Porous ceramics fired body

Abstract

To provide a low-emissivity material with high heat resistance and high oxidation resistance.SOLUTION: A material for reflective material of the present invention comprises a porous ceramics, in which the porous ceramics is composed of ceramic particles having an average particle size of 1 μm or more and 6 μm or less, and 40% or more of the ceramic particles have a particle size of 1 μm or more and 5 μm or less. An emissivity of the material for reflective material based on Kirchhoff's law in a wavelength range of 0.25 μm or more and 2.5 μm or less is 0.03 or less at 2000 K or more and 4000 K or less, and 0.06 or less at 4000 K or more and 6000 K or less is preferred.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention provides a lamp with high heat resistance and low emissivity. Porous ceramics fired body Regarding. [Background technology]

[0002] So-called low-emissivity materials are used for the purpose of blocking radiant light. For example, vacuum sintering furnaces, which perform heat treatment at high temperatures in a vacuum, use low-emissivity metals such as Mo, W, Ta, Nb, and alloys of these. Furthermore, artificial satellites use Ag, Al, and other materials to block solar radiant light. Furthermore, when used in the atmosphere, transparent fluororesins and BaSO4 powder compacts, which have relatively low emissivity, are used.

[0003] However, metal materials have the problem that when oxygen is present, an oxide film forms on their surface, which increases their emissivity.In addition, transparent fluororesin and BaSO4 have a heat resistance temperature of several hundred degrees, so if they are used in an environment with a higher temperature, they will not be able to maintain their shape.

[0004] Furthermore, when used in locations exposed to radiant light, prioritizing heat resistance and oxidation resistance results in increased heat loss.Furthermore, if the insulation layer is designed using a material with high porosity, the thickness of the insulation layer will be increased, resulting in wasted space and a decrease in strength.

[0005] Incidentally, ceramics are known as a material that can be used as an excellent reflective material with high heat resistance if the thermal conductivity, reflectivity, and emissivity are appropriately set.

[0006] For example, Patent Document 1 discloses an alumina sintered body containing cubic aluminum nitride, which is obtained by molding powder having an average particle size of 10 μm or less and sintering it at a temperature in the range of 1600 to 1825°C in a reducing nitrogen atmosphere, with the aim of providing an alumina sintered body having high thermal conductivity, high infrared emissivity, and excellent electrical insulation and chemical resistance.

[0007] That is, although conventionally known alumina sintered bodies have excellent electrical insulation and chemical resistance, they have low thermal conductivity and infrared emissivity, making it difficult to apply them to the base material of heat dissipation components. However, this problem can be solved by developing an alumina sintered body that has high thermal conductivity and infrared emissivity, and excellent electrical insulation and chemical resistance, and can be used as an insulating substrate, a base material for heat dissipation components, a semiconductor packaging material, etc.

[0008] Patent Document 2 also describes a pore having a pore volume of 0.2 ml / g or more and 2 ml / g or less for pores with a pore diameter of 0.5 μm or more and 10 μm or less, a pore volume of 0.1 ml / g or less for pores with a pore diameter of less than 0.5 μm, and an absorptivity of 5% or less in the wavelength range of 500 nm or more and 2500 nm or less, which is preferably MgAl2O4 or LaAl 11 O 18 There is disclosed a reflector made of porous ceramics.

[0009] That is, the reflective material of Patent Document 2 has high heat resistance, as it is produced by firing at high temperatures to produce porous ceramics, and for example, even when used in a temperature range of 500°C or higher, it has a stable high reflectivity over a wide range of light wavelengths, making it suitable as a reflective material for optical measuring instruments that are expected to be used in high-temperature environments, and as a reflective material for furnaces for ceramics, glass, steel, non-ferrous metals, etc.

[0010] In this way, Patent Documents 1 and 2 show that it is possible to obtain desired properties by appropriately controlling the thermal conductivity, emissivity, and reflectivity according to the intended use while taking advantage of the various excellent properties that ceramics inherently possess. [Prior art documents] [Patent documents]

[0011] [Patent Document 1] Japanese Patent Application Laid-Open No. 2015-151307 [Patent Document 2] Patent No. 6545641 Summary of the Invention [Problem to be solved by the invention]

[0012] In Patent Document 2, the porous ceramics made of MgAl2O4, which has excellent low thermal conductivity, particularly at high temperatures, are intended for use as a reflector, and the pore volume is set within a predetermined range to increase the reflectance in the wavelength range from visible light to the near-infrared, preferably to obtain a reflectance of 95% or more.

[0013] However, although the porous ceramics described in Patent Document 2 are also highly heat-resistant and low-emissivity materials, they are not necessarily suitable for use as reflectors in the above-mentioned vacuum sintering furnaces, artificial satellites, etc., as their strength has not been sufficiently considered.

[0014] In view of the above problems, the present invention provides a lamp having excellent heat resistance and low emissivity. Porous ceramics fired body The purpose is to provide. [Means for solving the problem]

[0015] The porous ceramic sintered body of the present invention is made of MgAl2O4 or LaAl 11 O 18 A porous ceramic sintered body made of porous ceramics composed of the following: At least 40% of the ceramic particles have a particle diameter of 1 μm or more and 5 μm or less, and the average particle diameter of the ceramic particles is 1 μm or more and 6 μm or less, and the temperature is 1965 K and 2318 K. Radiant light is used to bake a porous ceramic body 5 mm thick. 900 seconds When heated, the porous ceramic sintered body Transparent The heat flux is When compared with the case where the heat flux is 1 when there is no porous ceramic, It is characterized by a reduction of more than 90%.

[0016] As a result, Porous ceramics fired body Compared to conventional porous ceramics, it has high heat resistance, high oxidation resistance, low emissivity, and There is strength As it increases, Low-emissivity components using this porous ceramic sintered body This makes it possible to reduce the thickness when designing the device and improve the handling properties.

[0017] The present invention Porous ceramics fired bodyIn the case of a light source, the emissivity based on Kirchhoff's law in the wavelength range of 0.25 μm or more and 2.5 μm or less is preferably 0.03 or less at 2000 K or more and 4000 K or less, and 0.06 or less at more than 4000 K and 6000 K or less.

[0020] More preferably, the present invention Porous ceramics fired body has a compressive strength of 1 MPa or more. The porous ceramic sintered body can also be used in vacuum sintering furnaces or artificial satellites. [Effects of the Invention]

[0021] The present invention Porous ceramics fired body has high heat resistance and high oxidation resistance, as well as low emissivity and high strength. Porous ceramics fired body Compared to conventional porous ceramics, Low-emissivity components using this porous ceramic sintered body When designing 、 The thickness can be reduced, which improves handling. According to the present invention, it is possible to more efficiently reduce heat loss due to heat shielding of radiant light and reduce the size of the heat insulating layer. Ru, Excellent Porous ceramic sintered body can be provided. [Brief explanation of the drawings]

[0022] [Figure 1] 1 is an image showing the shape of a cross section of a porous ceramic sintered body according to one embodiment (Example 1) of the present invention, and a method for calculating the particle size. [Figure 2] FIG. 2 is a schematic diagram showing a method for measuring the heat flux of a porous ceramic sintered body of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0023] Hereinafter, the present invention Porous ceramics fired body The present invention will be described in more detail. Porous ceramics fired body teeth, MgAl 2 O 4 or LaAl 11 O 18 Consisting of Made from porous ceramics A porous ceramic sintered body,The porous ceramic Fired body is composed of ceramic particles having an average particle size of 1 μm or more and 6 μm or less, and 40% or more of the ceramic particles are particles having a particle size of 1 μm or more and 5 μm or less, When a porous ceramic sintered body with a thickness of 5 mm is heated with radiant light equivalent to 2000 K, the heat flux from the surface of the porous ceramic sintered body is reduced by 90% or more.

[0024] The present invention In porous ceramic sintered bodies, "Porous ceramics Fired body As long as particles with a particle diameter of 1 μm or more and 5 μm or less account for 40% or more of the total ceramic particles and the average particle diameter is 1 μm or more and 6 μm or less, the effects of the present invention, such as low emissivity and sufficient strength, can be obtained, and do not depend greatly on the material, composition, pore distribution, porosity, etc. of the porous ceramic.

[0025] However, in order to obtain the effect of the present invention more effectively, the porous ceramic Fired body However, as will be described later, MgAl2O4 or LaAl 11 O 18 These materials have high heat resistance and it is relatively easy to obtain a desired particle size.

[0026] The present invention Porous ceramics fired body In the porous ceramics, particles with a particle diameter of 1 μm to 5 μm account for 40% or more of the total ceramic particles. In the present invention, the above structure is expressed in terms of particle size. The particle size will be explained below.

[0027] 1 is an image showing the cross-sectional shape of a porous ceramic according to one embodiment (Example 1) of the present invention, and a method for calculating the particle size. That is, a cross-section is obtained from an arbitrary location of the porous ceramic, and the particle diameters of individual ceramic particles (primary particles and secondary particles) are measured in a predetermined area (e.g., 500 μm square) using various microscopes such as an SEM. The maximum length and the diameter of the perpendicular bisector of the maximum length within each particle are measured, and the average value is taken as the particle diameter.

[0028] Then, when the particle size distribution of all particles observed within a specified area is taken, the percentage of particles with a particle size of 1 μm or more and 5 μm or less is calculated. This series of steps can be performed by visual observation or using image analysis software. The percentage of particles with a particle size of 1 μm or more and 5 μm or less is expressed as the particle size.

[0029] Light undergoes diffuse reflection due to Mie scattering when the size of the scatterer is approximately the same as the wavelength of light. Therefore, diffuse reflection can be expected if the pore or particle diameter is the same as the wavelength of light, specifically, 2000-6000K and 0.25-5μm. By reducing the heat input to the material through diffuse reflection, heat transfer can be reduced by insulating the material.

[0030] Porous ceramic sintered body as a low-emissivity material When designing as The member Making it thinner would reduce wasted space, but in order to make it thinner, it would need to be strong enough to withstand handling.

[0031] Therefore, in the present invention, the particle size of the whole particles is set to 40% or more, and the particle size of the whole particles is set to 1 μm or more and 5 μm or less. This makes it possible to achieve both diffuse reflection of radiant light and intensity. Note that there is no particular upper limit on the particle size.

[0032] The average particle size of the ceramic particles is 1 μm or more and 6 μm or less. By making the average particle size of the ceramic particles 1 μm or more, By reducing the number of fine particles with a particle diameter of less than 1 μm, the specific surface area can be reduced, which is expected to have the effect of suppressing the decrease in emissivity due to moisture adsorption. Mie scattering is caused by scatterers that are the same size as the wavelength of light, but the greater the number of scatterers, the greater the number of scatterings, and the larger the size of the scatterers, the greater the scattering intensity. According to Planck's law, the wavelength peak of the blackbody radiation spectrum shifts to the shorter wavelength side as the temperature increases. According to Wien's displacement law, the central wavelength shifts from 1.4 μm to 0.5 μm from 2000 K to 6000 K. The wavelength range is 0.25 μm to 5 μm from 2000 K to 6000 K. In this wavelength range, if the size of the scatterer is about the same as the wavelength range of light, the larger it is, the greater the intensity will be. Here, By setting the average particle size of ceramic particles to 6 μm or less, the particle size can be reduced to 5 μm. By reducing the number of large particles exceeding this value and reducing the number of particles that do not contribute as scatterers of radiated light, it is possible to obtain the effect of increasing the number of scatterings due to Mie scattering.

[0033] Porous ceramics having such particle size and average particle diameter Fired body teeth, After obtaining the molded body, primary firing is carried out, and the fired body is pulverized and alumina fiber is added. When firing is carried out in a 100% oxygen atmosphere, Preferably, it is obtained by firing at a high temperature of 1700°C or higher. When primary firing is not performed, the ceramic is preferably produced by firing at a high temperature exceeding 1700°C. That is, the porous ceramic Fired body can be used as a low-emissivity material having high heat resistance and high oxidation resistance that can be used up to such firing temperatures.

[0034] When firing at 1700°C or higher and achieving a particle size of 40% or more between 1 μm and 5 μm, it is necessary to use a substance with a high melting point to make the porous body. For example, porous MgAl2O4 or LaAl2O4 made from hydraulic alumina is used as the raw material. 11 O 18 Examples include porous bodies.

[0035] In the present invention, the whole is MgAl2O4 or LaAl 11 O 18 However, other materials with different compositions and shapes may also be included. Suitable examples include porous MgAl2O4 and LaAl 11 O 18 To obtain strength, porous bodies can be produced by firing at temperatures above 1700°C to promote sintering of particles smaller than 1 μm, increasing the interparticle bonding strength and bulk density. Furthermore, alumina fibers can be added to improve handling, resulting in a composite. Alternatively, sintering aids such as SiO2 can be added to increase the interparticle bonding strength.

[0036] And the present invention Porous ceramics fired body Its excellent effects include, firstly, an emissivity based on Kirchhoff's law in the wavelength range of 0.25 μm or more and 2.5 μm or less, of 0.03 or less at 2000 K or more and 4000 K or less, and of 0.06 or less at temperatures greater than 4000 K and 6000 K or less.

[0037] Conventional ceramic materials such as those described in Patent Documents 1 and 2 are not designed to have the particle size and particle diameter of the present invention, and therefore do not have low emissivity and strength with respect to radiant light equivalent to 2000 to 6000 K. In contrast, the material for reflectors of the present invention is a material that has heat resistance of 1700°C or higher, a compressive strength of 1 MPa or higher, and a low emissivity with respect to radiant light emitted at temperatures equivalent to 2000 to 6000 K.

[0038] In addition, the present invention Porous ceramics fired body is a porous ceramic material with a thickness of 5 mm, which emits radiation equivalent to 2000K. Fired body When heated, the porous ceramic Fired body The heat flux from the surface is reduced by more than 90%. In other words, it is a highly heat-insulating material that can suppress heat transfer with a thin design by blocking heat on the surface, even if it is not designed to be thick as an insulating material.

[0039] Furthermore, the present invention Porous ceramics fired body The compressive strength of the porous ceramic material is 1 MPa or more. Fired body has a necessary and sufficient strength (1 MPa or more) compared to conventional porous ceramics, particularly the porous ceramics described in Patent Document 2.

[0040] Porous ceramics according to the present invention Fired body is a known porous ceramic Fired body For example, the pore volume can be adjusted by adding a pore former or a foaming agent, or by the firing temperature. In the present invention, by appropriately adjusting the particle size distribution and the average particle size, it is possible to further improve the strength while maintaining a balance between the emissivity and the heat resistance.

[0041] Here, the porous ceramic according to the present invention Fired bodyIn the above, there are no particular limitations on the pore portion, but in a preferred embodiment, the volume of pores with a pore size of 0.5 μm or more and 10 μm or less is less than 0.5 ml / g, and the volume of pores with a pore size of 0.1 μm or more and less than 0.5 μm is less than 0.05 ml / g. The pore volume in this case is calculated from the measured value obtained according to JIS R 1655:2003 "Test method for pore size distribution of molded fine ceramics by mercury intrusion porosimetry."

[0042] In the present invention, porous ceramics Fired body There is no particular limitation on the average porosity of the brick, but it is preferably 40% or more. This average porosity is calculated according to JIS R 2614 "Method for measuring specific gravity and true porosity of insulating firebricks." [Example]

[0043] The present invention will be specifically described below based on examples, but the present invention is not limited to the examples shown below.

[0044] (Examples 1 and 2 and Comparative Example 1) 11 mol of hydraulic alumina powder (BK-112: manufactured by Sumitomo Chemical Co., Ltd.) and 9 mol of magnesium oxide powder (MGO11PB: manufactured by Kojundo Chemical Laboratory Co., Ltd.) were weighed and mixed to obtain a mixture. Pure water was added to this mixture in a predetermined ratio to form a slurry, which was then hydraulically molded to obtain a 60 mm x 70 mm x 20 mm molded body.

[0045] The compacts obtained above were fired in an atmosphere of 100% oxygen at a firing temperature of 1800°C for 3 hours (Example 1), at a firing temperature of 1850°C for 3 hours (Example 2), or at a firing temperature of 1700°C for 3 hours (Comparative Example 1), to obtain spinel porous ceramics made of MgAlO.

[0046] (Examples 3 and 4 and Comparative Example 2) 11 mol of hydraulic alumina powder (BK-112: manufactured by Sumitomo Chemical Co., Ltd.) and 9 mol of magnesium oxide powder (MGO11PB: manufactured by Kojundo Chemical Laboratory Co., Ltd.) were mixed and purified water was added to prepare a slurry. This was then hydraulically molded into a 60 mm x 70 mm x 20 mm green body, which was then subjected to primary firing at 1500°C for 1 hour.

[0047] The fired body obtained above was pulverized in an alumina mortar, and 10 wt% of alumina fiber (Denka Arsen B97: Denka Corporation) was added internally. The resulting mixture was fired in a 100% oxygen atmosphere at a firing temperature of 1700°C for 3 hours (Example 3), at a firing temperature of 1850°C for 3 hours (Example 4), and at a firing temperature of 1600°C for 3 hours (Comparative Example 2), to obtain spinel porous ceramics made of MgAlO to which fiber had been added.

[0048] (Examples 5 to 7) 11 mol of hydraulic alumina and 1 mol of lanthanum oxide were mixed and the same weight of pure water was added to form a slurry, which was then cast into a 60 mm x 70 mm x 20 mm compact.

[0049] The compacts obtained above were fired in a 100% oxygen atmosphere at a firing temperature of 1700°C for 3 hours (Example 5), at a firing temperature of 1800°C for 3 hours (Example 6), and at a firing temperature of 1850°C for 3 hours (Example 7), to obtain LaAl 11 O 18 The lanthanum hexaaluminate porous ceramics were obtained.

[0050] (Comparative Example 3) A heat insulating material made of alumina fiber (Fibermax 1600P manufactured by Isolite Kogyo Co., Ltd.) was used.

[0051] Comparative Example 4 A general-purpose low soda alumina dense body was used.

[0052] The particle size percentage of all particles and the average particle size were calculated by measuring the diameter of SEM photographs. Figure 1 shows an example of diameter measurement using SEM photographs of Example 1. The calculated particle sizes and average particle sizes of particles with particle sizes of 1 to 5 μm among all particles are shown in Table 1. Here, Comparative Example 3 was composed of alumina fibers with diameters of 4 μm to 6 μm, and Comparative Example 4 was a dense body, so no corresponding particles were detected.

[0053] The compressive strength was measured using a universal strength testing machine (Shimadzu Corporation, Autograph AG-2000C) on a cube with a sample size of 25 mm on each side. For the alumina dense body of Comparative Example 4, a literature value was used. The measured compressive strengths are shown in Table 1.

[0054] [Table 1]

[0055] The emissivity was calculated using the following procedure. First, reflectance and transmittance were measured in the wavelength range of 0.25 to 2.5 μm using a UV-VIS-NIR spectrophotometer and a 150 mm diameter integrating sphere. The calculated absorptance was then used to determine the spectral emissivity in the wavelength range of 0.25 to 2.5 μm according to Kirchhoff's law. Next, the emissivity at each temperature was calculated from the blackbody emissivities at 2000 K, 3000 K, 4000 K, and 6000 K. Note that these temperatures correspond to the wavelengths emitted by a tungsten lamp, argon lamp, carbon arc, and mercury arc, respectively. The calculated emissivities are shown in Table 2.

[0056] [Table 2]

[0057] For Examples 3 and 4 and Comparative Examples 2, 3, and 4, the heat-shielding effect of radiant heating was verified using a surface-irradiation type infrared vacuum furnace (IVF29VS manufactured by Thermo Riko) using a tungsten lamp. A disk-shaped specimen with a diameter of 40 mm and a thickness of 5 mm was heated with the lamp for 900 seconds, and the average value from 800 to 900 seconds was used to calculate the heat flux ratio with and without the sample, assuming the heat flux without the sample to be 1 (schematic diagram q shown in Figure 2). s / q L The tungsten lamp was adjusted to measure two levels: 50% (equivalent to a wavelength temperature of 1965 K) and 80% (equivalent to a wavelength temperature of 2318 K). The calculated heat flux ratios with and without the sample are shown in Table 3.

[0058] [Table 3]

[0059] As can be seen from Table 1, in Examples 1 to 7, particles with a particle size of 1 to 5 μm accounted for 40% or more of all particles, the average particle size was 1 to 6 μm, and the compressive strength was 1 MPa or more. On the other hand, in Comparative Examples 1 and 2, particles with a particle size of 1 to 5 μm accounted for less than 40% of all particles, the average particle size was less than 1 μm, and the compressive strength was less than 1 MPa.

[0060] As shown in Table 2, in Examples 1 to 7, the emissivity calculated from Kirchhoff's law is 0.03 or less at temperatures between 2000 K and 4000 K and 0.06 or less at temperatures between 4000 K and 6000 K. On the other hand, Comparative Examples 1 and 2 exhibit emissivity less than half that of Comparative Examples 3 and 4 at temperatures between 2000 K and 6000 K. As shown in Table 1, in Comparative Examples 1 and 2, the proportion of particles with a particle size of 1 to 5 μm among all particles is less than 40%, but 10% or more. Furthermore, the average particle size is less than 1 μm, but 0.5 μm or more. Under these conditions, the compressive strength is less than 1 MPa, but the emissivity can be lower than that of general fiber-based ceramics or dense ceramics, such as Comparative Examples 3 and 4, which are not designed with a structure that causes Mie scattering. Although Examples 3 and 4 contain alumina fibers, Comparative Example 3, which contains only alumina fibers, and Comparative Example 4, which is an alumina dense body, have a large emissivity of 0.06 or more. Therefore, it can be said that the effects of the present invention are not due to the alumina fibers, but due to the limited particle size distribution and particle diameter.

[0061] The reason why there is a difference in emissivity between 2000K and 4000K and between 4000K and 6000K is that the range of emitted wavelengths shifts to the shorter wavelength side as the temperature increases, reducing the scattering efficiency.

[0062] Furthermore, Examples 1 to 7 have lower emissivity values than Comparative Examples 1 and 2. This is because the particle diameter is larger than Comparative Examples 1 and 2, which reduces the surface area and therefore the amount of adsorbed moisture, resulting in a lower spectral emissivity.

[0063] As can be seen from Table 3, regardless of the output value, the heat flux ratios of Examples 3 and 4 and Comparative Example 2 were approximately half of those of Comparative Examples 3 and 4. At a thickness of 5 mm, the heat flux transmission ratio was reduced to 0.06 or less, i.e., by 90% or more. For reference, in Comparative Example 3, the fiber diameter was 4 to 6 μm, which is within the size range that causes Mie scattering, and since the fiber is not particulate, the effect is not that great. However, a scattering effect was observed in Comparative Example 3 compared to Comparative Example 4, and Comparative Example 3 had a smaller transmission ratio.

[0064] Furthermore, Examples 3 and 4 have a heat flux ratio similar to that of Comparative Example 2, that is, good heat shielding properties, while also having high compressive strength as shown in Table 1.

[0065] The porous ceramics described in Patent Document 2 regulates the diffuse reflection due to Mie scattering by controlling the pore size, with the pore volume of pores with a diameter of 0.5 μm to 10 μm being 0.2 ml / g to 2 ml / g, and the volume of pores with a diameter of less than 0.5 μm being 0.1 ml / g or less. While these ceramics aim to increase the number of scatterings by increasing the number of pores, they do not take into consideration the strength required for actual use. The present invention focuses on particle size to promote sintering to increase strength and to enhance diffuse reflection. By having particles with a diameter of 1 μm to 5 μm account for 40% or more of the total, and by having an average particle diameter of 1 μm to 6 μm, the number of scatterings is reduced, but by increasing the scattering intensity of the particles, strength can be obtained while maintaining the properties of diffuse reflection.

Claims

1. MgAl 2 O 4 or LaAl 11 O 18 A porous ceramic sintered body made of a porous ceramic comprising: 40% or more of the ceramic particles of the porous ceramic fired body have a particle diameter of 1 μm or more and 5 μm or less, and the average particle diameter of the ceramic particles is 1 μm or more and 6 μm or less; A porous ceramic sintered body characterized in that when a 5 mm thick porous ceramic sintered body is heated for 900 seconds with radiant light of 1965 K and 2318 K, the heat flux passing through the porous ceramic sintered body is reduced by 90% or more compared to the heat flux when the porous ceramic is not present, which is set to 1.

2. 2. The porous ceramic sintered body according to claim 1, wherein the compressive strength is 1 MPa or more.

3. 3. The porous ceramic sintered body according to claim 1 or 2, which is used in a vacuum sintering furnace or an artificial satellite.

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