Solid Phase And Molten Salt Method Preparation Of Caesium Tungsten Bronze Nano-powder And Study On The Optical Properties

Building energy consumption occupies about 1/3 of the total energy consumption in China.Nearly 40%building energy consumption is lost through the glass windows,so energy-saving technologies of building glass has been widespread concern.At present,the commonly used energy saving technologies for building glass mainly include radiation-reducing glass,conduction-reducing glass and transparent thermal insulation coating glass.The transparent thermal insulation coating not only has high visible light transmittance and excellent near-infrared shielding performance,but also has the advantages of low cost and environmentally friendly.It is the main development direction of energy-saving technology for building energy saving glass.Tungsten bronze stands out from a variety of transparent thermal insulation coating because of its environmental friendliness and low-cost.The wide-range NIR shielding ability of tungsten bronze should be ascribed to the appearance of small-polaron absorption and a strong LSPR absorption,It is the best heat insulation material at present.The tungsten bronze was preparated by hydrothermal and solvothermal methods.Solvothermal method has the disadvantages of toxic organic solvent,high cost and easy volatilization.The hydrothermal method has the disadvantages of long reaction time.The both methods have the problem of too low yield.The traditional solid state method has the advantages of fast production and high yield.In this work,cesium tungsten bronze?Cs_xWO₃?powder was prepared by solid phase method,The influlence of annealing temperature in solid state method on phase,microstructure and optical property were reseached.In order to further reduce the reaction temperature,Cs_xWO₃powder was prepared by molten salt method.The molten salt not only enhanced mass transport of the Cs_xWO₃ formation reaction and the reaction time was shorted,but also protected Cs_xWO₃ from air oxidization.These merits enabled us to prepare Cs_xWO₃ at a relatively low temperature in air.The reaction mechanism of molten salt method and the influence of powder phase,microstructure and optical properties prepared by this method were investigated.The main contents and results are listed as follows:?1?With cesium tungsten bronze?CsOH·H₂O?as cesium source,tungstic acid?H₂WO₄?as tungsten source,tungsten powder?W?as reducing agent,Cs_xWO₃ nanocrystalline powders were prepared by solid state method.The effect of annealing temperature on nano-powders was studied.The experimental results show that the crystallinity of Cs_xWO₃ is very poor when annealing temperature is 500°C,and when the annealing temperature rises to 600,700,800°C,Cs_xWO₃ has high crystallinity degree.The SEM results show that the size of the product is large at 800°C,which is not conducive to the subsequent treatment processes.Under the condition that the visible light?60%?is almost the same,the best near infrared shielding performance of tungsten bronze prepared at 600°C is the best,and its infrared shileding value is 90%.In summary,the annealing temperature of 600°C is the most suitable temperature for the preparation of tungsten bronze in this paper.?2?Because the solid reaction temperature is too high and the atmosphere is needed.In this work,pure phase Cs_xWO₃ were synthesized at 400°C in air by a molten salt synthesis method.The reaction raw material is the same as the solid phase method,and the molten salt is the mixed salt of LiCl/KCl.The influlence of Cs_xWO₃ on phase,microstructure and optical property was studied.The results showed that the morphology of the products was dominated by nanorods.The TG result showed that from room-temperature to 150°C,the surface adsorbed water was released.Between 150-220°C,the coordination water was lossed.At 345°C,the molten salt Li Cl-KCl begins to melt and accelerates mass transfer of reactants and isolates air.As a result,Cs_xWO₃ can be formed.Optical measurement revealed that the obtained Cs_xWO₃ delivered a visible transmittance of 53.5%and a NIR shielding ability of 94%.