Thermal insulation material

Abstract

This thermal insulation material contains fumed silica and a fumed composite metal oxide. According to the present invention, it is possible to provide a thermal insulation material that exhibits excellent thermal insulation performance at high temperatures while also having high hardness.

Description

Insulation

[0001] This invention relates to thermal insulation materials.

[0002] In Japan, 60-70% of primary energy consumption is not effectively utilized, and much of it is ultimately emitted as heat. Insulation technology aims to reduce or effectively utilize such heat loss, and is therefore an extremely important technology for achieving energy conservation. Insulation technology reduces heat transfer and heat conduction through the physical and chemical properties of materials, and by reducing heat dissipation from high-temperature components, it reduces energy input and achieves energy conservation. In particular, at high temperatures, the temperature difference between high-temperature and low-temperature components becomes large, so high-performance insulation materials are required. On the other hand, hardness is also required to accommodate the stress caused by thermal expansion of the contents at high temperatures, as well as for handling during assembly and installation of insulation materials.

[0003] Conventionally, ultrafine silica powder, such as fumed silica, has been commonly used as a raw material for thermal insulation materials. For example, Patent Document 1 discloses a technology for obtaining a silica molded body with good thermal insulation properties and moldability by devising the powder properties, microstructure of the molded body, and molding method for forming an ultrafine silica powder into a porous body on its own.

[0004] Patent Document 2 reports that by containing fumed silica and an infrared opaque material in predetermined proportions and setting the pore distribution to predetermined values, an insulating material can be obtained that exhibits excellent heat insulation performance at high temperatures and possesses high strength and hardness.

[0005] Patent Document 3 reports an infrared shielding material nanoparticle dispersion having a predetermined composition, which sufficiently transmits light in the visible region and shields light in the near-infrared region.

[0006] Japanese Patent Publication No. 2007-169158, Japanese Patent Publication No. 7529881, Japanese Patent Publication No. 2006-299086

[0007] In the technology described in Patent Document 1, since ultrafine silica powder is molded by itself, there is a concern that the thermal insulation performance will rapidly decrease at high temperatures (400°C or higher) where the effect of radiation becomes significant. In other words, the silica molded body (thermal insulation material) obtained by the technology described in Patent Document 1 had problems with thermal insulation performance, especially at high temperatures.

[0008] The technology described in Patent Document 2 uses an infrared opaque material, but it uses particles of several micrometers in size, limiting the amount of infrared opaque material that can be incorporated. Therefore, there is a concern that the probability of the infrared opaque material being present in the cross-section through which infrared rays pass decreases, and effective heat insulation may not be possible.

[0009] The technology described in Patent Document 3 uses composite oxide nanoparticles in the infrared shielding material nanoparticle dispersion, and it has been reported that resin or glass is used as the medium for the dispersion. In this configuration, the medium melts at high temperatures and does not exhibit thermal insulation performance, making it unsuitable for thermal insulation at high temperatures, which is the problem that the invention aims to solve.

[0010] This invention has been made in view of the above circumstances, and aims to provide an insulating material that has excellent thermal insulation performance at high temperatures and also possesses high hardness.

[0011] The inventors of the present invention conducted diligent research to achieve the above objectives and found that a thermal insulation material containing a predetermined amount of fumed silica and fumed composite metal oxide exhibits good thermal insulation performance at high temperatures and high hardness, thus completing the present invention.

[0012] Accordingly, the present invention provides the following thermal insulation materials: [1] A thermal insulation material containing fumed silica and a fumed composite metal oxide. [2] The thermal insulation material according to [1], wherein the fumed composite metal oxide is a composite metal oxide of silica and at least one metal oxide selected from the group consisting of titania, alumina, iron oxide, zirconium silicate, zinc oxide, and nickel oxide. [3] The thermal insulation material according to [1] or [2], wherein the content of metal oxides other than silica in the thermal insulation material is 5 to 30% by mass. [4] The BET specific surface area of ​​the fumed composite metal oxide is 50 to 450 m². ２A thermal insulation material according to any one of [1] to [3] above, wherein the amount is / g. [5] A thermal insulation material according to any one of [1] to [4] above, wherein the fumed composite metal oxide is a composite metal oxide of silica and at least one oxide selected from the group consisting of titania, iron oxide, zirconium silicate, and zinc oxide, which has an infrared impermeability function, and the domain diameter of the infrared impermeability function of the metal oxide in the fumed composite metal oxide is less than 500 nm. [6] A thermal insulation material according to any one of [1] to [5] above, wherein the pore volume of pores with a pore diameter of 70 nm or less in the total pore volume is 30 volume% or more. [7] A thermal insulation material according to any one of [1] to [6] above, wherein the fumed composite metal oxide is a composite metal oxide in which silica coats at least a part of the surface of at least one metal oxide selected from the group consisting of titania, alumina, iron oxide, zirconium silicate, zinc oxide, and nickel oxide.

[0013] According to the present invention, it is possible to provide an insulating material that has excellent heat insulation performance at high temperatures and also possesses high hardness.

[0014] The thermal insulation material of the present invention contains fumed silica and fumed composite metal oxide.

[0015] The fumed silica used in the thermal insulation material of the present invention is preferably a material with high purity and high heat resistance of 800°C or higher. Fumed silica is obtained by introducing vaporized silicon tetrachloride into an oxygen-hydrogen flame and burning it, thereby generating ultrafine silica particles through a hydrolysis reaction. Primary particles combine with other particles in the flame to form primary aggregates. The inventors have found that by forming infrared opaque domains in a fumed composite metal oxide composed of silica and other metal oxides, the probability of the infrared opaque material being present in the infrared-transmitting cross-section is increased, making it possible to lower the thermal conductivity at high temperatures and increase the hardness of the thermal insulation material compared to conventional materials.

[0016] Conventional technologies use a mixture of fumed silica and an infrared opaque material to construct thermal insulation. However, because the melting points of fumed silica and the infrared opaque material differ, it is difficult to achieve both good thermal insulation and high hardness without selecting an appropriate processing temperature. If the processing temperature is too high, the contact between particles increases and hardness rises, but the increased contact area leads to increased heat conduction and collapse of pores, preventing the desired thermal insulation performance from being achieved. Conversely, if the processing temperature is too low, the contact area and pores are maintained, but it is difficult to achieve the desired hardness. In contrast, by using a thermal insulation material containing fumed silica and a fumed composite metal oxide, processing temperature control becomes easier, making it possible to achieve both excellent thermal insulation performance and high hardness. From this viewpoint, it is preferable that the fumed composite metal oxide is a fumed composite metal oxide of silica and a metal oxide other than silica. Since the melting point of fumed silica is almost the same as the melting point of silica in the fumed composite metal oxide, it becomes easy to select an appropriate processing temperature, making it easy to achieve both good thermal insulation and high hardness.

[0017] Fumed composite metal oxides are powders of composite metal compounds produced by gas-phase reactions. Fumed composite metal oxides can be produced, for example, by hydrolysis reactions, which occur when two or more vaporized raw materials are introduced into an oxygen-hydrogen flame and burned. Examples of raw materials include metal chlorides and organic substances of the target metal oxide. For example, fumed composite metal oxides of silica and metal oxides other than silica can be produced by co-firing silicon tetrachloride with metal chlorides or metal complexes in the presence of hydrogen or oxygen. For example, fumed composite metal oxides having a core-shell structure with titania as the core and silica as the shell can be produced by introducing titanium tetrachloride and silicon tetrachloride into an oxygen-hydrogen flame and burning them.

[0018] As described above, the thermal insulation material of the present invention contains fumed silica and fumed composite metal oxide. The content of fumed silica in the thermal insulation material is preferably 10 to 80% by mass, more preferably 15 to 75% by mass, and even more preferably 20 to 70% by mass. The content of fumed composite metal oxide is preferably 10 to 80% by mass, more preferably 15 to 75% by mass, and even more preferably 20 to 70% by mass. By adopting such a configuration, the thermal conductivity of the thermal insulation material can be adjusted, improving thermal insulation performance at high temperatures and making it easier to achieve high hardness. The thermal insulation material of the present invention can be obtained by molding a mixture containing the above components. Having the above-mentioned content ranges for fumed silica and fumed composite metal oxide is advantageous for low thermal conductivity at high temperatures. Note that the above-mentioned content percentages are the proportions of the mixture or the entire thermal insulation material.

[0019] The composite metal oxide of the above-mentioned fumed composite metal oxide is not particularly limited, but it is preferably a composite metal oxide of silica and at least one metal oxide selected from the group consisting of titania, alumina, iron oxide, zirconium silicate, zinc oxide, and nickel oxide. These metal oxides are preferable from the viewpoint of availability and economy because they have lower thermal conductivity compared to silica under operating conditions at room temperature and high temperature ranges, and have different melting points than silica, making it easier to achieve mode diameters in the range of 70 nm or less. Among these, it is preferable that the composite metal oxide of silica and at least one metal oxide selected from the group consisting of titania, iron oxide, zirconium silicate, and zinc oxide has infrared opacity.

[0020] The specific composite state of the fumed composite metal oxide described above is not particularly limited, but it is preferable that silica covers at least a portion of the surface of at least one metal oxide selected from the group consisting of titania, alumina, iron oxide, zirconium silicate, zinc oxide, and nickel oxide (core-shell structure). In this case, the silica may cover the entire surface of the metal oxide or only a portion of the surface of the metal oxide. It is preferable that the silica covers, for example, 50 to 100% of the surface of the metal oxide. By adopting this form, the affinity with the fumed silica contained in the insulation material is increased, improving the insulation performance and hardness of the insulation material.

[0021] In the thermal insulation material of the present invention, the content of metal oxides other than silica contained in fumed silica and fumed composite metal oxide is preferably 5 to 30% by mass, and more preferably 5 to 25% by mass, relative to the total thermal insulation material. By keeping it within this range, it is possible to suppress the decrease in thermal conductivity due to reduced heat transfer by radiation and the decrease in hardness due to the relative decrease in the content of fumed silica. Furthermore, from the viewpoint of reducing thermal conductivity and increasing hardness at high temperatures, the content of silica components contained in the thermal insulation material is preferably 70 to 90% by mass, and more preferably 75 to 85% by mass, relative to the total thermal insulation material.

[0022] The specific surface area (BET method, N) of fumed silica contained in the thermal insulation material of the present invention ２ Adsorption (BET specific surface area) is 10-500 m². ２ It is preferably / g, and 10 to 400m ２It is more preferable that the specific surface area is 1 / g. A larger specific surface area results in lower thermal conductivity and higher strength. In other words, a smaller specific surface area results in larger pore diameters and higher thermal conductivity. However, if the specific surface area is too large, the cohesive force becomes strong, making it difficult to disperse the aggregates, and there is a concern that the heat resistance will decrease as sintering will proceed more easily due to the small size of the primary particles. In addition, fumed alumina or precipitated alumina may be included in the mixture to improve heat resistance by suppressing sintering. The specific surface area of ​​fumed silica can be adjusted by the flame temperature and the amount of raw material supplied.

[0023] The specific surface area (BET method, N) of the fumed composite metal oxide contained in the thermal insulation material of the present invention ２ Adsorption (BET specific surface area) is 50-450 m². ２ It is preferable that the value be / g, and 70 to 400m ２ A value of / g is more preferable. This range is advantageous because it results in point contact between particles and smaller pore sizes. The specific surface area of ​​the fumed composite oxide can also be adjusted by the flame temperature, the amount of raw material supplied, and other factors.

[0024] At high temperatures (600°C or above), heat transfer by radiation is significantly greater than that by conduction or convection. Therefore, reducing radiation is an effective way to suppress heat transfer at high temperatures. For this reason, the thermal insulation material of the present invention preferably contains the above-mentioned metal oxide as a material that reflects or absorbs infrared rays within the metal oxide constituting the fumed composite metal oxide. In order to efficiently reflect radiant heat, considering the cross-sectional area in the thermal insulation material, the average particle size (D50) of the above-mentioned infrared opaque metal oxide is preferably less than 500 nm, preferably between 10 nm and 500 nm, and more preferably between 50 nm and 300 nm. This average particle size is the domain diameter of the infrared opaque metal oxide in the fumed composite metal oxide. When considering only the wavelength of infrared rays, it is preferable that the above-mentioned metal oxide has a particle size of several μm, which corresponds to the infrared wavelength. However, if large particles are included, the absence of pores results in good heat conduction paths, which tends to reduce thermal insulation performance. In addition, regions where the infrared opaque material does not exist tend to occur in the infrared transmission cross-section of the thermal insulation material, which tends to reduce thermal insulation performance. On the other hand, by defining a lower limit to the particle size range of the metal oxide, it is possible to reduce the problem of insufficient shielding of infrared rays when the particle size is excessively small. Furthermore, the content and dispersibility in the insulating material are also important for shielding such infrared rays (radiation), and it is preferable to disperse and mix the fumed silica with the fumed silica using a mixer or the like so that the content of the infrared opaque material in the insulating material of the fumed composite metal oxide is within the range described above. When the fumed composite metal oxide has a core-shell structure with the metal oxide as the infrared opaque material as the core and silica as the shell, the domain diameter of the metal oxide as the infrared opaque material is the average particle size of the core. The method for measuring the domain diameter of the metal oxide as the infrared opaque material is not particularly limited, but for example, 20 fumed composite metal oxides within the measurement field of view can be observed with a transmission electron microscope (TEM) to measure the particle size of the metal oxide as the infrared opaque material, and the average value can be taken as the domain diameter of the metal oxide as the infrared opaque material.

[0025] In addition, in order to improve the shape retention property, the heat insulating material of the present invention may contain inorganic fibers. Inorganic fibers are fibers made of inorganic substances, and silica fibers, glass fibers, alumina fibers, etc. can be used. Considering heat resistance and cost, it is preferable to use silica fibers (SiO ２ content rate of 95% by mass or more). The content rate of the inorganic fibers in the mixture of the heat insulating material is preferably 1 to 10% by mass, more preferably 2 to 5% by mass, from the viewpoints of moldability and workability. Further, as the shape of the inorganic fibers, it is preferable that the average fiber diameter is 4 to 12 μm and the average fiber length is 3 to 10 mm. A more preferable range is that the average fiber diameter of the inorganic fibers is 5 to 9 μm and the average fiber length is 5 to 8 mm. When silica fibers are included, the amount of silica in the entire heat insulating material increases.

[0026] In addition, the heat insulating material of the present invention can contain a binder for the purpose of a shape retention agent. The content rate of this binder is not particularly limited, but is preferably 0 to 20% by mass, more preferably 0 to 10% by mass.

[0027] The bulk density of the heat insulating material is preferably higher in order to obtain hardness and strength, but if it is too high, the heat insulating property may deteriorate, and if it is too low, the strength may decrease. Therefore, it is preferably 0.24 to 0.35 g / cm ３ and more preferably 0.26 to 0.31 g / cm ３ . The bulk density of the heat insulating material can be measured by the method described in the examples below.

[0028] The heat insulating material of the present invention is preferably composed of a pore structure body. The pore structure body constituting the heat insulating material preferably has a structure in which a plurality of particles are connected to form a skeleton and has pores inside. The size of the pores formed between the skeletons of the porous structure body is about 100 nm, and many of the pores are preferably so-called mesopores. Since the mesopores are smaller than the average free path of air, the transfer of heat is inhibited. Therefore, when the pore structure body constituting the heat insulating material has mesopores, the heat insulating material having the heat insulating layer can exhibit an excellent heat insulating effect. The pore distribution of the heat insulating material can be measured by the method described in the examples below.

[0029] In the thermal insulation material of the present invention, the volume of pores with a diameter of 70 nm or less in the total pore volume is preferably 30 volume% or more, and more preferably 35 volume% or more. This range is advantageous in terms of low thermal conductivity.

[0030] The thermal insulation material of the present invention preferably has a thermal conductivity of 0.06 W / (m·K) or less at 600°C, and more preferably 0.05 W / (m·K) or less. Within this range, it can be determined that the thermal insulation material of the present invention provides sufficient thermal insulation performance in the high-temperature range. Furthermore, the thermal conductivity of the thermal insulation material of the present invention preferably has a thermal conductivity of 0.07 W / (m·K) or less at 25°C, and more preferably 0.06 W / (m·K) or less. The thermal conductivity of the thermal insulation material can be measured in accordance with JIS R 1611.

[0031] The hardness of the thermal insulation material of the present invention is preferably 70 or higher on the Asker C hardness scale, and more preferably 75 or higher. If the hardness of the thermal insulation material falls within this range, the handling of the thermal insulation material will be even easier. The hardness of the thermal insulation material can be measured by the method described in the examples below.

[0032] The thermal insulation material of the present invention can be manufactured by a mixing step of obtaining a mixture containing predetermined amounts of the above-mentioned fumed silica and fumed composite metal oxide, and optionally further containing predetermined amounts of inorganic fibers, inorganic binders, etc., and a molding step of molding the mixture using a press molding machine or the like.

[0033] In the mixing process described above, each component is mixed to achieve the desired composition of the final insulating material. The mixing method is not particularly limited and can be carried out using conventional methods. By thoroughly crushing and dispersing the fumed silica in the mixing process, the pore size is reduced and the number of pores is increased, resulting in a reduction in thermal conductivity and an improvement in hardness. Similarly, by thoroughly crushing and dispersing the fumed composite metal oxide, the infrared opaque material in the insulating material can be uniformly distributed, resulting in an insulating material with high thermal insulation properties even at high temperatures.

[0034] The mixing means used in the mixing process is not particularly limited, and a mixer having a shearing force, an impact force, etc. suitable for crushing powders (especially aggregates) can be appropriately used. Specifically, a Henschel mixer, a super mixer, a Spartan mixer, etc. can be exemplified. In addition, the shape of the blades used in the mixer is not particularly limited as long as it can exhibit a high shearing force, and can be appropriately selected. The rotation speed and mixing time of the mixer can also be appropriately set, and conditions such as 2000 rpm for 10 minutes can be exemplified.

[0035] In the above molding process, the mixture obtained in the mixing process is molded with a press molding machine or the like to obtain a molded body. The method for obtaining the molded body is not particularly limited and can be carried out according to a conventional method. For example, uniaxial dry molding with a press molding machine having upper and lower press parts provided with a large number of holes can be exemplified. The conditions such as the molding pressure at that time are not particularly limited, but conditions such as dry uniaxial pressure molding for 1 minute while degassing at a molding pressure of about 0.2 MPa can be exemplified.

[0036] In addition, the heat insulating material of the present invention can be manufactured at a low heating temperature and a short tact time for the molded body obtained in the above-described molding process, and both the initial cost and the running cost can be suppressed, so that the total manufacturing cost can be reduced. Furthermore, since the amount of CO ２ emissions during manufacturing is small, it also contributes to carbon neutrality. The specific conditions of the heating process can be appropriately set, but the heating temperature is preferably 600 to 800°C, more preferably 625 to 775°C. The heating time is preferably 0.5 to 6 hours, more preferably 1 to 4 hours. As described above, in the manufacturing method of the heat insulating material of the present invention, post-treatment such as heat treatment is simple, so that not only is the cost low, but also the manufacturing is simple and the tact time is short, and a heat insulating material having high heat resistance, low thermal conductivity and high hardness can be obtained.

[0037] Although the use of the heat insulating material of the present invention is not particularly limited, for example, it can be used in steelmaking furnaces such as ladles, hot metal cars, tundishes, rolling furnaces such as soaking pits and heating furnaces, heat treatment furnaces such as carburizing furnaces, metal sintering furnaces, and induction treatment furnaces, non-ferrous metal furnaces such as melting furnaces and fuel heating furnaces, ceramic furnaces such as glass melting furnaces, cement firing furnaces, and refractory firing furnaces, or for heat insulation between cells and modules of secondary batteries, and high-temperature parts such as reformers and cell stacks of fuel cells.

[0038] Hereinafter, examples and comparative examples will be shown to explain the present invention in more detail, but the present invention is not limited thereto.

[0039] Regarding the heat insulating materials of the examples and comparative examples, the measurement methods of the physical property values shown in Table 2 are as follows. Unless otherwise specified, the measurement was performed at room temperature (about 20 to 25 °C). [Pore distribution] The pore distribution of the heat insulating material was measured by a mercury porosimeter (manufactured by Thermo Scientific, trade name "Pascal 240") based on JIS R1655. The sample was processed into a size that could be inserted into the holder (length, width, and thickness of 12 mm or less), and the measurement conditions were a surface tension of 480 N / cm and a contact angle of 141.3°. The measurement range was 0.015 to 40 μm, and in the Log differential pore volume distribution (dV / d(log D)), the pore diameter at the peak within the range of 70 nm or less was defined as the "mode diameter in the range of 70 nm or less of the pore distribution" (hereinafter referred to as "mode diameter (≤70 nm)"). Regarding the total number of pores (number / g), assuming the shape of the pores is spherical, the volume per pore (mL / number) was obtained using the formula for the volume of a sphere (4 / 3 × π × (radius) ３ ) from the average pore diameter (4V / A) obtained by measurement with a mercury porosimeter, and then the total pore volume (mL / g) was obtained by dividing the total pore volume by the volume per pore.

[0040] [Thermal conductivity] The thermal conductivity (W / (m·K)) of the heat insulating material was measured by a thermal conductivity measuring device using the laser flash method (manufactured by NETZSCH, trade name "LFA457"). The measurement atmosphere was air, and the temperature setting was room temperature (25 °C) or 600 °C. The sample size was a diameter of 10 mm and a thickness of 6 mm.

[0041] [Hardness] The hardness of the insulation material was measured using a durometer (Type C, compliant with JIS K 7312 / JIS S 6050). The sample size was 50 mm in length, 50 mm in width, and 20 mm in thickness. Five arbitrary points were measured, and the average value was calculated.

[0042] [Bulk Density] Bulk density of insulation material (g / cm³) ３ For the thermal conductivity measurement, the dimensions and mass of the sample were measured, and the mass was divided by the volume obtained from the dimensions to calculate the value.

[0043] [Example 1] Fumed silica (BET specific surface area 300 m²) was used as a raw material for the insulation material. ２ / g) 1.08 kg (27 mass%), Fumed composite metal oxide 1 (BET specific surface area 100 m²) ２ 2.68 kg (67 mass%) of silica-titania composite oxide (with a titania content of 30 mass%, domain diameter of 50 nm, and a core-shell structure with titania as the core and silica as the shell) was prepared, along with 0.20 kg (5 mass%) of inorganic fibers (silica fibers (average fiber diameter approximately 10 μm, average fiber length approximately 8 mm)). In addition, 0.160 kg (1 mass% (based on solid content)) of colloidal silica (silica sol) solution (25 mass%) was prepared as a binder (total of 4 kg of solid content for each raw material and binder). The fumed silica-titania composite metal oxide was manufactured as follows: 1.02 kg of octamethylcyclotetrasiloxane and 1.26 kg of tetraisopropoxytitanium were pre-mixed uniformly. This mixture was supplied at room temperature to a burner located at the top of a vertical fuel reactor. It was then atomized into fine droplets using air via a spray nozzle attached to the burner tip, and combusted with an auxiliary flame from hydrogen combustion. Table 1 shows the burner supply amounts of the mixture, air, oxygen, and hydrogen. The resulting composite metal oxide was air-cooled and collected using a bag filter.

[0044] First, the fumed silica, fumed composite metal oxide 1, and inorganic fibers were dry-mixed for 10 minutes in a Henschel mixer (rotation speed approximately 2000 rpm). Then, the entire amount of binder was added in small amounts while dry-mixing for another 10 minutes in the Henschel mixer (rotation speed approximately 2000 rpm) to obtain a powdered mixture (total mixing time 20 minutes). Subsequently, a mesh was placed on the bottom side of the press surface of the metal frame in a press molding machine, and approximately 1.00 kg of the mixture was placed inside. A mesh was also placed on the top side, and the mixture was dry-formed by uniaxial pressure molding for 1 minute at a molding pressure of approximately 0.2 MPa using the upper and lower press sections, which have numerous holes, while degassing. After the pressure molding, the resulting molded body was fired at a temperature of 800°C to obtain the thermal insulation material of the present invention, and each test piece was obtained by slicing. The results are shown in Table 2.

[0045] [Examples 2-5, Comparative Example 1] Except for preparing the raw materials to have the composition described in Table 2, the thermal insulation material was fabricated in the same manner as in Example 1, and test pieces were obtained. The results are shown in Table 2. In addition to the above, the following was used as a raw material: Fumed composite metal oxide 2: Fumed silica-titania composite metal compound (BET specific surface area 30 m²) ２ ( / g, titania content 67% by mass, silica-titania composite oxide, domain diameter 80 nm, titania content 67% by mass, core-shell structure with titania as the core and silica as the shell) The fumed silica-titania composite metal oxide was manufactured as follows: 0.51 kg of octamethylcyclotetrasiloxane and 3.0 kg of tetraisopropoxytitanium were premixed uniformly. This mixture was supplied at room temperature to a burner located at the top of a vertical fuel reactor, and atomized into fine droplets with air using a spray nozzle attached to the tip of the burner, and burned with an auxiliary flame from the combustion of hydrogen. The burner supply amounts of the mixture, air, oxygen, and hydrogen are shown in Table 1. The generated composite metal oxide was air-cooled and collected with a bag filter. Fumed composite metal oxide 3: Fumed silica-zirconium silicate composite metal compound (BET specific surface area 40 m²) ２( / g, zirconia content 30% by mass, silica-zirconia composite oxide, domain diameter 70 nm, core-shell structure with zirconium silicate as the core and silica as the shell) The fumed silica-zirconium silicate composite metal compound was prepared as follows: 0.90 kg of octamethylcyclotetrasiloxane and 0.84 kg of zirconium(IV) tetrapropoxide were premixed uniformly. This mixture was supplied at room temperature to a burner located at the top of a vertical fuel reactor, and atomized into fine droplets using air with a spray nozzle attached to the tip of the burner, and burned with an auxiliary flame from the combustion of hydrogen. The burner supply amounts of the mixture, air, oxygen, and hydrogen are shown in Table 1. The generated composite metal oxide was air-cooled and collected with a bag filter. Infrared opaque material: Titania (average particle size (D50) 5 μm)

[0046]

[0047]

[0048] The results from the examples and comparative examples demonstrate that the thermal insulation material of the present invention has low thermal conductivity at high temperatures, high thermal insulation properties, and good hardness.

Claims

1. Thermal insulation material containing fumed silica and fumed composite metal oxides.

2. The thermal insulation material according to claim 1, wherein the fumed composite metal oxide is a composite metal oxide of silica and at least one metal oxide selected from the group consisting of titania, alumina, iron oxide, zirconium silicate, zinc oxide, and nickel oxide.

3. The thermal insulation material according to claim 1 or 2, wherein the content of metal oxides other than silica in the thermal insulation material is 5 to 30% by mass.

4. The BET specific surface area of ​​the fumed composite metal oxide is 50 to 450 m². ２ The thermal insulation material according to claim 1 or 2, wherein the value is / g.

5. The thermal insulation material according to claim 1 or 2, wherein the fumed composite metal oxide is a composite metal oxide of silica and at least one oxide selected from the group consisting of titania, iron oxide, zirconium silicate, and zinc oxide, which has infrared opacity, and the domain diameter of the infrared opacity metal oxide in the fumed composite metal oxide is less than 500 nm.

6. The thermal insulation material according to claim 1 or 2, wherein the volume of pores with a pore diameter of 70 nm or less in the total pore volume is 30 volume percent or more.

7. The thermal insulation material according to claim 2, wherein the fumed composite metal oxide is formed by coating at least a portion of the surface of at least one metal oxide selected from the group consisting of titania, alumina, iron oxide, zirconium silicate, zinc oxide, and nickel oxide with silica.

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