A radiation-cooling coating, its preparation method and application

Abstract

This invention discloses a radiation-cooling coating, its preparation method, and its application. The raw materials for the radiation-cooling coating include: functional powder, infrared resin matrix, and solvent. The functional powder consists of β-Si3N4 grains and a Y-Si-O-N compound film layer on the surface of the β-Si3N4 grains. The diameter of the β-Si3N4 grains is 0.1 μm to 6 μm; the thickness of the Y-Si-O-N compound film layer is 1 nm to 5 nm. Compared with existing radiation-cooling coatings, the radiation-cooling coating provided by this invention achieves high solar reflectivity, high atmospheric window emissivity, and high thermal conductivity using only one functional filler, resulting in excellent cooling performance. Furthermore, the preparation method is simple, environmentally friendly, and suitable for mass production, making it promising for widespread application in fields such as building refrigeration.

Description

Technical Field

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

[0002] With the accelerating pace of global urbanization, traditional cooling methods such as air conditioning consume a significant amount of energy annually to cool buildings in cities, and the use of refrigerants can also lead to a series of environmental problems. Radiant cooling, on the other hand, is a passive cooling method that can cool object surfaces without consuming electricity, and has received widespread attention in recent years.

[0003] The principle of radiative cooling is to reflect sunlight and emit the heat of an object into outer space as infrared radiation, thereby cooling the object. Therefore, to achieve a cooling effect below the ambient temperature during the day, the radiative cooling material must have good spectral selectivity. That is, it must not only have high reflectivity in the solar radiation band (0.3–2.5 μm) to reduce the absorption of solar radiation heat, but also have high emissivity in the atmospheric window band (8–13 μm) to increase its ability to emit infrared radiation into outer space.

[0004] Radiation-cooling coatings can achieve good spectral selectivity through filler compounding, thereby obtaining excellent cooling effects. The functional fillers are key to determining the spectral selectivity and cooling performance of radiation-cooling coatings. Currently used functional fillers generally struggle to simultaneously meet the performance requirements of band gap width and refractive index, while mixing multiple functional fillers inevitably increases the viscosity of the coating, leading to greater processing difficulty. Furthermore, existing radiation-cooling coatings generally neglect the influence of heat conduction, which is detrimental to achieving optimal cooling effects. Therefore, it is necessary to provide a radiation-cooling coating with simple composition, high spectral selectivity, and good cooling performance. Summary of the Invention

[0005] In view of the above problems, the purpose of this invention is to provide a radiation cooling coating. Compared with existing radiation cooling coatings, the radiation cooling coating provided by this invention uses only one functional filler to simultaneously achieve high solar reflectivity, high atmospheric window emissivity and high thermal conductivity. It has excellent cooling effect and the preparation process is simple and easy to mass-produce.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] In a first aspect, the present invention provides a radiation-cooling coating, the raw materials of which include: functional powder, infrared resin matrix and solvent; the functional powder is composed of: β-Si3N4 grains and Y-Si-ON compound film layer located on the surface of β-Si3N4 grains; the diameter of β-Si3N4 grains is 0.1μm to 6μm; the thickness of Y-Si-ON compound film layer is 1nm to 5nm.

[0008] The radiation-cooling coating of this invention is mainly composed of randomly dispersed spectrally selective functional powders and an infrared resin matrix. The functional powders exhibit high reflectivity in both the solar and atmospheric window wavelengths. Specifically, the β-Si3N4 grains, due to the inherent properties of β-Si3N4 material, its suitable phase composition, and its diameter distribution matching the wavelength of sunlight, endow the functional powders with high spectral selectivity. Furthermore, the Y-Si-ON compound film uniformly coated on the surface of the grains possesses a high refractive index, further enhancing the scattering effect of the functional powders on sunlight. In addition, the structural size of this functional powder ensures that the β-Si3N4 grains overlap within the resin matrix, forming interconnected heat conduction pathways, thereby imparting higher thermal conductivity to the radiation-cooling coating.

[0009] Furthermore, the mass ratio of the functional powder to the infrared resin matrix is ​​2–10:1–9; preferably 3–8:3–5; wherein, the radiation-cooling coating with this ratio can form a film on its own; more preferably, it is 6–8:3–4. The radiation-cooling coating with this composition ratio has a better cooling effect.

[0010] Furthermore, the infrared resin matrix is ​​at least one selected from polyvinylidene fluoride, polyvinylidene fluoride (PVDF), polychlorotrifluoroethylene, polytetrafluoroethylene, and polyvinylidene fluoride-hexafluoropropylene. The infrared resin matrix provided by this invention exhibits superior radiative cooling performance.

[0011] For example, the solvent is N,N-dimethylformamide (DMF), acetone, etc.

[0012] Furthermore, the β-Si3N4 grains have a hexagonal prism structure and / or a long columnar structure; preferably, they have a hexagonal prism structure; the average aspect ratio of the β-Si3N4 grains is 3 to 6. The average aspect ratio refers to the ratio of the major axis to the minor axis, i.e., the average aspect ratio; the hexagonal prism structure is not limited to a standard hexagonal prism structure but also includes structures that are approximately hexagonal prisms.

[0013] It is understood that when the β-Si3N4 grains have a hexagonal prism structure, their diameter refers to the distance between the diagonals of the hexagonal base faces.

[0014] Furthermore, the Y-Si-ON compound film is amorphous;

[0015] Preferably, the β phase content of the β-Si3N4 grains is ≥95%.

[0016] For example, the method for preparing the functional powder includes the following steps:

[0017] The functional powder is obtained by weighing silicon powder, α-Si3N4 powder and Y2O3 powder in proportion, mixing them and then carrying out a combustion synthesis reaction in nitrogen.

[0018] Among them, the functional powder obtained by combustion synthesis reaction using α-Si3N4 as a diluent has better spectral selectivity than that obtained by using β-Si3N4 as a diluent. This is mainly because the dissolution and precipitation process of the α-Si3N4 to β-Si3N4 phase transition can diffuse lattice defects to the outside of the lattice, and the high reactivity of α-Si3N4 is also conducive to the formation of hexagonal prism grain shape of β-Si3N4 grains.

[0019] For example, the silicon powder has a particle size of 1 μm to 5 μm, and the α-Si3N4 powder has a particle size of 0.5 μm to 8 μm. The particle size of the silicon powder and α-Si3N4 powder affects the reaction temperature and the grain size of the reaction product. If the particle size is too large, it not only leads to incomplete reaction, but also increases the diameter of the functional powder.

[0020] For example, the α-phase content in the α-Si3N4 powder is 80% to 95%.

[0021] For example, the mass ratio of silicon powder to α-Si3N4 powder is 1-3:1-3; the mass ratio of Y2O3 powder to silicon powder is 0.01-1:20, preferably 0.1-1:20.

[0022] For example, the reaction pressure of the combustion synthesis reaction is 1 MPa to 10 MPa; preferably 3 MPa to 10 MPa.

[0023] For example, the combustion synthesis reaction specifically includes the following steps:

[0024] The uniformly mixed reaction materials are loaded into a material frame lined with carbon felt and placed in a combustion synthesis reactor. Nitrogen gas is introduced into the reactor, and after ignition, the reaction materials spontaneously undergo a combustion synthesis reaction.

[0025] Secondly, the present invention provides a method for preparing the above-mentioned radiation-cooling coating, comprising the following steps:

[0026] The functional powder is mixed with a solvent and ultrasonically dispersed for 10–20 min to obtain a suspension;

[0027] The infrared resin matrix is ​​mixed with the suspension and heated and stirred until the infrared resin matrix dissolves in the solvent.

[0028] Thirdly, the present invention provides a radiation cooling coating, which is obtained by applying the above-mentioned radiation cooling coating to the surface of a substrate or equipment.

[0029] Furthermore, the coating includes, but is not limited to, machine spraying, manual dipping, brushing, spraying, or any other process.

[0030] Furthermore, the substrate is selected from one of the following: metal, plastic, rubber, concrete, cement, asphalt, ceramic tile, glass, and organic synthetic materials.

[0031] Furthermore, the thickness of the radiation cooling coating is 100μm-500μm; preferably 250μm-350μm.

[0032] It should also be noted that, unless otherwise specified, any range described in this invention includes the endpoints, any values ​​between the endpoints, and any subranges formed by the endpoints or any values ​​between the endpoints. Unless otherwise specified, the preparation methods in this invention are conventional methods, and the raw materials used can be obtained from publicly available commercial sources or prepared according to existing technology. Unless otherwise specified, all reagents are of analytical grade.

[0033] Beneficial effects of the present invention

[0034] The radiation-cooling coating provided by this invention has good spectral selectivity, specifically in the solar wavelength range (0.3–2.5 μm) with an average reflectance (R0). Solar The average emissivity (ε) in the atmospheric window band (8–13 μm) is ≥0.80, and the average emissivity (ε) is ≥0.90. Furthermore, this radiation-cooling coating features simple composition, good stability, and excellent processing performance, enabling it to adhere well to various substrates and meet diverse needs in various refrigeration fields.

[0035] The method for preparing radiation cooling coatings provided by this invention is simple to operate, environmentally friendly, and easy to mass-produce, and is expected to be widely used in fields such as building cooling. Attached Figure Description

[0036] Figure 1 The surface elemental composition diagram of the functional powder prepared in Experimental Example 4 is shown.

[0037] Figure 2 The microstructure of the Y-Si-ON compound film in the functional powder prepared in Experimental Example 4 is shown.

[0038] Figure 3 The XRD patterns of the functional powders prepared in Experimental Examples 2, 4, and 10 are shown.

[0039] Figure 4 The microstructure diagram of the functional powder prepared in Experimental Example 4 is shown.

[0040] Figure 5 A cross-sectional SEM image of the radiation-cooling coating of Example 3 is shown.

[0041] Figure 6 The solar reflectance curve of Example 1 is shown.

[0042] Figure 7 The solar reflectance curve of Example 2 is shown.

[0043] Figure 8 The solar reflectance curve of Example 3 is shown.

[0044] Figure 9 The solar reflectance curve of Example 4 is shown.

[0045] Figure 10 The solar reflectance curve of Comparative Example 1 is shown.

[0046] Figure 11 The solar reflectance curve of Comparative Example 2 is shown.

[0047] Figure 12 The solar reflectance curve of Comparative Example 3 is shown.

[0048] Figure 13 The solar reflectance curve of Comparative Example 4 is shown.

[0049] Figure 14 The solar reflectance curve of Comparative Example 5 is shown.

[0050] Figure 15 The infrared emissivity curve of the radiation-cooling coating of Example 1 is shown.

[0051] Figure 16 The infrared emissivity curve of the radiation-cooling coating of Example 2 is shown.

[0052] Figure 17 The infrared emissivity curve of the radiation-cooling coating of Example 3 is shown.

[0053] Figure 18 The infrared emissivity curve of the radiation-cooling coating of Example 4 is shown.

[0054] Figure 19 The infrared emissivity curve of the radiation-cooled coating in Comparative Example 1 is shown.

[0055] Figure 20 The infrared emissivity curve of the radiation-cooled coating in Comparative Example 2 is shown.

[0056] Figure 21 The infrared emissivity curve of the radiation-cooled coating in Comparative Example 3 is shown.

[0057] Figure 22 The infrared emissivity curve of the radiation-cooled coating in Comparative Example 4 is shown.

[0058] Figure 23 The infrared emissivity curve of the radiation-cooled coating in Comparative Example 5 is shown.

[0059] Figure 24 The thermal conductivity comparisons of Comparative Examples 1, 3-5 and Example 3 are shown.

[0060] Figure 25 The cooling effects of Examples 1-4 and Comparative Examples 1-5 are shown in comparison. Detailed Implementation

[0061] The present invention will now be described in detail through embodiments. It should be noted that these embodiments are only used to further illustrate the present invention and should not be construed as limiting the scope of protection of the present invention. Those skilled in the art can make some non-essential improvements and adjustments based on the above description. Unless otherwise specified, the embodiments and features described in the present invention can be combined with each other.

[0062] Unless otherwise specified, all raw materials used in this invention can be obtained from publicly available commercial sources or prepared according to existing technology.

[0063] In this invention, the method for testing solar reflectivity is as follows:

[0064] The reflectance curves of the combustion-synthesized β-Si3N4 sample in the ultraviolet-visible band (λ~0.3-2.5μm) were measured using a UV-VIS-NIR spectrophotometer (Agilent Cray 7000, America). The reflectance curves were then compared with ASTM G173 Global Solar Irradiance Standard. Solar (λ) weighted average yields the average solar reflectance.

[0065]

[0066] The method for testing atmospheric window emissivity is as follows:

[0067] The reflectance R and transmittance T in the infrared band (λ ~ 2.5-25 μm) were measured using an infrared spectrophotometer (Bruker INVENIO S, Germany), and the emissivity ε was then calculated as 1 - RT. The emissivity curve for the atmospheric window band (λ ~ 8-13 μm) was then compared with the atmospheric transmittance I. BB The average atmospheric window emissivity is obtained by weighting (T,λ).

[0068] The method for testing thermal conductivity is as follows:

[0069] The specific heat C of the radiation-cooled thin film was measured using a differential scanning calorimeter (DSC 200F3, Netzsch, Germany). p The thermal diffusivity α of the radiation-cooled thin film was measured using a laser thermal conductivity analyzer (NETZSCH LFA467, Germany). The thermal conductivity λ was calculated using the following formula: λ=α·ρ·C p .

[0070] The method for testing the cooling effect is as follows: First, connect the thermocouple to a stainless steel substrate coated with a radiation cooling coating. Place an insulating polystyrene foam block under the substrate. Then, place the radiation cooling coating of each experimental group and the irradiance meter together in a foam box covered with aluminum foil. This allows the testing device to simultaneously measure the sample's temperature, solar irradiance, and relative humidity. Take the average temperature during the daytime direct sunlight period (10:00-15:00) * T1. Subtract * T1 from the average ambient temperature during the same period * T2 to obtain the radiation cooling effect. The calculation formula is: Δ * T = * T2 - * T1.

[0071] Investigation 1: Synthesis of Functional Powders

[0072] Test Example 1

[0073] Using 49.9g of silicon powder with a particle size of 2.7μm, 49.9g of α-Si3N4 diluent with a particle size of 6μm, and 0.2g of Y2O3 sintering aid as raw materials, the total mass of raw materials was 100g. The raw materials were mixed for 30 minutes using a horizontal mixer, with a ball-to-material ratio of 2:1 during the dry mixing process. The mixed reactants were then placed in a material frame lined with carbon felt, and a certain amount of titanium powder was placed inside the reaction mixture at one end of the material frame. A wound tungsten coil was brought into contact with the titanium powder to ignite the reactants. Nitrogen gas at 5MPa was then introduced into the combustion synthesis reactor, and the reactants were ignited with a current of 10A to undergo a combustion synthesis reaction. After the reaction was completed, the product was ground and sieved to obtain functional powder 1.

[0074] Test Example 2

[0075] Using 49.75g of silicon powder with a particle size of 2.7μm, 49.75g of α-Si3N4 diluent with a particle size of 6μm, and 0.5g of Y2O3 sintering aid as raw materials, the total mass of raw materials was 100g. The raw materials were mixed for 30 minutes using a horizontal mixer, with a ball-to-material ratio of 2:1 during the dry mixing process. The mixed reactants were then placed in a material frame lined with carbon felt, and a certain amount of titanium powder was placed inside the reaction mixture at one end of the material frame. A wound tungsten coil was brought into contact with the titanium powder to ignite the reactants. Nitrogen gas at 5MPa was then introduced into the combustion synthesis reactor, and the reactants were ignited with a current of 10A to undergo a combustion synthesis reaction. After the reaction was completed, the product was ground and sieved to obtain functional powder 2.

[0076] Experimental Example 3

[0077] Using 49.5g of silicon powder with a particle size of 2.7μm, 49.5g of α-Si3N4 diluent with a particle size of 6μm, and 1g of Y2O3 sintering aid as raw materials, the total mass of raw materials was 100g. The raw materials were mixed for 30 minutes using a horizontal mixer, with a ball-to-material ratio of 2:1 during the dry mixing process. The mixed reactants were then placed in a material frame lined with carbon felt, and a certain amount of titanium powder was placed inside the reaction mixture at one end of the material frame. A wound tungsten coil was brought into contact with the titanium powder to ignite the reactants. Nitrogen gas at 5MPa was then introduced into the combustion synthesis reactor, and the reactants were ignited with a current of 10A to undergo a combustion synthesis reaction. After the reaction was completed, the product was ground and sieved to obtain functional powder 3.

[0078] Test Example 4

[0079] Using 49g of silicon powder with a particle size of 2.7μm, 49g of α-Si3N4 diluent with a particle size of 6μm, and 2g of Y2O3 sintering aid as raw materials, the total mass of raw materials was 100g. The raw materials were mixed for 30 minutes using a horizontal mixer, with a ball-to-material ratio of 2:1 during the dry mixing process. The mixed reactants were then placed in a material frame lined with carbon felt, and a certain amount of titanium powder was placed inside the reaction mixture at one end of the material frame. A wound tungsten coil was brought into contact with the titanium powder to ignite the reactants. Nitrogen gas at 5MPa was then introduced into the combustion synthesis reactor, and the reactants were ignited with a current of 10A to undergo a combustion synthesis reaction. After the reaction was completed, the product was ground and sieved to obtain functional powder 4.

[0080] Depend on Figure 2 It can be seen that the thickness of the Y-Si-ON compound film in functional powder 4 is between 1 and 5 nm.

[0081] Experimental Example 5

[0082] Using 48.5g of silicon powder with a particle size of 2.7μm, 48.5g of α-Si3N4 diluent with a particle size of 6μm, and 3g of Y2O3 sintering aid as raw materials, the total mass of raw materials was 100g. The raw materials were mixed for 30 minutes using a horizontal mixer, with a ball-to-material ratio of 2:1 during the dry mixing process. The mixed reactants were then placed in a material frame lined with carbon felt, and a certain amount of titanium powder was placed inside the reaction mixture at one end of the material frame. A wound tungsten coil was brought into contact with the titanium powder to ignite the reactants. Nitrogen gas at 5MPa was then introduced into the combustion synthesis reactor, and the reactants were ignited with a current of 10A to undergo a combustion synthesis reaction. After the reaction was completed, the product was ground and sieved to obtain functional powder 5.

[0083] Experimental Example 6

[0084] Using 47.5g of silicon powder with a particle size of 2.7μm, 47.5g of α-Si3N4 diluent with a particle size of 6μm, and 5g of Y2O3 sintering aid as raw materials, the total mass of raw materials was 100g. The raw materials were mixed for 30 minutes using a horizontal mixer, with a ball-to-material ratio of 2:1 during the dry mixing process. The mixed reactants were then placed in a material frame lined with carbon felt, and a certain amount of titanium powder was placed inside the reaction mixture at one end of the material frame. A wound tungsten coil was brought into contact with the titanium powder to ignite the reactants. Nitrogen gas at 5MPa was then introduced into the combustion synthesis reactor, and the reactants were ignited with a current of 10A to undergo a combustion synthesis reaction. After the reaction was completed, the product was ground and sieved to obtain functional powder 6.

[0085] Experimental Example 7

[0086] The raw materials consisted of 39.2g of silicon powder with a particle size of 2.7μm, 58.8g of α-Si3N4 diluent with a particle size of 6μm, and 2g of Y2O3 sintering aid, with a total raw material mass of 100g. The raw materials were mixed for 30 minutes using a horizontal mixer, with a ball-to-material ratio of 2:1 during the dry mixing process. The mixed reactants were then placed in a material frame lined with carbon felt, and a certain amount of titanium powder was placed inside the reaction mixture at one end of the material frame. A wound tungsten coil was brought into contact with the titanium powder to ignite the reactants. Nitrogen gas at 5MPa was then introduced into the combustion synthesis reactor, and the reactants were ignited with a current of 10A to undergo a combustion synthesis reaction. After the reaction was completed, the product was ground and sieved to obtain functional powder 7.

[0087] Experimental Example 8

[0088] Using 58.8g of silicon powder with a particle size of 2.7μm, 39.2g of α-Si3N4 diluent with a particle size of 6μm, and 2g of Y2O3 sintering aid as raw materials, the total mass of raw materials was 100g. The raw materials were mixed for 30 minutes using a horizontal mixer, with a ball-to-material ratio of 2:1 during the dry mixing process. The mixed reactants were then placed in a material frame lined with carbon felt, and a certain amount of titanium powder was placed inside the reaction mixture at one end of the material frame. A wound tungsten coil was brought into contact with the titanium powder to ignite the reactants. Nitrogen gas at 5MPa was then introduced into the combustion synthesis reactor, and the reactants were ignited with a current of 10A to undergo a combustion synthesis reaction. After the reaction was completed, the product was ground and sieved to obtain functional powder 8.

[0089] Experimental Example 9

[0090] Using 49g of silicon powder with a particle size of 2.7μm, 49g of α-Si3N4 diluent with a particle size of 6μm, and 2g of Y2O3 sintering aid as raw materials, the total mass of raw materials was 100g. The raw materials were mixed for 30 minutes using a horizontal mixer, with a ball-to-material ratio of 2:1 during the dry mixing process. The mixed reactants were then placed in a material frame lined with carbon felt, and a certain amount of titanium powder was placed inside the reaction mixture at one end of the material frame. A wound tungsten coil was brought into contact with the titanium powder to ignite the reactants. Nitrogen gas at 1MPa was then introduced into the combustion synthesis reactor, and the reactants were ignited with a current of 10A to undergo a combustion synthesis reaction. After the reaction was completed, the product was ground and sieved to obtain functional powder 9.

[0091] Experimental Example 10

[0092] Using 49g of silicon powder with a particle size of 2.7μm, 49g of α-Si3N4 diluent with a particle size of 6μm, and 2g of Y2O3 sintering aid as raw materials, the total mass of raw materials was 100g. The raw materials were mixed for 30 minutes using a horizontal mixer, with a ball-to-material ratio of 2:1 during the dry mixing process. The mixed reactants were then placed in a material frame lined with carbon felt, and a certain amount of titanium powder was placed inside the reaction mixture at one end of the material frame. A wound tungsten coil was brought into contact with the titanium powder to ignite the reactants. Nitrogen gas at 3MPa was then introduced into the combustion synthesis reactor, and the reactants were ignited with a current of 10A to undergo a combustion synthesis reaction. After the reaction was completed, the product was ground and sieved to obtain functional powder 10.

[0093] Experimental Example 11

[0094] Using 49g of silicon powder with a particle size of 2.7μm, 49g of α-Si3N4 diluent with a particle size of 6μm, and 2g of Y2O3 sintering aid as raw materials, the total mass of raw materials was 100g. The raw materials were mixed for 30 minutes using a horizontal mixer, with a ball-to-material ratio of 2:1 during the dry mixing process. The mixed reactants were then placed in a material frame lined with carbon felt, and a certain amount of titanium powder was placed inside the reaction mixture at one end of the material frame. A wound tungsten coil was brought into contact with the titanium powder to ignite the reactants. Nitrogen gas at 7MPa was then introduced into the combustion synthesis reactor, and the reactants were ignited with a current of 10A to undergo a combustion synthesis reaction. After the reaction was completed, the product was ground and sieved to obtain functional powder 11.

[0095] Experimental Example 12

[0096] Using 49g of silicon powder with a particle size of 2.7μm, 49g of α-Si3N4 diluent with a particle size of 6μm, and 2g of Y2O3 sintering aid as raw materials, the total mass of raw materials was 100g. The raw materials were mixed for 30 minutes using a horizontal mixer, with a ball-to-material ratio of 2:1 during the dry mixing process. The mixed reactants were then placed in a material frame lined with carbon felt, and a certain amount of titanium powder was placed inside the reaction mixture at one end of the material frame. A wound tungsten coil was brought into contact with the titanium powder to ignite the reactants. Nitrogen gas at 9MPa was then introduced into the combustion synthesis reactor, and the reactants were ignited with a current of 10A to undergo a combustion synthesis reaction. After the reaction was completed, the product was ground and sieved to obtain functional powder 12.

[0097] Experimental Example 13

[0098] Using 49.95g of silicon powder with a particle size of 2.7μm, 49.95g of α-Si3N4 diluent with a particle size of 6μm, and 0.1g of Y2O3 sintering aid as raw materials, the total mass of raw materials was 100g. The raw materials were mixed for 30min using a horizontal mixer, with a ball-to-material ratio of 2:1 during the dry mixing process. The mixed reactants were then placed in a material frame lined with carbon felt, and a certain amount of titanium powder was placed inside the reaction mixture at one end of the material frame. A wound tungsten coil was brought into contact with the titanium powder to ignite the reactants. Nitrogen gas at 5MPa was then introduced into the combustion synthesis reactor, and the reactants were ignited with a current of 10A to undergo a combustion synthesis reaction. After the reaction was completed, the product was ground and sieved to obtain functional powder 13.

[0099] Performance comparison:

[0100] The relevant properties of the functional powders in Experiment Examples 1-12 are summarized in Table 1.

[0101] Table 1:

[0102]

[0103]

[0104] In summary, based on the data in Table 1, we can see that as the amount of sintering aid Y2O3 added to the raw materials increases from 0 to 1 wt%, the solar reflectivity of the functional powder significantly improves. However, when the amount of Y2O3 added further increases to 2 wt%, the solar reflectivity of the functional powder remains essentially unchanged. Secondly, when the nitrogen pressure increases from 1 MPa to 3 MPa, the solar reflectivity of the functional powder improves to some extent, but further increases in nitrogen pressure have little effect on the solar reflectivity. This is because when the nitrogen pressure in the reaction system is low, the reactants cannot react fully, thus the residual reactants in the combustion synthesis system will affect its solar reflectivity. Once the nitrogen pressure reaches a level sufficient for the reactants to react fully, further increases in nitrogen pressure have little impact.

[0105] Investigation 2: Preparation of Radiation-Coating and Radiation-Coating Coatings

[0106] Example 1

[0107] Synthetic radiation-cooling coating: 8.13g of functional powder 4 synthesized in Example 4 was mixed with 31.32g of solvent DMF and ultrasonically dispersed for 15min to obtain a uniform dispersion system; then 3.48g of PVDF was added to the suspension and mixed evenly, and the temperature was raised to 60℃ using a magnetic heating stirrer to dissolve the PVDF in the solvent to obtain the radiation-cooling coating.

[0108] The surfaces of two 10cm x 10cm stainless steel substrates were sanded and then wiped clean with alcohol. After the radiation-cooling coating cooled to room temperature, it was sprayed onto the surfaces of the two substrates using a spray gun. After drying in an oven at 80°C, the coating was peeled off the substrate surface, resulting in a 100μm thick radiation-cooling coating composed of 70wt% functional powder and 30wt% PVDF. The average reflectance (Ro) of the coating in the solar radiation band is [not specified]. Solar The average emissivity (ε) in the atmospheric window band is approximately 0.8553, and the temperature test shows that the substrate coated with this radiation-cooling coating is 0.38℃ lower than the ambient temperature.

[0109] Example 2

[0110] Synthetic radiation-cooling coating: 16.26g of functional powder 4 was mixed with 62.64g of solvent DMF and ultrasonically dispersed for 15min to obtain a uniform dispersion system; then 6.96g of PVDF was added to the suspension and mixed evenly, and the temperature was raised to 60℃ using a magnetic heating stirrer to dissolve the PVDF in the solvent to obtain the radiation-cooling coating.

[0111] The surfaces of two 10cm x 10cm stainless steel substrates were sanded and then wiped clean with alcohol. After the radiation-cooling coating cooled to room temperature, it was sprayed onto the surfaces of the two substrates using a spray gun. After drying in an oven at 80°C, the coating was peeled off the substrate surface, resulting in a radiation-cooling coating with a thickness of 200μm, composed of 70wt% functional powder / 30wt% PVDF. The average reflectance (Ro) of the coating in the solar radiation band... Solar The average emissivity (ε) in the atmospheric window band is approximately 0.8644, and the temperature test shows that the substrate coated with this radiation-cooling coating is 0.56℃ lower than the ambient temperature.

[0112] Example 3

[0113] Synthetic radiation-cooling coating: 24.39g of functional powder 4 was mixed with 93.96g of solvent DMF and ultrasonically dispersed for 15min to obtain a uniform dispersion system; then 10.44g of PVDF was added to the suspension and mixed evenly, and the temperature was raised to 60℃ using a magnetic heating stirrer to dissolve the PVDF in the solvent to obtain the radiation-cooling coating.

[0114] The surfaces of two 10cm x 10cm stainless steel substrates were sanded and then wiped clean with alcohol. After the radiation-cooling coating cooled to room temperature, it was sprayed onto the surfaces of the two substrates using a spray gun. After drying in an oven at 80°C, the coating was peeled off the substrate surface, resulting in a radiation-cooling coating with a thickness of 300μm, composed of 70wt% functional powder / 30wt% PVDF. The average reflectance (Ro) of the coating in the solar radiation band is [not specified]. Solar The average emissivity (ε) in the atmospheric window band is approximately 0.8687, the thermal conductivity (λ) is approximately 2.22 W / m·K, and temperature tests show that the substrate coated with this radiation-cooling coating is 4.69 °C lower than the ambient temperature.

[0115] Two 10cm×10cm acrylic sheets and two 10cm×10cm wooden boards were provided and cleaned with alcohol. Radiation cooling coating was sprayed onto the surfaces of the four substrates using a spray gun. After drying in an oven at 80°C, a radiation cooling coating with a thickness of 300μm and a composition of 70wt% functional powder / 30wt% PVDF was obtained. Both coatings adhered well to the surfaces. This result indicates that the radiation cooling coating in this example can adhere well to a variety of substrates, has good stability, and can meet the different needs of different refrigeration fields.

[0116] Example 4

[0117] Synthetic radiation-cooling coating: 32.52g of functional powder 4 was mixed with 125.28g of solvent DMF and ultrasonically dispersed for 15min to obtain a uniform dispersion system; then 13.92g of PVDF was added to the suspension and mixed evenly, and the temperature was raised to 60℃ using a magnetic heating stirrer to dissolve the PVDF in the solvent to obtain the radiation-cooling coating.

[0118] The surfaces of two 10cm x 10cm stainless steel substrates were sanded and then wiped clean with alcohol. After the radiation-cooling coating cooled to room temperature, it was sprayed onto the surfaces of the two substrates using a spray gun. After drying in an oven at 80°C, the coating was peeled off the substrate surface, resulting in a radiation-cooling coating with a thickness of 400μm, composed of 70wt% functional powder and 30wt% PVDF. The average reflectance (Ro) of the coating in the solar radiation band is [not specified]. Solar The average emissivity (ε) in the atmospheric window band is approximately 0.8656, and the temperature test shows that the substrate coated with this radiation-cooling coating is 3.67°C lower than the ambient temperature.

[0119] Comparative Example 1

[0120] Synthetic radiation-cooling coating: Add 8.01g of PVDF to 72.09g of solvent DMF and mix evenly. Use a magnetic heating stirrer to heat to 60℃ to dissolve the PVDF in the solvent to obtain the radiation-cooling coating.

[0121] The surfaces of two 10cm x 10cm stainless steel substrates were sanded and then wiped clean with alcohol. After the radiation-cooling coating cooled to room temperature, it was sprayed onto the surfaces of the two substrates using a spray gun. After drying in an oven at 80°C, the coating was peeled off the substrate surface, resulting in a 100μm thick PVDF coating. The average reflectance (Ro) of the coating in the solar radiation band is... Solar The average emissivity (ε) in the atmospheric window band is approximately 0.8905, and the thermal conductivity (λ) is approximately 0.15 W / m·K. Temperature tests show that the substrate coated with this radiation-cooling coating is 15.71 °C higher than the ambient temperature.

[0122] Comparative Example 2

[0123] Synthetic radiation-cooling coating: 0.84g of functional powder 4 was mixed with 67.77g of solvent DMF and ultrasonically dispersed for 15min to obtain a uniform dispersion system; then 7.53g of PVDF was added to the suspension and mixed evenly, and the temperature was raised to 60℃ using a magnetic heating stirrer to dissolve the PVDF in the solvent to obtain the radiation-cooling coating.

[0124] The surfaces of two 10cm x 10cm stainless steel substrates were sanded and then wiped clean with alcohol. After the radiation-cooling coating cooled to room temperature, it was sprayed onto the surfaces of the two substrates using a spray gun. After drying in an oven at 80°C, the coating was peeled off the substrate surface, resulting in a 100μm thick radiation-cooling coating composed of 10wt% functional powder / 90wt% PVDF. The average reflectance (Ro) of the coating in the solar radiation band is [not specified]. Solar The average emissivity (ε) in the atmospheric window band is approximately 0.9426. Temperature tests show that the substrate coated with this radiation-cooling coating is 12.04℃ higher than the ambient temperature.

[0125] Comparative Example 3

[0126] Synthetic radiation-cooling coating: 24.39g of commercial β-Si3N4 (short rods) was mixed with 93.96g of solvent DMF and ultrasonically dispersed for 15min to obtain a uniform dispersion system; then 10.44g of PVDF was added to the suspension and mixed evenly, and the temperature was raised to 60℃ using a magnetic stirrer to dissolve the PVDF in the solvent to obtain the radiation-cooling coating.

[0127] The surfaces of two 10cm x 10cm stainless steel substrates were sanded and then wiped clean with alcohol. After the radiation-cooling coating cooled to room temperature, it was sprayed onto the surfaces of the two substrates using a spray gun. After drying in an oven at 80°C, the coating was peeled off the substrate surface, resulting in a radiation-cooling coating with a thickness of 300μm and a composition of 70wt% β-Si3N4 / 30wt% PVDF. The average reflectance (Ro) of the coating in the solar radiation band is [not specified]. Solar )≈0.6249.

[0128] Comparative Example 4

[0129] Synthetic radiation-cooling coating: 24.39g of commercial α-Si3N4 and 93.96g of solvent DMF were mixed and ultrasonically dispersed for 15min to obtain a uniform dispersion system; then 10.44g of PVDF was added to the suspension and mixed evenly, and the temperature was raised to 60℃ using a magnetic heating stirrer to dissolve the PVDF in the solvent to obtain the radiation-cooling coating.

[0130] The surfaces of two 10cm × 10cm stainless steel substrates were sanded and then wiped clean with alcohol. After the radiation-cooling coating cooled to room temperature, it was sprayed onto the surfaces of the two substrates using a spray gun and dried in an oven at 80℃. The results showed that there were gaps between the coating and the substrate, indicating poor adhesion of the coating prepared using commercial α-Si3N4 as the functional powder. A radiation-cooling coating with a thickness of 300μm and a composition of 70wt% α-Si3N4 / 30wt% PVDF was obtained. The thermal conductivity of the coating (λ) was approximately 1.16 W / m·K, and temperature tests showed that the substrate temperature coated with this radiation-cooling coating was 6.02℃ higher than the ambient temperature.

[0131] Comparative Example 5

[0132] Synthetic radiation-cooling coating: 32.47g of commercial TiO2 and 125.28g of solvent DMF were mixed and ultrasonically dispersed for 15min to obtain a uniform dispersion system; then 13.92g of PVDF was added to the suspension and mixed evenly, and the temperature was raised to 60℃ using a magnetic heating stirrer to dissolve the PVDF in the solvent to obtain the radiation-cooling coating.

[0133] The surfaces of two 10cm x 10cm stainless steel substrates were sanded and then wiped clean with alcohol. After the radiation-cooling coating cooled to room temperature, it was sprayed onto the surfaces of the two substrates using a spray gun. After drying in an oven at 80°C, a radiation-cooling coating with a thickness of 300μm and a composition of 70wt% TiO2 / 30wt% PVDF was obtained. The average reflectance (Ro) of this coating in the solar radiation band was measured. Solar The average emissivity (ε) in the atmospheric window band is approximately 0.8244, the thermal conductivity (λ) is approximately 1.14 W / m·K, and temperature tests show that the substrate coated with this radiation-cooling coating is 6.27 °C higher than the ambient temperature.

[0134] Performance comparison:

[0135] The relevant properties of the radiation-cooled coatings in each embodiment and comparative example are summarized in Table 1.

[0136] Table 1:

[0137]

[0138] Summary: 1) The coating ratio and the thickness of the radiation-cooled coating have a significant impact on its solar reflectivity. As the amount of functional powder added to the coating increases, the average reflectivity also increases. However, as the coating thickness increases, the average reflectivity initially increases and then remains relatively constant. Therefore, considering both the performance and preparation cost of the radiation-cooled coating, a thickness of 300 μm and a composition of 70 wt% β-Si3N4 / 30 wt% PVDF are considered the optimal preparation process parameters for the radiation-cooled coating. Furthermore, the cooling effect tests of each embodiment also show that the substrate with a 300 μm thick radiation-cooled coating composed of 70 wt% β-Si3N4 / 30 wt% PVDF exhibits the best cooling effect, which is consistent with the optical performance test results; 2) Although the coating obtained using commercial TiO2 as a functional powder has high thermal conductivity, the band gap of TiO2 is relatively narrow (Eg = 3.0 eV). Figure 7 It can also be seen that the coatings prepared from it exhibit energy absorption in the shorter wavelength violet and ultraviolet light bands, limiting their application areas; similarly, coatings prepared using α-Si3N4 as a functional powder have high thermal conductivity, but these coatings not only have average adhesion, but also... Figure 13 It can be seen that it also exhibits energy absorption in the shorter wavelength violet and ultraviolet light bands, limiting its application areas; while the coating obtained using commercial β-Si3N4 as the functional powder has a low average reflectivity, making it difficult to meet the basic requirements of radiation-cooling coatings; 3) The radiation-cooling coating provided by this invention can achieve a reflectivity of 479W / m 2 The cooling effect is 4.69°C lower than the ambient temperature under solar irradiance, and 97W / m 2 The cooling power is high, and its thermal conductivity (λ) is ≥2W / m·K. Its performance will be even better in radiative cooling at temperatures higher than ambient temperature, indicating that this radiative cooling coating has practical application value.

[0139] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. For those skilled in the art, other variations or modifications can be made based on the above description. It is impossible to exhaustively list all the implementation methods here. All obvious variations or modifications derived from the technical solutions of the present invention are still within the protection scope of the present invention.

Claims

1. A radiation-cooling coating, characterized in that, Its raw materials include: functional powder, infrared resin matrix, and solvent; the composition of the functional powder is as follows: β -Si3N4 grains, and located in β -Y-Si-ON compound film on the surface of Si3N4 grains; β The diameter of the -Si3N4 grains is 0.1μm~6μm; the thickness of the Y-Si-ON compound film is 1nm~5nm; The β -Si3N4 grains have a hexagonal prismatic structure and / or a long columnar structure; the β The average aspect ratio of Si3N4 grains is 3~6; The β When Si3N4 grains have a hexagonal prism structure, their diameter refers to the distance between the diagonals of the hexagonal base faces. The β- Si3N4 grains β Phase content ≥95%.

2. The radiation cooling coating as described in claim 1, characterized in that, The mass ratio of the functional powder to the infrared resin matrix is ​​2~10:1~9.

3. The radiation cooling coating as described in claim 1, characterized in that, The mass ratio of the functional powder to the infrared resin matrix is ​​3~8:3~5.

4. The radiation cooling coating as described in claim 1, characterized in that, The mass ratio of the functional powder to the infrared resin matrix is ​​6~8:3~4.

5. The radiation cooling coating as described in claim 1, characterized in that, The infrared resin matrix is ​​at least one of polyvinylidene fluoride, polyvinylidene fluoride, polychlorotrifluoroethylene, polytetrafluoroethylene, and polyvinylidene fluoride-hexafluoropropylene.

6. The radiation cooling coating as described in claim 1, characterized in that, The β -Si3N4 grains have a hexagonal prismatic structure.

7. The radiation cooling coating as described in claim 1, characterized in that, The Y-Si-ON compound film is amorphous.

8. The method for preparing the radiation-cooling coating as described in any one of claims 1 to 7, characterized in that, Includes the following steps: The functional powder is mixed with a solvent and ultrasonically dispersed for 10-20 minutes to obtain a suspension; The infrared resin matrix is ​​mixed with the suspension and heated and stirred until the infrared resin matrix dissolves in the solvent.

9. A radiation-cooling coating, characterized in that, Obtained by applying the radiation cooling coating as described in any one of claims 1 to 7 to the surface of a substrate or equipment.

10. The radiation-cooling coating as described in claim 9, characterized in that, The substrate is selected from one of the following: metal, plastic, rubber, concrete, cement, asphalt, ceramic tile, and glass.

11. The radiation cooling coating as described in claim 9, characterized in that, The thickness of the radiation cooling coating is 100μm~500μm.

12. The radiation cooling coating as described in claim 9, characterized in that, The thickness of the radiation cooling coating is 250μm~350μm.

Images