Preparation And Characterization Of Low Valence Vanadium Oxide Nanopowder

As the leading science and technology of the21st century, nanotechnology will bring an unprecedented new industrial revolution. Nanomaterials have special properties that many common materials do not available, such as small size, large surface area, excellent chemical and catalytic activity and special properties such as electrical, thermal, magnetic and mechanical, which making them having been widely used in various fields. Vanadium oxide is a typical kind of nanomaterials, which exhibits excellent physical and chemical properties in the optical, electrical, magnetic, etc. Some vanadium oxide possess phase transition characteristics, the physical properties such as optics, electricity and magnetism will be different before and after the phase transition. It can change the phase transition temperature after doping. Therefore it is widely applied in intelligent temperature control material, thermistor devices, etc. However, preparation technology of vanadium oxide thin films is very mature, but the vanadium oxide powder preparation is still in research stage. In order to expand its application range, we need select the appropriate doping source to change the phase transition temperature. In this article, the hydrothermal method with different reducing agent is used to prepare Vanadium oxides with different valences, the preparation and properties of VO2and doped VO2are mainly studied. Besides, the preparation of V2O3and V3O7·H2O is also researched. The main contents and conclusions are as follows:(1) VO2powder has been prepared with double reduction of oxalic acid and ethanol by hydrothermal method. By XRD, SEM, DSC, EDX and other test to study the influence of hydrothermal time, hydrothermal temperature and reductant species to crystal structure and morphology of the product, and the phase transition temperature of VO2powder with different sizes were compared. The results showed that, with the increase of reaction time, the valence state of product transfers from V+5to V+4, and the mechanism of the reduction process is clearly known; By change the hydrothermal temperature, it is found that the high temperature is benefit for crystal growth; crystal stucture of the product obtained by double reduction agent is better than single agent. Finally, the DSC analysis of VO2powder with different sizes is compared, the phase transition temperature of small size is lower than the large size, which is due to dimensional effect of nanometer materials.(2) Tungsten doped VO2powder was obtained by the optimum conditions of the preparation of VO2powders, dopant source is the tungsten compounds. By XRD, SEM and DSC test to study the influence of the content of doped tungsten on the crystal structure, morphology and the phase transition temperature of VO2. The results showed that, the amount of doped tungsten have no obvious effect on crystal structure and morphology. The crystal structure are still VO2and the position of2θ peak deviate slightly after doping tungsten, which attribute to that the atom of tungsten inject into the crystal lattice of VO2by replacing partial atom of vanadium. Most of their morphologies is rod. However, the amount of doped tungsten have great effect on the phase transition temperature of VO2. For example, the phase transition temperature drops to51℃when1.0%tungsten is doped. When the doping amount is further increased to2.0%, the phase transition temperature has dropped to about30℃. Therefore, we can reduce the phase transition temperature of VO2effectively by changing the amount of doped tungsten.(3) By hydrothermal method with tartaric acid and boric acid as the reductant, V2O3microsphere powder and ViO7·H2O nanoparticles were prepared respectively. Product performance was analyzed through different test. The results showed that, V2O3has morphology of micro spherical in2-3μm. DSC showed that the secondary phase transition of low temperature paramagnetic metal phase (PM) to the high-temperature paramagnetic metal phase (PM1) will happen at140℃. This is consistent with the literature. By one step hydrothermal method with use of boric acid as a reducing agent, V3O7·H2O nanoparticles beyond20μm in length, below50nm in width was prepared. It opens up new avenues for the preparation of different valence vanadium oxides.