A method for preparing a high thermal conductivity radiation refrigeration material

Abstract

The present invention relates to a method for preparing a high thermal conductivity radiation refrigeration material, and belongs to the field of high thermal management material technology and radiation refrigeration thermal conductive material technology. The present invention is a preparation method that is to stir and disperse a boron source and a nitrogen source in a solvent in a certain mass ratio, and then obtain a sample A in a stainless steel reactor; then anneal the sample A to obtain hollow boron nitride microspheres; finally, the obtained hollow boron nitride microspheres are mixed with an organic polymer to obtain a radiation refrigeration material with high thermal conductivity. Beneficial effects of the present invention: hollow microspheres are compounded with organic polymers by phase transition, and a composite material with a porous structure is obtained by regulation, which further improves the infrared emissivity and solar reflectivity of the material. The refrigeration material can be in a powder state or a slurry state, suitable for a variety of scenarios, easy to seal, and has good application prospects.

Description

Technical Field

[0001] The present invention relates to the field of high thermal management material technology and radiation cooling heat conductive material technology, and in particular to a method for preparing a high thermal conductivity radiation cooling and heat dissipation material. Background Art

[0002] Energy crisis and global warming are major challenges facing the world today. At present, refrigeration energy consumption accounts for about 20% of the world's total building electricity consumption and 10% of the world's total electricity consumption. Improving the efficiency of existing refrigeration systems and exploring new refrigeration technologies have become urgent tasks. Radiative refrigeration technology uses the ultra-high sunlight reflectivity of materials to block heat input. At the same time, it can also emit its own heat into the space atmosphere in the form of infrared thermal radiation, thereby achieving a refrigeration effect below the ambient temperature. This technology has the advantages of zero energy consumption, no pollution, and high cooling performance. It is considered to be an ideal choice to replace energy-intensive refrigeration methods at this stage. The emergence of various materials and new preparation methods has played a huge role in promoting the development of refrigeration materials. Therefore, passive radiative refrigeration technology is expected to be widely used in building energy conservation, wearable devices, photovoltaics, 5G base stations, mobile smart terminals and other fields.

[0003] Patent CN110317521A discloses a selective radiation cooling coating, which includes a radiation cooling functional layer with a special structure particle filler, which is used to reflect ultraviolet light and / or visible light and / or near-infrared light in sunlight, and emit heat through the atmospheric window in the form of infrared radiation. The radiation cooling functional layer includes a rod-shaped structure particle filler and a radiation cooling functional layer resin, and the particle filler is distributed in the radiation cooling functional layer resin, and finally achieves a reflectivity of >80% and an infrared emissivity of >80%. Patent CN113372612A discloses a method for preparing a cellulose-based radiation temperature regulating material, which is prepared by functionally modifying cellulose to prepare a cellulose aerogel with a three-dimensional porous structure, showing a solar reflectivity of nearly 94% and an infrared emissivity of 95%. However, the radiation cooling materials currently developed only focus on reducing the input of heat from the outside, and the materials used generally have the problem of low thermal conductivity, which will hinder the heat conduction of the internal high-temperature heat source, which may cause thermal runaway of the device. The key to solving this problem lies in developing a radiative cooling material that can quickly and directedly export heat from the inside to the outside, thereby achieving an ideal internal space cooling effect. Summary of the invention

[0004] The present invention aims to solve the problem that existing radiation refrigeration materials only focus on the reflection of sunlight, but lack effective conduction and regulation means for the thermal radiation generated by internal heat sources, and provides a method for preparing a radiation refrigeration material with high thermal conductivity. The material has the characteristics of high thermal conductivity and radiation refrigeration, which can quickly transfer heat from the inside to the outside, while minimizing the external heat from entering the inside and selectively emitting the internal heat to outer space in the form of thermal radiation. It is a multifunctional radiation refrigeration material. The preparation method of the material is to prepare hollow boron nitride microspheres of different particle sizes by hydrothermal and high-temperature pyrolysis methods. The microspheres can be directly mixed with an organic polymer matrix to make a precursor for coatings or thin film materials, which has important application value.

[0005] The present invention is achieved through the following technical solutions:

[0006] A high thermal conductivity radiation refrigeration material is composed of high thermal conductivity boron nitride hollow microspheres and organic polymers; the boron nitride hollow microspheres have high thermal conductivity, high refractive index, wide band gap characteristics, and the microspheres have a special surface plasmon effect. After the infrared radiation is absorbed by the material, it causes collective oscillation of surface electrons, and can obtain a high emissivity in the mid- and far-infrared bands. At the same time, the hollow structure performs multiple reflections and scattering of the incident sunlight, thereby weakening the absorption of solar radiation, solving the problems of low reflectivity and poor refrigeration effect caused by the original nano-microspheres absorbing sunlight of a certain wavelength. Mixing the hollow microspheres with organic polymers further improves the infrared emissivity and solar reflectivity of the material.

[0007] A method for preparing a high thermal conductivity radiation refrigeration material according to the present invention comprises the following steps:

[0008] (1) The boron source and the nitrogen source are stirred and dispersed in a solvent in a certain mass ratio, and then sealed in a stainless steel reactor with polytetrafluoroethylene, and hydrothermally reacted at 150-250° C. for 6-48 hours, and naturally cooled to room temperature to obtain sample A;

[0009] (2) annealing the sample A obtained in step (1) to obtain hollow boron nitride microspheres; if the microspheres are washed with water and alcohol multiple times before annealing, the effect is better;

[0010] (3) The boron nitride hollow microspheres obtained in step (2) are mixed with an organic polymer to obtain a radiation refrigeration material with high thermal conductivity.

[0011] Preferably, the boron source in step (1) is one or more of boric acid, boric oxide, borax, ammonium tetrafluoroborate, borazine, and sodium borohydride, and the nitrogen source is one or more of melamine, urea, cyanuric acid, sodium azide, dicyandiamide, or sodium amide, and the mass ratio of the boron source to the nitrogen source is 1:0.1-10.

[0012] Preferably, the solvent in step (1) is one or more of water, acetonitrile, ethanol, methanol, tert-butyl alcohol, isopropanol, dimethyl sulfoxide, styrene, perchloroethylene, trichloroethylene, ethylene glycol ether, or triethanolamine.

[0013] Preferably, the annealing temperature in step (2) is 450-1200°C, and the annealing time is 2-12 hours. The particle size of the obtained hollow boron nitride microspheres is controlled to be 0.1-100 μm, and the wall thickness is 0.05-2 μm.

[0014] Preferably, the organic polymer in step (3) is one or more of fluororesin, epoxy resin, polyester, polyurethane, acrylic resin, silicone resin, acrylate polymer, silicone rubber polymer, and fluorine-containing polymer.

[0015] Preferably, the boron nitride microspheres and the organic polymer in step (3) are mixed by physical stirring, the stirring and mixing temperature is 20-150° C., and the mass ratio of the boron nitride microspheres to the organic polymer is 1:0.1-10.

[0016] Compared with the prior art, the present invention has the following beneficial effects:

[0017] (1) The excellent thermal conductivity of the boron nitride material itself is utilized to achieve rapid heat transfer from the inside to the outside, so that the inside achieves an ideal cooling effect, solving the problem that the existing radiation refrigeration materials lack heat conduction capacity, resulting in internal heat accumulation and affecting product performance.

[0018] (2) By constructing boron nitride microspheres with a hollow structure and utilizing the high refractive index, wide band gap characteristics of boron nitride and the special surface plasmon effect of the microspheres, infrared radiation is absorbed by the material, causing collective oscillation of surface electrons, and a high emissivity can be obtained in the mid- and far-infrared bands. At the same time, the hollow structure reflects and scatters the incident sunlight multiple times, thereby weakening the absorption of solar radiation and improving the cooling effect. This solves the problems of low reflectivity and poor cooling effect caused by the original nano-microspheres absorbing sunlight of a certain wavelength.

[0019] (3) Organic polymers are selected as the polymer substrate, and phase changes are utilized to obtain a porous structure. By adjusting the pore size, a perfect match of the micropore size is achieved to effectively scatter sunlight of all wavelengths, thereby reducing the solar radiation heat to a greater extent, thus solving the problem that traditional radiation cooling materials require a sputtered metal layer to increase the reflectivity of sunlight.

[0020] (4) The prepared radiation cooling material can be in powder or slurry state, can be applied in a variety of scenarios, is easy to seal, and has good application prospects. DETAILED DESCRIPTION

[0021] The present invention will be further described below in conjunction with specific examples. These implementation cases are only used to illustrate the present invention and are not intended to limit the scope of the present invention. In addition, after reading the content taught by the present invention, those skilled in the art may make various changes or modifications to the present invention, and these equivalent forms also fall within the scope limited by the appended claims of the application.

[0022] Embodiment 1:

[0023] (1) Boric acid and dicyandiamide in a mass ratio of 1:1 were stirred and dispersed in a mixed solvent of water and acetonitrile, and then sealed in a stainless steel reactor with polytetrafluoroethylene, kept at 150°C for 48 hours, and naturally cooled to room temperature to obtain sample A.

[0024] (2) After the sample A obtained in step (1) is washed three times with water and alcohol alternately, it is annealed at 1000° C. for 2 h to obtain hollow boron nitride microspheres.

[0025] (3) The boron nitride hollow microspheres obtained in step (2) are stirred and mixed with an acrylic polymer at 120° C. in a mass ratio of 1:1 to obtain a radiation refrigeration material with high thermal conductivity.

[0026] The heat-conductive radiation cooling material prepared in this embodiment has a reflectivity of 97.9% to sunlight, an infrared emissivity of 0.89, and an in-plane thermal conductivity of 3.1 W / m·K. This material can not only be used for outdoor radiation cooling, but also achieve a cooling effect of up to 9.5°C under sunlight irradiation conditions. Compared with pure acrylic polymers, it has a higher temperature than pure acrylic polymers under sunlight irradiation and 1000 W / m 2 When there is an internal heat source, the heat dissipation effect of up to 24°C can be achieved.

[0027] Embodiment 2:

[0028] (1) Boric acid and dicyandiamide in a mass ratio of 2:1 were stirred and dispersed in a mixed solvent of water and acetonitrile, and then sealed in a stainless steel reactor with polytetrafluoroethylene, kept at 150°C for 48 hours, and naturally cooled to room temperature to obtain sample A.

[0029] (2) After the sample A obtained in step (1) is washed three times with water and alcohol alternately, it is annealed at 1000° C. for 2 h to obtain hollow boron nitride microspheres.

[0030] (3) The boron nitride hollow microspheres obtained in step (2) are stirred and mixed with an acrylic polymer at 120° C. in a mass ratio of 1:1 to obtain a radiation refrigeration material with high thermal conductivity.

[0031] The heat-conductive radiation cooling material prepared in this embodiment has a reflectivity of 97.8% to sunlight, an infrared emissivity of 0.88, and an in-plane thermal conductivity of 3.8W / m·K. This material can not only be used for outdoor radiation cooling, but also achieve a cooling effect of up to 9°C under sunlight irradiation. Compared with pure acrylic polymers, it has a higher thermal conductivity under sunlight irradiation and 1000W / m 2 When there is an internal heat source, the maximum heat dissipation effect of 25°C can be achieved.

[0032] Embodiment 3:

[0033] (1) Boric acid and dicyandiamide in a mass ratio of 1:1 were stirred and dispersed in a mixed solvent of water and acetonitrile, and then sealed in a stainless steel reactor with polytetrafluoroethylene, kept at 150°C for 48 hours, and naturally cooled to room temperature to obtain sample A.

[0034] (2) After the sample A obtained in step (1) is washed three times with water and alcohol alternately, it is annealed at 1200° C. for 2 h to obtain hollow boron nitride microspheres.

[0035] (3) The boron nitride hollow microspheres obtained in step (2) are stirred and mixed with an acrylic polymer at 120° C. in a mass ratio of 1:1 to obtain a radiation refrigeration material with high thermal conductivity.

[0036] The heat-conductive radiation cooling material prepared in this embodiment has a reflectivity of 97.1% to sunlight, an infrared emissivity of 0.91, and an in-plane thermal conductivity of 4.2W / m·K. This material can not only be used for outdoor radiation cooling, but also achieve a cooling effect of up to 11.5°C under sunlight irradiation conditions. Compared with pure acrylic polymers, it has a higher temperature than pure acrylic polymers under sunlight irradiation and 1000W / m 2 When there is an internal heat source, the heat dissipation effect of up to 25.5℃ can be achieved.

[0037] Embodiment 4:

[0038] (1) Ammonium tetrafluoroborate and cyanuric acid in a mass ratio of 1:1 were stirred and dispersed in a mixed solvent of water and ethanol, and then sealed in a stainless steel reactor with polytetrafluoroethylene, kept at 120°C for 24 hours, and naturally cooled to room temperature to obtain sample A.

[0039] (2) After the sample A obtained in step (1) is washed three times with water and alcohol alternately, it is annealed at 500° C. for 4 h to obtain hollow boron nitride microspheres.

[0040] (3) The boron nitride hollow microspheres obtained in step (2) are stirred and mixed with epoxy resin at 115° C. in a mass ratio of 2:1 to obtain a radiation refrigeration material with high thermal conductivity.

[0041] The heat-conductive radiation cooling material prepared in this embodiment has a reflectivity of 98.9% to sunlight, an infrared emissivity of 0.87, and an in-plane thermal conductivity of 4.1 W / m·K. This material can not only be used for outdoor radiation cooling, but also achieve a cooling effect of up to 11.5°C under sunlight irradiation. Compared with pure epoxy resin, it has a higher temperature than pure epoxy resin under sunlight irradiation and 1000 W / m 2 When there is an internal heat source, the maximum heat dissipation effect of 26°C can be achieved.

[0042] Embodiment 5:

[0043] (1) Ammonium tetrafluoroborate and cyanuric acid in a mass ratio of 1:1 were stirred and dispersed in a mixed solvent of water and ethanol, then sealed in a stainless steel reactor with polytetrafluoroethylene, kept at 180°C for 24 hours, and naturally cooled to room temperature to obtain sample A.

[0044] (2) After the sample A obtained in step (1) is washed three times with water and alcohol alternately, it is annealed at 500° C. for 4 h to obtain hollow boron nitride microspheres.

[0045] (3) The boron nitride hollow microspheres obtained in step (2) are stirred and mixed with epoxy resin at 115° C. in a mass ratio of 2:1 to obtain a radiation refrigeration material with high thermal conductivity.

[0046] The heat-conductive radiation cooling material prepared in this embodiment has a reflectivity of 96.9% to sunlight, an infrared emissivity of 0.88, and an in-plane thermal conductivity of 4.2W / m·K. This material can not only be used for outdoor radiation cooling, but also achieve a cooling effect of up to 10.5°C under sunlight irradiation. Compared with pure epoxy resin, it has a higher temperature than pure epoxy resin under sunlight irradiation and 1000W / m 2 When there is an internal heat source, the maximum heat dissipation effect of 25°C can be achieved.

[0047] Embodiment 6:

[0048] (1) Ammonium tetrafluoroborate and cyanuric acid in a mass ratio of 1:1 were stirred and dispersed in a mixed solvent of water and ethanol, then sealed in a stainless steel reactor with polytetrafluoroethylene, kept at 180°C for 24 hours, and naturally cooled to room temperature to obtain sample A.

[0049] (2) After the sample A obtained in step (1) is washed three times with water and alcohol alternately, it is annealed at 1000° C. for 4 h to obtain hollow boron nitride microspheres.

[0050] (3) The boron nitride hollow microspheres obtained in step (2) are stirred and mixed with epoxy resin at 115° C. in a mass ratio of 2:1 to obtain a radiation refrigeration material with high thermal conductivity.

[0051] The heat-conductive radiation cooling material prepared in this embodiment has a reflectivity of 98.9% to sunlight, an infrared emissivity of 0.91, and an in-plane thermal conductivity of 4.9 W / m·K. This material can not only be used for outdoor radiation cooling, but also achieve a cooling effect of up to 12.5°C under sunlight irradiation. Compared with pure epoxy resin, it has a higher temperature than pure epoxy resin under sunlight irradiation and 1000 W / m 2 When there is an internal heat source, the heat dissipation effect of up to 26.5℃ can be achieved.

[0052] Embodiment 7:

[0053] (1) Boron oxide and sodium azide in a mass ratio of 1:2 are stirred and dispersed in a mixed solvent of water and dimethyl sulfoxide, then sealed in a stainless steel reactor with polytetrafluoroethylene, kept at 200° C. for 48 hours, and naturally cooled to room temperature to obtain sample A.

[0054] (2) After the sample A obtained in step (1) is washed three times with water and alcohol alternately, it is annealed at 800° C. for 6 h to obtain hollow boron nitride microspheres.

[0055] (3) The boron nitride hollow microspheres obtained in step (2) are stirred and mixed with epoxy resin at 115° C. in a mass ratio of 2:1 to obtain a radiation refrigeration material with high thermal conductivity.

[0056] The heat-conductive radiation cooling material prepared in this embodiment has a reflectivity of 95.9% to sunlight, an infrared emissivity of 0.91, and an in-plane thermal conductivity of 3.5W / m·K. This material can not only be used for outdoor radiation cooling, but also achieve a cooling effect of up to 10.5°C under sunlight irradiation. Compared with pure epoxy resin, it has a higher temperature than pure epoxy resin under sunlight irradiation and 1000W / m 2 When there is an internal heat source, the maximum heat dissipation effect of 25°C can be achieved.

[0057] Embodiment 8:

[0058] (1) Boric oxide and melamine in a mass ratio of 1:2 were stirred and dispersed in a mixed solvent of water, methanol and acetonitrile, then sealed in a stainless steel reactor with polytetrafluoroethylene, kept at 180°C for 24 hours, and naturally cooled to room temperature to obtain sample A.

[0059] (2) After the sample A obtained in step (1) is washed three times with water and alcohol alternately, it is annealed at 800° C. for 6 h to obtain hollow boron nitride microspheres.

[0060] (3) The boron nitride hollow microspheres obtained in step (2) are stirred and mixed with epoxy resin at 115° C. in a mass ratio of 2:1 to obtain a radiation refrigeration material with high thermal conductivity.

[0061] The heat-conductive radiation cooling material prepared in this embodiment has a reflectivity of 96.9% to sunlight, an infrared emissivity of 0.89, and an in-plane thermal conductivity of 3.6W / m·K. This material can not only be used for outdoor radiation cooling, but also achieve a cooling effect of up to 10.5°C under sunlight irradiation. Compared with pure epoxy resin, it has a higher temperature than pure epoxy resin under sunlight irradiation and 1000W / m 2 When there is an internal heat source, the heat dissipation effect of up to 25.5℃ can be achieved.

[0062] Comparative Example 1:

[0063] Commercial flake boron nitride and acrylic polymer in a mass ratio of 1:1 were stirred and mixed at 120°C to obtain a radiation refrigeration material with thermal conductivity.

[0064] The heat-conductive radiation cooling material prepared in this comparative example has a reflectivity of 87.9% to sunlight, an infrared emissivity of 0.69, and an in-plane thermal conductivity of only 2.5W / m·K. The material can be used for outdoor radiation cooling, achieving a maximum cooling effect of 1.5°C under sunlight irradiation conditions. Compared with pure acrylic polymers, it has a lower temperature under sunlight irradiation and 1000W / m 2 When there is an internal heat source, the maximum heat dissipation effect of 9°C can be achieved.

[0065] Compared with the high thermal conductivity radiation refrigeration material prepared in Example 1, its refrigeration and heat dissipation effect is significantly weakened, which shows that the microsphere structure of boron nitride has obvious advantages in sunlight reflectivity and infrared emissivity compared with flake boron nitride, and is a key factor in radiation refrigeration.

[0066] Comparative Example 2:

[0067] (1) Boric acid and dicyandiamide in a mass ratio of 1:1 were stirred and dispersed in a mixed solvent of water and acetonitrile, and then sealed in a stainless steel reactor with polytetrafluoroethylene, kept at 150°C for 48 hours, and naturally cooled to room temperature to obtain sample A.

[0068] (2) Sample A obtained in step (1) is directly mixed with an acrylic polymer at 120° C. in a mass ratio of 1:1 to obtain a radiation refrigeration material with high thermal conductivity.

[0069] The heat-conductive radiation cooling material prepared in this comparative example has a reflectivity of 77.9% to sunlight, an infrared emissivity of 0.69, and an in-plane thermal conductivity of more than 1.2W / m·K. The material can be used for outdoor radiation cooling, achieving a maximum cooling effect of 4.1°C under sunlight irradiation conditions. Compared with pure acrylic polymers, it has a higher temperature than pure acrylic polymers under sunlight irradiation and 1000W / m 2 When there is an internal heat source, a heat dissipation effect of up to 11°C can be achieved.

[0070] Compared with the high thermal conductivity radiation refrigeration material prepared in Example 1, its in-plane thermal conductivity is significantly reduced, and the refrigeration and heat dissipation effect is less than 50% of that in Example 1, which indicates that the unannealed boron nitride microspheres have poor crystallinity, resulting in a decrease in their thermal conductivity, affecting the refrigeration effect.

[0071] Comparative Example 3:

[0072] (1) Boric acid and dicyandiamide were mixed in a mass ratio of 1:1 and then annealed at 1000°C for 2h to obtain a boron nitride sample.

[0073] (2) The boron nitride obtained in step (1) and the acrylic polymer are stirred and mixed at 120° C. in a mass ratio of 1:1 to obtain a radiation refrigeration material with high thermal conductivity.

[0074] The heat-conductive radiation cooling material prepared in this comparative example has a reflectivity of 88.1% to sunlight, an infrared emissivity of 0.77, and an in-plane thermal conductivity of more than 2.1W / m·K. This material can not only be used for outdoor radiation cooling, but also achieve a cooling effect of up to 5.5°C under sunlight irradiation conditions. Compared with pure acrylic polymers, it has a higher thermal conductivity under sunlight irradiation and 1000W / m 2 When there is an internal heat source, the maximum heat dissipation effect of 14°C can be achieved.

[0075] Compared with the high thermal conductivity radiation refrigeration material prepared in Example 1, the present comparative example did not undergo a hydrothermal process, and the boron nitride hollow microspheres could not be prepared by a single calcination process, resulting in a poor radiation refrigeration effect. This indicates that the microsphere structure of boron nitride is one of the important factors for radiation refrigeration.

Claims

1. A method for preparing a high thermal conductivity radiation refrigeration material, characterized in that: The following steps are involved: (1) Stirring and dispersing a boron source and a nitrogen source in a solvent in a certain mass ratio, keeping the temperature at 150-250° C. for 6-48 hours, and cooling naturally to room temperature to obtain sample A; the boron source is one or more of boric acid, boric oxide, borax, ammonium tetrafluoroborate, borazine, or sodium borohydride; the nitrogen source is one or more of melamine, urea, cyanuric acid, sodium azide, dicyandiamide, or sodium amide; the solvent is one or more of water, acetonitrile, ethanol, methanol, tert-butyl alcohol, isopropanol, dimethyl sulfoxide, styrene, perchloroethylene, trichloroethylene, ethylene glycol ether, or triethanolamine; after the boron source and the nitrogen source are dispersed in the solvent, they are placed in a stainless steel reactor sealed with polytetrafluoroethylene for reaction; the mass ratio of the boron source to the nitrogen source is 1:0.1-10; (2) annealing the sample A obtained in step (1) to obtain hollow boron nitride microspheres; the particle size of the obtained hollow boron nitride microspheres is controlled to be 0.1-100 μm, and the wall thickness is 0.05-2 μm; (3) The hollow boron nitride microspheres obtained in step (2) are mixed with an organic polymer to obtain a radiation refrigeration material with high thermal conductivity; the organic polymer is one or more of fluororesin, epoxy resin, polyester, polyurethane, acrylic resin, silicone resin, acrylic polymer, silicone rubber polymer, or fluorine-containing polymer; the boron nitride microspheres and the organic polymer are mixed by physical stirring at a stirring temperature of 20-150° C., and the mass ratio of the boron nitride microspheres to the organic polymer is 1:0.1-10.

2. The method for preparing a high thermal conductivity radiation refrigeration material according to claim 1, characterized in that: The annealing temperature in step (2) is 450-1200°C, and the annealing time is 2-12h.

3. The method for preparing a high thermal conductivity radiation refrigeration material according to claim 1, characterized in that: In step (2), sample A is washed with water and alcohol multiple times and then annealed.