Method for manufacturing a heat storage body

Abstract

The present invention provides a method for manufacturing a heat storage body in which, even when a structure in which multiple segments of a silicon carbide ceramic sintered body having a honeycomb structure are joined together with a bonding agent is used as a heat storage body at high temperatures in an oxygen-containing atmosphere, delamination of the segments due to oxidation of the bonding layer is prevented. [Solution] A segment 10 having a honeycomb structure comprising a plurality of cells 15 partitioned by partition walls 13 arranged in a single direction is made of a silicon carbide ceramic sintered body, a plurality of segments 10 are joined together with a bonding agent in a direction perpendicular to the axial direction of the cells 15 to form a honeycomb joint, and the surface of the honeycomb joint is covered with an oxidation-preventive layer of silicate glass to form a heat storage body 1. As the bonding agent, an oxide-based bonding agent is used that contains aluminum oxide components, silicon dioxide components, and colloidal silica which is an aqueous suspension, and even if silicon carbide is included, the proportion of it in the solid content of the bonding agent is less than 2% by mass.

Description

Technical Field

[0001] The present invention relates to a method for manufacturing a regenerator in which a plurality of silicon carbide-based ceramic sintered bodies having a honeycomb structure are joined in a direction orthogonal to the axial direction of the cells.

Background Art

[0002] As an example of a regenerator disposed in a gas flow path and exchanging heat with a gas, a regenerator disposed in a heat exchange section of a regenerative burner can be cited. A regenerative burner is a burner used in industrial furnaces such as forging furnaces, heat treatment furnaces, melting furnaces, and firing furnaces. In order to alternately circulate exhaust gas that has become high temperature due to combustion of the burner and gas newly supplied for combustion of the burner through the heat exchange section, the gas flow direction is switched at predetermined time intervals. A regenerator is disposed in the heat exchange section, and the heat of the exhaust gas is recovered by the regenerator, and the newly supplied gas is preheated by the recovered heat.

[0003] As the regenerator, solid balls made of alumina have been widely used. On the other hand, technologies for using honeycomb structures of ceramics such as alumina, cordierite, and mullite as regenerators have also been proposed (see, for example, Patent Document 1). The honeycomb structure has a large number of cells partitioned by partition walls, and the cells extend in a single direction, so there is an advantage that the pressure loss associated with the flow of gas is small. In addition, the honeycomb structure also has an advantage that its surface area is very large compared to solid balls.

[0004] Furthermore, the present applicant has proposed a regenerator composed of a silicon carbide-based ceramic sintered body (see Patent Document 2). Silicon carbide is a material having a 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 regenerator composed of a silicon carbide-based ceramic sintered body has high heat exchange efficiency.

[0005] In addition, the thermal expansion coefficient of silicon carbide is 4.0~4.5 (×10⁻⁶). -6 Its thermal conductivity (K) is low. In other words, silicon carbide has high thermal conductivity and low thermal expansion coefficient, resulting in excellent thermal shock resistance. Therefore, a heat storage body made of silicon carbide ceramic sintered body is suitable as a heat storage body that continuously undergoes temperature changes associated with repeated heat storage and heat release.

[0006] However, silicon carbide has the problem of oxidizing when used at high temperatures in an oxygen-containing atmosphere. Therefore, the invention described in Patent Document 2 employs a method of forming an oxidation-preventive layer of silicate glass on the surface of a substrate, which is a silicon carbide ceramic sintered body. This silicate glass layer prevents contact between the silicon carbide of the substrate and oxygen, thereby effectively suppressing the oxidation of the silicon carbide.

[0007] On the other hand, honeycomb structures are generally formed by extrusion molding, and it is difficult to form large molded bodies with extrusion molding. Therefore, in order to increase the amount of gas that flows through, multiple segments of the honeycomb structure are joined in a direction perpendicular to the axial direction of the cell, thereby increasing the area of ​​the cross-section perpendicular to the axial direction of the cell (see, for example, Patent Document 3).

[0008] When joining multiple segments in this manner, it has been conventionally considered desirable to use a bonding agent (joining material) with a composition similar to that of the ceramic material constituting the segments. By doing so, the thermal expansion coefficients of the segments and the joining layer become similar, making it less likely for thermal stress to occur and cracks caused by it to develop. For this reason, in the invention of Patent Document 3, the segments having a honeycomb structure are made of a silicon carbide ceramic sintered body, and the main components of the bonding agent are coarse and fine powders of silicon carbide, to which a binder and inorganic fibers are added to adjust the viscosity and elasticity.

[0009] However, when a honeycomb-structured segment is made of silicon carbide ceramic sintered material and the main component of the bonding agent is silicon carbide, using a structure made by joining multiple segments as a heat storage body results in oxidation of not only the segments but also the bonding layer when used at high temperatures in an oxygen-rich atmosphere. This leads to cracks and delamination in the bonding layer, causing the segments that were supposed to be joined together to separate. This is not a problem when using a structure made by joining multiple silicon carbide ceramic sintered segments as a DPF (diesel particulate filter). This is because the operating temperature in the DPF is at most around 200°C. In contrast, when using a structure made by joining multiple silicon carbide ceramic sintered segments as a heat storage body, the operating temperature is 900°C or higher. In this environment, oxidation of silicon carbide progresses easily in an oxygen-rich atmosphere, and if silicon carbide is contained in the bonding layer, the separation of segments due to oxidation of the bonding layer, as described above, becomes a problem. [Prior art documents] [Patent Documents]

[0010] [Patent Document 1] Japanese Patent Publication No. 2003-287379 [Patent Document 2] Patent No. 5709007 [Patent Document 3] Patent No. 6560536 [Overview of the project] [Problems that the invention aims to solve]

[0011] Therefore, in view of the above circumstances, the present invention aims to provide a method for manufacturing a heat storage body in which, even when a structure in which multiple segments, which are sintered silicon carbide ceramics having a honeycomb structure, are joined together with a bonding agent, delamination of the segments due to oxidation of the bonding layer is prevented, even when the structure is used as a heat storage body at high temperatures in an oxygen-containing atmosphere. [Means for solving the problem]

[0012] To solve the above problems, the method for manufacturing a heat storage body according to the present invention is: "A segment having a honeycomb structure comprising multiple cells partitioned by partitions arranged in a row and extending in a single direction is constructed from a silicon carbide ceramic sintered body." Multiple of the aforementioned segments are joined together with a bonding agent in a direction perpendicular to the axial direction of the cell to form a honeycomb joint. The surface of the honeycomb joint is covered with an oxidation-preventive layer of silicate glass to form a heat storage body. The aforementioned bonding agent is an oxide-based bonding agent containing an aluminum oxide component, a silicon dioxide component, and colloidal silica in an aqueous suspension. Even if the bonding agent contains silicon carbide, the proportion of silicon carbide in the total solid content of the bonding agent is less than 2% by mass.

[0013] As mentioned above, conventionally, when joining multiple segments made of silicon carbide ceramic sintered bodies with a bonding agent, a bonding agent mainly composed of silicon carbide was used. This was because it was believed that having similar compositions for the materials constituting the segments and the materials constituting the bonding agent would result in higher affinity and thus higher bonding strength. In contrast, the present invention has devised a means that would not have been conceived by those skilled in the art before, which is to use an oxide-based bonding agent, that is, a "dissimilar material," as a bonding agent for joining segments made of non-oxide silicon carbide ceramic sintered bodies. This oxide-based bonding agent does not contain silicon carbide, or if it does, it contains only a very small amount. When the bonding agent contains silicon carbide, as will be described in detail later, the proportion of silicon carbide in the total solid content of the bonding agent is less than 2% by mass.

[0014] The inventors have discovered that by including colloidal silica, which is a water suspension, in addition to aluminum oxide and silicon dioxide components in the oxide-based bonding agent, segments composed of silicon carbide ceramic sintered bodies can be joined together using a bonding agent that is a "dissimilar material."

[0015] Therefore, according to the present invention, since the bonding agent is an oxide-based bonding agent, even when the heat storage body is used at a high temperature in an atmosphere where oxygen is present, there is no risk of the segments peeling off due to damage caused by oxidation of the bonding layer.

[0016] In addition to the above configuration, the method for manufacturing a heat storage body according to the present invention "The diameter of the silicon dioxide particles in the colloidal silica is 5 nm to 22 nm, and the concentration of silicon dioxide in the colloidal silica is 18% by mass to 21% by mass" can be adopted.

[0017] With this configuration, as will be described later in detail, when the heat storage body is used at a high temperature in an atmosphere where oxygen is present, in addition to no damage being caused by oxidation of the bonding layer, the segments are joined to each other through the bonding layer with a higher practical bonding strength. Thus, a heat storage body having a positive effect can be obtained.

[0018] <000008D>Instead of the above configuration, the method for manufacturing a heat storage body according to the present invention "The ratio of silicon dioxide derived from the colloidal silica in the total solid content of the bonding agent is 5.6% by mass to 6.5% by mass" can be adopted.

[0019] With this configuration, as will be described later in detail, when the heat storage body is used at a high temperature in an atmosphere where oxygen is present, in addition to no damage being caused by oxidation of the bonding layer, the segments are joined to each other through the bonding layer with a higher practical bonding strength. Thus, a heat storage body having a positive effect can be obtained.

Advantages of the Invention

[0020] As described above, according to the present invention, even when a structure in which a plurality of segments, which are silicon carbide-based ceramic sintered bodies having a honeycomb structure, are joined with a bonding agent is used as a heat storage body at a high temperature in an atmosphere where oxygen is present, peeling between the segments due to oxidation of the bonding layer is prevented. A method for manufacturing a heat storage body can be provided.

Brief Description of the Drawings

[0021] [Figure 1] It is a perspective view of a heat storage body manufactured by the method for manufacturing a heat storage body according to an embodiment of the present invention (however, the oxidation prevention layer is omitted in the drawing). [Figure 2] It is a perspective view of a heat storage body suitable for installation in a tube of a regenerative radiant tube burner (however, the oxidation prevention layer is omitted in the drawing).

Embodiments for Carrying Out the Invention

[0022] Hereinafter, a method for manufacturing a heat storage body 1, which is a specific embodiment of the present invention, will be described with reference to FIG. 1. The heat storage body 1 is a structure in which a plurality of segments 10 made of a silicon carbide-based ceramic sintered body having a honeycomb structure are joined with a binder in a direction orthogonal to the axial direction of the cells 15.

[0023] The method for manufacturing the heat storage body 1 includes a molding step of molding a molded body having a honeycomb structure, which is composed of a plurality of cells 15 partitioned by partition walls 13 extending in a single axial direction and made of a raw material that becomes a silicon carbide-based ceramic sintered body by firing; a firing step of firing the molded body in a non-oxidizing atmosphere to obtain segments 10 of a silicon carbide-based ceramic sintered body; a joining step of obtaining a honeycomb joined body by joining a plurality of segments 10 with a binder; and an oxidation prevention layer forming step of coating the surface of the honeycomb joined body with an oxidation prevention layer.

[0024] More specifically, in the molding step, a raw material that becomes a silicon carbide-based ceramic sintered body by firing is mixed with water together with additives such as a binder and a surfactant to form a kneaded product, and this is extruded to obtain a molded body having a honeycomb structure. Since a plurality of segments 10 are joined in a direction orthogonal to the axial direction of the cells 15 in the subsequent steps, the molded body has an outer shape of a rectangular parallelepiped shape (including a cubic shape), that is, a shape in which the side peripheral surface where the cells 15 are not open is composed of a plurality of planes.

[0025] Here, as the ceramic raw material that becomes a silicon carbide ceramic sintered body by firing, a raw material containing silicon carbide powder can be used. Alternatively, a raw material containing a silicon source and a carbon source that generate silicon carbide by heating can be used, and the sintering can be carried out while reacting to generate silicon carbide (reaction sintering).

[0026] When reaction-sintering silicon carbide, a mixture of silicon carbide powder (which serves as aggregate) and a silicon and carbon source for generating silicon carbide can be used as raw materials. The silicon carbide powder as aggregate should preferably be present in an amount of 65% to 95% by mass relative to the mixed raw materials. If the proportion of silicon carbide powder as aggregate is less than 65% by mass, the resulting sintered body tends to have low strength. On the other hand, if it is more than 95% by mass, sintering may become difficult. A ratio of 75% to 85% by mass for silicon carbide powder as aggregate relative to the mixed raw materials is more desirable, as it balances the aforementioned conflicting effects.

[0027] Regarding the silicon and carbon sources for generating silicon carbide, when the molar ratio of silicon to carbon (Si / C) is 1, silicon carbide is generated stoichiometrically without excess or deficiency. However, it is desirable to set the Si / C ratio to 0.5 to 1.5. If the Si / C ratio is less than 0.5, there is too much residual carbon, which can cause large air pores and may inhibit the particle growth of the generated silicon carbide. Furthermore, a large amount of residual carbon further reduces the affinity with the bonding agent. On the other hand, if the Si / C ratio is greater than 1.5, the amount of silicon carbide generated is small, and reaction sintering tends to be insufficient. Ideally, the Si / C ratio should be between 0.8 and 1.2, as this minimizes excess or deficiency of silicon and carbon. As a silicon source, silicon nitride or elemental silicon can be used, and as a carbon source, graphite, coal, coke, and charcoal are examples. A drying process may be performed after the molding process and before the firing process to dry the resulting molded body.

[0028] In the firing process, the heating furnace is maintained in a non-oxidizing atmosphere at a temperature of 1800°C to 2300°C for a certain period of time. In the case of reaction sintering, if the firing temperature is lower than 1800°C, the reaction and formation of silicon carbide may be insufficient. If the firing temperature exceeds 2350°C, there is a risk that the silicon carbide will sublimate. A firing temperature of 2000°C to 2200°C is more desirable because a sintered body with sufficient strength can be obtained in a relatively short time. The non-oxidizing atmosphere can be an inert gas atmosphere such as argon or helium, a nitrogen gas atmosphere, a mixture of these gases, or a vacuum atmosphere.

[0029] Through the above process, a segment 10, which is a silicon carbide ceramic sintered body having a honeycomb structure, is obtained. Multiple segments 10 are manufactured.

[0030] In the joining process, multiple segments 10 are joined together with a bonding agent. The direction of joining is perpendicular to the axial direction of the cells 15 in each segment 10. In other words, in each segment 10, the sides where the cells 15 are not open are brought together and joined. Furthermore, as a result of joining, the end faces where the cells 15 are open in each segment 10 are joined to be on the same plane. Through this joining, a honeycomb joint is obtained in which the area of ​​the end face where the cells 15 are open is n times the area of ​​the end face of each segment 10 (where n is the number of segments 10 joined).

[0031] As the bonding agent, an oxide-based bonding agent is used, which is a mixture of aluminum oxide and silicon dioxide (solid) components with colloidal silica (aqueous suspension). It is unprecedented to use an oxide-based bonding agent when the segment 10 to be bonded is a non-oxide silicon carbide ceramic sintered body. As will be described later, the colloidal silica should preferably have a silica particle diameter of 5 nm to 22 nm and a silica concentration of 18% to 21% by mass. The silicon dioxide (solid) component in the bonding agent can be an antioxidant as described later.

[0032] After joining multiple segments 10 with an adhesive, heat treatment is performed at a temperature of 90°C to 120°C. This dries the adhesive, forming a bonding layer 30, and a honeycomb joint is obtained in which adjacent segments 10 are fixed together via the bonding layer 30.

[0033] The oxidation prevention layer formation process consists of a coating step in which an antioxidant slurry is coated onto the surface of the honeycomb joint, and a heat treatment step in which the antioxidant is used to form an oxidation prevention layer of silicate glass (not shown in the figure).

[0034] The antioxidant is a solid powder, primarily composed of silicon dioxide. Besides silica powder, glass powder (glass frit) can be used as the silicon dioxide. In addition to silicon dioxide, the antioxidant can contain other trace components. For example, adding a small amount of boron oxide (B2O3) to the antioxidant can adjust the viscosity (fluidity) and durability of the glass. Furthermore, a small amount of silicon carbide can be added to the antioxidant. The silicon carbide contained in the antioxidant is more easily oxidized than the silicon carbide ceramic sintered body constituting segment 10, and readily oxidizes to silicon dioxide under heating. The newly formed silicon dioxide is more reactive and more easily vitrified than the silicon dioxide initially included as the main component of the antioxidant. Therefore, by including silicon carbide in the antioxidant, an oxidation-preventive layer of the silicate glass can be efficiently formed in the heat treatment process described later.

[0035] The coating process can involve applying or spraying a slurry, which is a mixture of an antioxidant with a liquid medium such as water or a binder, onto the surface of the honeycomb assembly; immersing the honeycomb assembly in the antioxidant slurry; or impregnating the honeycomb assembly with the antioxidant slurry.

[0036] The heat treatment process involves melting silicon dioxide by heating and then cooling it to a temperature below the glass transition temperature to form a silicate glass. In the heat treatment process, the honeycomb joint coated with an antioxidant slurry is heated in an air atmosphere at approximately 100°C to remove the liquid medium in the slurry, followed by a drying treatment. The temperature is then raised to 900°C to 1000°C for a predetermined time, and then cooled. Through this process, the silicon dioxide contained in the antioxidant melts and spreads across the surface of the honeycomb joint, then solidifies to form a silicate glass, resulting in the formation of a dense and airtight antioxidant layer that adheres closely to the surface of the honeycomb joint. This antioxidant layer covers both end faces where the cells 15 are open, the side surfaces (surfaces where the cells 15 are not open), the inner surface of the cells 15, and the outer surface of the bonding layer 30 of the honeycomb joint. Since the bonding layer 30 contains silicon dioxide, which is the main component of the antioxidant layer, it adheres well to the antioxidant layer, making it easy to form a uniform antioxidant layer on the entire surface of the honeycomb joint.

[0037] Through the above process, a heat storage body 1 is manufactured in which multiple segments 10, which are sintered silicon carbide ceramics having a honeycomb structure, are joined by an oxide-based bonding layer 30 in a direction perpendicular to the axial direction of the cell 15, and the end faces where the cell 15 is open, the side surfaces where the cell 15 is not open, the inner surface of the cell 15, and the bonding layer 30 are covered with an oxidation-preventive layer of silicate glass.

[0038] In the heat storage body 1, the material constituting the segments 10 is a silicon carbide ceramic sintered body, but since the surface is covered with an oxidation-preventive layer of silicate glass, oxidation of silicon carbide is suppressed even when the heat storage body 1 is used at high temperatures in an oxygen-containing atmosphere. In addition, since the bonding layer 30 that joins multiple segments 10 is a layer formed of an oxide-based bonding agent, the bonding layer 30 does not oxidize even when the heat storage body 1 is used at high temperatures in an oxygen-containing atmosphere. Unlike conventional designs in which the bonding layer was formed with a bonding agent mainly composed of silicon carbide, the problem of the joined segments peeling off due to oxidation of the bonding layer 30 is not present. [Examples]

[0039] As described above, the heat storage body manufactured by the manufacturing method of this embodiment has an oxide-based bonding layer that joins multiple segments, so there is no risk of the bonding layer oxidizing in the environment in which it is used as a heat storage body. However, this is a bonding of "dissimilar materials": segments, which are non-oxide silicon carbide ceramic sintered bodies, are bonded with an oxide-based bonding agent. Conventionally, it was thought that if the bonding agent used to bond the segments and the segments themselves are dissimilar materials, the affinity would be low and sufficient bonding strength could not be obtained. Therefore, the bonding strength using an oxide-based bonding agent was investigated as follows.

[0040] First, a mixture of raw materials with the following composition was mixed and kneaded with water, an organic binder, and a surfactant to form a compound, which was then extruded to obtain a molded body having a honeycomb structure (molding process). The obtained molded body was fired at a temperature of 2300°C in a non-oxidizing atmosphere to obtain segments of silicon carbide ceramic sintered body (firing process). The outer shape of the segments was a rectangular parallelepiped, the thickness of the partitions in the honeycomb structure was 0.4 mm, and the cell density was 200 cells / square inch. <Composition of mixed raw materials> Silicon carbide as aggregate (average particle size 12 μm): 75% by mass Silicon nitride as a silicon source (average particle size 10 μm): 20% by mass Graphite as a carbon source (average particle size 15 μm): 5% by mass

[0041] The segments obtained after the firing process had an average pore diameter of 10 μm and an apparent porosity of 42%. Here, the average pore diameter was determined as the median diameter (the diameter when the cumulative pore volume is 50% of the total pore volume) from the pore size distribution measured by the mercury intrusion method using a mercury porosimeter (Micromeritics, Autopore IV9500). The apparent porosity was calculated from the volume of mercury injected into the sample and the sample volume during the measurement of the average pore diameter.

[0042] Two segments manufactured under identical conditions were joined together with a bonding agent in a direction perpendicular to the axial direction of the cell, that is, with the non-opening sides of the cell facing each other (joining process). The two segments were joined so that the two end faces, where the cells are open, were on the same plane.

[0043] As a bonding agent, a mixture of mullite, clay (30% Al2O3, 70% SiO2), an antioxidant, colloidal silica (aqueous suspension), and an organic binder was used in the composition shown in Table 1. The antioxidant used was entirely SiO2 powder.

[0044] [Table 1]

[0045] Using the compositions shown in Table 1, 14 different bonding agents were used, each with a different SiO2 particle diameter in the colloidal silica (aqueous suspension) ranging from 5 nm to 22 nm, and a different SiO2 concentration in the colloidal silica (aqueous suspension) ranging from 11% by mass to 29% by mass. Two segments were joined as described above, and the bonding agents were dried to obtain 14 types of honeycomb assemblies E1 to E14.

[0046] The three-point bending strength was measured for each of the honeycomb joints E1 to E14. The measurement conditions were a support distance of 10 cm and a head speed of 1 mm / min. For each type of honeycomb joint E1 to E14, multiple samples were prepared under the same conditions, and the three-point bending strength was the average value of these samples. The results, along with the diameter of SiO2 particles in the colloidal silica bonding agent and the SiO2 concentration used for each of the honeycomb joints E1 to E14, are shown in Table 2.

[0047] If the three-point bending strength was 5 MPa or higher and the fracture occurred in the joint layer, it was evaluated as sufficient joint strength ("○"). If the three-point bending strength was less than 5 MPa, it was evaluated as insufficient joint strength ("×"). Furthermore, even if the three-point bending strength was 5 MPa or higher, if the fracture occurred inside the segment rather than the joint layer, it was evaluated as lacking practicality ("××"). The evaluation results are shown in Table 2. The reason for focusing on whether the fracture occurs in the joint layer or inside the segment is that if the fracture occurs in the joint layer, the heat storage body can be used as a heat storage body for a short period until replacement is necessary, provided that the heat storage body is located in a casing such as a radiant tube, and the joint layer is considered to be exerting a stress-relaxing effect. On the other hand, if the fracture occurs inside the segment rather than the joint layer, there is a risk that the cell may become blocked due to the destruction of the partition wall dividing the cell, and the function of circulating gas within the cell will not be achieved. It was thought that this type of fracture within the segment occurred when the bonding strength of the bonding layer was too high, causing the honeycomb joint to function like a single rigid body.

[0048] [Table 2]

[0049] Table 2 suggests that a suitable bonding strength for practical use can be obtained when the diameter of SiO2 particles in colloidal silica (aqueous suspension) is 5 nm to 22 nm, and the SiO2 concentration in colloidal silica (aqueous suspension) is 18 mass% to 21 mass%.

[0050] Furthermore, the sum of the Al2O3 component derived from mullite and the Al2O3 component derived from clay is considered to be the Al2O3 component in the bonding agent. The sum of the SiO2 component derived from mullite, the SiO2 component derived from clay, the SiO2 component derived from the antioxidant, and the SiO2 component (solid) derived from colloidal silica (aqueous suspension) is considered to be the SiO2 component in the bonding agent. The sum of the Al2O3 component in the bonding agent and the SiO2 component in the bonding agent is considered to be the total solid content. In this case, if the SiO2 concentration in colloidal silica (aqueous suspension) is in the range of 18% to 21% by mass, the proportion of total solid content (excluding the solid content of the organic binder) in the bonding agent is 77% to 78% by mass, and the proportion of SiO2 (solid) derived from colloidal silica (aqueous suspension) in the total solid content is 5.6% to 6.5% by mass. Note that the solid content of the organic binder is not included in the total solid content of the bonding agent. Originally, the solid content concentration in organic binders is small, and since the organic binder content in the bonding agent of this embodiment is only 3% by mass, the solid content of the organic binder can be ignored.

[0051] When a bonding agent is applied to the surface of colloidal silica, which forms the interface between segments to be joined, its fluidity and wettability are thought to be affected. As mentioned above, the apparent porosity of the segments is 42%, making them porous. Therefore, the bonding agent needs to penetrate to a certain depth from the surface of the segments into the open pores and also adhere sufficiently to the surface of the segments. When the SiO2 concentration in the colloidal silica (aqueous suspension) is low, the fluidity of the bonding agent is high, causing it to penetrate deeply from the surface of the segments into the open pores, resulting in insufficient adhesion to the surface of the segments. On the other hand, when the SiO2 concentration in the colloidal silica (aqueous suspension) is high, the fluidity of the bonding agent decreases, making it difficult to penetrate into the open pores. Additionally, the wettability decreases, causing it to be repelled from the surface of the segments, resulting in insufficient adhesion to the surface of the segments.

[0052] As mentioned above, antioxidants may contain silicon carbide. In that case, the proportion of silicon carbide in the antioxidant (solid powder) is at most 10% by mass. Therefore, in the bonding agent composition shown in Table 1, we consider the antioxidant, which is present in the bonding agent at a concentration of 14% by mass, as 100% by mass, and assume that 10% of that is silicon carbide. We then consider the sum of the Al2O3 component, the SiO2 component, and the silicon carbide derived from the antioxidant in the bonding agent as the total solid content. If the SiO2 concentration in colloidal silica (aqueous suspension) is in the range of 18% to 21% by mass, the proportion of total solid content (excluding the solid content of the organic binder) in the bonding agent is 78% to 79% by mass, and the proportion of silicon carbide derived from the antioxidant in the total solid content is 1.7% to 1.8% by mass. Consequently, even if silicon carbide is included in the antioxidant contained in the bonding agent, the proportion of silicon carbide in the total solid content of the bonding agent is less than 2% by mass. If silicon carbide is not included in the antioxidants contained in the bonding agent, then naturally the proportion of silicon carbide in the total solid content of the bonding agent is zero by mass.

[0053] Although preferred embodiments of the present invention have been described above, the present invention is not limited to the above embodiments, and various improvements and design changes are possible without departing from the spirit of the present invention, as shown below.

[0054] For example, in the above embodiment, a heat storage body 1 in which a plurality of rectangular parallelepiped-shaped segments 10 are joined together is illustrated using Figure 1. However, it is not limited to this, and as shown in Figure 2, a heat storage body 1B can be made in a shape that is arranged in the cylindrical straight tube section of the radiant tube of a regenerative radiant tube burner. Such a heat storage body 1B is manufactured by joining a plurality of segments 10, which are extruded into a rectangular parallelepiped shape and fired, with a bonding agent in a direction perpendicular to the axial direction of the cell 15 to form a honeycomb joint, then processing the outer shape of the cross section perpendicular to the axial direction of the cell 15 to be circular, and circular holes 20 concentric with this outer circle to penetrate the honeycomb joint in the axial direction, and then performing an oxide layer formation process to cover the surface with an oxidation-preventive layer of silicate glass. In other words, the processing process is performed after the joining process and before the oxide layer formation process. Since the side surface of the honeycomb joint after processing will have cell openings, the opened cells may be filled with an outer periphery coating agent and then the surface may be covered with an oxidation-preventive layer. [Explanation of Symbols]

[0055] 1,1B Heat storage body 10 segments 13 Bulkhead 15 cells 30 Bonding layer

Claims

1. A segment having a honeycomb structure comprising multiple cells partitioned by partition walls arranged in a row and extending in a single direction is constructed from a silicon carbide ceramic sintered body. Multiple of the aforementioned segments are joined together with a bonding agent in a direction perpendicular to the axial direction of the cell to form a honeycomb joint. The surface of the honeycomb joint is covered with an oxidation-preventive layer of silicate glass to form a heat storage body. The aforementioned bonding agent is an oxide-based bonding agent containing an aluminum oxide component, a silicon dioxide component, and colloidal silica in an aqueous suspension. Even if the bonding agent contains silicon carbide, the proportion of silicon carbide in the total solid content of the bonding agent is less than 2% by mass. A method for manufacturing a heat storage body, characterized by the above.

2. The diameter of the silicon dioxide particles in the colloidal silica is 5 nm to 22 nm, and the concentration of silicon dioxide in the colloidal silica is 18% to 21% by mass. A method for manufacturing a heat storage body according to feature 1.

3. The proportion of silicon dioxide derived from the colloidal silica in the total solid content of the bonding agent is 5.6% by mass to 6.5% by mass. A method for manufacturing a heat storage body according to feature 1.

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