Preparation Of ZnO@ZIF-8 Composite Coating And Research For Thermal Control Performance

The low-absorption white thermal control coating plays an important part in the spacecraft thermal control system,which can effectively achieve temperature-control on the outer surface of the spacecraft.The organic white thermal control coating with Zn O as the pigment is one of the most commonly used low-absorption thermal control coating,which possesses high solar reflectance and high infrared thermal emissivity.With the continuous development of Chinese aerospace,higher requirements are placed on the optical performance of thermal control coatings,and it is essential to further improving the solar reflectance and infrared thermal emittance of the coating.The polyhedral Zn O@ZIF-8 nanoparticles are designed as the modified pigments,combined with the high emittance characteristic of SiO₂ particles.The SiO₂-Zn O@ZIF-8 composite thermal control coating with excellent properties has been fabricated.It could provide theoretical and technical support for the development of novel thermal control coating.The Zn O@ZIF-8 core-shell particles are successfully prepared by liquid phase coordination assembly with Zn O as the zinc source and 2-methylimidazole as the ligand,and then fabricated the organic thermal control coating with methyl silicone resin.The morphology,structure,solar reflectance and thermal emittance of the coating were explored through XRD,SEM,TEM and FTIR characterization methods.The results showed that the solar reflectance of the Zn O@ZIF-8 thermal control coating is 90.8% and the infrared thermal emittance of the coating is 95.3% after modification.Polyhedralscattering mechanism of Zn O@ZIF-8 nanoparticles,porous scattering mechanism of coating and the vibrations of the functional groups well explain the performance of the coating.The thermal control performance of Zn O@ZIF-8 white coating was evaluated,and the result of infrared thermal imaging shows that under the light intensity of 1000 W/m²,the temperature of the coating could be reduced by more than 7 ℃ contrast with the substrate.SiO₂-Zn O@ZIF-8 composite white thermal control coating was prepared by magnetron sputtering SiO₂,spin-coating SiO₂ microspheres,spraying SiO₂ microspheres,respectively.The infrared thermal emittance of the coating has been further improved,and the particle size of the SiO₂ microspheres has been optimized through FDTD Solutions.The result shows that the SiO₂ microsphere with diameter of 8 μm has the highest scattering efficiency for infrared light,and further explain the enhancement mechanism of SiO₂ compound to the thermal emittance of the coating.In addition,the patterning surface of the coating is designed.With the assist of 3D printing for the predesigned patterning templates,the patterning array composed of SiO₂ microspheres could be printed on the coating surface.The theoretical cooling power of SiO₂-Zn O@ZIF-8 coating was evaluated.The result demonstrates that the coating exhibits the cooling power of 31.5 W/m² under the certain condition.The polyhedral Zn O@ZIF-8 nanoparticle pigment and the design of the SiO₂ patterned surface for coating provide a new path for developing of high-performance thermal control coating with low-absorption and high thermal emittance.