Radiation refrigeration low-temperature co-fired Al2O3 ceramic chip and preparation method thereof

Abstract

The invention discloses a radiation refrigeration low-temperature co-fired Al2O3 ceramic chip and a preparation method thereof in the field of constructional engineering materials. The method comprises the following steps: 1) adding glass powder, an Al2O3 filler, an organic adhesive and a dispersing aid into a high-speed mixer, stirring and mixing at a low rotating speed, adding a plasticizer, starting high-speed stirring and mixing until the temperature reaches 70 + / -5 DEG C, rotating to a low rotating speed, adding a solvent, and continuously stirring and mixing to obtain tape casting slurry; 2) defoaming the tape casting slurry in a vacuum stirring defoaming machine, and discharging the slurry to a tape casting machine to obtain a tape casting belt; and 3) carrying out hot pressing on the casting belt according to requirements to obtain a green body, and placing the green body in a high-temperature kiln to remove organic matters in the green body to obtain the radiation refrigeration low-temperature co-fired Al2O3 ceramic material.The Al2O3 ceramic chip sintered at low temperature by the method has the effect of completely reflecting or approximately totally reflecting sunlight.

Description

TECHNICAL FIELD

[0001] The application relates to the field of building engineering materials, and more particularly to a radiation refrigeration low-temperature co-fired Al2O3 ceramic sheet and a preparation method. BACKGROUND

[0002] The building refrigeration energy consumption in China accounts for more than 17% of the total energy consumption, and shows an increasing trend year by year, which has become an important restricting factor for China to achieve the "double carbon" goal. In recent years, radiation refrigeration has stood out as an important building energy-saving technology. Its cooling mechanism reflects solar radiation (0.28-2.5 μm) and emits heat in the form of radiation to the low-temperature outer space through the atmospheric long-wave infrared transmission window (8-13 μm), thereby achieving the cooling of buildings. Although the current application scale is limited and relatively scattered, the radiation refrigeration technology has shown significant energy-saving potential, which can reduce more than 40% of the refrigeration energy consumption in large buildings, and has significant value for promoting the low-carbon development of the building industry in China.

[0003] Radiative cooling materials are the core technology for developing building energy saving and green buildings. It is difficult and hot in the field to achieve the performance of completely reflecting or nearly completely reflecting sunlight and excellent weather resistance. International journal articles Nature 2014, 515, 540-544 and Nano Letters, 2022, 22(12): 4925-32 proposed various multilayer stacked optical structure designs to achieve high solar reflectance and long-wave infrared emissivity. However, the solar reflectance of these materials mainly relies on metal materials (such as silver and aluminum, etc.), and the solar reflectance is still lower than 95%, leaving a lot of room for improvement in the so-called solar light full reflection performance. In addition, it is almost impossible to produce and apply these nano-micron scale optical structures on a large scale. These optical structure designs often need to use precise lithography or deposition technology, which seriously hinders their popularization in practical applications. In order to popularize radiative cooling technology in practical applications, international journal articles Science, 2018, 362: 315-319, Nature Nanotechnology, 2021, 16: 153-158, Nano Energy, 2023, 114: 108625, Proceedings of the National Academy of Sciences, 2020, 117: 14657-14666, Advanced Materials, 2022, 34: 2208236 reported that the refractive index difference between the air holes or white dielectric fillers (such as Al2O3, TiO2 and ZnO, etc.) and the polymer makes the sunlight strongly scattered at the interface between the air holes or white dielectric fillers and the polymer to achieve the performance of nearly completely reflecting sunlight, while the polymer matrix realizes high long-wave infrared emissivity. However, the weather resistance of polymer materials under the combined environmental stress of heat and humidity cycles, ultraviolet light irradiation, etc. is poor. The performance degradation caused by this environmental sensitivity seriously restricts the long-term stable operation of polymer-based radiative cooling composites in outdoor environments. International journal articles Science, 2023, 382: 691-697 and Science, 2023, 382: 644-645 reported radiative cooling porous Al2O3 ceramics, which achieved nearly 100% solar reflectance and excellent weather resistance. However, pure Al2O3 ceramics need high-temperature sintering (>1000℃), which will lead to high processing cost. International journal article Science, 2023, 382, 684-691 proposed a low-temperature co-fired ceramic technology solution, using low-melting-point glass as a binder to encapsulate Al2O3 particles, which can effectively reduce the energy consumption and cost of Al2O3 ceramics.However, due to the similar refractive index of glass and Al2O3, the solar scattering efficiency is reduced, and the solar reflectivity of the material is far less than that of porous Al2O3 radiation cooling ceramic, which needs to be further improved, and more new disruptive technology is needed.

[0004] In addition, in the prior art, the invention patents with publication numbers CN111234296A and CN111391263A disclose the construction of a porous structure in polymers such as polypropylene and polyvinyl chloride to achieve the performance of approximately total reflection of solar light, but for example, the polymer materials such as polypropylene and polyvinyl chloride will experience a double failure mechanism under long-term outdoor ultraviolet radiation conditions: on the one hand, photo-oxidation reaction will accelerate the decline of mechanical properties, on the other hand, photo-degradation of polymer molecular chains will cause material surface yellowing phenomenon, and then lead to irreversible decline of solar reflectivity, and finally cause functional failure of the material. This photo-mechanical coupling failure mechanism makes it difficult for the material to maintain performance stability throughout the life cycle under the combined environmental stresses of heat and humidity, ultraviolet radiation, etc. The invention patent with publication number CN117534506A invents a porous Al2O3 ceramic, whose solar reflectivity is as high as 0.99, thereby achieving very good radiation cooling effect. However, the sintering temperature of this porous ceramic material is still relatively high, resulting in large preparation energy consumption, thereby causing high production cost of the product.

[0005] In summary, the current solar light total reflection and excellent weather resistance radiation cooling material mainly uses porous Al2O3 ceramic, which achieves a solar reflectivity of more than 0.99, thereby achieving very good cooling effect. However, the current porous Al2O3 ceramic requires a high sintering temperature (>1000℃), which results in large preparation energy consumption and increases the production cost of the material. Although the low-temperature co-firing scheme uses low-melting-point glass to reduce the sintering temperature, the refractive index of glass and Al2O3 is similar, which results in solar reflectivity far less than that of porous Al2O3 ceramic. Only the radiation cooling material with complete reflection or approximately total reflection of solar light can have very good cooling effect. Therefore, in order to solve the problems and deficiencies in the prior art, it is necessary to develop a radiation cooling material with complete reflection or approximately total reflection of solar light performance and excellent weather resistance and a corresponding preparation method to meet the needs of the development of green building engineering materials. SUMMARY

[0006] The purpose of this invention is to address the shortcomings and problems existing in the prior art by providing a radiation-cooled low-temperature co-fired Al2O3 ceramic sheet and its preparation method. This low-temperature co-fired Al2O3 ceramic sheet exhibits total or near total reflection of sunlight and high emission of long-wave infrared light, thus achieving a very good cooling effect. This method eliminates the need for the ultra-high sintering temperature of traditional Al2O3 ceramics. Instead, it utilizes a low-melting-point glass as a binder, encapsulating a special porous Al2O3 filler derived from a metal-organic framework material near its melting point. This results in ceramic materials and sheets that exhibit complete or near total reflection of sunlight and high emission of long-wave infrared light, achieving a very good cooling effect.

[0007] Therefore, the present invention is achieved through the following technical solution: a method for preparing radiation-cooled low-temperature co-fired Al2O3 ceramic sheets, comprising the following steps:

[0008] 1) Add glass powder, Al2O3 filler, organic binder, and dispersant to a high-speed mixer and stir at a low speed of ≤500 rpm. After adding plasticizer, start high-speed stirring at ≥1000 rpm until the temperature reaches 70±5℃. Then switch to a low speed of ≤500 rpm, add solvent, and continue stirring to obtain a cast slurry. The glass powder is low-melting-point glass powder; the organic binder is styrene-butadiene thermoplastic elastomer; the dispersant is polyvinylpyrrolidone K30; the plasticizer is cycloalkane oil; the solvent is tetrahydrofuran. The temperature should be controlled at 25~30℃ when adding the solvent, and the stirring time should be no less than 4 hours after adding the solvent.

[0009] The mass amounts of each component are as follows:

[0010] 15-40 parts of low-melting-point glass;

[0011] Al2O3 25-60 parts;

[0012] 3-5 parts organic binder;

[0013] 1-2 parts of dispersant;

[0014] 2-3 parts plasticizer;

[0015] Solvent 25-30 parts;

[0016] 2) Degas the cast slurry in a vacuum stirring degassing machine. The pressure inside the vacuum stirring degassing machine is -0.08 to -0.09 MPa. The degassed slurry is discharged into the casting machine to obtain the cast tape.

[0017] 3) The cast tape is hot-pressed as needed to obtain a green body. The green body is then placed in a high-temperature kiln to remove organic matter and obtain radiation-cooled low-temperature co-fired Al2O3 ceramic material.

[0018] Further, the specific method of step 3) is as follows: hot-press the multilayer cast tapes together, controlling the hot-pressing temperature to be 180-200℃, the pressure to be 10-15MPa, and the time to be 15-20min, and then cold-pressing to obtain a green body with uniform thickness; place the green body in a muffle furnace, raise it from room temperature to 500-600℃ at a rate of 5-10℃ / min, hold it at 500-600℃ for 3-5h to remove organic matter from the green body, and then rapidly raise the temperature to 800-1200℃ and hold it for 15-30min. After the muffle furnace cools to room temperature, a radiation-cooled low-temperature co-fired ceramic is obtained.

[0019] The styrene-butadiene thermoplastic elastomer is a styrene-butadiene-styrene triblock copolymer with a styrene / butadiene mass ratio of 23 / 77. Under a load of 5 kg and a test temperature of 200 °C, the melt flow rate is 0.05–0.20 g / 10 min. Choosing a styrene-butadiene-styrene triblock copolymer imparts thermoplasticity and elasticity to the green body, meeting the practical engineering needs of subsequent hot pressing and custom shaping.

[0020] The cycloalkane oil is a medium-viscosity cycloalkane oil, with a kinematic viscosity of 50–70 cSt at 40°C. Choosing a medium-viscosity cycloalkane oil can improve the flowability of styrene-butadiene thermoplastic elastomers, reduce the amount of organic solvent used, and lower costs.

[0021] Further improvements are made in that the Al2O3 filler is a hexagonal plate-shaped porous Al2O3 filler derived from a metal-organic framework (MOF), a hexagonal prismatic porous Al2O3 filler derived from an MOF, or a precipitated spherical Al2O3 filler. Since the precipitated spherical Al2O3 filler requires a high filling ratio to achieve good solar reflectivity, the MOF-derived technology can endow the Al2O3 filler with different morphologies and multi-layered porous structures. The special morphology of the filler and the increase of solar scattering points inside can improve the solar scattering efficiency. Therefore, the hexagonal plate-shaped porous Al2O3 filler derived from an MOF has the lowest filling coefficient and the highest solar reflectivity compared to the hexagonal prismatic porous Al2O3 filler derived from an MOF and spherical alumina.

[0022] Among them, the metal-organic framework-derived hexagonal plate-shaped porous Al2O3 filler uses hexagonal plate-shaped MIL-96(Al) as a precursor. The Al2O3 filler obtained by calcination exhibits a hexagonal plate-like morphology and a multi-layered internal porous structure. The diameter of the hexagonal plates is 500–950 nm, the thickness is 150–250 nm, and the internal pore size is 2.31–19.41 nm. The metal-organic framework-derived hexagonal prism-shaped porous Al2O3 filler also uses hexagonal prism-shaped MIL-96(Al) as a precursor. The Al2O3 filler obtained by calcination exhibits a hexagonal prism-like morphology and a multi-layered internal porous structure. The diameter of the hexagonal prism plates is 350–800 nm, the length is 2.5–7 μm, and the internal pore size is 2.52–20.50 nm. The precipitated spherical Al2O3 filler is obtained by calcining homogeneous precipitated Al(OH)3 as a precursor to obtain Al2O3 filler with a spherical structure, and the diameter of the sphere is 850-1250 nm.

[0023] Further, in step 2), the thickness of the cast tape is 100±10μm; it also includes a drying step of the cast tape, in which the cast tape is placed in a drying oven and the temperature is controlled at 30±5℃ to obtain a fully dried cast tape.

[0024] Solar Reflectance Testing: The solar reflectance of radiation-cooled low-temperature co-fired Al2O3 ceramics was tested using an Agilent Technologies UV-Vis-NIR spectrophotometer (Carry-5000). The sample size was 30 mm in diameter and 500 μm thick. Specifically, the UV-Vis-NIR spectrophotometer was set to diffuse reflectance mode, and a white PTFE substrate was used for baseline calibration. After baseline calibration, the sample was placed in the test window to measure the reflectance within the solar wavelength range (200-2500 nm). Integrating the reflectance (r(λ)) at each wavelength (λ) yielded the average solar reflectance (R0). solar The integral formula is as follows:

[0025]

[0026] Where i(λ) is the solar radiation energy (per unit area per unit wavelength) derived from ASTM G173.

[0027] Long-wave infrared emissivity testing: The solar reflectivity of radiation-cooled low-temperature co-fired Al2O3 ceramics was tested using a Fourier transform infrared spectrometer (PerkinElmer Frontiers) equipped with a gold integrating sphere (PIKE Technologies). The sample size was 30 mm in diameter and 500 μm thick. Specifically, the Fourier transform infrared spectrometer was set to diffuse reflectance mode, and a gold substrate was used for baseline correction. After baseline correction, the sample was placed in the test window to measure the reflectivity and transmittance in the long-wave infrared band (2.5-16 μm). The average long-wave infrared emissivity (ε) can be calculated by integrating the absorbance (α(λ)) at each wavelength (λ). LWIR The integral formula is as follows:

[0028]

[0029] Where I BB (T, λ) is the radiation intensity of a blackbody at temperature (T) and wavelength (λ).

[0030] Outdoor actual cooling effect test: A self-made testing device was assembled, consisting of a measuring module and expanded polystyrene foam. The measuring module included a sample, thermocouple, and aluminum plate. A K-type thermocouple was placed between the sample and the aluminum plate to monitor the real-time temperature, and the thermometer reading was recorded every 1 minute. The measuring module was embedded in a groove (9.5×5.0cm) on the top surface of the expanded polystyrene foam (30×30×30cm) to minimize conduction and convection heat exchange with the environment. The entire device was placed at a 32° southward tilt on the 16th floor of Jinlun New City, Hanjiang District, Yangzhou, Jiangsu Province (32°15'N, 119°01'E). The test time was from 00:00 to 24:00 on August 24, 2024.

[0031] Compared with existing technologies, this invention offers the following advantages: Currently, the main materials used for total internal reflection and excellent weather-resistant radiative cooling primarily employ porous Al2O3 ceramics, requiring high sintering temperatures (>1000℃), resulting in high energy consumption and increased material preparation costs. Furthermore, low-temperature co-fired ceramic methods utilize low-melting-point glass to lower the sintering temperature; however, the refractive indices of glass and Al2O3 are similar, leading to a significantly lower solar reflectivity compared to porous Al2O3 ceramics. This invention utilizes metal-organic framework materials to derive Al2O3 fillers, improving solar scattering efficiency through filler morphology control and the construction of a porous internal structure, achieving near-total internal reflection or total internal reflection performance. Scattering efficiency simulations reveal that hexagonal plate-shaped Al2O3 exhibits significantly higher solar backscattering efficiency than hexagonal prismatic and spherical Al2O3. Moreover, the porous internal structure of the filler facilitates Rayleigh scattering, further enhancing the solar backscattering efficiency of hexagonal plate-shaped Al2O3. Experimental results also show that when the mass of Al2O3 accounts for more than 50% of the total mass of glass powder and Al2O3, the low-temperature co-fired ceramics containing metal-organic framework-derived lamellar porous Al2O3 achieve a high solar reflectance of 0.98. In contrast, when the mass of Al2O3 accounts for more than 70% of the total mass of glass powder and Al2O3, the solar reflectance of low-temperature co-fired ceramics containing precipitated spherical and metal-organic framework-derived hexagonal prismatic Al2O3 are only 0.95 and 0.96, respectively. Furthermore, the low-temperature co-fired ceramics containing metal-organic framework-derived lamellar porous Al2O3 also outperform those containing precipitated spherical and metal-organic framework-derived hexagonal prismatic Al2O3 in terms of long-wave infrared emissivity.

[0032] In summary, the low-temperature co-fired Al2O3 ceramic sheet of this invention exhibits a solar reflectivity of 0.98–0.99, truly realizing the function of reflecting sunlight. Its cooling performance surpasses existing technologies and products, significantly enriching market supply and providing users with more diverse choices. Furthermore, compared to porous Al2O3 ceramic sheets, this low-temperature co-fired Al2O3 ceramic sheet not only has a lower sintering temperature but also possesses a higher long-wave infrared emissivity. On the other hand, this ceramic sheet can be customized into various complex three-dimensional shapes according to requirements, and defective products generated during the production process and products after their service life can be crushed and reused, demonstrating good sustainability and economy. Attached Figure Description

[0033] Figure 1 SEM (a) and TEM (b) images of hexagonal sheet-like porous Al2O3 fillers derived from metal-organic framework materials in Examples 1-5.

[0034] Figure 2SEM images of hexagonal prismatic porous Al2O3 fillers derived from metal-organic framework materials in Examples 6-10.

[0035] Figure 3 SEM images of spherical Al2O3 fillers obtained by precipitation method in Comparative Examples 1-5.

[0036] Figure 4 The images are SEM images of the whole (a), cross-section at low magnification (b), and cross-section at high magnification (c) of Example 3.

[0037] Figure 5 The solar reflectance curves (a) and long-wave infrared emissivity curves (b) are for Examples 1-5.

[0038] Figure 6 The solar reflectance curves (a) and long-wave infrared emissivity curves (b) for Examples 6-10 are shown.

[0039] Figure 7 The solar reflectance curves (a) and long-wave infrared emissivity curves (b) are shown in Comparative Examples 1-5.

[0040] Figure 8 This is a comparison of the optical performance of Example 3 and Comparative Example 6.

[0041] Figure 9 This is a comparison of the actual outdoor cooling effects of Example 3 and Comparative Example 6.

[0042] Figure 10 This is a digital photograph of a complex three-dimensional shape, as shown in Example 3. Detailed Implementation

[0043] The present invention is illustrated below with reference to specific embodiments, but the present invention is not limited to these embodiments.

[0044] The materials used in the following embodiments are as follows:

[0045] Low melting point glass powder, with a melting point of 400-700℃.

[0046] Al2O3 fillers: There are three types, namely hexagonal plate-shaped porous Al2O3 fillers derived from metal-organic framework materials, hexagonal prismatic porous Al2O3 fillers derived from metal-organic framework materials, and precipitated spherical Al2O3 fillers.

[0047] The mechanical binder is styrene-butadiene thermoplastic elastomer (SBS); it is a styrene-butadiene-styrene triblock copolymer with a styrene / butadiene mass ratio of 23 / 77.

[0048] The dispersing agent is polyvinylpyrrolidone K30 (PVP).

[0049] The plasticizer is a cycloalkane oil.

[0050] The solvent is tetrahydrofuran (THF).

[0051] Example 1

[0052] Raw material formulation (mass ratio, parts): 40 parts low melting point glass, 15 parts metal-organic framework material-derived hexagonal porous Al2O3, 3 parts SBS (melt mass flow rate = 0.05 g / 10 min at 5 kg load and 200 °C), 1.5 parts PVP, 2 parts naphthenic oil (kinematic viscosity = 70 cSt at 40 °C), and 25 parts THF.

[0053] Preparation process: First, glass powder, Al2O3 filler, organic binder, and dispersant are added to a high-speed mixer and stirred at low speed (below 500 rpm) for at least 3 minutes. Then, plasticizer is added, and high-speed stirring (above 1000 rpm) is resumed until the temperature reaches 65℃. The speed is then reduced to low speed (below 500 rpm), solvent is added, and the temperature is controlled at 30℃. Stirring is continued for 4 hours to obtain a casting slurry. The casting slurry is degassed in a vacuum stirrer (pressure -0.08 MPa) for 30 minutes. The degassed slurry is discharged into a casting machine to obtain a casting tape with a thickness of 100±10 μm. The casting tape is placed in a drying oven at a controlled temperature of 25℃ to obtain a fully dried casting tape. Multiple layers of casting tape are hot-pressed together at a controlled temperature of 180℃, a pressure of 10 MPa, and a time of 15 minutes. Finally, cold pressing is performed to obtain a green body with uniform thickness. The green body was placed in a muffle furnace and heated from room temperature to 500℃ at a rate of 10℃ / min. The temperature was held at 500℃ for 3 hours to remove organic matter from the green body. Then, the temperature was rapidly increased to 800℃ and held for 15 minutes. After the muffle furnace cooled to room temperature, the radiation-cooled low-temperature co-fired Al2O3 ceramic was obtained. Its properties are shown in Table 1.

[0054] Example 2

[0055] Raw material formulation (mass ratio, parts): Low melting point glass 30, metal-organic framework material derived hexagonal porous Al2O3 32, SBS (melt mass flow rate = 0.10g / 10min at 5kg load and 200℃) 3.5, PVP 1, naphthenic oil (kinematic viscosity = 70cSt at 40℃) 2.5, THF 27.

[0056] Preparation process: First, glass powder, Al2O3 filler, organic binder, and dispersant are added to a high-speed mixer and stirred at low speed (below 500 rpm) for at least 3 minutes. Then, plasticizer is added, and high-speed stirring (above 1000 rpm) is resumed until the temperature reaches 70℃. The speed is then reduced to low speed (below 500 rpm), solvent is added, and the temperature is controlled at 30℃. Stirring is continued for 4.5 hours to obtain a casting slurry. The casting slurry is degassed in a vacuum stirrer (pressure -0.08 MPa) for 30 minutes. The degassed slurry is discharged into a casting machine to obtain a casting tape with a thickness of 100±10 μm. The casting tape is placed in a drying oven at a controlled temperature of 25℃ to obtain a fully dried casting tape. Multiple layers of casting tape are hot-pressed together at a controlled temperature of 180℃, a pressure of 12 MPa, and a time of 15 minutes. Finally, cold pressing is performed to obtain a green body with uniform thickness. The green body was placed in a muffle furnace and heated from room temperature to 500℃ at a rate of 8℃ / min. The temperature was held at 500℃ for 3 hours to remove organic matter from the green body. Then, the temperature was rapidly increased to 800℃ and held for 15 minutes. After the muffle furnace cooled to room temperature, the radiation-cooled low-temperature co-fired Al2O3 ceramic was obtained. Its properties are shown in Table 1.

[0057] Example 3

[0058] Raw material formulation (mass ratio, parts): Low melting point glass 24, metal-organic framework material derived hexagonal porous Al2O3 38, SBS (melt mass flow rate = 0.15g / 10min at 5kg load and 200℃) 4, PVP 1.5, naphthenic oil (kinematic viscosity = 70cSt at 40℃) 2.6, THF 28.

[0059] Preparation process: First, glass powder, Al2O3 filler, organic binder, and dispersant are added to a high-speed mixer and stirred at low speed (below 500 rpm) for at least 3 minutes. Then, plasticizer is added, and high-speed stirring (above 1000 rpm) is resumed until the temperature reaches 70℃. The speed is then reduced to low speed (below 500 rpm), solvent is added, and the temperature is controlled at 25℃. Stirring is continued for 4.5 hours to obtain a casting slurry. The casting slurry is degassed in a vacuum stirrer (pressure -0.09 MPa) for 30 minutes. The degassed slurry is discharged into a casting machine to obtain a casting tape with a thickness of 100±10 μm. The casting tape is placed in a drying oven at a controlled temperature of 30℃ to obtain a fully dried casting tape. Multiple layers of casting tape are hot-pressed together at a controlled temperature of 190℃, a pressure of 12 MPa, and a time of 15 minutes. Finally, cold pressing is performed to obtain a green body with uniform thickness. The green body was placed in a muffle furnace and heated from room temperature to 600℃ at a rate of 6℃ / min. The temperature was held at 600℃ for 4 hours to remove organic matter from the green body. Then, the temperature was rapidly increased to 850℃ and held for 15 minutes. After the muffle furnace cooled to room temperature, the radiation-cooled low-temperature co-fired Al2O3 ceramic was obtained. Its properties are shown in Table 1.

[0060] Example 4

[0061] Raw material formulation (mass ratio, parts): low melting point glass 18, metal-organic framework material derived hexagonal porous Al2O3 44, SBS (melt mass flow rate = 0.10g / 10min at 5kg load and 200℃) 4.5, PVP 1.5, cycloalkane oil (kinematic viscosity = 65cSt at 40℃) 3, THF 30.

[0062] Preparation process: First, glass powder, Al2O3 filler, organic binder, and dispersant are added to a high-speed mixer and stirred at low speed (below 500 rpm) for at least 3 minutes. Then, plasticizer is added, and high-speed stirring (above 1000 rpm) is resumed until the temperature reaches 70℃. The speed is then reduced to low speed (below 500 rpm), solvent is added, and the temperature is controlled at 25℃. Stirring is continued for 5 hours to obtain a casting slurry. The casting slurry is degassed in a vacuum stirrer (pressure -0.09 MPa) for 30 minutes. The degassed slurry is discharged into a casting machine to obtain a casting tape with a thickness of 100±10 μm. The casting tape is placed in a drying oven at a controlled temperature of 30℃ to obtain a fully dried casting tape. Multiple layers of casting tape are hot-pressed together at a controlled temperature of 190℃, a pressure of 13 MPa, and a time of 18 minutes. Finally, cold pressing is performed to obtain a green body with uniform thickness. The green body was placed in a muffle furnace and heated from room temperature to 600℃ at a rate of 6℃ / min. The temperature was held at 600℃ for 4 hours to remove organic matter from the green body. Then, the temperature was rapidly increased to 850℃ and held for 20 minutes. After the muffle furnace cooled to room temperature, the radiation-cooled low-temperature co-fired Al2O3 ceramic was obtained. Its properties are shown in Table 1.

[0063] Example 5

[0064] Raw material formulation (mass ratio, parts): low melting point glass 15, metal-organic framework material derived hexagonal porous Al2O3 50, SBS (melt mass flow rate = 0.20g / 10min at 5kg load and 200℃) 5, PVP 2, cycloalkane oil (kinematic viscosity = 65cSt at 40℃) 3, THF 30.

[0065] Preparation process: First, glass powder, Al2O3 filler, organic binder, and dispersant are added to a high-speed mixer and stirred at low speed (below 500 rpm) for at least 3 minutes. Then, plasticizer is added, and high-speed stirring (above 1000 rpm) is resumed until the temperature reaches 70℃. The speed is then reduced to low speed (below 500 rpm), solvent is added, and the temperature is controlled at 25℃. Stirring is continued for 6 hours to obtain a casting slurry. The casting slurry is degassed in a vacuum stirrer (pressure -0.09 MPa) for 30 minutes. The degassed slurry is discharged into a casting machine to obtain a casting tape with a thickness of 100±10 μm. The casting tape is placed in a drying oven at a controlled temperature of 30℃ to obtain a fully dried casting tape. Multiple layers of casting tape are hot-pressed together at a controlled temperature of 200℃, a pressure of 15 MPa, and a time of 20 minutes. Finally, cold pressing is performed to obtain a green body with uniform thickness. The green body was placed in a muffle furnace and heated from room temperature to 600℃ at a rate of 5℃ / min. The temperature was held at 600℃ for 5 hours to remove organic matter from the green body. Then, the temperature was rapidly increased to 900℃ and held for 30 minutes. After the muffle furnace cooled to room temperature, the radiation-cooled low-temperature co-fired Al2O3 ceramic was obtained. Its properties are shown in Table 1.

[0066] Example 6

[0067] Raw material formulation (mass ratio, parts): 40 parts low melting point glass, 15 parts metal-organic framework material derived hexagonal prism porous Al2O3, 3 parts SBS (melt mass flow rate = 0.05 g / 10 min at 5 kg load and 200 °C), 1 part PVP, 2 parts naphthenic oil (kinematic viscosity = 70 cSt at 40 °C), and 25 parts THF.

[0068] Preparation process: First, glass powder, Al2O3 filler, organic binder, and dispersant are added to a high-speed mixer and stirred at low speed (below 500 rpm) for at least 3 minutes. Then, plasticizer is added, and high-speed stirring (above 1000 rpm) is resumed until the temperature reaches 65℃. The speed is then reduced to low speed (below 500 rpm), solvent is added, and the temperature is controlled at 30℃. Stirring is continued for 4 hours to obtain a casting slurry. The casting slurry is degassed in a vacuum stirrer (pressure -0.08 MPa) for 30 minutes. The degassed slurry is discharged into a casting machine to obtain a casting tape with a thickness of 100±10 μm. The casting tape is placed in a drying oven at a controlled temperature of 25℃ to obtain a fully dried casting tape. Multiple layers of casting tape are hot-pressed together at a controlled temperature of 180℃, a pressure of 10 MPa, and a time of 15 minutes. Finally, cold pressing is performed to obtain a green body with uniform thickness. The green body was placed in a muffle furnace and heated from room temperature to 500℃ at a rate of 10℃ / min. The temperature was held at 500℃ for 3 hours to remove organic matter from the green body. Then, the temperature was rapidly increased to 800℃ and held for 15 minutes. After the muffle furnace cooled to room temperature, the radiation-cooled low-temperature co-fired Al2O3 ceramic was obtained. Its properties are shown in Table 1.

[0069] Example 7

[0070] Raw material formulation (mass ratio, parts): Low melting point glass 30, metal-organic framework material derived hexagonal prism porous Al2O3 32, SBS (melt mass flow rate = 0.10g / 10min at 5kg load and 200℃) 3.5, PVP 1, naphthenic oil (kinematic viscosity = 70cSt at 40℃) 2.5, THF 25.

[0071] Preparation process: First, glass powder, Al2O3 filler, organic binder, and dispersant are added to a high-speed mixer and stirred at low speed (below 500 rpm) for at least 3 minutes. Then, plasticizer is added, and high-speed stirring (above 1000 rpm) is resumed until the temperature reaches 70℃. The speed is then reduced to low speed (below 500 rpm), solvent is added, and the temperature is controlled at 30℃. Stirring is continued for 4.5 hours to obtain a casting slurry. The casting slurry is degassed in a vacuum stirrer (pressure -0.08 MPa) for 30 minutes. The degassed slurry is discharged into a casting machine to obtain a casting tape with a thickness of 100±10 μm. The casting tape is placed in a drying oven at a controlled temperature of 25℃ to obtain a fully dried casting tape. Multiple layers of casting tape are hot-pressed together at a controlled temperature of 180℃, a pressure of 12 MPa, and a time of 15 minutes. Finally, cold pressing is performed to obtain a green body with uniform thickness. The green body was placed in a muffle furnace and heated from room temperature to 500℃ at a rate of 8℃ / min. The temperature was held at 500℃ for 3 hours to remove organic matter from the green body. Then, the temperature was rapidly increased to 800℃ and held for 15 minutes. After the muffle furnace cooled to room temperature, the radiation-cooled low-temperature co-fired Al2O3 ceramic was obtained. Its properties are shown in Table 1.

[0072] Example 8

[0073] Raw material formulation (mass ratio, parts): Low melting point glass 24, metal-organic framework material derived hexagonal prism porous Al2O3 38, SBS (melt mass flow rate = 0.10 g / 10 min at 5 kg load and 200 °C) 4, PVP 1.5, naphthenic oil (kinematic viscosity = 70 cSt at 40 °C) 2.6, THF 25.

[0074] Preparation process: First, glass powder, Al2O3 filler, organic binder, and dispersant are added to a high-speed mixer and stirred at low speed (below 500 rpm) for at least 3 minutes. Then, plasticizer is added, and high-speed stirring (above 1000 rpm) is resumed until the temperature reaches 70℃. The speed is then reduced to low speed (below 500 rpm), solvent is added, and the temperature is controlled at 25℃. Stirring is continued for 4.5 hours to obtain a casting slurry. The casting slurry is degassed in a vacuum stirrer (pressure -0.09 MPa) for 30 minutes. The degassed slurry is discharged into a casting machine to obtain a casting tape with a thickness of 100±10 μm. The casting tape is placed in a drying oven at a controlled temperature of 30℃ to obtain a fully dried casting tape. Multiple layers of casting tape are hot-pressed together at a controlled temperature of 190℃, a pressure of 12 MPa, and a time of 15 minutes. Finally, cold pressing is performed to obtain a green body with uniform thickness. The green body was placed in a muffle furnace and heated from room temperature to 600℃ at a rate of 6℃ / min. The temperature was held at 600℃ for 4 hours to remove organic matter from the green body. Then, the temperature was rapidly increased to 800℃ and held for 15 minutes. After the muffle furnace cooled to room temperature, the radiation-cooled low-temperature co-fired Al2O3 ceramic was obtained. Its properties are shown in Table 1.

[0075] Example 9

[0076] Raw material formulation (mass ratio, parts): low melting point glass 18, metal-organic framework material derived hexagonal prism porous Al2O3 44, SBS (melt mass flow rate at 200℃ and a load of 5kg = 0.15g / 10min) 4.5, PVP 1.5, cycloalkane oil (kinematic viscosity at 40℃ = 65cSt) 2.5, THF 27.

[0077] Preparation process: First, glass powder, Al2O3 filler, organic binder, and dispersant are added to a high-speed mixer and stirred at low speed (below 500 rpm) for at least 3 minutes. Then, plasticizer is added, and high-speed stirring (above 1000 rpm) is resumed until the temperature reaches 70℃. The speed is then reduced to low speed (below 500 rpm), solvent is added, and the temperature is controlled at 25℃. Stirring is continued for 5 hours to obtain a casting slurry. The casting slurry is degassed in a vacuum stirrer (pressure -0.09 MPa) for 30 minutes. The degassed slurry is discharged into a casting machine to obtain a casting tape with a thickness of 100±10 μm. The casting tape is placed in a drying oven at a controlled temperature of 30℃ to obtain a fully dried casting tape. Multiple layers of casting tape are hot-pressed together at a controlled temperature of 190℃, a pressure of 13 MPa, and a time of 18 minutes. Finally, cold pressing is performed to obtain a green body with uniform thickness. The green body was placed in a muffle furnace and heated from room temperature to 600℃ at a rate of 6℃ / min. The temperature was held at 600℃ for 4 hours to remove organic matter from the green body. Then, the temperature was rapidly increased to 850℃ and held for 20 minutes. After the muffle furnace cooled to room temperature, the radiation-cooled low-temperature co-fired Al2O3 ceramic was obtained. Its properties are shown in Table 1.

[0078] Example 10

[0079] Raw material formulation (mass ratio, parts): low melting point glass 15, metal-organic framework material derived hexagonal prism porous Al2O3 50, SBS (melt mass flow rate = 0.20g / 10min at 5kg load and 200℃) 4, PVP 1.5, cycloalkane oil (kinematic viscosity = 65cSt at 40℃) 2.5, THF 27.

[0080] Preparation process: First, glass powder, Al2O3 filler, organic binder, and dispersant are added to a high-speed mixer and stirred at low speed (below 500 rpm) for at least 3 minutes. Then, plasticizer is added, and high-speed stirring (above 1000 rpm) is resumed until the temperature reaches 70℃. The speed is then reduced to low speed (below 500 rpm), solvent is added, and the temperature is controlled at 25℃. Stirring is continued for 6 hours to obtain a casting slurry. The casting slurry is degassed in a vacuum stirrer (pressure -0.09 MPa) for 30 minutes. The degassed slurry is discharged into a casting machine to obtain a casting tape with a thickness of 100±10 μm. The casting tape is placed in a drying oven at a controlled temperature of 30℃ to obtain a fully dried casting tape. Multiple layers of casting tape are hot-pressed together at a controlled temperature of 200℃, a pressure of 15 MPa, and a time of 20 minutes. Finally, cold pressing is performed to obtain a green body with uniform thickness. The green body was placed in a muffle furnace and heated from room temperature to 600℃ at a rate of 5℃ / min. The temperature was held at 600℃ for 5 hours to remove organic matter from the green body. Then, the temperature was rapidly increased to 850℃ and held for 30 minutes. After the muffle furnace cooled to room temperature, the radiation-cooled low-temperature co-fired Al2O3 ceramic was obtained. Its properties are shown in Table 1.

[0081] Comparative Example 1

[0082] Raw material formulation (mass ratio, parts): 40 parts low melting point glass, 15 parts precipitated spherical Al2O3, 3 parts SBS (melt mass flow rate = 0.15 g / 10 min at 5 kg load and 200 °C), 1.5 parts PVP, 2 parts naphthenic oil (kinematic viscosity = 70 cSt at 40 °C), and 25 parts THF.

[0083] Preparation process: First, glass powder, Al2O3 filler, organic binder, and dispersant are added to a high-speed mixer and stirred at low speed (below 500 rpm) for at least 3 minutes. Then, plasticizer is added, and high-speed stirring (above 1000 rpm) is resumed until the temperature reaches 65℃. The speed is then reduced to low speed (below 500 rpm), solvent is added, and the temperature is controlled at 30℃. Stirring is continued for 4 hours to obtain a casting slurry. The casting slurry is degassed in a vacuum stirrer (pressure -0.08 MPa) for 30 minutes. The degassed slurry is discharged into a casting machine to obtain a casting tape with a thickness of 100±10 μm. The casting tape is placed in a drying oven at a controlled temperature of 25℃ to obtain a fully dried casting tape. Multiple layers of casting tape are hot-pressed together at a controlled temperature of 180℃, a pressure of 10 MPa, and a time of 15 minutes. Finally, cold pressing is performed to obtain a green body with uniform thickness. The green body was placed in a muffle furnace and heated from room temperature to 500℃ at a rate of 10℃ / min. The temperature was held at 500℃ for 3 hours to remove organic matter from the green body. Then, the temperature was rapidly increased to 800℃ and held for 15 minutes. After the muffle furnace cooled to room temperature, the radiation-cooled low-temperature co-fired Al2O3 ceramic was obtained. Its properties are shown in Table 1.

[0084] Comparative Example 2

[0085] Raw material formulation (mass ratio, parts): Low melting point glass 30, precipitated spherical Al2O3 32, SBS (melt mass flow rate = 0.15g / 10min at load 5kg and temperature 200℃) 3, PVP 1, naphthenic oil (kinematic viscosity = 70cSt at 40℃) 2, THF 25.

[0086] Preparation process: First, glass powder, Al2O3 filler, organic binder, and dispersant are added to a high-speed mixer and stirred at low speed (below 500 rpm) for at least 3 minutes. Then, plasticizer is added, and high-speed stirring (above 1000 rpm) is resumed until the temperature reaches 70℃. The speed is then reduced to low speed (below 500 rpm), solvent is added, and the temperature is controlled at 30℃. Stirring is continued for 4.5 hours to obtain a casting slurry. The casting slurry is degassed in a vacuum stirrer (pressure -0.08 MPa) for 30 minutes. The degassed slurry is discharged into a casting machine to obtain a casting tape with a thickness of 100±10 μm. The casting tape is placed in a drying oven at a controlled temperature of 25℃ to obtain a fully dried casting tape. Multiple layers of casting tape are hot-pressed together at a controlled temperature of 180℃, a pressure of 12 MPa, and a time of 15 minutes. Finally, cold pressing is performed to obtain a green body with uniform thickness. The green body was placed in a muffle furnace and heated from room temperature to 500℃ at a rate of 8℃ / min. The temperature was held at 500℃ for 3 hours to remove organic matter from the green body. Then, the temperature was rapidly increased to 800℃ and held for 15 minutes. After the muffle furnace cooled to room temperature, the radiation-cooled low-temperature co-fired Al2O3 ceramic was obtained. Its properties are shown in Table 1.

[0087] Comparative Example 3

[0088] Raw material formulation (mass ratio, parts): low melting point glass 24, precipitated spherical Al2O3 38, SBS (melt mass flow rate = 0.20 g / 10 min at 5 kg load and 200 °C) 3, PVP 1.5, naphthenic oil (kinematic viscosity = 70 cSt at 40 °C) 2, THF 27.

[0089] Preparation process: First, glass powder, Al2O3 filler, organic binder, and dispersant are added to a high-speed mixer and stirred at low speed (below 500 rpm) for at least 3 minutes. Then, plasticizer is added, and high-speed stirring (above 1000 rpm) is resumed until the temperature reaches 70℃. The speed is then reduced to low speed (below 500 rpm), solvent is added, and the temperature is controlled at 25℃. Stirring is continued for 4.5 hours to obtain a casting slurry. The casting slurry is degassed in a vacuum stirrer (pressure -0.09 MPa) for 30 minutes. The degassed slurry is discharged into a casting machine to obtain a casting tape with a thickness of 100±10 μm. The casting tape is placed in a drying oven at a controlled temperature of 30℃ to obtain a fully dried casting tape. Multiple layers of casting tape are hot-pressed together at a controlled temperature of 190℃, a pressure of 12 MPa, and a time of 15 minutes. Finally, cold pressing is performed to obtain a green body with uniform thickness. The green body was placed in a muffle furnace and heated from room temperature to 600℃ at a rate of 6℃ / min. The temperature was held at 600℃ for 4 hours to remove organic matter from the green body. Then, the temperature was rapidly increased to 850℃ and held for 15 minutes. After the muffle furnace cooled to room temperature, the radiation-cooled low-temperature co-fired Al2O3 ceramic was obtained. Its properties are shown in Table 1.

[0090] Comparative Example 4

[0091] Raw material formulation (mass ratio, parts): low melting point glass 18, precipitated spherical Al2O3 44, SBS (melt mass flow rate = 0.20g / 10min at 5kg load and 200℃) 3.5, PVP 1.5, naphthenic oil (kinematic viscosity = 65cSt at 40℃) 2.5, THF 27.

[0092] Preparation process: First, glass powder, Al2O3 filler, organic binder, and dispersant are added to a high-speed mixer and stirred at low speed (below 500 rpm) for at least 3 minutes. Then, plasticizer is added, and high-speed stirring (above 1000 rpm) is resumed until the temperature reaches 70℃. The speed is then reduced to low speed (below 500 rpm), solvent is added, and the temperature is controlled at 25℃. Stirring is continued for 5 hours to obtain a casting slurry. The casting slurry is degassed in a vacuum stirrer (pressure -0.09 MPa) for 30 minutes. The degassed slurry is discharged into a casting machine to obtain a casting tape with a thickness of 100±10 μm. The casting tape is placed in a drying oven at a controlled temperature of 30℃ to obtain a fully dried casting tape. Multiple layers of casting tape are hot-pressed together at a controlled temperature of 190℃, a pressure of 13 MPa, and a time of 18 minutes. Finally, cold pressing is performed to obtain a green body with uniform thickness. The green body was placed in a muffle furnace and heated from room temperature to 600℃ at a rate of 6℃ / min. The temperature was held at 600℃ for 4 hours to remove organic matter from the green body. Then, the temperature was rapidly increased to 850℃ and held for 20 minutes. After the muffle furnace cooled to room temperature, the radiation-cooled low-temperature co-fired Al2O3 ceramic was obtained. Its properties are shown in Table 1.

[0093] Comparative Example 5

[0094] Raw material formulation (mass ratio, parts): low melting point glass 15, precipitated spherical Al2O3 50, SBS (melt mass flow rate = 0.15g / 10min at load 5kg and temperature 200℃) 2, PVP 2, naphthenic oil (kinematic viscosity = 65cSt at 40℃) 2.5, THF 27.

[0095] Preparation process: First, glass powder, Al2O3 filler, organic binder, and dispersant are added to a high-speed mixer and stirred at low speed (below 500 rpm) for at least 3 minutes. Then, plasticizer is added, and high-speed stirring (above 1000 rpm) is resumed until the temperature reaches 70℃. The speed is then reduced to low speed (below 500 rpm), solvent is added, and the temperature is controlled at 25℃. Stirring is continued for 6 hours to obtain a casting slurry. The casting slurry is degassed in a vacuum stirrer (pressure -0.09 MPa) for 30 minutes. The degassed slurry is discharged into a casting machine to obtain a casting tape with a thickness of 100±10 μm. The casting tape is placed in a drying oven at a controlled temperature of 30℃ to obtain a fully dried casting tape. Multiple layers of casting tape are hot-pressed together at a controlled temperature of 200℃, a pressure of 15 MPa, and a time of 20 minutes. Finally, cold pressing is performed to obtain a green body with uniform thickness. The green body was placed in a muffle furnace and heated from room temperature to 600℃ at a rate of 5℃ / min. The temperature was held at 600℃ for 5 hours to remove organic matter from the green body. Then, the temperature was rapidly increased to 900℃ and held for 30 minutes. After the muffle furnace cooled to room temperature, the radiation-cooled low-temperature co-fired Al2O3 ceramic was obtained. Its properties are shown in Table 1.

[0096] Comparative Example 6

[0097] Raw material formulation (mass ratio, parts): Al2O3 60, SBS (melt mass flow rate = 0.20g / 10min at load 5kg and temperature 200℃) 2, PVP 1, naphthenic oil (kinematic viscosity = 50cSt at 40℃) 1, THF 20.

[0098] Preparation process: First, glass powder, Al2O3 filler, organic binder, and dispersant are added to a high-speed mixer and stirred at low speed (below 500 rpm) for at least 3 minutes. Then, plasticizer is added, and high-speed stirring (above 1000 rpm) is resumed until the temperature reaches 65℃. The speed is then reduced to low speed (below 500 rpm), solvent is added, and the temperature is controlled at 30℃. Stirring is continued for 4 hours to obtain a casting slurry. The casting slurry is degassed in a vacuum stirrer (pressure -0.08 MPa) for 30 minutes. The degassed slurry is discharged into a casting machine to obtain a casting tape with a thickness of 100±10 μm. The casting tape is placed in a drying oven at a controlled temperature of 35℃ to obtain a fully dried casting tape. Multiple layers of casting tape are hot-pressed together at a controlled temperature of 180℃, a pressure of 10 MPa, and a time of 15 minutes. Finally, cold pressing is performed to obtain a green body with uniform thickness. The green body was placed in a muffle furnace and heated from room temperature to 500℃ at a rate of 10℃ / min. The temperature was held at 500℃ for 3 hours to remove organic matter from the green body. Then, the temperature was rapidly increased to 1200℃ and held for 30 minutes. After the muffle furnace cooled to room temperature, pure Al2O3 ceramic was obtained. Its properties are shown in Table 1.

[0099] Table 1. Performance Overview of Radiation-Coated Low-Temperature Co-fired Al2O3 Ceramic Sheets

[0100]

[0101] This invention is not limited to the above embodiments. Based on the technical solutions disclosed in this invention, those skilled in the art can make some substitutions and modifications to some of the technical features without creative effort, and all such substitutions and modifications are within the protection scope of this invention.

Claims

1. A method for preparing radiation-cooled low-temperature co-fired Al2O3 ceramic sheets, characterized in that, Includes the following steps: 1) Add glass powder, Al2O3 filler, organic binder, and dispersant to a high-speed mixer and stir at a low speed of ≤500 rpm. After adding plasticizer, start high-speed stirring at ≥1000 rpm until the temperature reaches 70±5℃. Then switch to a low speed of ≤500 rpm, add solvent, and continue stirring to obtain a cast slurry. The glass powder is low-melting-point glass powder; the organic binder is styrene-butadiene thermoplastic elastomer; the dispersant is polyvinylpyrrolidone K30; the plasticizer is cycloalkane oil; the solvent is tetrahydrofuran. The temperature should be controlled at 25~30℃ when adding the solvent, and the stirring time should be no less than 4 hours after adding the solvent. The mass amounts of each component are as follows: 15-40 parts of low-melting-point glass; Al2O3 25~60 parts; 3-5 parts organic binder; 1-2 parts dispersant; 2-3 parts plasticizer; Solvent 25-30 parts; 2) Degas the casting slurry in a vacuum stirring degassing machine. The pressure inside the vacuum stirring degassing machine is -0.08~-0.09MPa. The degassed slurry is discharged into the casting machine to obtain the casting tape. 3) The cast tape is hot-pressed as needed to obtain a green body. The green body is then placed in a high-temperature kiln to remove organic matter and obtain radiation-cooled low-temperature co-fired Al2O3 ceramic material.

2. The method for preparing a radiation-cooled low-temperature co-fired Al2O3 ceramic sheet according to claim 1, characterized in that, The specific method of step 3) is as follows: hot-press the multi-layer cast tape together, control the hot-pressing temperature to be 180~200℃, the pressure to be 10~15MPa, and the time to be 15~20min, and then cold-press to shape to obtain a green body with uniform thickness; place the green body in a muffle furnace, raise it from room temperature to 500~600℃ at a rate of 5~10℃ / min, hold it at 500~600℃ for 3~5h to remove organic matter from the green body, and then rapidly raise the temperature to 800~1200℃ and hold it for 15~30min. After the muffle furnace cools down to room temperature, the radiation-cooled low-temperature co-fired ceramic is obtained.

3. The method for preparing a radiation-cooled low-temperature co-fired Al2O3 ceramic sheet according to claim 1, characterized in that, The styrene-butadiene thermoplastic elastomer is a styrene-butadiene-styrene triblock copolymer with a styrene / butadiene mass ratio of 23 / 77. Under a load of 5 kg and a test temperature of 200 °C, the melt mass flow rate is 0.05~0.20 g / 10 min.

4. The method for preparing a radiation-cooled low-temperature co-fired Al2O3 ceramic sheet according to claim 1, characterized in that, The cycloalkane oil is a medium-viscosity cycloalkane oil with a kinematic viscosity of 50~70 cSt at 40°C.

5. The method for preparing a radiation-cooled low-temperature co-fired Al2O3 ceramic sheet according to claim 1, characterized in that, The Al2O3 filler is a hexagonal plate-shaped porous Al2O3 filler derived from metal-organic framework materials, a hexagonal prism-shaped porous Al2O3 filler derived from metal-organic framework materials, or a spherical Al2O3 filler obtained by precipitation.

6. The method for preparing a radiation-cooled low-temperature co-fired Al2O3 ceramic sheet according to claim 5, characterized in that, The metal-organic framework material-derived hexagonal plate-shaped porous Al2O3 filler is an Al2O3 filler with a hexagonal plate-shaped morphology and an internal multi-layered porous structure obtained by calcination using hexagonal plate-shaped MIL-96(Al) as a precursor. The diameter of the hexagonal plate is 500~950nm, the thickness is 150~250nm, and the internal pore size of the filler is 2.31~19.41nm.

7. The method for preparing a radiation-cooled low-temperature co-fired Al2O3 ceramic sheet according to claim 5, characterized in that, The metal-organic framework material-derived hexagonal prismatic porous Al2O3 filler, using hexagonal prismatic MIL-96(Al) as a precursor, is calcined to obtain an Al2O3 filler with a hexagonal prismatic morphology and an internal multi-layered porous structure. The diameter of the hexagonal prisms is 350~800nm, the length is 2.5~7μm, and the internal pore size of the filler is 2.52~20.50nm.

8. The method for preparing a radiation-cooled low-temperature co-fired Al2O3 ceramic sheet according to claim 5, characterized in that, The precipitated spherical Al2O3 filler is obtained by calcining homogeneous precipitated Al(OH)3 as a precursor to obtain Al2O3 filler with a spherical structure, and the diameter of the sphere is 850~1250nm.

9. The method for preparing a radiation-cooled low-temperature co-fired Al2O3 ceramic sheet according to claim 1, characterized in that, In step 2), the thickness of the cast tape is 100±10μm; it also includes a step of drying the cast tape, in which the cast tape is placed in a drying oven and the temperature is controlled at 30±5℃ to obtain a fully dried cast tape.

10. A radiation-cooled low-temperature co-fired Al2O3 ceramic sheet prepared by the method according to any one of claims 1-9.

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