamber, external heating / drying, internal heating / drying by microwave irradiation, or the like. Furthermore, when the raw material for the compact is a reactive firing raw material that produces silicon carbide by heating, a decarbonization process can be carried out after the firing / fixing process in the integration process for the purpose of burning and removing any carbon source that may remain unused in the silicon carbide production reaction. This decarbonization process can be carried out by holding the material in an oxidizing atmosphere (air atmosphere) at a temperature of 600°C to 1200°C for 1 hour to 15 hours. At these heating temperatures and holding times, oxidation of silicon carbide hardly occurs in the decarbonization process.

[0036] After the integration process, a base 30 with protrusions, in which a plurality of protrusions 20 made of ceramic sintered body protrude from the surface of a spherical base 10 made of silicon carbide ceramic sintered body and the base 10 and the protrusions 20 are integrated, is formed. Next, an anti-oxidation layer formation process is carried out.

[0037] The antioxidant layer forming process includes a coating process in which the surface of the base 30 with protrusions, i.e., the surface of the base 10 and the surfaces of the numerous protrusions 20, is coated with an antioxidant containing silicon dioxide, and a vitrification process in which the silicon dioxide is melted by heating and then cooled to convert the antioxidant into an antioxidant layer 31 of silicate glass.

[0038] The coating process can be a process of applying or spraying an antioxidant onto the surface of the protruding base 30, a process of immersing the protruding base 30 in an antioxidant, or a process of impregnating the protruding base 30 with an antioxidant.

[0039] Antioxidants are slurries that turn into silicate glass upon heating. They consist of a silicon dioxide source mixed with a liquid medium such as water and a binder. The silicon dioxide source can be silica powder, glass powder (glass frit), or clay, either alone or in combination. In addition to the above components, antioxidant raw materials can also contain other components. The addition of boron oxide (B2O3) can adjust the viscosity (fluidity) and durability of glass. Alkali metal oxides (e.g., Na2O, K2O, Li2O) reduce the viscosity and glass transition temperature of glass. Alkaline earth metal oxides (e.g., CaO, MgO, BaO, SrO) enhance the chemical durability of glass and affect its amorphization and crystallization. Aluminum oxide enhances the chemical durability of glass.

[0040] The vitrification process involves heating and melting silicon dioxide, followed by cooling to a temperature below its glass transition point to form silicate glass. In this process, the protrusion-equipped base 30 coated with an antioxidant is heated in an air atmosphere at 90°C to 100°C to remove the liquid medium from the antioxidant, followed by a drying process to remove the liquid medium from the antioxidant. The temperature is then raised to 800°C to 1200°C, where the base 10 and the protrusions 20 are heated for a predetermined period of time, and then the base 10 and the protrusions 20 are cooled. This process melts the silicon dioxide contained in the antioxidant and spreads over the surfaces of the base 10 and the protrusions 20. The silicon dioxide then solidifies and becomes silicate glass, forming a dense, airtight antioxidant layer 31 that adheres closely to the surfaces of the base 10 and the protrusions 20. The antioxidant layer 31 can have a thickness of 10 μm to 300 μm.

[0041] The heat storage body 1 having the above configuration can be obtained through the above steps. Even when the heat storage body 1 is used at high temperatures in an oxygen-containing atmosphere, the oxidation prevention layer 31 of silicate glass that airtightly coats the surface of the base 10 prevents the base 10, which is made of silicon carbide ceramic, from oxidizing. Furthermore, even when the ceramic sintered body that forms the protruding piece 20 is a non-oxide ceramic sintered body such as silicon carbide ceramic, the oxidation prevention layer 31 of silicate glass that airtightly coats the surface of the protruding piece 20 prevents the protruding piece 20 from oxidizing.

[0042] Furthermore, since the anti-oxidation layer 31 of silicate-based glass softens at high temperatures, if the surface of the heat storage body is coated with the anti-oxidation layer 31, there is a risk that adjacent heat storage bodies will become firmly attached to each other through the silicate-based glass that has softened and solidified, or that the heat storage body will become firmly attached to the casing. However, in the heat storage body 1, the presence of the protrusions 20 effectively prevents such strong adhesion.

[0043] More specifically, the crushed pieces that are the source of the protrusions 20 are obtained by roughly crushing a ceramic sintered body, and are irregular in shape with sharp corners. Therefore, the protrusions 20 protruding from the surface of the base 10 in the heat storage body 1 also have irregular shapes with sharp corners. After being coated with the antioxidant layer 31, the sharpness of the corners of the protrusions 20 is somewhat reduced, but the irregular shape with corners is maintained. This "irregular shape" is defined as "a shape in which the outer shapes of multiple end faces cut by an arbitrary plane S perpendicular to an imaginary line L connecting the center of gravity of the protrusions 20 and the center of the base 10 are polygons that are not similar to each other."

[0044] For example, as shown in Figure 3(a), the outer shapes of multiple end faces obtained by cutting a protrusion 20 on planes S11, S12...S1n perpendicular to an imaginary line L1 connecting the center P0 of the base 10 and the center of gravity P1 of a certain protrusion 20 are approximately polygonal shapes that are not similar to each other, as shown in Figure 3(b). Similarly, in Figure 3, Figure 3(c) shows the outlines of multiple end faces of a protrusion 20 cut along planes S21, S22...S2n that are perpendicular to an imaginary line L2 connecting the center P0 of the base 10 and the center of gravity P2 of the protrusion 20, Figure 3(d) shows the outlines of multiple end faces of the protrusion 20 cut along planes S31, S32...S3n that are perpendicular to an imaginary line L3 connecting the center P0 of the base 10 and the center of gravity P3 of the protrusion 20, and Figure 3(e) shows the outlines of multiple end faces of the protrusion 20 cut along planes S41, S42...S4n that are perpendicular to an imaginary line L4 connecting the center P0 of the base 10 and the center of gravity P4 of the protrusion 20. Note that the antioxidant layer 31 is not shown in the end views of Figures 3(b) to 3(e).

[0045] Theoretically, the contact between the spheres is point contact, but in the case of a conventional heat storage body in which the spherical base without the protrusions 20 is coated with an antioxidant layer, when the silicate-based glass softens at high temperatures, the oxidation-resistant layer deforms, easily resulting in surface contact. Furthermore, in the case of a spherical base without the protrusions 20, the surface is gently curved toward the contact point, so the softened silicate-based glass tends to flow and gather near the contact point. As a result, the contact area with the silicate-based glass increases in both adjacent heat storage bodies, and after the silicate-based glass cools and solidifies, the heat storage bodies become firmly attached to each other through this. The same applies to adhesion between the heat storage body and the casing.

[0046] In contrast, in the case of the heat storage body 1, the tips of the protruding pieces 20 protruding from the surface of the base 10 come into contact with the adjacent heat storage body 1 or the casing. Because the protruding pieces 20 have sharp corners, the corners are likely to become contact points. Therefore, even if the silicate-based glass softens at the contact points, it is unlikely to result in surface contact, and even if some surface contact does occur, the degree of surface contact is low. Furthermore, because the protruding pieces 20 protrude from the surface of the base 10, even if the softened silicate-based glass flows, it is unlikely to flow toward the tips of the protruding pieces 20. As a result, an increase in the area of ​​contact with the silicate-based glass is suppressed in both adjacent heat storage bodies 1, or in both adjacent heat storage bodies 1 and casings, and this suppresses strong adhesion between the heat storage bodies 1 via the silicate-based glass after it cools and solidifies.

[0047] In addition, the heat storage body 1 has a significantly increased surface area compared to a heat storage body without the protrusions 20 (compared to a heat storage body having a spherical base of the same diameter) by the amount of the protrusions 20. As a result, the contact area with the flowing gas is large, and the rate of heat exchange with the gas is also increased. [Example]

[0048] Next, the results of comparing the adhesion prevention effect of the heat storage bodies of Examples 1 to 5 with that of the Comparative Example are shown. The heat storage body samples of Examples 1 to 5 used crushed pieces and base 10 manufactured under the same conditions. The crushed pieces were made by roughly crushing and classifying a silicon carbide ceramic sintered body to have a maximum length of 1 mm to 3 mm. The molded body from which base 10 is made was made by molding raw materials containing silicon carbide as an aggregate and a silicon source and a carbon source for reacting to produce silicon carbide into a spherical shape. The molded body with the crushed pieces attached was fired in a non-oxidizing atmosphere to form base 30 with protruding pieces. The diameter of base 10 after firing was 19 mm ± 2 mm. Both the crushed pieces and base 10 were made of 98 mass % or more silicon carbide.

[0049] Because the crushed pieces are sintered bodies, the size of the protrusions 20 can be considered to be maintained even after they have been fixed to the base 10 through the sintering and fixing process, with a maximum length of 1 mm to 3 mm. Therefore, the size ratio of the protrusions to the base, which has a diameter of 19 mm ± 2 mm, is 5% to 18%.

[0050] In Examples 1 to 5, the mass ratio of the protruding pieces was varied between 5% and 40%, as shown in Table 1. If the mass ratio of the protruding pieces exceeded 40%, it was difficult to adhere the crushed pieces to the spherical compact in the adhering step, and the adhered crushed pieces were likely to detach from the compact during the process from the adhering step to the sintering and fixing step, making this impractical.

[0051] For comparison, a spherical molded body prepared under the same conditions as the molded bodies used in Examples 1 to 5 was fired in a non-oxidizing atmosphere without adhering crushed pieces to form a comparative example substrate 10.

[0052] The surfaces of the protrusion-equipped substrates 30 of Examples 1 to 5 and the substrate of the Comparative Example were coated with an antioxidant of the same composition. The protrusion-equipped substrates 30 of Examples 1 to 5 and the substrate of the Comparative Example, whose surfaces were coated with the antioxidant, were heated to a temperature of about 90°C and dried, then heated at a temperature of 900°C for a certain period of time, and then cooled to room temperature, whereby the antioxidant was converted into an antioxidant layer of silicate glass.

[0053] For the heat storage bodies of Examples 1 to 5 and the comparative example, an adhesion test was carried out to evaluate the adhesion caused by the softening of the silicate glass at high temperatures.

[0054] The adhesion test was carried out by stacking multiple heat storage units so that their surfaces were in contact with each other, heating them to a predetermined temperature, holding the temperature for 24 hours, and then cooling them to room temperature. Two heating temperatures were used: 1100°C and 1200°C.

[0055] After the test, if the heat storage materials were not adhered to each other, or if they were slightly adhered but easily separated, they were evaluated as having well-controlled adhesion and marked with "◎". If the heat storage materials were adhered to each other but could be separated by manually applying external force, they were evaluated as having controlled adhesion and marked with "〇". If the heat storage materials were adhered to each other and the adhesion was strong and difficult to separate, they were evaluated as having adhered and marked with "×".

[0056] [Table 1]

[0057] As shown in Table 1, in the comparative example of the heat storage body without the protruding pieces 20, when placed under high temperatures, the heat storage bodies 1 adhered to each other, and the adhesion was so strong that they could not be separated. In contrast, in Examples 1 to 5 having the protruding pieces 20, adhesion between the heat storage bodies 1 was suppressed, and even if they did adhere, they could be separated easily or by manually applying external force. This is thought to be because, due to the presence of the protruding pieces 20, the contact points between the heat storage bodies 1 are the corners of the protruding pieces 20, so even if the silicate-based glass softens, the contact area is small, and in addition, the softened silicate-based glass is less likely to collect at the contacting parts, so the amount of silicate-based glass at the contacting parts can be reduced.

[0058] In particular, in Example 4, where the protruding piece mass ratio was 37%, and Example 5, where the protruding piece mass ratio was 40%, even if the heat storage materials 1 adhered to each other, they were easily separated, and adhesion between the heat storage materials 1 was effectively suppressed. From this, it was thought that the larger the protruding piece mass ratio, the greater the effect of suppressing adhesion. However, as mentioned above, if the protruding piece mass ratio exceeds 40%, it becomes difficult to adhere the crushed pieces to the spherical molded body that is the basis of the base 10, and the adhered crushed pieces become more likely to detach from the molded body. In consideration of this situation, it is desirable that the protruding piece mass ratio be 37% to 40%.

[0059] The present invention has been described above by citing preferred embodiments, but the present invention is not limited to the above embodiments, and various improvements and design changes are possible as described below, without departing from the spirit of the present invention.

[0060] For example, in the heat storage body 1 of the embodiment, the protruding pieces 20 (crushed pieces) are made of a silicon carbide ceramic sintered body, but the protruding pieces 20 (crushed pieces) may be made of another ceramic sintered body. Even if the protruding pieces 20 are made of another ceramic sintered body, the presence of the protruding pieces 20 can provide the effect of reducing the amount of silicate-based glass at the contact portions between the heat storage bodies 1 having the oxidation prevention layer 31, or between the heat storage body 1 having the oxidation prevention layer 31 and the casing.

[0061] If the protruding pieces 20 are sintered oxide ceramics, there is no need to cover the protruding pieces 20 with an antioxidant layer 31 to prevent oxidation, but the green body that is the basis of the base 10 and the pulverized pieces that will become the protruding pieces 20 must be fixed by firing, and the base 30 with protruding pieces that has been integrated by firing and fixing will be coated with an antioxidant. Therefore, even in this case, the protruding pieces 20 are covered with the antioxidant layer 31. [Explanation of symbols]

[0062] 1 Heat storage body 10 Base 20 protrusion piece 30 Base with protrusion 31 Antioxidant layer

Claims

1. a spherical base body made of a silicon carbide ceramic sintered body, and a base body with protrusions made of a ceramic sintered body and having a plurality of protrusions protruding from a surface of the base body; an anti-oxidation layer of silicate glass covering the surface of the base body with protrusions; The shape of each of the plurality of protrusions is irregular, such that the outer shapes of the plurality of end faces cut along any plane perpendicular to an imaginary line connecting the center of gravity of the protrusion and the center of the base are substantially polygonal and not similar to each other. A heat storage body characterized by:

2. the protruding piece is a silicon carbide ceramic sintered body, a ratio of a maximum length of each of the plurality of projection pieces in the outer shape to a diameter of the base body is 5% to 18%; The ratio of the total mass of the plurality of protruding pieces to the mass of the base is 5% to 40%.

2. The heat storage body according to claim 1.

3. The ratio of the total mass of the plurality of protruding pieces to the mass of the base is 37% to 40%.

3. The heat storage body according to claim 2.

4. The ceramic sintered body is pulverized into pulverized pieces having corners, a plurality of the crushed pieces are attached to a surface of a spherically molded body made of silicon carbide ceramic raw material, with each piece being partially embedded; the compact having the plurality of pulverized pieces attached to its surface is fired to form the compact into a base of a silicon carbide ceramic sintered body, and the pulverized pieces into protruding pieces integrated with the base; The surface of the base and the surfaces of the plurality of protruding pieces are coated with an antioxidant containing silicon dioxide, and the silicon dioxide is then melted by heating and cooled to form the antioxidant into an antioxidant layer of silicate glass. A method for manufacturing a heat storage body, comprising:

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