Passive radiation cooling ceramic and preparation method thereof

Abstract

The present application discloses a passive radiation cooling ceramic and a preparation method thereof, wherein the passive radiation cooling ceramic comprises a first coating formed on the surface of a substrate, the first coating reflects visible light, near infrared light and ultraviolet light in sunlight, and emits mid-infrared light, and the first coating is a metal oxide coating with a porous structure. Through the above method, the energy crisis can be effectively alleviated, the urban climate can be improved, greenhouse gases can be reduced, and pollution can be reduced.

Description

Technical Field

[0001] The present application relates to the technical field of refrigeration materials, and in particular to a passive radiation refrigeration ceramic and a preparation method thereof. Background Art

[0002] According to statistics, building energy consumption accounts for more than 34% of the world's growing energy demand. At the same time, the cooling load accounts for more than 50% of the total building energy consumption, and the accumulation of greenhouse gases has exacerbated the urban heat island effect. The refrigerants widely used in traditional air conditioners and refrigerators have exacerbated climate change and ozone depletion. Therefore, it has become a top priority to alleviate the high energy consumption of traditional air conditioning and refrigeration systems and eliminate the use of refrigerants.

[0003] Passive radiative cooling is a promising cooling technology that does not require electrical input. It is a process of radiating heat from the sky-facing surface to the cold universe (-270°C), cooling the surface to below ambient temperature. As a noise-free, refrigerant-free, energy-free sub-ambient cooling source, passive radiative cooling has been widely used in green buildings. Summary of the invention

[0004] To solve the above problems, the present application provides a passive radiation cooling ceramic and a preparation method thereof, which can effectively alleviate the energy crisis, improve urban climate, reduce greenhouse gases and reduce pollution.

[0005] A technical solution adopted in the present application is: to provide a passive radiation cooling ceramic, which includes a first coating, the first coating is formed on the surface of a substrate, the first coating reflects visible light, near-infrared light and ultraviolet light in sunlight, and emits mid-infrared light, and the first coating is a metal oxide coating with a porous structure.

[0006] In one embodiment, the metal oxide is any one or any combination of Al2O3, TiO2, ZnO, ZrO2, MgO and CaCO3.

[0007] In one embodiment, the porosity of the first coating layer is 60%-90%.

[0008] In one embodiment, the pore size of the first coating layer is 50 nm-10 μm.

[0009] In one embodiment, the thickness of the first coating layer is 100 μm-50000 μm.

[0010] In one embodiment, the passive radiation cooling ceramic further includes a second coating, which is disposed on a side of the first coating away from the substrate, and is a pigment coating.

[0011] Another technical solution adopted in the present application is: to provide a method for preparing passive radiation cooling ceramics, the preparation method comprising: placing metal oxide powder into a polymer solution to form a casting liquid; coating the casting liquid on a substrate; placing the substrate coated with the casting liquid in an ethanol solution to form a ceramic precursor; drying the ceramic precursor; and sintering the dried ceramic precursor to obtain passive radiation cooling ceramics.

[0012] In one embodiment, metal oxide powder is placed in a polymer solution to form a casting solution, including: placing polyethersulfone in an organic solution; stirring the organic solution containing polyethersulfone using a magnetic stirrer to obtain a polymer solution; placing metal oxide powder in the polymer solution; and stirring the polymer solution containing the metal oxide powder.

[0013] In one embodiment, the dried ceramic precursor is sintered to obtain a passive radiation cooling ceramic, including: placing the dried ceramic precursor in a sintering space for sintering to obtain a passive radiation cooling ceramic, the temperature of the sintering space is increased from room temperature to 800-1200°C at a rate of 4-6°C / min, and maintained at 800-1200°C for 2-4 hours and then cooled to room temperature, and the air supply speed of the sintering space is 100-300ml / min.

[0014] In one embodiment, the method further comprises: coating a pigment liquid on the sintered passive radiation cooling ceramic; and sintering the passive radiation cooling ceramic coated with the pigment liquid.

[0015] The passive radiation cooling ceramic provided by the present application includes a first coating, the first coating is formed on the surface of the substrate, the first coating reflects visible light, near infrared light and ultraviolet light in sunlight, and emits mid-infrared light, and the first coating is a metal oxide coating with a porous structure. Through the above method, a passive radiation cooling ceramic is formed on the substrate, which has a significant reflection effect on ultraviolet light, visible light and near infrared bands, and also has a very high radiation effect on the band of the atmospheric window. Having a high reflectivity for ultraviolet light, visible light and near infrared bands (solar radiation) can reduce the heat absorption of solar radiation by the object, and having a high emissivity for the mid-infrared band can help the heat dissipation of the object itself. Therefore, the passive radiation cooling ceramic of the present application is a green and pollution-free environmentally friendly material, which has a good heat-resistant effect, can effectively alleviate the energy crisis, improve urban climate, reduce greenhouse gases and reduce pollution, and is of great promotion significance. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For those skilled in the art, other drawings can be obtained based on these drawings without creative work.

[0017] Figure 1 It is a structural schematic diagram of the first embodiment of the passive radiation cooling ceramic provided by the present application;

[0018] Figure 2 is an experimental graph of spectral reflectance / emissivity of a passive radiation cooling ceramic in one embodiment;

[0019] Figure 3 It is a structural schematic diagram of the second embodiment of the passive radiation cooling ceramic provided by the present application;

[0020] Figure 4 It is a schematic flow chart of the first embodiment of the method for preparing passive radiation cooling ceramics provided by the present application;

[0021] Figure 5 yes Figure 4 A schematic diagram of a flow chart of an embodiment of step S41;

[0022] Figure 6a is a schematic cross-sectional view of a passive radiation cooling ceramic in one embodiment under a scanning electron microscope (SEM) (scale bar: 500 μm);

[0023] Figure 6b is a schematic cross-sectional view of a passive radiation cooling ceramic in one embodiment under a scanning electron microscope (SEM) (scale bar: 20 μm);

[0024] Figure 7 It is a schematic flow chart of a second embodiment of a method for preparing a passive radiation cooling ceramic provided by the present application;

[0025] Figure 8 It is a schematic flow chart of the third embodiment of the method for preparing passive radiation cooling ceramics provided in the present application. DETAILED DESCRIPTION

[0026] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work are within the scope of protection of this application.

[0027] In the description of the present application, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside" and the like indicate positions or positional relationships based on the positions or positional relationships shown in the accompanying drawings, which are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present application. In addition, the terms "first" and "second" are only used for descriptive purposes, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Therefore, the features defined as "first" and "second" may explicitly or implicitly include one or more of the said features. In the description of the present application, the meaning of "multiple" is two or more, unless otherwise clearly and specifically defined.

[0028] “A and / or B” includes the following three combinations: A only, B only, and a combination of A and B.

[0029] The use of "suitable for" or "configured to" in this application is meant to be open and inclusive language, which does not exclude devices that are suitable for or configured to perform additional tasks or steps. In addition, the use of "based on" is meant to be open and inclusive, because the process, step, calculation or other action "based on" one or more stated conditions or values ​​can be based on additional conditions or values ​​beyond the stated values ​​in practice.

[0030] In this application, the word "exemplary" is used to mean "used as an example, illustration, or description." Any embodiment described in this application as "exemplary" is not necessarily to be construed as being preferred or advantageous over other embodiments. The following description is given to enable any technician in the field to implement and use the present application. In the following description, details are listed for the purpose of explanation. It should be understood that a person of ordinary skill in the art can recognize that the present application can be implemented without using these specific details. In other instances, well-known structures and processes will not be elaborated in detail to avoid obscuring the description of the present application with unnecessary details. Therefore, the present application is not intended to be limited to the embodiments shown, but is consistent with the widest scope consistent with the principles and features disclosed in the present application.

[0031] See also Figure 1 , Figure 1 It is a structural schematic diagram of the first embodiment of the passive radiation cooling ceramic provided by the present application. The passive radiation cooling ceramic includes a first coating 10, which is formed on the surface of a substrate 100. The first coating 10 reflects visible light, near-infrared light and ultraviolet light in sunlight, and emits mid-infrared light.

[0032] Understandably, on a clear day, solar radiation is mainly composed of three types of radiation: 6% ultraviolet radiation with a wavelength of 0.1-0.38μm, 52% visible light radiation with a wavelength of 0.38-0.78μm, and 42% near-infrared radiation with a wavelength of 0.78-2.5μm. Among them, visible light and near-infrared light in the solar spectrum are the main causes of environmental heating, especially in areas with hotter climates, where the heating effect of visible light and near-infrared radiation is more significant.

[0033] Understandably, all objects with a temperature above -270℃ can spontaneously release radiant heat. For terrestrial objects (-40~40℃), the emitted radiation is mainly concentrated in the wavelength of 8-13μm, where the atmosphere is almost transparent. In this case, the emitted radiant heat can easily escape to the cold outer space for cooling. At night, under the conditions of low heat transfer rates of heat conduction and heat convection, the surface cooling effect is relatively easy to obtain because passive radiative cooling plays a dominant role in thermal balance. During the day, passive radiative coolers are needed to reflect strong solar radiation (i.e., ultraviolet, visible, and near-infrared radiation) with wavelengths mainly between 0.25-2.5μm, and strongly emit thermal radiation from the 8-13μm atmospheric window. Passive radiative coolers can passively produce cooling effects even under direct sunlight due to their high thermal radiation emission and obvious sunlight reflection.

[0034] Ceramic products are usually used for architectural decoration, and can be specifically divided into ceramic tiles, ceramic thin tiles, ceramic thin plates, architectural glazed products, decorative tiles, ceramic pipes, etc., among which ceramic tiles are the main products. These products are widely used in the decoration of private and public buildings, with the advantages of excellent performance, stable quality and beautiful appearance.

[0035] Specifically, the passive radiative cooling ceramic (PRCC) provided in this embodiment is an ultra-white ceramic with a porous structure. It has a high reflectivity in the solar wavelength range (0.25-2.5 μm), namely ultraviolet light (accounting for 3% of solar radiation), visible light (accounting for 44% of solar radiation) and near-infrared light (accounting for 53% of solar radiation), and has a high emissivity in the mid-infrared wavelength range (8-13 μm). Therefore, when applied to the roof or exterior wall of a building, it can produce a cooling effect through radiation even under strong direct sunlight. Preliminary field investigations have shown that at 140 W / m 2Under the cooling power of 1.37 W, the white PRCC can achieve a sub-ambient (below ambient) average temperature of about 4°C. Most importantly, the proposed PRCC has a temperature reduction of 0°C to 10°C compared with commercial tiles, showing a significant cooling performance. In summary, passive radiant cooling ceramics have significant benefits in indoor environmental comfort, alleviating the global energy crisis, improving urban climate, and reducing greenhouse gases and waste.

[0036] Optionally, in one embodiment, the metal oxide of the first coating 10 is any one of Al2O3, TiO2, ZnO, ZrO2, MgO and CaCO3, or a mixture of any two or more thereof.

[0037] Optionally, in one embodiment, the porosity of the first coating 10 is 60%-90%.

[0038] Optionally, in one embodiment, the pore size of the first coating 10 is 50 nm-10 μm.

[0039] Optionally, in one embodiment, the thickness of the first coating 10 is 100 μm-50000 μm.

[0040] In a preferred embodiment, the first coating 10 is entirely composed of Al2O3. Depending on different application scenarios, the thickness of the radiation cooling ceramic is about 100μm to 50000μm. The shape of the radiation cooling ceramic can be customized during the manufacturing process according to the shape of the mold. The radiation cooling ceramic also has a porous structure with a porosity of more than 70%. Most importantly, the proposed white radiation cooling ceramic has a high solar reflectivity of 99.6% and a high and medium infrared emission of 96.5%, achieving a passive radiation cooling effect.

[0041] Further reading Figure 2 , Figure 2 This is an experimental diagram of the spectral reflectance / emissivity of passive radiation cooling ceramics in one embodiment. Figure 2 The horizontal axis is wavelength, and the vertical axis is reflectivity (=1-emissivity%). It can be seen from the figure that high reflectivity in the ultraviolet, visible and near-infrared (solar range) ranges can reduce the heat obtained from sunlight, while high emissivity in the mid-infrared range can enhance the heat dissipation of objects. The radiative cooling ceramic has an average solar reflectivity of 99.6% and a mid-infrared emissivity of 96.5%, which has significant performance in achieving radiative cooling effects.

[0042] It can be understood that the passive radiation cooling ceramic of this embodiment is arranged on a substrate, which can be wood, concrete, tile, glass, metal and plastic; or, the substrate is the surface of a main body, which is a building, a car, a train, a ship, a road, an oil tank or a pipeline. The passive radiation cooling composite coating of the present invention can be used on the surface of any object to cool it down and maintain a stable temperature.

[0043] The passive radiation cooling ceramic provided in this embodiment includes a first coating, which is formed on the surface of the substrate, and the first coating reflects visible light, near-infrared light and ultraviolet light in sunlight, and emits mid-infrared light. The first coating is a metal oxide coating with a porous structure. Through the above method, a passive radiation cooling ceramic is formed on the substrate, which has a significant reflection effect on ultraviolet light, visible light and near-infrared bands, and also has a very high radiation effect on the band of the atmospheric window. Having a high reflectivity to ultraviolet light, visible light and near-infrared bands (solar radiation) can reduce the heat absorption of solar radiation by the object, and having a high emissivity to the mid-infrared band can help the heat dissipation of the object itself. Therefore, the passive radiation cooling ceramic of the present application is a green and pollution-free environmentally friendly material, which has a good heat-resistant effect, can effectively alleviate the energy crisis, improve urban climate, reduce greenhouse gases and reduce pollution, and is of great promotion significance.

[0044] See also Figure 3 , Figure 3 It is a structural schematic diagram of the second embodiment of the passive radiation cooling ceramic provided by the present application, and the passive radiation cooling ceramic includes a first coating 10 and a second coating 20. The first coating 10 is formed on the surface of a substrate 100. The first coating 10 reflects visible light, near-infrared light and ultraviolet light in sunlight, and emits mid-infrared light. The second coating 20 is arranged on a side of the first coating 10 away from the substrate 100, and the second coating 20 is a pigment coating.

[0045] It can be understood that, based on the white passive radiation cooling ceramics of the first embodiment, this embodiment further forms a colored second coating 20 on the first coating 10. Depending on the color, the colored radiation cooling ceramics can still have a solar reflectivity 10% to 24% higher than that of ordinary commercial colored tiles, and their temperature is 3.1 to 4.9°C lower than that of commercial tiles of the same color.

[0046] The following describes a method for preparing passive radiation cooling ceramics in combination with the first embodiment and the second embodiment.

[0047] like Figure 4 As shown, Figure 4 1 is a flow chart of a first embodiment of a method for preparing a passive radiation cooling ceramic provided by the present application, the method comprising:

[0048] S41: placing metal oxide powder into a polymer solution to form a casting solution.

[0049] The metal oxide powder may be any one of Al2O3, TiO2, ZnO, ZrO2, MgO and CaCO3, or a mixture of any multiple powders.

[0050] Wherein, the polymer solution is a solution formed by dissolving a polymer in an organic solution, and the polymer can be any one or any combination of polyvinylidene fluoride (PVDF), polydimethylsiloxane (PDMS) or polymethyl methacrylate (PMMA). Optionally, in one embodiment, the polymer is polyethersulfone, and the organic solution is NMP (N-methylpyrrolidone). Polyethersulfone (PES for short) is a polymer compound consisting of a polymer chain and a cross-linked structure. It has many excellent properties, such as good heat resistance, chemical resistance, UV resistance and flexibility. N-methylpyrrolidone is an organic substance with a chemical formula of C5H9NO. It is a colorless to light yellow transparent liquid with a slight ammonia smell. It is miscible with water in any proportion, soluble in ether, acetone, esters, halogenated hydrocarbons, aromatic hydrocarbons and other organic solvents, and is completely mixed with almost all solvents.

[0051] In an optional embodiment, if Figure 5 As shown, Figure 5 yes Figure 4 The flowchart of step S41 in the embodiment of FIG. 1 is shown in FIG. 1 , and step S41 may specifically include:

[0052] S411: Drying the oxide powder and polyethersulfone.

[0053] Specifically, the oxide powder (such as Al2O3 powder) and polyethersulfone can be placed in an oven for drying. The specific drying time can be determined according to demand, for example, it can be dried for 12 hours. This step is mainly to remove moisture from the oxide powder and polyethersulfone.

[0054] S412: Place polyethersulfone in an organic solution.

[0055] Alternatively, polyethersulfone is placed in NMP.

[0056] S413: Using a magnetic stirrer, stirring the organic solution containing polyethersulfone to obtain a polymer solution.

[0057] Specifically, the organic solution containing polyethersulfone is stirred by a magnetic stirrer until the polymer solution becomes transparent.

[0058] S414: placing metal oxide powder into the polymer solution.

[0059] S415: Stirring the polymer solution containing the metal oxide powder.

[0060] Specifically, the polymer solution containing the metal oxide powder is stirred until the metal oxide powder is evenly dispersed without obvious agglomeration, and then the bubbles are removed by slow stirring to degas the suspension.

[0061] S42: coating a casting solution on a substrate.

[0062] It can be understood that the substrate here can be set to any shape according to requirements, so that the casting liquid coated on its surface also has a specific shape after solidification.

[0063] S43: placing the substrate coated with the casting liquid in an ethanol solution to form a ceramic precursor.

[0064] Specifically, the substrate coated with the casting liquid is placed in an ethanol solution for immersion, and the immersion time can be set as required, for example, it can be immersed for 24 hours to complete the phase inversion process. Phase inversion refers to the polymer separation membrane that is converted from a polymer solution to a solid phase during the film-making process of the casting liquid. The polyethersulfone casting liquid is a polymer solution with N-methyl pyrrolidone as a continuous phase. After being scraped into a uniform liquid film on the substrate, it is immediately immersed in ethanol, and N-methyl pyrrolidone is dissolved in ethanol, which makes the polymer solution with the solvent as the continuous phase, converted into a three-dimensional macromolecular network gel with polyethersulfone as the continuous phase, forming a polyethersulfone separation membrane. This transformation process is called phase inversion.

[0065] S44: Drying the ceramic precursor.

[0066] Specifically, the soaked ceramic precursor is dried, and the drying time can be set according to demand, for example, it can be dried at room temperature for 24 hours.

[0067] Optionally, in one embodiment, the dried ceramic precursor can be cut into any shape as needed.

[0068] S45: Sintering the dried ceramic precursor to obtain passive radiation cooling ceramics.

[0069] The sintering process can be carried out in a furnace. In an optional embodiment, step S45 may specifically include: placing the dried ceramic precursor in a sintering space for sintering to obtain a passive radiation cooling ceramic, the temperature of the sintering space (i.e., the furnace) is increased from room temperature to 800-1200°C at a rate of 4-6°C / min, and maintained at 800-1200°C for 2-4 hours and then cooled to room temperature. The air supply rate of the sintering space is 100-300ml / min.

[0070] In a specific embodiment, the temperature of the sintering space is increased from room temperature to 1000°C at a rate of 5°C / min, and is maintained at 1000°C for 3 hours and then cooled to room temperature. The air supply rate of the sintering space is 100-300ml / min to ensure that the polyethersulfone is completely burned out during the sintering process.

[0071] It can be understood that the passive radiation cooling ceramic of this embodiment is arranged on a substrate, which can be wood, concrete, tile, glass, metal and plastic; or, the substrate is the surface of a main body, which is a building, a car, a train, a ship, a road, an oil tank or a pipeline. The passive radiation cooling composite coating of the present invention can be used on the surface of any object to cool it down and maintain a stable temperature.

[0072] Optionally, in other embodiments, the substrate may also be other dielectric materials, and the passive radiation cooling ceramics are prepared on the dielectric material by the above-mentioned process method, and then the dielectric material is set on the building, car, train, ship, road, oil tank or pipeline that needs to be cooled by bonding or other means.

[0073] Further reading Figure 6a and Figure 6b , Figure 6a is a schematic cross-sectional view of a passive radiation cooling ceramic in one embodiment under a scanning electron microscope (SEM) (scale bar: 500 μm), Figure 6b This is a schematic cross-sectional view of a passive radiation cooling ceramic in an embodiment under an electron microscope (SEM) (scale: 20 μm). It can be understood that in one experiment, a passive radiation cooling ceramic is prepared by the above-mentioned manufacturing process, and a porous structure can be seen when observed using an electron microscope at different scales.

[0074] The preparation method of the passive radiation refrigeration ceramic provided in this embodiment includes: placing metal oxide powder in a polymer solution to form a casting liquid; coating the casting liquid on a substrate; placing the substrate coated with the casting liquid in an ethanol solution to form a ceramic precursor; drying the ceramic precursor; sintering the dried ceramic precursor to obtain a passive radiation refrigeration ceramic. In the above manner, a passive radiation refrigeration ceramic is formed on the substrate, which has a significant reflection effect on ultraviolet light, visible light and near-infrared bands, and also has a very high radiation effect on the band of the atmospheric window. Having a high reflectivity for ultraviolet light, visible light and near-infrared bands (solar radiation) can reduce the heat absorption of solar radiation by the object, and having a high emissivity for the mid-infrared band can help the heat dissipation of the object itself. Therefore, the passive radiation refrigeration ceramic of the present application is a green and pollution-free environmentally friendly material, which has a good heat-resistant effect, can effectively alleviate the energy crisis, improve urban climate, reduce greenhouse gases and reduce pollution, and has great promotion significance.

[0075] like Figure 7 As shown, Figure 7 : is a schematic flow chart of a second embodiment of a method for preparing a passive radiation cooling ceramic provided by the present application, the method comprising:

[0076] S71: placing metal oxide powder into a polymer solution to form a casting solution.

[0077] S72: coating a casting solution on a substrate.

[0078] S73: placing the substrate coated with the casting liquid in an ethanol solution to form a ceramic precursor.

[0079] S74: Drying the ceramic precursor.

[0080] S75: Sintering the dried ceramic precursor to obtain passive radiation cooling ceramics.

[0081] It can be understood that the above steps S71-S75 are similar to S41-S45 in the above first embodiment, and will not be repeated here.

[0082] S76: coating a pigment liquid on the sintered passive radiation cooling ceramic.

[0083] Optionally, the pigment liquid can be a water-based glaze liquid, which is made of quartz, feldspar, borax, clay, etc., diluted with water, applied to the surface of porcelain and pottery, and fired to have a glassy luster. In this embodiment, the content of various trace elements in the water-based glaze liquid can be adjusted to achieve the purpose of changing the glaze color, such as copper red, cobalt blue, iron black, lead green, etc.

[0084] S77: Sintering the passive radiation cooling ceramic coated with the pigment liquid.

[0085] Specifically, the sintering time of the passive radiation cooling ceramic coated with the pigment liquid can be set according to demand, for example, 3 hours.

[0086] Further reading Figure 8 , Figure 8 : is a schematic flow chart of a third embodiment of a method for preparing a passive radiation cooling ceramic provided by the present application, the method comprising:

[0087] S81: Put polyethersulfone into a container filled with NMP, and stir the organic solution of polyethersulfone with a magnetic stirrer until the polymer solution becomes transparent.

[0088] S82: Place Al2O3 powder in a container and stir until the Al2O3 powder is evenly dispersed without obvious agglomeration. Then, slowly stir to remove bubbles and degas the suspension.

[0089] S83: coating a casting liquid on a substrate, and placing the substrate coated with the casting liquid in an ethanol solution, for example, for 24 hours, to form a ceramic precursor.

[0090] S84: removing the ceramic precursor from the ethanol solution and drying the ceramic precursor for, for example, 24 hours.

[0091] S85: The dried ceramic precursor is sintered to obtain passive radiation cooling ceramics, wherein the temperature of the sintering space (i.e., the furnace) is increased from room temperature to 1000°C at a rate of 5°C / min, maintained at 1000°C for 3 hours, and then cooled to room temperature, and the air supply rate of the sintering space is 150ml / min.

[0092] S86: coating a pigment liquid on the sintered passive radiation cooling ceramic.

[0093] S87: Sintering the passive radiation cooling ceramic coated with the pigment liquid, for example, sintering at 1000° C. for 3 hours.

[0094] In combination with the above-mentioned embodiments of passive radiation cooling ceramics and preparation methods thereof, the invention of this case has the following effects:

[0095] 1. Environmental protection: Since this application uses refrigerant-free refrigeration technology, it is harmless to the environment, resulting in zero ozone loss, and most importantly, alleviating global warming.

[0096] 2. Energy-saving technology: Due to the zero energy consumption of passive radiation cooling ceramics, the electricity consumption of traditional AC systems in buildings can be significantly reduced.

[0097] 3. High cooling performance: The technology of this application has high reflectivity (>99%) in the visible and near-infrared regions, which can strongly reflect solar irradiance. At the same time, it has extremely high emissivity (>96%) in the mid-infrared region, which can dissipate heat energy into the cold universe for cooling. In this case, PRCC can provide a net cooling power of about 140W / m2 in the experiment. For colored glazed ceramics, their solar reflectivity is still 10% to 24% higher than that of commercial colored tiles of the same color. Compared with commercial colored tiles, colored passive radiation cooling ceramics reduce the temperature by 3.1 to 4.9°C under direct sunlight.

[0098] 4. Quiet: The traditional air conditioning system is a mechanical transmission structure, which will produce a lot of noise during operation. However, the present invention is silent during the cooling process.

[0099] 5. Inherent weather resistance and stain resistance: Passive radiation cooling ceramics have excellent stability and physical strength (i.e., washable and waterproof), and can be used as cooling ceramics on building surfaces (i.e., roofs, exterior walls, etc.) and are not easily damaged or degraded.

[0100] 6. Beautiful appearance: The present invention can display any color through glazing, and has higher heat dissipation performance compared with commercial tiles of the same color.

[0101] 7. Excellent strength: The present invention is resistant to high temperatures and acidic materials and is suitable for building facades.

[0102] Therefore, the passive radiation cooling ceramic of the present application is a green, pollution-free, environmentally friendly material with good heat insulation effect, which can effectively alleviate the energy crisis, improve urban climate, reduce greenhouse gases and reduce pollution, and is of great promotion significance.

[0103] The display screen provided in the embodiment of the present application is introduced in detail above. Specific examples are used in this article to illustrate the principles and implementation methods of the present application. The description of the above embodiments is only used to help understand the method of the present application and its core idea. At the same time, for technical personnel in this field, according to the idea of ​​the present application, there will be changes in the specific implementation method and application scope. In summary, the content of this specification should not be understood as a limitation on the present application.

Claims

1. A passive radiation cooling ceramic, characterized in that: The passive radiation cooling ceramic has a reflectivity of >99% in the visible light and near-infrared regions, and an emissivity of >96% in the mid-infrared region. The passive radiation cooling ceramic includes a first coating formed on a surface of a substrate. The first coating reflects visible light, near-infrared light and ultraviolet light in sunlight, and emits mid-infrared light. The first coating is a metal oxide coating with a porous structure.

2. The passive radiation cooling ceramic according to claim 1, characterized in that: The metal oxide is any one or any combination of Al2O3, TiO2, ZnO, ZrO2, and MgO.

3. The passive radiation cooling ceramic according to claim 1, characterized in that: The porosity of the first coating layer is 60%-90%.

4. The passive radiation cooling ceramic according to claim 1, characterized in that: The pore size of the first coating layer is 50 nm-10 μm.

5. The passive radiation cooling ceramic according to claim 1, characterized in that: The thickness of the first coating layer is 100 μm-50000 μm.

6. The passive radiation cooling ceramic according to claim 1, characterized in that: The passive radiation cooling ceramic further includes a second coating, which is arranged on a side of the first coating away from the substrate, and is a pigment coating.

7. A method for preparing passive radiation cooling ceramics, characterized in that: The passive radiation cooling ceramic has a reflectivity of >99% in the visible light and near-infrared regions and an emissivity of >96% in the mid-infrared region. The preparation method comprises: Putting metal oxide powder into polymer solution to form a casting solution; Coating the casting solution on a substrate; placing the substrate coated with the casting solution in an ethanol solution to form a ceramic precursor; Drying the ceramic precursor; The dried ceramic precursor is sintered to obtain a passive radiation cooling ceramic, wherein the passive radiation cooling ceramic includes a metal oxide coating with a porous structure.

8. The method for preparing passive radiation cooling ceramics according to claim 7, characterized in that: The step of placing the metal oxide powder into the polymer solution to form a film casting solution comprises: placing polyethersulfone in an organic solution; Using a magnetic stirrer to stir the organic solution containing the polyethersulfone to obtain a polymer solution; placing metal oxide powder into the polymer solution; The polymer solution containing the metal oxide powder is stirred.

9. The method for preparing passive radiation cooling ceramics according to claim 7, characterized in that: The step of sintering the dried ceramic precursor to obtain a passive radiation cooling ceramic comprises: The dried ceramic precursor is placed in a sintering space for sintering to obtain a passive radiation cooling ceramic. The temperature of the sintering space is increased from room temperature to 800-1200°C at a rate of 4-6°C / min, and is maintained at 800-1200°C for 2-4 hours and then cooled to room temperature. The air supply speed of the sintering space is 100-300ml / min.

10. The method for preparing passive radiation cooling ceramics according to claim 7, characterized in that: The method further comprises: coating a pigment liquid on the sintered passive radiation cooling ceramic; The passive radiation cooling ceramic coated with the pigment liquid is sintered.

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