CN115928020A - Space cryogenic thermal control coating and preparation method thereof - Google Patents
Space cryogenic thermal control coating and preparation method thereof Download PDFInfo
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- CN115928020A CN115928020A CN202211164097.0A CN202211164097A CN115928020A CN 115928020 A CN115928020 A CN 115928020A CN 202211164097 A CN202211164097 A CN 202211164097A CN 115928020 A CN115928020 A CN 115928020A
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Abstract
The invention discloses a space cryogenic thermal control coating and a preparation method thereof, belonging to the field of new materials; the cryogenic thermal control coating material consists of a surface radiation layer, an intermediate reflection layer and a back surface protection layer, wherein the surface radiation layer is suitable for having higher long-wave infrared cut-off frequency such as fluoride; the middle reflecting layer is used for efficiently reflecting solar heat flow, such as Ag and Al layers; the backside protection layer is used to protect the coating from steric oxygen oxidation, such as a nickel film layer. The prepared coating has a fluoride/Ag/nickel three-layer composite structure. The solar absorption ratio of the coating is as low as 0.03, the infrared reflection cutoff wavelength is 8 to 12 mu m, and the thermal equilibrium temperature of the coating is as low as 50K, so that the coating can be applied to the thermal control system of low-temperature equipment of various spacecrafts serving in space. In addition, the coating also has a radiation refrigeration effect in a ground environment, can obtain a cooling effect of more than 5 ℃ lower than the atmospheric environment temperature, and can be used for cooling and energy saving of buildings and industrial equipment.
Description
Technical Field
The invention relates to a space cryogenic thermal control coating and a preparation method thereof, belonging to the field of new materials.
Background
With the rapid development of the current aerospace technologies such as deep space exploration, astronomical observation and long-term space station, low-temperature working components of a spacecraft, such as a liquid oxygen storage tank, infrared optical equipment, a superconducting motor, a sensor and the like, need to work at the temperature of liquid nitrogen or below, and therefore, the development of a low-temperature thermal control coating which can enable an object without an internal heat source in a space environment to reach a cryogenic state without additional energy input is urgently needed. The method not only can ensure that devices such as a james weber telescope surface array, a superconducting device and the like which need to work in a cryogenic environment can normally run, but also can ensure that the spacecraft can store propellants such as liquid oxygen and the like for a long time so as to realize the target of deep space detection.
However, the balance temperature which can be achieved by the traditional low-absorption thermal control coating is far insufficient to realize space deep cooling, and active refrigeration means such as a Stirling refrigerator and the like not only occupy effective volume and weight, but also consume energy and have short service life. For example, under ideal spatial conditions, at 1 astronomical unit from the sun, the surface heat equilibrium temperature of a spherical black body is about 278K, and a conventional white thermal control coating (e.g., α) is applied s ＝0.09，ε H = 0.91) can reduce the surface temperature to 157K, and the OSR glass secondary surface mirror thermal control coating (such as alpha) in the patent (satellite solar substrate surface glass type secondary surface mirror thermal control coating and the preparation method CN 109705645A) is coated s ＝0.06，ε H = 0.83) can reduce its surface temperature to 144K, but still well above the 50K temperature control requirement for liquid fuel/coolant tanks and the like. Documents [ Robert C.Youngquist, mark A.Nurge.J.Spacecraft.Rockets.2018,55,622-631]The stable temperature of an object covered with an ideal coating at 1 astronomical unit is described as a function of the material cut-off wavelength. It was found that the temperature gradually decreased with increasing cutoff wavelength, and that the equilibrium temperature was about 88K at an ir cut-off of 4 μm, reaching the storage liquid oxygen temperature, but not sufficient to provide the operating temperature of the superconducting material. When the cut-off wavelength reaches 8 μm, the equilibrium temperature can reach 50K, which can achieve both superconducting working conditions and storage of high density liquid oxygen under low pressure conditions.
Objects in space are heated by external heat flow such as direct radiation of solar heat flow, solar radiation reflected by the earth or other planets, and infrared heat radiation from the earth or other planets, and radiate heat to the cosmic space at a temperature equivalent to 4K. Therefore, in order to obtain cryogenic low temperature of an object, it is necessary to reflect solar heat flow, reflect infrared rays radiated from planets such as the earth (the peak radiation wavelength of the earth is 9.7 μm), and radiate the heat of the object itself. Therefore, the cryogenic temperature control requirement on space low-temperature working equipment can be realized by preparing the thermal control coating which can reflect most of solar heat flow and has far infrared radiation heat exchange performance.
Disclosure of Invention
The invention aims at the low-temperature control requirement of the current deep space exploration spacecraft, and aims to provide a space deep cooling type low-temperature thermal control coating and a preparation method thereof based on spectral design and energy band regulation and control principle so as to obtain the temperature control level as low as 50K in a space environment. The cryogenic thermal control coating is a fluoride/Ag/nickel three-layer composite structure and can be widely applied to the fields of various spacecraft low-temperature control equipment serving in space extreme environments, industrial passive radiation refrigeration and the like.
The invention is realized by the following steps:
the coating comprises a surface radiation material, an intermediate reflection layer and a back protection layer, wherein the surface radiation layer, the intermediate reflection layer and the back protection layer form the cryogenic thermal control coating, the cryogenic thermal control coating is of a three-layer composite structure, and the three-layer composite structure is a fluoride/Ag/nickel or fluoride/Al/nickel three-layer composite structure.
The coating reflects most of solar radiation heat flow, and simultaneously emits absorbed solar radiation and self heat generation through self and low-temperature radiation heat exchange of the space, so that the temperature control target is radiated and refrigerated to low temperature. The surface radiation material is BaF 2 、MgF 2 、CaF 2 (ii) one having an infrared reflection cutoff wavelength between 8 and 12 μm; the intermediate reflecting layer is made of one or more of Al and Ag and is used for reflecting most of solar heat flow with the wavelength of 0.2um-7 mu m. The back surface protection layer is a metallic nickel layer to prevent intermediate inversionOxidation erosion of the radiation layer in the space atomic oxygen environment.
Further, the back protective layer has an excellent heat transfer coefficient, so that heat generated by the temperature controlled device can be effectively transferred outwards and finally emitted in a radiation mode.
The preparation method of the space cryogenic thermal control coating comprises the following steps:
step one, baF 2 、MgF 2 、CaF 2 One of the transparent crystals is ultrasonically cleaned and dried by acetone, and then put into a film plating machine for vacuum evaporation of an Ag reflecting film or an Al reflecting film; step two, evaporating a Ni protective film on one surface of the silver plating of the crystal obtained in the step one; and step three, taking out the sample subjected to vapor deposition in the step two, cleaning and drying, wherein the balance temperature of the prepared cryogenic coating sample is 48K.
Further, the thickness of the reflecting film subjected to vacuum evaporation in the first step is 200nm; and in the second step, the thickness of the nickel film is 50nm.
Adopt the produced beneficial effect of above-mentioned technical scheme to lie in:
the space cryogenic heat control coating provided by the invention has the advantages that through the combined design of materials with different spectral characteristics, the coating has extremely low absorption rate in a region with more solar radiation energy distribution, and has extremely high emissivity in a long wave region with very small solar radiation energy distribution, so that the space cryogenic effect can be realized, and compared with the temperature control effect of about 160K under the ideal condition of the traditional low-absorption high-emission heat control white paint space, the space cryogenic heat control coating can obtain the temperature control effect as low as 50K. The coating has the advantages of simple structure, low cost, large-scale production and the like, and can be widely applied to thermal control systems of various spacecraft low-temperature working equipment, such as application scenes of fuel storage, space superconducting devices, low-temperature astronomical telescope observation and the like. The prepared coating has an outstanding radiation refrigeration effect in a ground environment, can obtain a refrigeration effect which is lower than the atmospheric environment by more than 5 ℃, and can be applied to energy conservation and emission reduction of buildings and outdoor industrial equipment.
Drawings
FIG. 1 is a schematic view of the working principle of the high solar spectral reflectivity radiation refrigeration coating of the present invention;
FIG. 2 shows solar spectral reflectance and IR emissivity of a spatial cryogenic coating junction according to the present invention.
Detailed Description
In order to make the objects, technical solutions and effects of the present invention more clear, the present invention is further described in detail by referring to examples below. It should be noted that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.
Example 1
Step one, baF with the thickness of 1mm and the diameter of 2 inches is put in 2 Carrying out acetone ultrasonic cleaning and drying on the transparent crystal, and putting the transparent crystal into a film coating machine for vacuum evaporation of an Ag reflecting film, wherein the thickness of the silver film is 200nm;
step two, the BaF obtained in the step one 2 The Ag crystal is plated with Ni film 50n thick on one side of silver
And step three, taking out the sample subjected to evaporation plating in the step two, cleaning and drying, and testing the ultraviolet-visible-near infrared reflection spectrum and the infrared absorption spectrum respectively, so that the solar absorption ratio of the cryogenic coating prepared by the invention is 0.030, the emissivity is 0.693, and the equilibrium temperature of the sample is 48K. Compared with a traditional cerium glass silvering secondary surface mirror (OSR), the solar absorption ratio of the OSR is 0.06, the emissivity is 0.83, and the heat equilibrium temperature of the OSR under an ideal condition in space is 144K, which is far higher than the equilibrium temperature of the cryogenic coating.
Example 2
Step one, mgF with the thickness of 1mm and the diameter of 2 inches is put into 2 Carrying out acetone ultrasonic cleaning and drying on the transparent crystal, and putting the transparent crystal into a film coating machine for vacuum evaporation of an Ag reflecting film, wherein the thickness of the silver film is 200nm;
step two, mgF obtained in the step one 2 The Ag crystal is coated with a Ni protective film by evaporation on one surface of the silver coating, and the thickness of the nickel film is 50nm;
and step three, taking out the sample subjected to evaporation plating in the step two, cleaning and drying, and testing the ultraviolet-visible-near infrared reflection spectrum and the infrared absorption spectrum respectively, so that the solar absorption ratio of the cryogenic coating prepared by the invention is 0.033, the emissivity is 0.621, and the equilibrium temperature of the sample is 60K.
Example 3
Step one, caF with the thickness of 1mm and the diameter of 2 inches is put in 2 Carrying out acetone ultrasonic cleaning and drying on the transparent crystal, and putting the transparent crystal into a film coating machine for vacuum evaporation of an Ag reflecting film, wherein the thickness of the silver film is 200nm;
step two, the CaF obtained in the step one 2 The Ag crystal is coated with a Ni protective film by evaporation on one surface of the silver coating, and the thickness of the nickel film is 50nm;
and step three, taking out, cleaning and drying the sample evaporated in the step two, and respectively testing the ultraviolet-visible-near infrared reflection spectrum and the infrared absorption spectrum of the sample, so that the solar absorption ratio of the cryogenic coating prepared by the invention is 0.045, the emissivity of the cryogenic coating is 0.570, and the equilibrium temperature of the cryogenic coating is 52K. FIG. 1 is a schematic structural diagram of a cryogenic coating, wherein a surface radiation layer is fluoride crystals, an intermediate layer is a metal reflecting layer, and a back bottom is a nickel protective layer. FIG. 2 is a spectrum of reflectance and emissivity of the coating. It can be seen that the ultraviolet-visible-near infrared heat flow (0.2-2.5 μm) and part of the mid-infrared (CaF) of solar radiation 2 2.5-10 μm) is reflected by the intermediate Ag, low-temperature far infrared and long-wave infrared rays of a temperature-controlled object such as a liquid oxygen storage tank are radiated from the surface fluoride radiation layer, and the back bottom protection layer is used for protecting the oxidation effect of the intermediate metal layer.
And step four, placing the sample obtained in the step three on a spacious outdoor wooden table top, standing for half an hour, and testing by an infrared thermometer or a temperature sensor to find that the coating has excellent radiation refrigeration effect. At an outdoor atmospheric ambient temperature of 7 ℃, the coating surface temperature is only 2 ℃.
Example 4
Step one, adding CaF with the thickness of 1mm and the diameter of 2 inches 2 Carrying out acetone ultrasonic cleaning and drying on the transparent crystal, and putting the transparent crystal into a coating machine for vacuum evaporation coating of an Al reflective film, wherein the thickness of an aluminum film is 200nm;
step two, the CaF obtained in the step one 2 Plating a Ni protective film on one surface of the Al crystal plated with silver by evaporation, wherein the thickness of the nickel film is 50nm;
and step three, taking out the sample subjected to evaporation plating in the step two, cleaning and drying, and testing the ultraviolet-visible-near infrared reflection spectrum and the infrared absorption spectrum respectively, so that the solar absorption ratio of the cryogenic coating prepared by the invention is 0.055, the emissivity is 0.565, and the equilibrium temperature is 55K.
And step four, placing the sample obtained in the step three on an outdoor spacious wooden table top, standing for half an hour, and testing by an infrared thermometer or a temperature sensor to find that the coating has excellent radiation refrigeration effect. When the temperature of the outdoor atmosphere environment is 8 ℃, the surface temperature of the coating is 3.5 ℃.
The foregoing is only a preferred embodiment of the present invention, and it should be noted that modifications can be made by those skilled in the art without departing from the principle of the present invention, and these modifications should also be construed as the protection scope of the present invention.
Claims (4)
1. A space cryogenic thermal control coating is characterized in that the cryogenic thermal control coating is of a three-layer composite structure and comprises a surface radiation layer, a middle reflection layer and a back protection layer; the surface radiation layer of the cryogenic thermal control coating has higher long-wave infrared cut-off frequency; the middle reflecting layer is used for efficiently reflecting solar heat flow; the back surface protection layer is used for protecting the space atomic oxygen oxidation of the coating; the cryogenic heat control coating reflects most of solar radiation heat flow, and simultaneously emits absorbed solar radiation and self heat through self low-temperature radiation heat exchange with the space so as to achieve the purpose of radiating and refrigerating the temperature control target to low temperature;
the surface radiation layer is made of BaF 2 、MgF 2 、CaF 2 One of (1); the middle reflecting layer is made of one or more of Al and Ag; the back protective layer is a metal nickel layer.
2. The spatial cryogenic thermal control coating according to claim 1, wherein the infrared reflection cutoff wavelength of the surface radiation material is between 8 and 12 μm; the middle reflecting layer reflects most of solar heat flow with the wavelength of 0.2um-6 um; the back protective layer is a metal nickel layer to prevent the oxidation erosion of the middle reflecting layer in the space atomic oxygen environment.
3. The preparation method of the space cryogenic thermal control coating according to any one of claims 1 to 2, characterized by comprising the following steps:
step one, baF 2 、MgF 2 、CaF 2 One of the transparent crystals is ultrasonically cleaned and dried by acetone, and then put into a film plating machine for vacuum evaporation of an Ag reflecting film or an Al reflecting film;
step two, evaporating a Ni protective film on the silver-plated surface of the crystal obtained in the step one;
and step three, taking out the sample subjected to vapor deposition in the step two, cleaning and drying, wherein the balance temperature of the prepared cryogenic coating sample is 48K.
4. The method for preparing the spatial cryogenic thermal control coating according to claim 3, wherein the thickness of the vacuum evaporated reflective film in the first step is 200nm; and in the second step, the thickness of the nickel film is 50nm.
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| CN202211164097.0A CN115928020A (en) | 2022-09-23 | 2022-09-23 | Space cryogenic thermal control coating and preparation method thereof |
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| CN202211164097.0A CN115928020A (en) | 2022-09-23 | 2022-09-23 | Space cryogenic thermal control coating and preparation method thereof |
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