Study On Hydrothermal Preparation And Properties Of Thermal Induced Phase Transition VO₂Powder

VO2is a kind of metallic oxide which has distinct characteristics of phasetransition. It can undergo a phase transition from metal phase to semiconductor phaseaccompanied a sudden change of electrical property and optical property. VO2coatedglass which has the thermochromic properties can be made by compounding finegrained VO2powder and organic polymer. This coating can be applied to glass ofhouse to decrease the energy consumption of buildings. VO2(M) powder was preparedby hydrothermal-calcinations method firstly. Then the phase transition temperature isreduced by doping w element and VO2coated glass was prepared by VO2(M) powderand silicone acrylic emulsion. Main research contents and solutions are shown asfollows:1、 VO2(B) powder was prepared with The molar ratio of NH4VO3andC2H2O4·2H2O as raw material by hydrothermal method. The influence of reactantsmolar ratio, reaction temperature and time on morphology, crystal structure and sizeof VO2(M) powder were investigated to obtain high performance VO2(M) powder.XRD and SEM analysis show that NH4VO3and C2H2O4·2H2O has great effect onmorphology, crystal structure and size of VO2(B) powder while hydrothermaltemperature has a certain effect on morphology and size of VO2(B) powder andhydrothermal time has a little effect on morphology and size of VO2(B) powder. To study these hydrothermal conditions is to provide support for preparing VO2(M)powder which has a specific morphology and size.2、VO2(B) powder was as precursor which was prepared when the ratio ofNH4VO3and C2H2O4·2H2O is1:1.5,the hydrothermal temperature is200℃and thehydrothermal time is36h calcined at400℃,500℃,600℃and700℃. The XRD, DSCand SEM analysis show that VO2(B) was completely transformed to VO2(M) whenthe calcinations temperature is500℃, and with the increasing of the calcinationstemperature, the VO2(M) size is greater, the latent heat of phase change is greater.3、XRD,DSC and SEM analysis show that doping (NH4)10H2(W2O7)6has thelargest effect on phase transition temperature when doping (NH4)10H2(W2O7)6,Na2WO4·2H2O and H2WO4. And the phase transition temperature of VO2(M) wasreduced to42.1℃when doping4%(NH4)10H2(W2O7)6. The morphology of(NH4)10H2(W2O7)6-doped VO2(M) is spherical and rod while size is100nm-500nm.4、Organic VO2film was prepared by compounding VO2(M) powder made at600℃calcinations temperature and silicone acrylic emulsion. DSC and UV-Vis-IRspectrophotometric test analysis show that VO2(M) glass coating has goodcharacteristics of phase transition and good film forming property. Visible lighttransmittance is45.02%while infrared transmittance is52.24%.Heat insulationtemperature difference test show that VO2(M) glass coating not only has certain effecton heat insulation but also has a sudden change on infrared transmittance in theprocess of phase transition.