Preparation And Study On Infrared Emissivity And Thermochromic Properties Of Zn_1-xCo_xO

ZnO materials have broad application prospect in many fields such as aerospace aviation due to the low light absorbance and high radiation dispersion in the visible regio.Co is a transition metal,with multiple shell structures and variable oxidation state.It has high solubility limit in ZnO due to the similar ionic radius with Zn²⁺atom and Co-doped ZnO can regulate and control many properties of ZnO.In the past several years,many studies referred to Co-doped ZnO have focused on the magnetic properties.The properties of variable emissivity and thermochromic,however,are neglected.The doping of the Co element can change the color change of Zinc Oxide by changing the energy level structure,and can also change the emissivity of Zinc Oxide.In this paper,green Zn_1-xCo_xO nanopowders were synthesized via solid-state reaction.The properties characterization was investigated by X-ray diffraction?XRD?,scanning electron microscopy?SEM?,energy dispersive spectroscopy?EDS?,X-ray photoelectron spectroscopy?XPS?,UV-visible absorption spectroscopy,Raman spectroscopy and IR-2dual-band infrared emissometer,respectively.The obtained researching works and results are as follow:?1?The color and infrared emissivity of pure ZnO was investigated.The results show that the color of the material is related to the absorption spectrum.Pure ZnO is white because it does not absorb visible light.It was found that the color of pure crystalline ZnO can change from white to yellow at high temperature.The decrease of optical energy band gap is very beneficial to thermochromism properties.After calcination the emissivity values are decreased.?2?the sintering temperature have an important impact on crystallite sizes,lattice parameters and microstructure.The attained particle size has increased with the increasing of the calcination temperature.The proper calcination temperature can improve crystalline quality.The best thermochromism properties can be achieved at the calcination temperature of 1000?.In addition,the changing rates of infrared emissivity has increased with the increase of annealing temperature.?3?The doping concentration of Zn_1-xCo_xO nanopowders have no impact on microstructure and it should be less than 5%,otherwise the impurity phase will be Precipitation.The best thermochromism properties can be achieved at the doping concentration between 1%and 5%.The changing rates of infrared emissivity has increased with the increase of doping concentration.?4?The infrared emissivity of samples annealed in N₂ is higher than that of annealed in air.When the samples annealed in air,the changing rates of infrared emissivity is larger than that of annealed in N₂.?5?The annealing time plays an important role in the technical process of morphology-controlled synthesis.The best properties of variable emissivity and thermochromiccan be achieved at the annealing time between 15h and 20h.