Prepared Method And Radiative Properties Of Flexible Thrmochromic Emittance Variable Film

Thermal control device based on thermochromic phoneomenon plays an important role in spacecrafts and satellites thermal management by automatically adjusting its radiative properities in response to large temperature gradients.At present,the thermochromic emittance variable coating of which the substrate is aluminum(Al)or yttria stabilized zirconia(YSL),and the base material is organic resin has the high emissivity adjustable range,but its substrate is rigid material,and it has no flexibility and frivolity.The work which makes the thermochromic emittance variable coating to change from rigidity to flexibility is of great importance to ensure the performance and reliability of small spacecraft.The content of this thesis include the following three parts:(1)Preparation and properties of polyimide polymerPolyimide was prepared by two step process.The precursor polyamic acid was obtained from two anhydride and two amine monomer,and then polyimide was produced by closed loop heating or chemical method.Four polyimides were prepared including PMDA-ODA(PI-1),BAPP-6FDA(PI-2),BAPP-TFB-6FDA(PI-3)and TFB-6FDA(PI-4).To measure the spectral transmittance and reflectance,and to calculate solar absorptance and infrared emissivity of various types of polyimide.In addition,the thermal stability of each sample and measuring the thermal conductivity of the glass transition temperature,partial,density,viscosity,surface roughness and other physical parameters including UV irradiation experiments of fluorinated polyimide are measured,in order to fully understand the characteristics of film.(2)Preparation and properties of theromochromic emittance variable filmNano scale theromochromic powder filler La0.8Sr0.2MnO3 was prepared by sol-gel method and molten salt method.The thermochromic variable emissivity film was prepared by polyimide as based material.The phase structure,rmicromorphology and magnetic properties of the variable emissivity film with different doping share were studied.(3)Characteristics and radiative properties of theromochromic emittance variable filmThe emissivity of theromochromic emittance variable films is measured in the temperature range of 173K?373K.The influences of base material,filler type and filler ratio on the radiation characteristics of the films are analyzed,and the thermal stability,glass transition temperature,density and other physical properties of the film are measured.The results show that in the 173K-373K temperature range,the PI/LSMO thin films prepared by sol-gel method and PI-4 as the base material increase the emissivity by about 0.47.The emissivity of the film is different when the filler ratio is different.The emissivity increase with the increase of the packing ratio and the ratio of 20wt%5 the emissivity is the most adjustable.Packing accounted for 30wt%,the emissivity adjustable range reduces slightly.The lower the infrared transmittance of the substrate is,the smaller the emissivity adjustable range and the higher the overall emissivity of the film.The emissivity of PI/LSMO prepared by PI-1 increases by 0.39,and its emissivity in the high temperature and low temperature segnents increases obviously.