| Cesium tungsten bronze(CsxWO3),belonging to one kind of Tungsten Bronzes(TB),is a non-stoichiometric narrow band gap semiconductor material.The early studies found it had the electronic/ion conductivity and low-temperature superconductivity.In recent years,the studies showed that the cesium tungsten bronze(CsxWO3)film had good near infrared light shielding properties and high visible light transmittance,which are expected to be used as insulating window glass material in the building or car field,with a very attractive prospect.The purpose of this paper is to find a new simple and low-cost method for preparing CsxWO3 powders.The effects of different preparing methods and process conditions on the microstructure and properties have been.investigated.The micro structure,morphology,particle size and specific surface area have been characterized by XRD,SEM,laser particle size analyzer and BET instrument.The light absorption,near-infrared shielding properties and photochromatism performance have been investigated by the ultraviolet-visible spectrophotometer.Additionally.the heat insulation of the CsxWO3 films has been tested by using homemade heat insulation equipment.The results indicate that the crystal structure of CsxWO3 powders,prepared by precipitation method in ethanol solution using Na2WO4·2H2O and CsCl as raw materials,are not obvious and there is a variety of unknown crystalline phase diffraction peak.The diffuse reflectance absorption spectra of the powder show that its absorption in the near infrared are very weak,which are similar with that of tungsten oxide powder,and the near infrared absorption performance is not apparent.The near infrared absorption performance for the powder prepared by hydrothermal method using the same raw material is also not obvious,with the biggest absorbance is 0.8 at 1100 nm wavelength.Using sodium tungstate dihydrate and cesium carbonate as raw materials,cesium tungsten bronze(CsxWO3)powders were synthesized using citric acid as the organic inducer by hydrothermal method.The powder crystal diffraction peak become more obvious,with the miscellaneous peak disappearing.The diffuse reflectance spectra showed that are the powders showed strong near-infrared absorption,and the film showed good near-infrared shielding properties.In addition,after UV irradiation,the powders showed good photochromic properties and the near-infrared shielding properties were further improved.Especially,for the CsxWO3 samples prepared in the precursor with higher concentration of citric acid,the improvement of near-infrared shielding by UV irradiation was more obvious,and the heat insulation test showed that the film had good heat insulation performance.It was also found that the structure and near infrared absorption performance of CsxWO3 powder were improved with the extension of reaction time and increasing of citric acid concentration in the precursor.The crystalline structure of the as-prepared CsxWO3 powder is hexagonal tungsten bronze.The CsxWO3 powders,synthesized by hydrothermal reaction for 3d at 190? in the precursor with citric acid concentration 1.10 mol/L,exhibited filament and needles morphology,with the average minimum particle size 185nm and specific surface area 41.17m2/g.The synthesized powders showed remarkable near-infrared absorption,with the absorbance 1.96 at 1100nm wavelength.The transmittance spectra of the films showed most remarkable near infrared shielding,with 13?18%transmittance difference between the highest visible light transmittance and the lowest near infrared transmittance at 1100nm wavelength,and the transmittance difference can attain to 26%after UV irradiation.The films prepared from powders after heat-treatment in N,for 2h at 500? showed good near infrared shielding properties,with a 33%transmittance difference between the highest visible light transmittance and the lowest near infrared transmittance at 1100nm,and the heat insulation temperature difference can attain to 21?. |
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