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CN-115836232-B - Multilayer coating for optical solar reflectors

CN115836232BCN 115836232 BCN115836232 BCN 115836232BCN-115836232-B

Abstract

The invention relates to a product comprising a substrate (9) and a multilayer coating (1) for a thermally controlled surface (6), the multilayer coating comprising a first inner layer (2) for deposition on said surface, a second intermediate layer (3) applied on said first inner layer (2), and a third outer layer (4) applied on said second intermediate layer (3), wherein said first inner layer (2) comprises co-dispersion of electrically conductive nanoparticles and dielectric nanoparticles, wherein the volume fraction of electrically conductive nanoparticles increases along the thickness of said first inner layer away from said second intermediate layer (3), said second intermediate layer comprises a plurality of layers, wherein at least one dielectric material layer (3 ') transparent in visible light and having a high refractive index in visible light alternates with at least one dielectric material layer (3 ') transparent in visible light and having a low refractive index in visible light, and wherein each dielectric material layer having a high refractive index in visible light and a refractive index in visible light is made of less than 10 x 10 cm per adjacent dielectric material layer (3 ') transparent in visible light. An optical solar reflector comprising the product is also provided.

Inventors

  • Milco Simeoni
  • Alexandro Urbani
  • Sandro Mengari

Assignees

  • 列奥纳多股份公司

Dates

Publication Date
20260512
Application Date
20210923
Priority Date
20200923

Claims (15)

  1. 1. An optical solar reflector (5) comprising a substrate (9) and a multilayer coating (1) for thermally controlling a surface (6) of the substrate (9), the multilayer coating (1) comprising a first inner layer (2) for deposition on the surface, a second intermediate layer (3) applied on the first inner layer (2) and a third outer layer (4) applied on the second intermediate layer (3), wherein, -The first inner layer (2) comprises co-dispersion of conductive and dielectric nanoparticles, wherein the volume fraction of conductive nanoparticles increases along the thickness of the first inner layer away from the second intermediate layer (3), and wherein the first inner layer (2) has a hemispherical emissivity of between 0.5 and 0.8; The second intermediate layer comprises a plurality of layers, wherein at least one layer (3 ') of dielectric material transparent in visible light and having a high refractive index in visible light alternates with at least one layer (3') of dielectric material transparent in visible light and having a low refractive index in visible light, and wherein each layer (3 ') of dielectric material transparent in visible light and having a high refractive index in visible light has a refractive index higher than the refractive index of each adjacent layer (3') of dielectric material transparent in visible light and having a low refractive index in visible light, and -The third outer layer (4) is made of a conductive oxide having a resistivity less than 1 x 10 -3 ohm x cm, transparent in visible light.
  2. 2. An optical solar reflector (5) according to claim 1, characterized in that the conductive nanoparticles are in a material selected from the group consisting of aluminum, al x O, tiN, indium tin oxide, zinc aluminum oxide, steel, ti, mo, rare earths, transition metals and combinations thereof.
  3. 3. The optical solar reflector (5) according to claim 1, characterized in that the dielectric nanoparticles are in a material selected from the group consisting of Al 2 O 3 、Al、SiO 2 、Ta 2 O 5 、ZrO 2 、Nb 2 O 5 、Y 2 O 3 、TiO 2 、AlN and combinations thereof.
  4. 4. An optical solar reflector (5) according to claim 1, characterized in that the dielectric nanoparticles are made of Al 2 O 3 and the conductive nanoparticles are made of Al x O or Al.
  5. 5. Optical solar reflector (5) according to claim 1, characterized in that the first inner layer (2) has a thickness between 1 and 4 micrometers.
  6. 6. An optical solar reflector (5) according to claim 1, characterized in that the second intermediate layer (3) has a thickness between 5 and 15 micrometers.
  7. 7. Optical solar reflector (5) according to claim 1, characterized in that the second intermediate layer (3) comprises 45 to 150 dielectric layers transparent in visible light.
  8. 8. Optical solar reflector (5) according to claim 1, characterized in that the second intermediate layer (3) is made of a material selected from the group consisting of SiO 2 、MgF 2 、Ta 2 O 5 、ZrO 2 、TiO 2 、Nb 2 O 5 、Y 2 O 3 、YF 3 and mixtures thereof.
  9. 9. Optical solar reflector (5) according to claim 1, characterized in that the difference between the refractive index of the dielectric material layer (3') transparent in visible light and having a high refractive index in visible light and the refractive index of the dielectric material layer (3 ") transparent in visible light and having a low refractive index in visible light is at least 0.5.
  10. 10. Optical solar reflector (5) according to claim 1, characterized in that the dielectric material layer (3') transparent in visible light and having a high refractive index in visible light has a refractive index in visible light of 1.6 to 2.5.
  11. 11. Optical solar reflector (5) according to claim 1, characterized in that the dielectric material layer (3 ") transparent in visible light and having a low refractive index in visible light has a refractive index in visible light of 1.2 to 1.7.
  12. 12. An optical solar reflector (5) according to claim 1, characterized in that the third outer layer (4) is made of a material selected from the group consisting of indium tin oxide, aluminum oxide doped zinc oxide, cadmium oxide and its alloys, zinc oxide and its alloys, tin oxide and its alloys, antimony and fluorine doped tin oxide.
  13. 13. An optical solar reflector (5) according to claim 1, characterized in that the third outer layer (4) has a surface resistivity between 10 3 and 10 6 ohm/square.
  14. 14. Optical solar reflector (5) according to claim 1, characterized in that the substrate (9) is a flexible substrate (9).
  15. 15. Optical solar reflector (5) according to claim 14, characterized in that the flexible substrate (9) is a metal film, a polymer film, a composite material or a flexible glass.

Description

Multilayer coating for optical solar reflectors Cross Reference to Related Applications This patent application claims priority from italian patent application number 102020000022435 filed on 9/23 in 2020, the entire disclosure of which is incorporated herein by reference. Technical Field The present invention relates generally to a multilayer coating having thermo-optic properties. The present invention finds advantageous, although not exclusive, application in the field of space, for example in the manufacture of coatings for radiator panels or parts of spacecraft comprising antennas or other external structures that are required to mitigate temperature surges. In particular, the invention finds advantageous, although not exclusive, application in the manufacture of optical solar reflectors. Background The thermal control system of the satellite comprises one or more radiator panels having a space-facing surface designed to regulate the heat exchanged between the spacecraft or satellite and the external environment. More specifically, since the thermal control system is designed primarily to prevent overheating of the spacecraft during the thermal phase, the surface of the radiator panel must reflect solar radiation and radiatively dissipate heat generated on the spacecraft. These requirements are adjusted based on two thermo-optical parameters, solar absorptance α and hemispherical emittance ε. On the radiator panel surface, the solar absorptance α must be as low as possible (typically required to be +.0.20), the hemispherical emittance ε must be as high as possible (typically required to be +.0.80), and both values must remain constant during the life cycle of the satellite (15 years for a telecommunication satellite in geosynchronous orbit). In addition, the surface of the radiator panel must be able to dissipate to collect charges generated by interactions with electrons, protons and ionized particles that could otherwise cause electrostatic discharge and damage the instrumentation on the spacecraft. An economical way to control the thermo-optic properties of a surface is to coat the panel with a white paint composed of inorganic particles incorporated into an organic matrix. However, white paints have poor static dissipative properties and often age. In particular, α increases gradually due to the interaction of the organic matrix with UV radiation and particles. In addition, adhesion to the substrate may decrease due to prolonged exposure to radiation or rapid increases in temperature. A better way to control the surface properties is to cover the radiator panel with an Optical Solar Reflector (OSR), two types of OSR are available on the market today, quartz OSR and a second flexible surface mirror (SSM). The quartz OSR is a small quartz tile of about 40 x 40mm, about 100 to 200 microns thick, coated with a silver metal mirror protected by Inconel on the side facing the radiator. The quartz substrate provides a high epsilon value and the metal layer provides a low alpha value. The outward facing surface is coated with a thin layer of transparent and conductive oxide to allow charge dissipation. The tile is glued to the panel using a manually or robotically applied conductive resin. Quartz OSRs show excellent thermo-optic properties and durability in space environments, but have high procurement, application and emission costs, are prone to cracking and can only be applied to planar radiators. The flexible SSM is based on the same architecture and operating principles as the quartz OSR, but the quartz substrate is replaced by a transparent sheet of Fluorinated Ethylene Polymer (FEP). Flexible SSMs are relatively inexpensive and easy to handle and apply on flat or curved panels, but they tend to age quite rapidly due to the interaction of FEP films with the space environment and especially with UV radiation (which makes the film brittle and opaque) and with atomic oxygen (which attacks the film). Attempts to improve durability by adding a UV filter to the outward facing surface of the film have been only partially successful. Poor adhesion of the inorganic layer on FEP is one of the possible reasons. Typically, flexible SSM is not recommended for space missions longer than 5 to 6 years. Disclosure of Invention Thus, there is a need in the art for a new class of coatings that combine the thermo-optic properties and space durability of quartz OSRs with the ease of use and low cost of flexible SSMs. It is therefore an object of the present invention to provide a new coating having improved thermo-optical properties and space durability without the disadvantages of the known coatings. This object is achieved by the invention in that the invention relates to a multilayer coating according to claim 1, a product according to claim 13 and an optical solar reflector according to claim 14. In particular, according to a first aspect of the present invention, there is provided a multilayer coating for thermal con