The Preparation And Application Research Of Magnesium Phosphite Daytime Radiative Cooling Materials

Radiative cooling,as a new refrigeration mode could transmit heat to the outer space in the form of infrared ray and provided with advantages include zero energy consumption and mitigating the heat island effect,with compare to traditional air conditioning.Generally speaking,as the temperature of objects grows by the solar irradiation in the daytime,it will be of great significance to achieve daytime radiative cooling,which means that the radiative cooling materials should be provided with high solar spectrum reflectance and high emittance in the range of atmospheric window.This study is based on synthesizing magnesium phosphite powders hydrothermally with high reflectance and mid-infrared emittance,further improved the properties of the powder materials by coating the powder particles in the method of precipitation.And we directly fabricated functional film by compositing the powders with polymer in the method of electrospinning technology.The main work and results are as fallows:(1)We synthesized magnesium phosphite powders hydrothermally with high reflectance and mid-infrared emittance,and two types of magnesium phosphite,Mg(HPO3)H2O and Mg11(HPO3)8(OH)6 with various morphologies such as flake,urchin-like and flower-like were obtained by controlling reaction conditions(the p H value of the solution).The growth mechanism of the crystals were studied with reference to the crystallographic parameters and microstructures and the optimal reaction condition was decided;(2)Si O2 were coated on the surface of submicron particles through precipitation method,and when the concentration of Na2 Si O3 was 0.1mol/L,the reflectance of the submicron Mg11(HPO3)8(OH)6 was increased from 97.59% to 98.81%,the emittance was raised from 0.91 to 0.93.The powder materials were fabricated into a coating and the test results indicated that the temperature of the coating was 3~5℃ in the daytime and 8℃ at night below ambient air,respectively;(3)The submicron Mg11(HPO3)8(OH)6 particles were mixed in the PVDF(Poly(vinylidene fluoride))solution and then e-spun into high-performance films consist of polymer fibers.When the mass fraction of the powder in the film was 5%,the polymer film composited inorganic powder with R=99.18% in the 300-2500 nm range,ε=0.89 in the 8~13μm range was fabricated.The cooling test results shown that the temperature of the coating was 2~4℃ in the daytime and 8.5℃ at night below ambient air,respectively.And the daytime radiative cooling power was 70.4W/m2.Besides,the combination of inorganic and polymer materials is a new idea to expand the application of radiative cooling.