Preparation And Properties Of Thermostat Transparent Insulation Coating

Thermochromic vanadium dioxide VO2exhibits a semi-conducting to metallic phasetransition at68℃，involving great variations in optical transmittance of near infrared. Withthe social attention to energy-saving and environmental protection, higher requirements havebeen put forward tothe transparent and heat insulating performance of the glass for building.Being mixed VO2powders with organicsilicone-acrylicemulsion, transparent and thermalinsulative film with "smart thermostat" effect wasprepared by coating on the glass. The phasetransition temperature of VO2powder is on the high side relative to the ambient temperature,the VO2films was optimized with a series of methods, by contrast with ATO (antimony tinoxide) transparent insulation films.The primary contents, methods and results are asfollowing:VOSO4as raw material，pure VO2powder was prepared by the chemical liquidprecipitation for VO(OH)2precursorfollowing by segmentedheat treatment. The morphology,purity and phase transition temperature were characterized with SEM, XRD and DSC. Theresults show thatVO2powder was pure and its phase transition temperature was69.7℃. Thepowder was rough with broad distribution around5-10μm, which is contributed to the crystalgrowth and reconstruction in calcinations process.The phase transition temperature of VO2was reduced greatly by using Na2WO4asdopant. The decreasing rate along with the doping ratio of tungsten is around27.4℃/1at%.When the doping concentration of tungsten was raised to2%, the phase transition temperatureis reduced to14.9℃as well as the phase change enthalpywasalso linearly decreased at thesame time. The value was decreased14.35J/g as doping1at%Na2WO4. High performance nano-SiO2aerogel which the low thermal conductivity is0.02W/(m·K)and the holes size is around5~50nm is prepared by rapid and one-step process. The VO2powder was obtained via calcination under800℃after blended VO(OH)2precursor withSiO2aerogel in different proportions. The SEM result showed that the particle size of VO2significantly reduced to500-1000nm, while the DSC and XRD exhibited that SiO2aerogelhad negligible influence to properties of VO2powder.The transparent and thermal insulative coating with smart thermaostat properties wasprepared bythe mixtureof the refined powderof W-doped VO2and silicon-acrylic emulsion byconstrast to the coating with ATO powder. The two kinds of functional films were obtainedby using wire bar coater in coating on glass.94.35%of the infrared radiation was blockedwhile the visual light transmittance was44.27%for the film of nano ATO (ratio to emulsion1:5). These indicated the as-prepared nano ATO coated glass has high transmittance of visuallight and heat insulative performance. The heating rate of radiant absorption plate coveringwith VO2(Phase transition temperature38.1℃) film exhibited a decrease of21.1%comparedto that of blank glass, which is measured with self-made device. The results indicated the VO2coating gave feasible way to achieve the smart glass with thermaostat property.