Composite ceramic, starting material composition of composite ceramic, method for producing composite ceramic, heat storage body, heating system, and method for producing ceramic

Abstract

This composite ceramic comprises: a matrix phase that contains a first ceramic in which the average value of linear transmittance in the wavelength range of 1.5-3.3 µm is 80% or more as measured by a Fourier transform infrared spectrophotometer; and a dispersion phase that contains a second ceramic in which the average value of linear transmittance in the wavelength range of 1.5-3.3 µm is less than 20% as measured by a Fourier transform infrared spectrophotometer.

Description

Composite ceramic, raw material composition for composite ceramic, method for manufacturing composite ceramic, heat storage body, heating system, and method for manufacturing ceramic

[0001] The present disclosure relates to a composite ceramic, a raw material composition for the composite ceramic, a method for manufacturing the composite ceramic, a heat storage body, a heating system, and a method for manufacturing the ceramic.

[0002] Non-oxide ceramics such as silicon carbide and silicon nitride are expected to be used in a variety of applications due to their excellent thermal and chemical stability.

[0003] Japanese Patent Application Laid-Open No. 2007-238366

[0004] However, the raw materials are expensive and firing temperatures of 1800°C or higher are required, which means the high manufacturing costs are a hindrance to widespread use.

[0005] The present disclosure has been made in view of these problems, and its purpose is to provide a novel ceramic that can be manufactured inexpensively.

[0006] In order to solve the above problems, a composite ceramic according to an embodiment of the present disclosure includes: a matrix phase containing a first ceramic having an average linear transmittance of 80% or more in a wavelength range of 1.5 to 3.3 μm as measured with a Fourier transform infrared spectrophotometer; and a dispersed phase containing a second ceramic having an average linear transmittance of less than 20% in a wavelength range of 1.5 to 3.3 μm as measured with a Fourier transform infrared spectrophotometer.

[0007] Another aspect of the present disclosure is a raw material composition for a composite ceramic, which comprises 70 to 95 wt % of rice husk combustion ash containing amorphous silica, and 5 to 30 wt % of silicon nitride or silicon carbide, Al, and Si combined.

[0008] Yet another aspect of the present disclosure is a method for producing a composite ceramic, the method comprising firing the raw material composition described above.

[0009] Yet another aspect of the present disclosure is a heat storage body, which includes the composite ceramic described above.

[0010] Yet another aspect of the present disclosure is a heating system including a heating chamber, a heating element provided inside the heating chamber, and an electromagnetic wave irradiation unit that irradiates electromagnetic waves to the heating element, wherein the heating element includes the composite ceramic described above.

[0011] Yet another aspect of the present disclosure is a method for producing ceramics, comprising the steps of coating a powder containing a metal or metalloid with a water-soluble binder, suspending the powder in water, pouring the suspension into a porous mold to form the body, and firing the formed body.

[0012] According to the present disclosure, it is possible to provide a novel ceramic that can be manufactured inexpensively.

[0013] 1 is a flowchart showing the steps of a method for manufacturing a composite ceramic according to an embodiment;

[0023] FIG. 1 is a diagram showing the components of rice husk combustion ash;

[0024] FIG. 2 is a diagram showing a scanning electron microscope (SEM) image of a sample obtained by adding aluminum to rice husk combustion ash and heat-treating it at 1300°C for 3 hours;

[0025] FIG. 3 is a diagram showing the results of energy dispersive X-ray spectroscopy (EDX) measurement of the above sample;

[0026] FIG. 4 is a diagram showing a Raman spectrum of a sample obtained by adding aluminum powder to rice husk combustion ash and heat-treating it at 1300°C for 1 hour in an argon atmosphere;

[0027] FIG. 5 is a diagram showing a scanning electron microscope (SEM) image and the results of energy dispersive X-ray spectroscopy (EDX) measurement of the above sample;

[0028] FIG. 6 is a diagram showing a schematic configuration of a reduction-nitriding furnace for reducing and nitriding raw materials containing rice husk combustion ash;

[0029] FIG. 7 is a diagram showing a scanning electron microscope (SEM) image of the composite ceramic of Example 1;

[0029] FIG. 8 is a diagram showing an X-ray diffraction (XRD) pattern of the composite ceramic of Example 1;

[0029] FIG. 9 is a diagram showing the results of measurement of the thermal conductivity of the composite ceramic of Example 1;

[0029] FIG. 10 is a diagram showing the results of measurement of the thermal diffusivity of the composite ceramic of Example 1;

[0029] FIG. 11 is a diagram showing the results of measurement of the specific heat capacity of the composite ceramic of Example 1; 18(a1) 。 18(a1) is an enlarged view of a pore and its surrounding region b shown in FIG. 18(a1). ... FIG. 2 is a diagram showing the mass, density, mass change, mass change rate, and shrinkage rate of the composite ceramic solid-sphere heat storage medium produced.1 is a diagram showing temperature changes when the composite ceramic of Example 2 and the solid sphere of SiC are heated in a household microwave oven. FIG. 2 is a diagram showing a schematic configuration of a heating system according to an embodiment of the present disclosure.

[0014] As an embodiment of the present disclosure, a novel composite ceramic containing a silicon compound is proposed.

[0015] The composite ceramic according to the embodiment of the present disclosure includes a first ceramic (e.g., silicon oxide (SiO ２ ) and aluminum oxide (Al ２ O ３ ), which will be referred to as the "transmitting component" hereinafter), and a second ceramic (for example, silicon carbide (SiC) or silicon nitride (Si ３ N ４ ), hereinafter referred to as "absorbent components." Light incident on the composite ceramic is diffusely reflected while the transmitting component is transmitted, and is then absorbed by the absorbing component and converted into heat, resulting in excellent thermal properties. The use of such composite ceramics can significantly reduce the amount of carbon dioxide emitted from industrial furnaces, etc.

[0016] Such composite ceramics can be synthesized from raw materials containing, for example, rice husk combustion ash. FIG. 1 is a flowchart showing the steps of a method for manufacturing a composite ceramic according to an embodiment. Rice husks are burned at an appropriate temperature to obtain combustion ash (S10). The main components of the combustion ash include silicon oxide and carbon. The obtained combustion ash is pulverized (S12). Combustion ash is easier to crush than mineral silica and can be pulverized using a ball mill or the like. The pulverized combustion ash is mixed with a reducing agent, a binding agent, seed crystals, a binder, and the like to form a raw material composition (S14). The raw material composition is molded (S16) and fired (S18).

[0017] A part of the silicon oxide contained in the combustion ash is reduced to silicon by a reducing agent such as aluminum. SiO ２ [sl]+(4 / 3)Al[sl]→(2 / 3)Al ２ O ３[sl] + Si[sl] Here, s indicates solid, g indicates gas, and sl indicates both solid and liquid. Carbon remaining in the combustion ash also acts as a reducing agent. Silicon produced by the reduction of silicon oxide reacts with carbon and nitrogen contained in the combustion ash and atmosphere to produce silicon carbide and silicon nitride (reaction sintering). (3 / 4) Si[sl] + 2N ２ [g]→(1 / 4)Si ３ N ４ [s] Si[sl] + C[s] → SiC[s] Part of the silicon oxide reacts with alumina and nitrogen to produce a composite oxide of Si and Al and silicon oxynitride. XSiO ２ +YAl ２ O ３ →Si ｘ Al ｙ O ｚ SiO ２ +N ２ →Si ２ N ２ O

[0018] According to the method of this embodiment, composite ceramics containing silicon oxide or aluminum oxide as a permeating component and silicon carbide or silicon nitride as an absorbing component can be produced from inexpensive raw materials. Furthermore, as will be described later, the firing temperature can be kept lower than that of conventional non-oxide ceramics, further reducing production costs. Furthermore, rice husks, which are generated in huge quantities every year and have been difficult to dispose of, can be converted into high-value-added products, thereby reducing the amount of environmental waste. In this way, the technology disclosed herein can make significant contributions to society in both industrial and environmental aspects.

[0019] In the composite ceramic of the present disclosure, the first ceramic may be a ceramic having an average linear transmittance of 80% or more in the wavelength range of 1.5 to 3.3 μm measured with a Fourier transform infrared spectrophotometer. The average linear transmittance of the first ceramic in the wavelength range of 1.5 to 3.3 μm measured with a Fourier transform infrared spectrophotometer may be 60% or more, 65% or more, 70% or more, 75% or more, 80% or more, 85% or more, 90% or more, or 95% or more. The first ceramic may contain a crystalline phase or an amorphous phase of silicon oxide or aluminum oxide. The first ceramic may contain a substance such as silicon oxide derived from rice husk combustion ash.

[0020] In the composite ceramic of the present disclosure, the second ceramic may be a ceramic having an average reflectance of less than 20% in the wavelength region of 1.5 to 3.3 μm as measured by a Fourier transform infrared spectrophotometer. The average reflectance of the second ceramic in the wavelength region of 1.5 to 3.3 μm as measured by a Fourier transform infrared spectrophotometer may be less than 40%, less than 35%, less than 30%, less than 25%, less than 20%, less than 15%, less than 10%, or less than 5%. The second ceramic may contain any of silicon carbide, silicon nitride, carbon, and mixtures of any combinations thereof. The second ceramic may contain a substance such as silicon oxide derived from rice husk combustion ash or silicon carbide, silicon nitride, or carbon generated from carbon. In order to increase the radiation efficiency of the composite ceramic, iron oxide (Fe ３ O ４ ) may be added as the second ceramic.

[0021] The above-mentioned linear transmittance values ​​refer to linear transmittance values ​​measured for a single ceramic in order to define the types of the first ceramic and the second ceramic contained in the composite ceramic of the present disclosure, and do not refer to linear transmittance values ​​of the first ceramic or the second ceramic in the composite ceramic.

[0022] The composite ceramic of the present disclosure may include a matrix phase containing a first ceramic as a transmitting component and a dispersed phase containing a second ceramic as an absorbing component. This allows light to penetrate into the interior of the composite ceramic through the matrix phase of the transmitting component, making it possible to efficiently convert light into heat by efficiently utilizing not only the absorbing component present near the surface of the composite ceramic but also the absorbing component present inside the composite ceramic. This can improve the thermal properties of the composite ceramic.

[0023] The composite ceramic of the present disclosure further contains mullite (Al), which is a composite oxide of Si and Al. ４．５９ Si １．４１ O ９．７ )-based glass (Si ｘ Al ｙ O ｚ ) and oxynitride glass (Si ) in which part of the oxygen in silicate glass is replaced with nitrogen. ２ N ２ Mullite-based glasses have excellent thermal shock resistance, corrosion resistance, and chemical stability.

[0024] The composite ceramic of the present disclosure may further contain free carbon, which has a very high absorption rate for light in the above wavelength range, and can further improve the thermal properties of the composite ceramic.

[0025] The composite ceramic of the present disclosure may have a linear transmittance in one direction measured with an infrared-visible spectroscopic microscope of 2% or less. The composite ceramic of the present disclosure may have a linear transmittance measured with an infrared-visible spectroscopic microscope of 10% or less, 9% or less, 8% or less, 7% or less, 6% or less, 5% or less, 4% or less, 3% or less, 2% or less, 1.5% or less, 1% or less, or 0.5% or less. This makes it possible to provide a composite ceramic with excellent thermal properties.

[0026] The composite ceramic of the present disclosure may have a structure in which a region having an absorptance of 99% or more as measured by an infrared-visible spectroscopic microscope is localized. The region having an absorptance of 99% or more may be a region where a second ceramic or free carbon particles are present. The absorptance of this region as measured by the infrared-visible spectroscopic microscope may be 90% or more, 91% or more, 92% or more, 93% or more, 94% or more, 95% or more, 96% or more, 97% or more, 98% or more, or 99% or more. This makes it possible to provide a composite ceramic with excellent thermal properties.

[0027] The composite ceramic of the present disclosure may have a thermal conductivity of 2 W / m·K or less from room temperature to 800°C. The composite ceramic of the present disclosure may have a thermal conductivity of 10 W / m·K or less, 9 W / m·K or less, 8 W / m·K or less, 7 W / m·K or less, 6 W / m·K or less, 5 W / m·K or less, 4 W / m·K or less, 3 W / m·K or less, 2 W / m·K or less, or 1 W / m·K or less from room temperature to 800°C. This makes it possible to provide a composite ceramic with excellent thermal properties.

[0028] The composite ceramic of the present disclosure may have a spectral reflectance of 10% or less in a wavelength region of 1.5 to 3.3 μm as measured with a Fourier transform infrared spectrophotometer. The composite ceramic of the present disclosure may have a spectral reflectance of 20% or less, 19% or less, 18% or less, 17% or less, 16% or less, 15% or less, 14% or less, 13% or less, 12% or less, 11% or less, 10% or less, 9% or less, 8% or less, 7% or less, 6% or less, 5% or less, 4% or less, 3% or less, 2% or less, or 1% or less. This makes it possible to provide a composite ceramic with excellent thermal properties.

[0029] The composite ceramic of the present disclosure may contain 70 to 80 wt % of rice husk combustion ash containing amorphous silica, calculated as a raw material. This allows for the provision of a composite ceramic with excellent properties at low cost. The composite ceramic of the present disclosure may contain 80 to 95 wt % of rice husk combustion ash containing amorphous silica, calculated as a raw material. This allows for the improvement of the strength of the composite ceramic.

[0030] The composite ceramic of the present disclosure may contain 5 to 30 wt % of silicon nitride or silicon carbide, Al, and Si in total, calculated as raw materials.

[0031] The raw material composition for the composite ceramic of the present disclosure contains 70 to 95 wt % of rice husk combustion ash containing amorphous silica and 5 to 30 wt % of silicon nitride or silicon carbide, Al, and Si combined. Al acts as a reducing agent for reducing the silicon oxide contained in the rice husk combustion ash. Si acts as a binder. Silicon nitride or silicon carbide acts as seed crystals. The raw material composition for the composite ceramic may contain 70 wt % or more, 75 wt % or more, 80 wt % or more, 85 wt % or more, or 90 wt % or more of rice husk combustion ash containing amorphous silica. The raw material composition for the composite ceramic may contain 95 wt % or less, 90 wt % or less, 85 wt % or less, 80 wt % or less, or 75 wt % or less of rice husk combustion ash containing amorphous silica. The composite ceramic of the present disclosure can be produced by firing this raw material composition under a nitrogen atmosphere.

[0032] In S10 of FIG. 1 , the temperature at which rice husks are burned to produce rice husk combustion ash may be 1000°C or lower. When rice husks are burned at 1000°C or higher, most of the carbon component is lost, resulting in crystallized silicon oxide. When rice husks are burned at a low temperature of approximately 500°C, some of the carbon remains in the combustion ash, which can act as a reducing agent to reduce silicon oxide when the raw material composition is fired to produce a composite ceramic. Furthermore, because amorphous silicon oxide is obtained, it can be easily crushed into a fine powder. The temperature at which rice husks are burned may be 400°C or higher, 450°C or higher, 500°C or higher, 550°C or higher, 600°C or higher, 650°C or higher, or 700°C or higher. The temperature at which the rice husks are burned to ash may be 1000°C or less, 950°C or less, 900°C or less, 850°C or less, 800°C or less, 750°C or less, 700°C or less, 650°C or less, 600°C or less, 550°C or less, or 500°C or less.

[0033] The heat storage body of the present disclosure includes the composite ceramic. The heat storage body may have a solid structure or a hollow structure.

[0034] The preheated air temperature for silicon carbide is 1080°C, 70°C higher than that for alumina. Furthermore, the temperature rise time for silicon carbide is shorter than that for alumina. Thus, the heat storage medium of the present disclosure has high thermal responsiveness, resulting in a small dead volume that does not contribute to heat exchange. This improves energy efficiency and reduces carbon dioxide emissions from industrial furnaces and the like. Furthermore, it can be suitably used in regenerative burner systems that repeatedly store and release heat.

[0035] [Example 1] [Characteristics of rice husk combustion ash] Figure 2 shows the components of rice husk combustion ash. The main components of rice husk combustion ash are Si (as silicon oxide), C (as carbon), and O (as silicon oxide, aluminum oxide, potassium oxide, calcium oxide, etc.), and other mineral elements are relatively small.

[0036] Figure 3 shows a scanning electron microscope (SEM) image of a sample of rice husk combustion ash that was added with aluminum and heat-treated at 1,300°C for 3 hours. Figure 4 shows the results of energy dispersive X-ray spectroscopy (EDX) measurements of the above sample. The sample, in which rice husk combustion ash was reduced with aluminum, exhibits a complex morphology unique to bio-based materials. Simple quantitative analysis using the ZAF correction method revealed that the sample contained 33.41 wt% carbon, 30.75 wt% oxygen, 19.07 wt% aluminum, and 15.75 wt% silicon.

[0037] Figure 5 shows the Raman spectrum of a sample obtained by adding aluminum powder to rice husk combustion ash and heat-treating it at 1,300°C for 1 hour in an argon atmosphere. A peak indicating the presence of silicon was observed. Figure 6 shows a scanning electron microscope (SEM) image of the above sample and the results of energy dispersive X-ray spectroscopy (EDX). The presence of silicon and aluminum oxide was confirmed. This indicates that aluminum is an effective reducing agent for rice husk combustion ash.

[0038] [Preparation of Composite Ceramic Solid Sphere Heat Storage Body] Combustion ash obtained by burning rice husks at 500-600°C was pulverized in a ball mill. Raw materials containing the fine powder of rice husk combustion ash, aluminum and carbon as reducing agents, silicon nitride powder as seed crystals, and waste silicon powder as a binder were mixed in a mortar and pestle for 3 hours. The rice husk combustion ash content in the raw materials was 70% by weight or more. The mixed raw materials were mixed with starch paste as a binder, rolled into balls, and dried at 120°C for 24 hours. The dried molded bodies were fired at 1300-1600°C in a nitrogen atmosphere at a temperature increasing rate of 10°C per minute, followed by furnace cooling.

[0039] FIG. 7 shows a schematic diagram of a reduction-nitriding furnace 1 for reducing and nitriding raw materials including rice husk combustion ash. A sample 13 is placed on a pedestal (setter) 5 provided inside a furnace tube 4. The pedestal 5 is made of graphite, silicon nitride, or the like. It is more preferable that the pedestal 5 is made of silicon nitride. A heater 3 is provided outside the furnace tube 4 and heats the furnace tube 4. The furnace tube 4 is made of silicon nitride (Si ３ N ４ ) This improves the thermal shock resistance of the furnace core tube 4. The furnace material 2 is made of a heat-resistant material and covers the heater 3 and the furnace core tube 4. The connecting jig 8 is made of SUS or the like and secures the furnace core tube 4. A resin hose 10 is connected to the mullite pipe 6 via a joint 9 and supplies atmospheric gas such as nitrogen into the furnace core tube 4. The atmospheric gas is discharged from the SUS pipe 7 to a cooling pipe 11 and cooled with water 12.

[0040] The preferred firing conditions were the presence of seed crystals, aluminum and carbon as reducing agents, a heat treatment temperature of 1450° C., a connecting material containing 10% by weight of silicon, and a base 5 made of silicon nitride.

[0041] [Structure of Composite Ceramic] Fig. 8 shows scanning electron microscope (SEM) images of the composite ceramic of Example 1. Enlarged views of the rectangles in each SEM image are shown adjacent to the right. The composite ceramic of Example 1 is composed of fine particles and has few pores, which indicates that it has a large effective light-receiving area.

[0042] [Composition of Composite Ceramic] Fig. 9 shows the X-ray diffraction (XRD) pattern of the composite ceramic of Example 1. The composite ceramic contains residual silicon, silicon oxide as a transmitting component, aluminum oxide formed by oxidizing aluminum that functioned as a reducing agent, silicon nitride and silicon carbide as absorbing components, and mullite (Al ４．５９ Si １．４１ O ９．７ ), oxynitride glass (Si ２ N ２ The broad amorphous peak between 2θ=17° and 25° indicates the presence of amorphous silicon oxide and aluminum oxide.

[0043] In the composite ceramic of the present disclosure, the height of the peak derived from silicon oxide appearing near 2θ = 28° is at least twice the height of the peak derived from silicon carbide appearing near 2θ = 35.5°. In the composite ceramic of the present disclosure, the height of the peak derived from silicon oxide may be at least 1.5 times, 1.6 times, 1.7 times, 1.8 times, 1.9 times, 2 times, 2.1 times, 2.2 times, 2.3 times, 2.4 times, 2.5 times, 2.6 times, 2.7 times, 2.8 times, 2.9 times, or 3 times the height of the peak derived from silicon carbide.

[0044] [Thermal Properties of Composite Ceramics] The thermal properties of the composite ceramic of Example 1 were measured. A disk-shaped sample with a diameter of 12 mm and a thickness of 1 mm was cut out from the material block of the composite ceramic of Example 1. Black oxide films were formed on the front and back of the sample using a carbon particle-containing spray, and the thermal properties of the sample were then measured by the flash method using a NETZSCH LFA467HT HyperFlash. Furthermore, as comparative examples, the thermal properties of commercially available silicon carbide heat storage balls and commercially available alumina heat storage balls were also measured.

[0045] 10 shows the results of measuring the thermal conductivity of the composite ceramic of Example 1. In the low-temperature range from room temperature to 400°C, the thermal conductivity was such that commercial silicon carbide >> commercial alumina >> the composite ceramic of Example 1. In the high-temperature range from 400°C to 800°C, the thermal conductivity was such that commercial silicon carbide >> commercial alumina ≈ the composite ceramic of Example 1.

[0046] 11 shows the results of measuring the thermal diffusivity of the composite ceramic of Example 1. The thermal diffusivity in the low temperature range from room temperature to 400°C was such that commercially available silicon carbide >> commercially available alumina >> the composite ceramic of Example 1. The thermal diffusivity in the high temperature range from 400°C to 800°C was such that commercially available silicon carbide >> commercially available alumina ≈ the composite ceramic of Example 1.

[0047] 12 shows the measurement results of the specific heat capacity of the composite ceramic of Example 1. The specific heat capacity from room temperature to 800° C. was as follows: commercially available alumina > the composite ceramic of Example 1 > commercially available silicon carbide.

[0048] [Spectral Reflectance of Composite Ceramics] The spectral reflectance of the composite ceramics of Example 1 was measured. As comparative examples, the spectral reflectance of a commercially available silicon carbide heat storage sphere and a commercially available alumina heat storage sphere was measured. The device used was a Perkin Elmer System 2000 FTIR device. The integrating sphere was a Labsphere RSA-PE-200-ID, the inside of which was coated with gold, the integrating sphere entrance diameter was φ16 mm, and the measurement section diameter was φ24 mm. The measurement range was 370 to 7800 cm －１ (effective range 400-6000cm －１ ), the number of integrations is 200, the light source is the MIR-TGS detector, and the resolution is 16 cm －１ The beam splitter was optimized KBr, and the optical path from the light source to the detector was filled with nitrogen gas for purging.

[0049] Figure 13 shows the results of measuring the spectral reflectance of the composite ceramic of Example 1. Figure 14 shows the results of measuring the spectral reflectance of a commercially available silicon carbide heat storage sphere. Figure 15 shows the results of measuring the spectral reflectance of a commercially available alumina heat storage sphere. In the figures, the area surrounded by the dashed line indicates the peak wavelength range of light equivalent to high-temperature waste heat (approximately 600°C to 1200°C) from industrial furnaces, etc. The reflectance in the wavelength range equivalent to high-temperature waste heat was commercially available alumina >> commercially available silicon carbide > composite ceramic of Example 1. According to Kirchhoff's law, emissivity + transmittance (≒ 0) + reflectance = 1, so emissivity ≒ 1 - reflectance. The composite ceramic of Example 1 was shown to have higher absorption performance and emissivity than commercially available silicon carbide.

[0050] Fig. 16 shows the absorptance of the composite ceramic, silicon carbide, and aluminum oxide of Example 1 measured by an infrared-visible spectroscopic microscope. Fig. 17 shows the linear transmittance in one direction of the composite ceramic of Example 1 measured by a Fourier transform infrared spectrophotometer (FTIR). The linear transmittance of the composite ceramic in the wavelength range of 1.5 to 3.3 μm was almost zero, indicating that almost all incident light was absorbed by the composite ceramic.

[0051] [Composite Ceramic Microstructure] Figure 18 shows SEM and EDS images of the cross section of the composite ceramic of Example 1. As shown in (a1), the surface of the composite ceramic is rough and pores are present, increasing the surface area and the heat radiation area. Furthermore, as shown in (a2) to (a11), large black regions that can be identified as free carbon are present. Furthermore, the elements Si, Al, and O are most abundant and uniformly distributed. Taking into account the X-ray diffraction pattern measurement results, it can be inferred that the main structure of the composite ceramic of Example 1 is a glass phase of silicon oxide and aluminum oxide, with trace amounts of oxides such as potassium uniformly doped within it.

[0052] Figure 19 shows an enlarged view of the pore shown in (a1) of Figure 18 and the surrounding region b. As shown in (b2) to (b11), it can be seen that the pore is surrounded mainly by particles of carbon, Si, and silicon carbide produced by the reaction of carbon and Si. Meanwhile, it can be seen that the pores are densely packed and close to each other, and the carbon and silicon carbide particles are intertwined and distributed in the silicon oxide-aluminum oxide glass matrix phase.

[0053] FIG. 20 shows the absorptance of the composite ceramic of Example 1 in region c shown in (a1) of FIG. 18 . FIG. 21 shows the absorptance of the composite ceramic of Example 1 in region d shown in (a1) of FIG. 18 . The absorptance was measured using an infrared-visible spectroscopic microscope. It can be seen that the absorptance in the wavelength region of 1.5 to 3.3 μm in region c, where carbon particles are present, is high at 99% or more, approaching 100%. This suggests that the carbon particles have an absorptance close to 100% and have strong thermal radiation capabilities. The absorptance in the wavelength region of 1.5 to 3.3 μm in region d is also high at approximately 93%, indicating that region d, which consists of carbon particles, silicon carbide particles produced by the reaction, and a silicon oxide-aluminum oxide glass phase, also has strong thermal radiation capabilities.

[0054] FIG. 22 schematically illustrates the heat transfer structure of the composite ceramic of the present disclosure. When the composite ceramic of the present disclosure is heated at high temperatures, the rough surface increases the absorption area, allowing efficient absorption of radiant energy. The presence of carbon and silicon carbide particles with extremely high absorption rates on the surface allows rapid absorption of radiant energy, resulting in a rapid rise in surface temperature. Because carbon and silicon carbide particles are densely distributed throughout the composite ceramic, carbon and silicon carbide particles that absorb large amounts of radiant energy radiate radiant energy to their surroundings, and the surrounding carbon and silicon carbide particles also absorb radiant energy, rapidly raising the temperature in their vicinity. This radiation-based heat transfer mode is believed to enable the composite ceramic of the present disclosure to achieve rapid heating and cooling overall, as well as rapid heat storage and release in high-temperature ranges.

[0055] [Heat storage characteristics of composite ceramic solid sphere heat storage body] The heat storage characteristics of the composite ceramic solid sphere heat storage body were measured. A hole was drilled to the center of the spherical sample, and a sheathed thermocouple with a diameter of 0.5 mm was inserted and fixed with a heat-resistant adhesive. The sample was placed in a furnace at 800°C and removed after 240 seconds, and the change in temperature was measured. As comparative examples, the thermal characteristics of a commercially available silicon carbide heat storage ball and a commercially available alumina heat storage ball were also measured.

[0056] 23 shows the temperature change of the composite ceramic solid sphere heat storage medium. The composite ceramic solid sphere heat storage medium of Example 1 exhibited almost the same behavior as commercially available silicon carbide heat storage spheres.

[0057] Figure 24 shows the temperature change of the composite ceramic solid sphere heat storage medium. This figure shows the temperature change near the center of the heat storage sphere (1), near the surface (3), and near the midpoint between the center and the surface (2). The composite ceramic solid sphere heat storage medium of Example 1 has a higher thermal response near the surface (3) than near the center (1), reflecting its low thermal conductivity.

[0058] [Examples A to G] Seven composite ceramic solid sphere thermal accumulators were fabricated with different raw material blending ratios. Figure 25 shows the raw material blending ratios for each example. Figure 26 shows the mass, density, mass change, mass change rate, and shrinkage rate of the fabricated composite ceramic solid sphere thermal accumulators. Example E shows the cases where a graphite base 5 was used and where a silicon nitride base 5 was used. The firing conditions for Example E, which used a silicon nitride base 5, were the best.

[0059] [Preparation of composite ceramic hollow sphere heat storage body] To form a ceramic hollow body, slip casting of a slurry containing ceramic particles is a simple method. To reduce the environmental load, it is more desirable to use a water-based slurry. However, there are some materials for which it is difficult to prepare a slurry using water as a medium. For example, iron oxide (Fe ２ O ３Magnetic particles such as graphite particles and ferromagnetic particles agglomerate in water, making it difficult to prepare a slurry. Metals and semi-metals such as silicon are highly dangerous because they react with water to generate hydrogen. Magnesium oxide (MgO) is also highly dangerous because it generates heat when it reacts with water to form hydrates.

[0060] To solve these problems, the ceramic manufacturing method disclosed herein involves coating the surfaces of metal or semi-metal particles with a water-soluble binder, suspending them in water to form a slurry, and pouring the slurry into a porous mold for molding. This allows for easy and safe preparation of aqueous slurries for slip casting, even for materials that have traditionally been difficult to prepare.

[0061] Magnesium oxide (MgO), zirconia (ZrO ２ ), alumina (Al ２ O ３ ), yttrium (III) oxide (Y ２ O ３ The raw material, a mixture of oxides such as silicon dioxide and waste silicon powder, is crushed in a dry ball mill for 24 hours. A binder such as water-soluble organic matter or water-soluble silica is added to coat the surface of the silicon powder. Water is added and the mixture is stirred for one minute to create a slurry. The slurry is poured into a porous mold and sintered by heating above the melting point of silicon in a nitrogen-containing atmosphere.

[0062] This method can be used not only to produce composite ceramic hollow bodies using rice husk combustion ash as a raw material, but also to produce hollow bodies of silicon nitride and ceramic hollow bodies containing metals, semi-metals, iron oxide, graphite, magnesium oxide, etc.

[0063] [Example 2] [Preparation of composite ceramics] A raw material composition containing 270 g of rice husk combustion ash and 30 g of auxiliary components was mixed with 270 to 350 g of water and 20 g of an organic binder in a kneader, and the mixture was molded into a clay. After drying, the clay was fired in a nitrogen atmosphere at 1450°C for 3 hours. The auxiliary components were, by weight, 22% SiC, 13% Al, 43% Si, and 13% Al. ２ O ３ : 22%. ２ O ３The Al of the fiber may be in the form of a fiber or a powder. ２ O ３ The use of the above makes molding easier.

[0064] [Strength of Composite Ceramics] The composite ceramic of Example 1 produced from a raw material composition containing 80 wt % of rice husk combustion ash had an average strength of 43 MPa, while the composite ceramic of Example 2 produced from a raw material composition containing 90 wt % of rice husk combustion ash had a strength of 103 MPa. It was found that the composite ceramic produced from the raw material composition containing a larger amount of rice husk combustion ash had a higher strength.

[0065] [Thermal Properties of Composite Ceramics] Two solid spheres (φ19) of the composite ceramic and SiC of Example 2 were prepared and placed side by side in the center of a plate in a household microwave oven (2.45 GHz, 600 W) and heated for a predetermined period of time. Figure 27 shows the temperature change of the solid spheres. Ceramics that absorb 2.45 GHz microwaves are limited to certain ceramics, such as mica and SiC. Among them, SiC is the material with the best absorption properties and is used in the heat-generating portion of microwave heating furnaces. The solid sphere of the composite ceramic of Example 2 showed a faster temperature rise rate than the solid sphere of SiC, and its maximum temperature was approximately twice as high when heated for the same period of time. The mechanism behind this is believed to be that the presence of amorphous silica locally varies the Si-O-Si bond angle, making the polarization moment more likely to fluctuate and energy absorption more likely, and that the Al in mullite glass is more likely to increase the temperature. ３＋ is Si ４＋ The composite ceramics of Example 2 are similar in size to the SiC ceramics of Example 1 and are embedded in the silica network. However, the difference in charge between the two creates a charge imbalance within the network, resulting in local polarization points. Furthermore, the solid spheres of the composite ceramics of Example 2 have a thermal conductivity of 1.6 to 2.0 W / m / K, which is several tens of times lower than that of SiC. Therefore, even if internal heat is generated, the heat is less likely to be conducted to the outside, and the heat can be contained within, demonstrating properties suitable for use as a microwave heating element. Furthermore, the thermal expansion coefficient and Young's modulus of the composite ceramics of Example 2 are smaller than those of SiC, which reduces the thermal stress generated and makes them less likely to crack even when heated rapidly. These are also desirable properties for use as a microwave heating element.

[0066] [Heating System Using Composite Ceramics] As described above, the composite ceramics of the present disclosure have the property of absorbing electromagnetic waves and generating heat, and therefore can be used in a heating system for heating an object to be heated. Fig. 28 schematically shows the configuration of a heating system according to an embodiment of the present disclosure. The heating system 20 includes a cylindrical rotary kiln 21, which is an example of a heating chamber, a heating element 22 provided inside the rotary kiln 21, an electromagnetic wave irradiation unit 23 that irradiates the heating element 22 with electromagnetic waves such as microwaves, and a control unit 24 that controls the rotation of the rotary kiln 21 and the irradiation of electromagnetic waves by the electromagnetic wave irradiation unit 23. The heating chamber may be a furnace or kiln of any shape.

[0067] The heating element 22 includes the composite ceramic of the present disclosure. When the electromagnetic wave irradiation unit 23 irradiates electromagnetic waves to the composite ceramic contained in the heating element 22 inside the rotary kiln 21, the composite ceramic absorbs the electromagnetic waves and generates heat, thereby heating the interior of the rotary kiln 21 to a desired temperature. Because there is no need to provide wiring or the like for electrically heating the heating element 22, the heating system 20 can be realized with a simple configuration even when the heating chamber rotates or moves.

[0068] The present disclosure has been described above based on examples. These examples are merely illustrative, and it will be understood by those skilled in the art that various modifications are possible in the combination of the components and processing steps, and that such modifications are also within the scope of the present disclosure.

[0069] The present disclosure is applicable to composite ceramics, raw material compositions for composite ceramics, methods for manufacturing composite ceramics, heat storage bodies, and methods for manufacturing ceramics.

[0070] REFERENCE SIGNS LIST 1 reduction nitriding furnace, 2 furnace material, 3 heater, 4 furnace core tube, 5 base, 6 mullite pipe, 7 SUS pipe, 8 connecting jig, 9 joint, 10 resin hose, 11 cooling pipe, 12 water, 20 heating system, 21 rotary kiln, 22 heating element, 23 electromagnetic wave irradiation unit, 24 control unit.

Claims

1. A composite ceramic comprising: a matrix phase containing a first ceramic having an average linear transmittance of 80% or more in the wavelength range of 1.5 to 3.3 μm as measured with a Fourier transform infrared spectrophotometer; and a dispersed phase containing a second ceramic having an average linear transmittance of less than 20% in the wavelength range of 1.5 to 3.3 μm as measured with a Fourier transform infrared spectrophotometer.

2. The composite ceramic according to claim 1, wherein the first ceramic or the second ceramic contains a substance derived from rice husk combustion ash.

3. The composite ceramic according to claim 1, wherein the first ceramic contains amorphous silicon oxide or aluminum oxide.

4. The composite ceramic according to claim 1, wherein the second ceramic contains at least one of silicon carbide, silicon nitride, and carbon.

5. The composite ceramic according to claim 1, further comprising an amorphous composite oxide of Al and Si.

6. The composite ceramic according to claim 1, further comprising amorphous silicon oxynitride.

7. The composite ceramic according to any one of claims 1 to 6, which has an in-line transmittance of 2% or less as measured by an infrared-visible spectroscopic microscope.

8. A composite ceramic according to any one of claims 1 to 6, which has localized regions where the absorptance measured by an infrared-visible spectroscopic microscope is 99% or more.

9. A composite ceramic according to any one of claims 1 to 6, in which in an X-ray diffraction pattern, the height of the peak derived from silicon oxide appearing near 2θ = 28° is at least twice the height of the peak derived from silicon carbide appearing near 2θ = 35.5°.

10. The composite ceramic according to any one of claims 1 to 6, which has a thermal conductivity of 2 W / m·K or less from room temperature to 800°C.

11. The composite ceramic according to any one of claims 1 to 6, which has a spectral reflectance of 10% or less in the wavelength region of 1.5 to 3.3 μm as measured with a Fourier transform infrared spectrophotometer.

12. A composite ceramic according to any one of claims 1 to 6, which exhibits a faster rate of temperature rise when irradiated with microwaves of 2.45 GHz than silicon carbide.

13. A composite ceramic according to any one of claims 1 to 6, which reaches a higher temperature than silicon carbide when irradiated with 2.45 GHz microwaves for the same period of time.

14. The composite ceramic according to any one of claims 1 to 6, comprising, in raw material equivalents, 70 to 80% by weight of rice husk combustion ash containing amorphous silica, and 5 to 30% by weight of silicon nitride or silicon carbide, Al, and Si combined.

15. The composite ceramic according to any one of claims 1 to 6, comprising, in raw material equivalents, 80 to 95% by weight of rice husk combustion ash containing amorphous silica, and 5 to 30% by weight of silicon nitride or silicon carbide, Al, and Si combined.

16. A raw material composition for composite ceramics comprising 70 to 80% by weight of rice husk combustion ash containing amorphous silica, and 5 to 30% by weight of silicon nitride or silicon carbide, Al, and Si combined.

17. A raw material composition for composite ceramics comprising 80 to 95% by weight of rice husk combustion ash containing amorphous silica, and 5 to 30% by weight of silicon nitride or silicon carbide, Al, and Si combined.

18. A method for producing a composite ceramic, comprising a step of firing the raw material composition according to claim 16 or 17.

19. A heat storage body comprising the composite ceramic material according to any one of claims 1 to 6.

20. The heat storage body according to claim 19, having a solid structure.

21. The heat storage medium according to claim 19, having a hollow structure.

22. A heating system comprising: a heating chamber; a heating element provided inside the heating chamber; and an electromagnetic wave irradiation unit that irradiates electromagnetic waves to the heating element, wherein the heating element includes the composite ceramic according to any one of claims 1 to 6.

23. A method for producing ceramics, comprising the steps of: coating a powder containing a metal or semi-metal with a water-soluble binder; suspending the powder in water; pouring the suspension into a porous mold to form the powder; and firing the formed body.

24. The method of claim 23, wherein the step of firing the compact is carried out in an atmosphere containing nitrogen.

25. The method according to claim 23 or 24, wherein the powder contains silicon, and the step of sintering the compact includes heating to a temperature equal to or higher than the melting point of silicon.

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