A porous ceramic radiant refrigeration coating and a preparation method and application thereof

Abstract

The present application relates to the technical field of radiation refrigeration, in particular to a porous ceramic radiation refrigeration coating, and a preparation method and application thereof. The porosity of the coating is 20-50%, the diameter of the pore on the coating is 0.5-10 microns, and the reflectivity of the coating to sunlight is greater than or equal to 93.7%. The porous ceramic radiation refrigeration coating is prepared in situ by adopting a vacuum cold spraying mode, has a higher open porosity and a cleaner pore surface, and has excellent optical performance. Moreover, the coating is prepared at a low temperature, and the energy consumption and cost are lower.

Description

Technical Field

[0001] This invention relates to the field of radiation cooling technology, specifically to a porous ceramic radiation cooling coating, its preparation method, and its application. Background Technology

[0002] With the acceleration of global climate change and urbanization, the demand for building cooling is rising, leading to increasingly severe energy consumption problems. Especially in summer and high-temperature climates, air conditioning systems have become the primary means of ensuring indoor thermal comfort. However, the large-scale use of air conditioning not only increases building energy consumption but also results in significant greenhouse gas emissions, further exacerbating global warming. Against this backdrop, effectively reducing building cooling energy consumption has become one of the core issues urgently needing to be addressed in the energy and environment sectors.

[0003] In recent years, passive radiative cooling technology has attracted widespread attention due to its unique zero-energy cooling mechanism. This technology does not rely on external electricity or energy input; it utilizes the optical properties of the material surface to directly dissipate absorbed heat into outer space in the form of infrared radiation, thus achieving spontaneous cooling. In particular, passive radiative cooling coating materials can maintain cooling efficiency even under strong sunlight conditions, providing a highly promising solution for reducing building cooling loads. An ideal passive radiative cooling coating material must possess high solar reflectivity in the solar spectrum (0.3-2.5 μm) to minimize solar radiation absorption and prevent surface temperature rise, while also having high emissivity at atmospheric windows to efficiently radiate heat into outer space. Furthermore, the material must also possess excellent weather resistance, high-temperature resistance, and environmental friendliness for long-term service.

[0004] Currently, common daytime passive radiative cooling materials mainly include ceramic-based radiative cooling coatings, polymer-based composite materials, and photonic crystal structures. Among them, ceramic-based radiative cooling materials have attracted widespread attention due to their excellent high-temperature resistance, weather resistance, and optical properties. However, the current preparation of ceramic-based radiative cooling coatings mainly relies on micro-arc oxidation and high-temperature sintering methods. However, coatings prepared by micro-arc oxidation are usually limited in thickness, resulting in insufficient solar reflectivity and infrared emissivity, making it difficult to achieve efficient cooling. High-temperature sintering requires a high-temperature calcination process, which not only imposes stringent requirements on the heat resistance of the substrate material, limiting its applicability, but also involves high energy consumption and high cost, hindering its large-scale application. Therefore, how to prepare ceramic-based radiative cooling coatings at low or room temperature has become a key problem that urgently needs to be solved. Summary of the Invention

[0005] In view of this, the present invention provides a porous ceramic radiation cooling coating, its preparation method and application. The porous ceramic radiation cooling coating prepared in situ by vacuum cold spraying has a higher porosity and a cleaner pore surface, and also has excellent optical properties.

[0006] In a first aspect, the present invention provides a porous ceramic radiation cooling coating, wherein the porosity of the coating is 20-50%, the diameter of the pores on the coating is 0.5-10 μm, and the reflectivity of the coating to sunlight is ≥93.7%.

[0007] The porous ceramic radiation cooling coating described above has a thickness of 50–500 μm.

[0008] Secondly, the present invention provides a method for preparing a porous ceramic radiation cooling coating as described above, comprising the following steps: After mixing the materials, vacuum cold spraying is performed to deposit the mixture onto the surface of the substrate, resulting in a porous ceramic radiation cooling coating.

[0009] As described above, the material includes functional fillers and functional additives, and the volume percentage of the functional fillers to the functional additives is (40% to 80%): (20% to 60%).

[0010] As described above, the functional filler includes at least one of yttrium oxide, zirconium dioxide, aluminum oxide, magnesium oxide, titanium dioxide, and zinc oxide.

[0011] As described above, the functional additives include at least one of ammonium chloride, aluminum chloride, aluminum bromide, and aluminum iodide; and / or, the substrate includes at least one of ceramics, metals, polymer-based composite materials, cement-based materials, and glass.

[0012] As described above, during the vacuum cold spraying process, the vacuum degree is 100-1000 Pa.

[0013] The preparation method described above further includes grinding the materials before mixing them.

[0014] The grinding process described above includes at least one of ball milling, roller pressing, sand milling, vibratory milling, and air jet milling.

[0015] Thirdly, the present invention provides an application of a porous ceramic radiation cooling coating, wherein the porous ceramic radiation cooling coating is applied in at least one of construction and aerospace applications; wherein the porous ceramic radiation cooling coating is prepared by the porous ceramic radiation cooling coating method described above or by the preparation method described above.

[0016] The present invention, employing the above-described solution, has at least the following beneficial effects: In this application, a porous ceramic radiation-cooling coating prepared in situ using vacuum cold spraying exhibits a solar reflectivity of 93.7% or higher, reaching up to 99.4%, which minimizes solar radiation absorption and thus keeps the material surface heating rate as low as possible. Furthermore, the coating surface has numerous pores, resulting in high emissivity, with an infrared emissivity of 90% or higher, enabling efficient heat radiation and thus providing excellent cooling performance. Secondly, in the preparation of the porous ceramic radiation-cooling coating, vacuum cold spraying is employed, and the proportions and particle sizes of the raw materials are controlled. This allows for the preparation of a precisely structured and controllable porous ceramic radiation-cooling coating. Moreover, the preparation process is carried out at low temperatures, resulting in lower energy consumption and cost compared to traditional methods, which is beneficial for large-scale application. Attached Figure Description

[0017] This application can be further illustrated by the non-limiting embodiments given in the accompanying drawings.

[0018] Figure 1 This is a schematic diagram of the coating in Embodiment 1 of this application; Figure 2 These are optical images of the coating in Embodiment 1 of this application; Figure 3 This is a SEM image of the coating in Embodiment 1 of this application; Figure 4 This is the reflectance spectrum of the coating in Embodiment 1 of this application; Figure 5 This is the reflectance spectrum of the coating in Example 1 of this application before and after ultraviolet irradiation. Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below in conjunction with specific embodiments. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0020] To overcome the shortcomings of existing ceramic radiation-cooled coating preparation technologies (such as micro-arc oxidation and high-temperature sintering), including poor adaptability to substrate materials, high processing temperatures, high energy consumption, and difficulty in simultaneously meeting the requirements for high optical performance and coating strength, the inventors conducted research on the preparation of ceramic radiation-cooled coatings. By employing vacuum cold spraying, the inventors prepared porous ceramic radiation-cooled coatings in situ. These coatings not only could be prepared at low temperatures but also exhibited higher porosity, cleaner pore surface, excellent optical performance, and weather resistance.

[0021] In view of this, firstly, embodiments of this application propose a porous ceramic radiation cooling coating. The coating has a porosity of 20-50%, pore diameters of 0.5-10 μm, and a sunlight reflectivity ≥93.7%. By ensuring the prepared coating has good porosity and suitable, clean pore size, it can efficiently reflect sunlight. Combined with the coating's at least 93.7% sunlight reflectivity, it can minimize solar radiation absorption, thereby achieving a cooling effect.

[0022] In one embodiment of the invention, the coating has an infrared emissivity of ≥90%. By controlling the infrared emissivity, the cooling effect can be further improved.

[0023] In one embodiment of the present invention, the porosity of the coating can be 20%, 30%, 40%, 50%, or any value between two of these. By controlling the porosity of the coating, it is beneficial to hinder heat transfer and reduce the overall thermal conductivity of the coating, thereby improving the heat insulation and heat dissipation performance of the coating; at the same time, the pores in the coating further enhance the scattering of photons inside the coating, thereby enhancing the coating's ability to reflect sunlight.

[0024] In one embodiment of the present invention, the pore size on the coating can be 0.5 μm, 1 μm, 3 μm, 5 μm, 8 μm, 10 μm, or any value between two of these. By controlling the size of the pores on the coating, it is beneficial to improve the reflectivity of the coating to sunlight.

[0025] In one embodiment of the present invention, the coating thickness is 50–500 μm. Exemplarily, the thickness can be 50 μm, 100 μm, 200 μm, 300 μm, 500 μm, or any range between the above. By controlling the coating thickness, the coating can be applied in different scenarios.

[0026] Understandably, the reflectivity of a coating is specifically for sunlight. The reflectivity of a coating depends on the optical constants of the material (refractive index and band gap). Generally, the higher the refractive index of a material, the stronger its ability to scatter sunlight, allowing the coating to achieve high reflectivity with a lower thickness. Simultaneously, the size of the material's band gap determines its absorption range for visible and ultraviolet light. A larger band gap typically means absorption is mainly in the low-wavelength ultraviolet range, with less impact on sunlight. Furthermore, the coating's structure also matters; porous structures and characteristic micro / nanopore sizes can enhance the scattering of sunlight and improve the coating's reflectivity.

[0027] Secondly, the present invention provides a method for preparing a porous ceramic radiation cooling coating, comprising the following steps: After mixing the materials, vacuum cold spraying is performed to deposit the mixture onto the surface of the substrate, resulting in a porous ceramic radiation cooling coating.

[0028] In this embodiment, a porous coating is prepared in situ by using vacuum cold spraying, which can eliminate complicated post-processing steps, avoid residual clogging of pores by conventional pore-forming agent methods, obtain a higher porosity and a cleaner pore surface, and precisely control the pore size by adjusting the vacuum degree, material mixing ratio and material particle size, so that the coating has excellent optical properties.

[0029] In one embodiment of the invention, before mixing the materials, the process further includes grinding the materials. Grinding pulverizes and disperses the materials, which is beneficial for subsequent processing.

[0030] In one possible implementation, the grinding process includes at least one of ball milling, roller pressing, sand milling, vibratory milling, and air jet milling. It is understood that those skilled in the art can select a suitable processing method based on the actual situation.

[0031] In this embodiment, the grinding process is ball milling, which can thoroughly pulverize the material, which is beneficial for subsequent vacuum cold spraying. During the ball milling process, the rotation speed is 1000 rpm and the milling time is 24 hours, so that the particle size of the material after ball milling is 0.5-10 μm, which is beneficial for subsequent vacuum cold spraying.

[0032] In one embodiment of the present invention, the material includes functional fillers and functional additives. Through the interaction of the functional fillers and functional additives, a porous coating structure can be formed, and by combining this with vacuum cold spraying, the pore size of the coating can be controlled.

[0033] In one embodiment of the present invention, the volume percentage of functional filler to functional additive is (40%–80%):(20%–60%); exemplaryly, the volume percentage can be 40%:60%; 50%:50%; 60%:40%; 70%:30%; 80%:20%; or any range between two of the above ratios. By controlling the ratio of functional filler to functional additive, the porosity and pore size of the coating can be controlled.

[0034] In one embodiment of the present invention, the functional filler includes at least one selected from yttrium oxide, zirconium dioxide, aluminum oxide, magnesium oxide, titanium dioxide, and zinc oxide. It is understood that by using the above materials as functional fillers, the coating can possess advantages such as wear resistance, high-temperature insulation, UV aging resistance, corrosion resistance, flame retardancy, antibacterial self-cleaning properties, and high reflectivity.

[0035] In this embodiment, the particle size of the functional filler is 0.1–10 μm. For example, the particle size can be 0.1 μm, 0.5 μm, 1 μm, 3 μm, 5 μm, 8 μm, 10 μm, or any value between two of these. By controlling the particle size of the functional filler, on the one hand, it is easier to disperse it evenly, and on the other hand, it is beneficial to improve the reflection of sunlight.

[0036] In one embodiment of the present invention, the functional additive includes at least one selected from ammonium chloride, aluminum chloride, aluminum bromide, and aluminum iodide. It is understood that by using the above materials as functional additives, they can serve as sacrificial templates and be sublimated under a certain vacuum to form various pore sizes on the coating. Furthermore, by adjusting the ratio of functional filler to functional additive, the dispersion and connectivity of the pore sizes can be determined.

[0037] Understandably, the mixing ratio of functional fillers and functional additives determines the morphology of pore formation. The higher the ratio of functional fillers to functional additives, that is, the lower the content of functional additives, the easier it is to form isolated, small-sized pores; conversely, the lower the ratio of functional fillers to functional additives, the easier it is to form interconnected large pores.

[0038] In this embodiment, the particle size of the functional additive is 1–10 μm. Exemplarily, the particle size can be 1 μm, 3 μm, 5 μm, 8 μm, 10 μm, or any value between these two. By controlling the particle size of the functional additive, the basic size range of the pores is determined. When it acts as a sacrificial template in the coating, the particle size distribution of the functional additive directly corresponds to the original size of the pores in the coating before vaporization. It can be understood that the pore size can be precisely controlled by controlling the vacuum level, the mixing ratio of the functional filler and the functional additive, and the particle size of the functional additive.

[0039] In one embodiment of the present invention, the substrate includes at least one of ceramics, metals, polymer-based composite materials, cement-based materials, and glass. It is understood that the functional fillers and functional additives in this embodiment can be deposited on different substrates by vacuum cold spraying, and have a wide range of applications.

[0040] In one possible implementation, the metal includes iron, copper, aluminum, zinc, gold, silver, alloys, etc., and other suitable metals may be selected according to the actual situation.

[0041] In one possible implementation, the polymer-based composite material includes thermosetting polymer-based composite materials, thermoplastic polymer-based composite materials, rubber-based composite materials, etc., and a suitable polymer-based composite material can be selected according to the actual situation. It is understood that thermosetting polymer-based composite materials, thermoplastic polymer-based composite materials, and rubber-based composite materials are all materials in the prior art.

[0042] In one embodiment of the present invention, the vacuum degree is 100-1000 Pa during the vacuum cold spraying process. Exemplarily, the vacuum degree can be 100 Pa, 300 Pa, 500 Pa, 700 Pa, 1000 Pa, or any value between two of these. It is understood that the vacuum degree determines the efficiency of the functional additive vaporization products escaping from the coating. A higher vacuum degree results in a lower gas pressure around the particles on the coating, thus requiring a lower temperature and faster rate for the functional additive to sublimate / fractionate, allowing it to completely sublimate and form pores. Conversely, if the vacuum degree is insufficient, sublimation / decomposition is incomplete, resulting in the retention of some functional additives and clogging the pores, leading to a reduction in the actual pore size. By controlling the vacuum degree, a higher porosity and a cleaner pore surface can be obtained, as well as the pore size can be controlled to a certain extent.

[0043] In one possible embodiment, during the vacuum cold spraying process, the carrier gas includes at least one of compressed air, argon, hydrogen, and helium. In this embodiment, the carrier gas is preferably compressed air. It is understood that the compressed air is compressed air that has undergone processes such as dehydration, drying, impurity removal, filtration, pressure stabilization, and constant pressure treatment, wherein the processes of dehydration, drying, impurity removal, filtration, pressure stabilization, and constant pressure treatment of the compressed air are existing technologies.

[0044] In one possible implementation, the carrier gas flow rate is 40 to 80 L / min. For example, the flow rate can be 40 L / min, 50 L / min, 60 L / min, 80 L / min, or any value between the two. Those skilled in the art can also adjust and select a suitable flow rate according to the actual situation.

[0045] In one possible implementation, the spraying distance during vacuum spraying is 6 to 12 mm. For example, the spraying distance can be 6 mm, 8 mm, 10 mm, 12 mm, or any value between the two. Those skilled in the art can also adjust and select a suitable spraying distance according to the actual situation.

[0046] In one possible implementation, during vacuum spraying, the powder feeding rate of the powder feeder is 1.0 to 3.0 g / min. For example, the powder feeding rate can be 1.0 g / min, 1.5 g / min, 2.0 g / min, 3.0 g / min, or any value between the two. Those skilled in the art can also adjust and select a suitable powder feeding rate according to the actual situation.

[0047] In one possible embodiment, during the deposition of the mixture onto the substrate surface, the deposition temperature is 25–30°C. Exemplarily, the deposition temperature can be 25°C, 28°C, 30°C, or any value between two of these. It is understood that when the deposition temperature is 25–30°C, the reaction chamber is not heated. Compared to the typical vacuum spraying method of 90–500°C, the vacuum spraying of this application employs room temperature deposition, forming a vacuum cold spray.

[0048] Thirdly, the present invention provides an application of a porous ceramic radiation cooling coating. This porous ceramic radiation cooling coating is applied in at least one of the fields of construction and aerospace; wherein the porous ceramic radiation cooling coating is prepared using the aforementioned porous ceramic radiation cooling coating method or the aforementioned preparation method.

[0049] By applying porous ceramic radiation cooling coatings to building surfaces or aerospace components, they can achieve self-cooling effects as well as weather resistance, high temperature resistance, and environmental friendliness, enabling them to serve for a long time.

[0050] The preparation of porous ceramic radiation cooling coatings is described in detail below: Example 1

[0051] In this embodiment, the functional filler is zirconium dioxide and the functional additive is ammonium chloride.

[0052] The preparation of a porous ceramic radiation cooling coating includes the following steps: S1. Zirconia with a particle size of 1 μm and ammonium chloride with a particle size of 10 μm are added to a mechanical ball mill at a volume ratio of 70:30 and dispersed evenly to obtain a mixed powder.

[0053] S2. Using compressed air as the carrier gas, with a flow rate of 50 L / min, a spraying spacing of 8 mm, a powder feeder rate of 1.5 g / min, and a vacuum degree of 500 Pa as the vacuum cold spraying parameters, the mixed powder is deposited at room temperature onto the surface of an alumina ceramic substrate to obtain a porous zirconia ceramic radiation-cooled coating (e.g., Figure 1-2 (As shown).

[0054] Example 2

[0055] In this embodiment, the functional fillers and functional additives are the same as in Example 1.

[0056] The preparation of a porous ceramic radiation cooling coating includes the following steps: S1. Zirconia with a particle size of 1 μm and ammonium chloride with a particle size of 10 μm are added to a mechanical ball mill at a volume ratio of 40:60 and dispersed evenly to obtain a mixed powder.

[0057] S2. Using compressed air as the carrier gas, with a flow rate of 50 L / min, a spraying spacing of 8 mm, a powder feeding rate of 1.5 g / min, and a vacuum degree of 500 Pa as the vacuum cold spraying parameters, the mixed powder is deposited at room temperature on the surface of an alumina ceramic substrate to obtain a porous zirconia ceramic radiation cooling coating.

[0058] Example 3

[0059] In this embodiment, the functional fillers and functional additives are the same as in Example 1.

[0060] The preparation of a porous ceramic radiation cooling coating includes the following steps: S1. Zirconia with a particle size of 1 μm and ammonium chloride with a particle size of 10 μm are added to a mechanical ball mill at a volume ratio of 50:50 and dispersed evenly to obtain a mixed powder.

[0061] S2. Using compressed air as the carrier gas, with a flow rate of 50 L / min, a spraying spacing of 8 mm, a powder feeding rate of 1.5 g / min, and a vacuum degree of 500 Pa as the vacuum cold spraying parameters, the mixed powder is deposited at room temperature on the surface of an alumina ceramic substrate to obtain a porous zirconia ceramic radiation cooling coating.

[0062] Example 4

[0063] In this embodiment, the functional fillers and functional additives are the same as in Example 1.

[0064] The preparation of a porous ceramic radiation cooling coating includes the following steps: S1. Zirconia with a particle size of 1 μm and ammonium chloride with a particle size of 10 μm are added to a mechanical ball mill at a volume ratio of 80:20 and dispersed evenly to obtain a mixed powder.

[0065] S2. Using compressed air as the carrier gas, with a flow rate of 50 L / min, a spraying spacing of 8 mm, a powder feeding rate of 1.5 g / min, and a vacuum degree of 500 Pa as the vacuum cold spraying parameters, the mixed powder is deposited at room temperature on the surface of an alumina ceramic substrate to obtain a porous zirconia ceramic radiation cooling coating.

[0066] Example 5

[0067] In this embodiment, the functional fillers and functional additives are the same as in Example 1.

[0068] The preparation of a porous ceramic radiation cooling coating includes the following steps: S1. Zirconia with a particle size of 1 μm and ammonium chloride with a particle size of 10 μm are added to a mechanical ball mill at a volume ratio of 70:30 and dispersed evenly to obtain a mixed powder.

[0069] S2. Using compressed air as the carrier gas, with a flow rate of 50 L / min, a spraying spacing of 8 mm, a powder feeding rate of 1.5 g / min, and a vacuum degree of 1000 Pa as the vacuum cold spraying parameters, the mixed powder is deposited at room temperature on the surface of an alumina ceramic substrate to obtain a porous zirconia ceramic radiation cooling coating.

[0070] Example 6

[0071] In this embodiment, the functional fillers and functional additives are the same as in Example 1.

[0072] The preparation of a porous ceramic radiation cooling coating includes the following steps: S1. Zirconia with a particle size of 1 μm and ammonium chloride with a particle size of 10 μm are added to a mechanical ball mill at a volume ratio of 70:30 and dispersed evenly to obtain a mixed powder.

[0073] S2. Using compressed air as the carrier gas, with a flow rate of 50 L / min, a spraying spacing of 8 mm, a powder feeding rate of 1.5 g / min, and a vacuum degree of 100 Pa as the vacuum cold spraying parameters, the mixed powder is deposited at room temperature on the surface of an alumina ceramic substrate to obtain a porous zirconia ceramic radiation cooling coating.

[0074] Example 7

[0075] In this embodiment, the functional fillers and functional additives are the same as in Example 1.

[0076] The preparation of a porous ceramic radiation cooling coating includes the following steps: S1. Zirconia with a particle size of 3 μm and ammonium chloride with a particle size of 8 μm are added to a mechanical ball mill at a volume ratio of 70:30 and dispersed evenly to obtain a mixed powder.

[0077] S2. Using compressed air as the carrier gas, with a flow rate of 50 L / min, a spraying spacing of 8 mm, a powder feeding rate of 1.5 g / min, and a vacuum degree of 500 Pa as the vacuum cold spraying parameters, the mixed powder is deposited on the surface of an alumina ceramic substrate to obtain a porous zirconia ceramic radiation cooling coating.

[0078] Example 8

[0079] In this embodiment, the functional fillers and functional additives are the same as in Example 1.

[0080] The preparation of a porous ceramic radiation cooling coating includes the following steps: S1. Zirconia with a particle size of 10 μm and ammonium chloride with a particle size of 1 μm are added to a mechanical ball mill at a volume ratio of 70:30 and dispersed evenly to obtain a mixed powder.

[0081] S2. Using compressed air as the carrier gas, with a flow rate of 50 L / min, a spraying spacing of 8 mm, a powder feeding rate of 1.5 g / min, and a vacuum degree of 500 Pa as the vacuum cold spraying parameters, the mixed powder is deposited at room temperature on the surface of an alumina ceramic substrate to obtain a porous zirconia ceramic radiation cooling coating.

[0082] Example 9

[0083] In this embodiment, the preparation of the porous ceramic radiation cooling coating is the same as in Example 1, except that the functional filler is aluminum oxide and the functional filler is ammonium chloride.

[0084] Example 10

[0085] In this embodiment, the preparation of the porous ceramic radiation cooling coating is the same as in Example 1, except that the functional filler is magnesium oxide and the functional filler is ammonium chloride.

[0086] Example 11

[0087] In this embodiment, the preparation of the porous ceramic radiation cooling coating is the same as in Example 1, except that the functional filler is titanium dioxide and the functional filler is aluminum chloride.

[0088] Example 12

[0089] In this embodiment, the preparation of the porous ceramic radiation cooling coating is the same as in Example 1, except that the functional filler is zinc oxide and the functional filler is aluminum chloride.

[0090] Comparative Example 1 The preparation method of the coating in this comparative example is the same as that in Example 1, except that no functional additives were used and no grinding process was performed.

[0091] The preparation of the coating includes the following steps: Using compressed air as the carrier gas, with a flow rate of 50 L / min, a spraying spacing of 8 mm, a powder feeding rate of 1.5 g / min, and a vacuum degree of 500 Pa as the vacuum cold spraying parameters, zirconia powder with a particle size of 1 μm was deposited at room temperature on the surface of an alumina ceramic substrate to prepare a zirconia ceramic coating.

[0092] Comparative Example 2 The preparation method of the coating in this comparative example is the same as that in Example 1, except that the vacuum degree is 5000 Pa.

[0093] The preparation of the coating includes the following steps: S1. Zirconia with a particle size of 1 μm and ammonium chloride with a particle size of 10 μm are added to a mechanical ball mill at a volume ratio of 70:30 and dispersed evenly to obtain a mixed powder.

[0094] S2. Using compressed air as the carrier gas, with a flow rate of 50 L / min, a spraying spacing of 8 mm, a powder feeding rate of 1.5 g / min, and a vacuum degree of 5000 Pa as the vacuum cold spraying parameters, the mixed powder is deposited on the surface of an alumina ceramic substrate at room temperature to prepare a zirconia ceramic coating.

[0095] Comparative Example 3 The preparation method of the coating in this comparative example is the same as that in Example 1, except that the particle size of the functional additive is 20 μm.

[0096] The preparation of the coating includes the following steps: S1. Zirconia with a particle size of 1 μm and ammonium chloride with a particle size of 20 μm are added to a mechanical ball mill at a volume ratio of 70:30 and dispersed evenly to obtain a mixed powder.

[0097] S2. Using compressed air as the carrier gas, with a flow rate of 50 L / min, a spraying spacing of 8 mm, a powder feeding rate of 1.5 g / min, and a vacuum degree of 500 Pa as the vacuum cold spraying parameters, the mixed powder is deposited on the surface of an alumina ceramic substrate at room temperature to prepare a zirconia ceramic coating.

[0098] The coatings prepared in Examples 1-12 and Comparative Examples 1-3 were tested to determine their pore size distribution, porosity, solar reflectance, infrared emissivity, and cooling performance. Pore size distribution was tested using the gas adsorption method; porosity was tested using the mercury porosimetry method; solar reflectance was tested using an ultraviolet-visible-near-infrared spectrometer; infrared emissivity was tested using a Fourier transform infrared spectrometer; and cooling performance was tested according to GB / T 25261-2018 and JG / T 235-2014. For the cooling performance test, a heat insulation device was constructed using polyethylene foam, with a hygrometer recording humidity in real time, a thermocouple (or temperature recorder) collecting the temperature of the coating under sunlight, and an irradiance meter recording the solar radiation intensity in real time.

[0099] During the mercury intrusion porosimetry test, the coating prepared in Example 1 was tested. The coating sample size of Example 1 was 50*50*5mm. The test results are as follows: Figure 3 As shown, from Figure 3 It is known that the pores inside the coating are mainly micron-sized and nano-sized, with a pore size distribution of 0.5-4 μm, a porosity of 32%, and a coating thickness of 167 μm. This indicates that the coating prepared in the embodiments of this application has good porosity and clean pore surface, and the pore size can be precisely controlled by controlling the vacuum degree, material mixing ratio, and functional additive particle size.

[0100] The coating prepared in Example 1 was tested for solar reflectance and infrared emissivity. The sample size of the coating in Example 1 was 50*50*5mm. The test results are as follows. Figure 4 As shown; from Figure 4 It is known that the coating has a solar reflectivity of 99% and an infrared emissivity of 92%, exhibiting excellent reflectivity. This minimizes solar radiation absorption, thereby keeping the material surface temperature rise as low as possible.

[0101] Simultaneously, the coating prepared in Example 1 was subjected to ultraviolet irradiation in the ultraviolet band of 280–315 nm, with an irradiance of 0.35–1.2 W / m. 2 Power 320W, temperature and humidity: 35℃ / 75%, irradiation time 200h, test results as follows Figure 5 As shown; from Figure 5 It can be seen that the optical properties of the coating remain almost unchanged before and after ultraviolet irradiation, indicating that it has excellent weather resistance.

[0102] The specific test results are shown in Table 1: Table 1

[0103] As shown in Table 1, the pore size distribution range of Examples 1-12 is 0.5-10 μm, and more specifically, the pore size distribution range is 0.5-6.3 μm; the porosity is 20-50%, specifically 25-37%; the reflectivity of sunlight is ≥93.7%, with a maximum of 99.4%; the emissivity of infrared radiation is ≥90%, with a maximum of 93%; and the cooling performance can achieve a temperature reduction within the range of 2.8-6.8℃. This indicates that the porous ceramic radiation cooling coating prepared in the examples of this application has good porosity and a cleaner pore surface, as well as excellent optical and cooling performance, and weather resistance.

[0104] As shown in Table 1, in Comparative Example 1, the pore size distribution is <0.1 μm, the porosity is <0.5%, the reflectivity of sunlight is 75%, the emissivity of infrared radiation is 89%, and no cooling effect is achieved. This indicates that the use of functional additives and grinding treatment can synergistically form the target pore size (0.5–10 μm) in this application. This pore size is precisely located at the overlap scale of the high reflectivity region of the solar spectrum, thereby achieving low solar absorption.

[0105] As shown in Table 1, in Comparative Example 2, the pore size is mainly distributed in the range of 0.5 to 1 μm, the porosity is 12%, the solar reflectivity is 82%, the infrared emissivity is 91%, and the cooling effect cannot be achieved. This indicates that the vacuum degree in the embodiments of this application is conducive to the synergistic formation of the target pore size in this application, while an excessively large vacuum degree is not conducive to the formation of a suitable pore size and porosity.

[0106] As shown in Table 1, in Comparative Example 3, the pore size is mainly distributed in the range of 12 to 25 μm, the porosity is 20%, the solar reflectance is 84%, and the infrared emissivity is 91%. It cannot achieve a cooling effect, indicating that when the particle size of the functional additive is too large, the pore size in the coating will also be too large, but the porosity will be reduced, which is not conducive to the reflection of sunlight and the emission of infrared light.

[0107] In summary, the porous ceramic radiation cooling coating prepared in this application has a higher porosity and a cleaner pore surface, as well as excellent optical properties. It can effectively achieve a cooling effect, and by using vacuum cold spraying and controlling the vacuum degree, material mixing ratio and functional additive particle size, the pore size of the coating can be precisely controlled.

[0108] The above provides a detailed description of a porous ceramic radiation cooling coating, its preparation method, and its application. The specific embodiments are provided only to aid in understanding the method and core concepts of this invention. It should be noted that those skilled in the art can make various improvements and modifications to this invention without departing from its principles, and these improvements and modifications also fall within the scope of protection of the claims.

[0109] It should be noted that: for experimental steps or conditions not specified in the examples, the procedures and conditions described in conventional experimental procedures in the literature of this art can be followed. Reagents or instruments whose manufacturers are not specified are all commercially available conventional reagent products.

[0110] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A porous ceramic radiation cooling coating, characterized in that, The coating has a porosity of 20-50%, the pore diameter of the coating is 0.5-10 μm, and the reflectivity of the coating to sunlight is ≥93.7%.

2. The porous ceramic radiation cooling coating according to claim 1, characterized in that, The thickness of the coating is 50–500 μm.

3. A method for preparing a porous ceramic radiation-cooling coating as described in any one of claims 1-2, characterized in that, Includes the following steps: After mixing the materials, vacuum cold spraying is performed to deposit the mixture onto the surface of the substrate, resulting in a porous ceramic radiation cooling coating.

4. The preparation method according to claim 3, characterized in that, The material includes functional fillers and functional additives, and the volume percentage of the functional fillers to the functional additives is (40% to 80%): (20% to 60%).

5. The preparation method according to claim 4, characterized in that, The functional filler includes at least one of yttrium oxide, zirconium dioxide, aluminum oxide, magnesium oxide, titanium dioxide, and zinc oxide.

6. The preparation method according to claim 4, characterized in that, The functional additives include at least one of ammonium chloride, aluminum chloride, aluminum bromide, and aluminum iodide; and / or, the substrate includes at least one of ceramics, metals, polymer-based composite materials, cement-based materials, and glass.

7. The preparation method according to claim 4, characterized in that, During the vacuum cold spraying process, the vacuum level is 100-1000 Pa.

8. The preparation method according to any one of claims 4-7, characterized in that, Before mixing the materials, the process further includes grinding the materials.

9. The preparation method according to claim 8, characterized in that, The grinding process includes at least one of ball milling, roller pressing, sand milling, vibratory milling, and air jet milling.

10. An application of a porous ceramic radiation cooling coating, characterized in that, The porous ceramic radiation cooling coating is applied in at least one of the fields of construction and aerospace; wherein the porous ceramic radiation cooling coating is prepared by the porous ceramic radiation cooling coating as described in any one of claims 1-2 or by the preparation method described in any one of claims 3-9.

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