Preparation And Properties Of Vanadium Oxide Powder Based On Surface Modification

Vanadium dioxide(VO₂)has been extensively studied as a material with metal-insulating phase transition characteristics.In this paper,the high latent heat VO₂(M)powder was produced by the two-step process with surfactant polyvinylpyrrolidone(PVP).Through X-ray diffraction(XRD),X-ray electron spectroscopy(XPS),Raman Spectroscopy(Raman),Scanning Electron Microscope(SEM),Differential Scanning Calorimeter(DSC),Thermogravimetric Analysis(TGA),Fourier Transform Infrared Spectroscopy(FTIR)and other characterization to study phase composition,microscopic morphology,phase transition and the mechanism of PVP on VO₂ powder,and we use superconducting quantum interferometer to explore the magnetic refrigeration performance of VO₂.The main conclusions are as follows:(1)To study the effect of adding PVP before hydrothermal reaction on the microstructure and performance of VO₂ powder by the two-step method.With the increase of PVP,the M phase VO₂ powder becomes purer.PVP is beneficial to the growth of VO₂(M)powder,and the grain size increases with the increase of the PVP,up to 2um.The crystallinity of VO₂(M)powder modified by PVP is higher,and the latent heat becomes higher,up to 54.92J/g,it closes to the theoretical value.The magnetic entropy change of VO₂(M)powder modified by PVP is 7 times more than unmodified VO₂(M)powder.(2)To Study the effect of adding PVP after hydrothermal reaction on the microstructure and performance of VO₂ powder by the two-step method.With the increase of PVP,VO₂(M)powder becomes purer and larger,but it is less than the VO₂(M)powder made by adding PVP before hydrothermal.And the latent heat of VO₂(M)powder also increases with the increase of the content of PVP,the maximum can be 48.46J/g,which is less than the VO₂(M)powder made by adding PVP before hydrothermal.In addition,PVP is beneficial to made the VO₂(M)powder before or after the hydrothermal reaction,but the VO₂(M)powder prepared by adding the surfactant PVP before the hydrothermal reaction has better performance.(3)As a comparison,the influence of annealing on microstructure and performance of the PVP modified VO₂(M)nanopowder.Unlike the high latent heat VO₂ powder by the two-step method,the prepared surface-modified VO₂(M)powder is not pure,there are more V₆O₁₃ and V₂O₃,and the particle size of the prepared powder is very small,and the phase change performance is much lower than the high latent heat VO₂(M) powder.