Tungsten Oxide Thermal Control Coating Material

The use of the electrochromic effect of tungsten oxide makes it possible to use it as a thermal control coating material in spacecraft. Miniature aircraft have the problems of fewer use times, fewer heat sources, and smaller volumes. Therefore, a simple and easy-to-use thermal control method is required. Traditional active thermal control technologies, such as thermal control shutters, electric heaters, and heat pipes, add extra weight, volume, electronics, and power consumption. The passive thermal control technology, such as surface coating, phase change materials, and its flexibility, the temperature adjustment accuracy cannot achieve satisfactory results.

There is currently a more feasible solution in this area. One is MEMS shutters. The other is a variable emissivity thermal control coating coated with tungsten oxide electrochromism on the surface of the satellite. Varying the polarity of the voltage applied to the tungsten oxide thermal control coating can alter its optical properties, thereby adjusting the emissivity of the satellite surface, ie controlling the amount of heat radiated to the outside or reflected to the internal device. When the ion implants, it increases its infrared reflectivity. When the ions are extracted, they become transparent to infrared light. When it is in this state, the emissivity of the entire device is the highest.

Because this technology directly depends on the tungsten oxide thermal control coating material itself to achieve emissivity change, no mechanical transmission system is required, light weight, low energy consumption, and simple and reliable. Moreover, the parts that are very sensitive to heat can be directly covered with a tungsten oxide electrochromic film, so that better thermal control can be achieved. Therefore, it has become a research field with great development potential in satellite thermal control coating technology.

At present, mainly NASA in the United States, has conducted more research on the possibility of tungsten oxide electrochromic materials as a variable emissivity thermal control coating. Using thin-film deposition techniques such as magnetron sputtering, tungsten oxide, a typical electrochromic material, was used as a host material. A multi-layer composite tungsten oxide electrochromic functional film was deposited on an Au electrode. The electromagnetic spectrum that the material worked on was tested. At a measured temperature of 300 K, the extremum emissivity’s in the infrared spectral region of 2 to 13.8μm is 0.057 and 0.595, respectively. The change range reached 0.538, and the corresponding change multiple reached 10.4. These performance parameters are already comparable to those of conventional blind thermal control techniques.

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