The Preparation And Properties Of Thermal Control Coatings With Low Absorptivity Emissivity Ratio In Stratospheric Environment

With the integrated development of electronic equipment,the quantity of heat production increases greatly,which is easy to cause the local high temperature and destroy electronic devices.However,passive temperature control mode is adopted by adding thermal control coatings outside the equipment to achieve appropriate temperature of working environment and ensure the operation of the instrument.At present,thermal control coatings are mainly divided into coating-type thermal control coatings and secondary-surface-mirror thermal control coatings.The working principle of thermal control coatings is based on the low absorptivity/emissivity ratio（the ratio of solar absorbance to infrared emissivity）.In addition,the stratospheric environment such as high ozone concentration,ultraviolet radiation and low temperature,are vulnerable to damage equipment components,including coatings and other materials.Therefore,in order to ensure the operational performance and reliability of stratospheric airships,balloons and near-platform,the study of weather resistance under specific conditions has practical significance.In this paper,the preparation,radiation characteristics and weatherability of ultraviolet-high-reflection thermal control coatings and flexible thermal control films have been studied.1.Radiation characteristics of ultraviolet-high-reflection thermal control coatingsThe ultraviolet-high-reflection composite pigments ZnO/SBA-15 and Y₂Ce₂O₇/SBA-15were prepared by high temperature sintering.The effects of blending ratio,sintering temperature and type of pigments on the radiation characteristics of the composite pigments were studied,and the reasons were analyzed by microscopic images and X-ray diffraction images.Besides,coating-type thermal control coatings were prepared with binder and pigments.The influence of curing temperature,type of binder and type of the composite pigments on the radiation characteristics of thermal control coatings were researched.Finally,potassium silicate solution and ZnO/SBA-15 were selected as the binder and pigment to prepare thermal control coating with optimum optical properties.Furthermore,the curing temperature was set at room temperature,and the optimum pigments binder ratio was set at 1:1.In this way,the ultraviolet reflectance,solar absorptivity and infrared emissivity are nearly 100%,0.070,and 0.936,respectively.In addition,the temperature control effect of the thermal control coating was measured by optical irradiation method for practical application.2.Thermal stability and radiation characteristics of SiO₂@FPI/Ag thermal control filmsTaking SiO₂@FPI/Ag flexible thermal control films as the research object,the radiation characteristics of traditional yellow PI film,SiO₂@FPI film before and after silver plating and films with different SiO₂ content were compared,and the initial degradation temperature,specific heat capacity,thermal stability,glass transition temperature and density of the films were measured and studied.Finally,the 3wt%SiO₂@FPI/Ag film has the best radiation characteristics with the absorptivity emissivity ratio of 0.077,the initial degradation temperature of 490^oC,and the glass transition temperature of 194^oC,respectively.In addition,the effects of metal layer properties,film thickness and microsphere content on the radiation characteristics of SiO₂@FPI/Ag films were studied by an optical calculation software.It was found that the metal layer mainly affected solar absorptivity and thickness of film influenced infrared emissivity.Microspheres might cause Fr?hlich resonance,which can increase wave path and extinction coefficient.3.Weather resistance and common physical properties of thermal control coatings and filmsThe weatherability of thermal control coatings and thermal control films were tested,including ozone aging,high and low temperature aging,brine aging and outdoor aging exams.It was found that the former had weatherability,while the latter had an increase in absorptivity/emissivity ratio due to oxidation.In addition,common physical properties have been tested,such as adhesion,impact resistance,flexibility,bulk resistivity and so on,and they had been proved to have excellent performance.Through the theoretical calculation of stratospheric environment,it was found that the thermal control coatings with low absorptivity/emissivity ratio could reduce the temperature of electronic equipment by tens of degrees,and had a very effective temperature control effect.