Preparation Of Cs_xWO₃ Nanoparticles And Cs_xWO₃/SiO₂ Composite Coatings And Their Near-infrared Shielding Performance

Window glass is the main channel for energy exchange between buildings and environment,which is the main part of building energy consumption.The transparent thermal insulation material can shield the radiation of near infrared light,meanwhile maintain the transmittance of visible light,thereby reducing solar absorption,effectively reducing the energy consumption of air conditioning and realizing the purpose of building energy conservation.Currently,among the widely known near-infrared shielding nanomaterials,precious metal（Ag,Au,etc.）particles have low transmittance in the visible region.The rare earth hexaboride（LaB₆,PrB₆,NdB₆）possesses a great hardness and must be ground during the synthesis process,and semiconductor oxide（ATO,ITO,etc.）is relatively stable as well as has a high transmittance in the visible region,but they can only effectively shield part of the near-infrared light（wavelength greater than 1500 nm）.While tungsten bronze(M_xWO₃,M for Na⁺,K⁺,Rb⁺,Cs⁺and NH⁴⁺)exhibites a superior near-infrared shielding performance as it not only has a high visible light transmittance,but also can shiled the near infrared light with wavelength greater than 1000 nm.In this thesis,the influences of reaction solvent ratio,reaction temperature and Cs/W ratio during the synthesis of cesium tungsten bronze nanoparticles by solvent thermal method were studied.On the basis of determining the optimal reaction conditions,an attempt was made to prepare double-cation-doped Rb_xCs_yWO₃ nanoparticles,and the effects of different Rb/Cs molar ratios on the products were explored.In the end,this thesis used sol-gel method to prepare the cesium tungsten bronze/silica gel transparent insulation composite coating,and finally optimized the best preparation technology.The main research projects are listed follows:（1）In the second chapter,Cs_xWO₃ nanoparticles were prepared by solvent thermal method with WCl₆ and CsOH?H₂O as raw material,ethanol and acetic acid as reaction solvent.And then the effects of reaction solvent ratio,reaction temperature and Cs/W ratio on the composition,microstructure and near-infrared shielding performance were investigated.Results showed that when the ratio of solvent was 20%acetic acid and 80%ethanol,the reaction temperature was 220℃,Cs/W ratio is 0.6,the obtained product is a regular shaped rod of about 50 nm,giving rise to the best near-infrared shielding performance,with the visible transmittance of 63%and the near-infrared light transmittance of 5.8%.（2）Rb_xCs_yWO₃ nanoparticles with double cation doping were prepared by solvent thermal method with WCl₆,CsOH?H₂O and RbOH?xH₂O as raw material,ethanol and acetic acid as reaction solvent.The effects of different Rb/Cs mole ratios on Rb_xCs_yWO₃were investigated.It was found that mix valence states of W⁵⁺and W⁶⁺were present at different Rb/Cs molar ratio,and the Rb_xCs_yWO₃ nanocrystals were all nano-rod structures.The change of Rb/Cs mole ratio does not affect the overall trend of sample transmittance,which increases first,and then decreases,finally presented slightly upward trend.When Rb/Cs=2:1,the near-infrared shielding performance of RbxCsyWO3 was the best(T_visis max=71.0%,TNIR min=7.8%).（3）Silica sol was prepared by sol-gel method with TEOS as raw material,ethanol as reaction solvent and dilute hydrochloric acid as catalyst.Cesium tungsten bronze dispersion was then mixed with silica sol,and the cesium tungsten bronze/silica composite film was gained from spin coating on glass substrate and subsequent sintering.The cesium tungsten bronze/silica composite film was smooth,compact,with less defects and higher flatness.The preparation process of composite coating was that the coating was a two-spin film,the coating thickness was about 4μm,the mass ratio of Cs_xWO₃/SiO₂ is 10%.In this way,the visible light transmittance of the film was 68%and the penetration rate of near infrared light was 13%.