Preparation And Characterization Of Phase Change Materials VO₂ And V₂O₃

Since the metal-semiconductor phase transition was submitted, the material with the characteristics of this kind of transformation has grown up to be a hot research topic in materials science. The most noteworthy is the vanadium oxide in these phase change materials, especially VO2 and V₂O₃. They are the most typical "metal semiconductor" phase change material. With the change of temperature, the atomic arrangement of VO2 and V₂O₃ changes, which lead to the occurrence of a phase transition and make the VO2 and V₂O₃ materials has a variety of physical properties of mutations. Using this characteristic, the VO2 and V₂O₃ can be used in various kinds of optoelectronic devices, including smart window layer and memory layer.Low valence vanadium oxides are not stable in the air, easy to be oxidized with high valence oxide and influence its performance, especially V₂O₃. At present, preparation technology of VO2 and V₂O₃ is not mature. Moreover, existing methods get the disadvantages of high cost and difficulty in industrialization. Therefore, it is of profound significance to conduct the research on the preparation of VO2 and V₂O₃.The high pure V₂O₅ of purity 99.8% were prepared by the precipitation separation method with smelting vanadium products ammonium vanadate as raw material, and with high purity V₂O₅ as raw material, high purity VO2 and V₂O₃ were prepared by hydrothermal method, high temperature carbon thermal method and redox method. These are accessible to experimental basis for deep processing of vanadium smelting products and the preparation of vanadium oxide.A series of experimental conditions such as p H, filling degree, ultrasonic time, reaction temperature and reducing agent were studied by hydrothermal method with V₂O₅ as raw material, anhydrous sodium sulfite, oxalic acid and methanol as reducing agent. Optimum technological conditions obtained VO2 were purified with the mass fraction were 98.5%, 97.1% and 98.6%, the total yield was 85.46%, 84.18% and 91.01%. The XRD results showed that the high purity B phase VO2 all transformed into M phase after a calcination procedure for some time. The amount of reducing agent was determined to n（carbon）:n（V₂O₅）=0.5 and reaction time was determined to 5h through the exploration of dosage of reductant by high temperature carbon thermal method with V₂O₅ as raw material, activated carbon as reducing agent. After the purification, the mass fraction of VO2 was 99.6%. The total yield was 90.2%. The results of XRD analysis showed that the VO2 prepared by high temperature carbon thermal method was M phase, and the crystallinity was fine. Report to hydrothermal method, the method gets the advantages of short experimental period, simple operation, high purity and yield of products, but the size of VO2 prepared by high temperature carbon thermal method is only micron level. Hydrothermal method has the disadvantages of a long experimental period and bad repeatability, but the product has excellent crystallinity and size.A series of conditions such as precipitating the vanadium p H, precipitating vanadium time, precipitating vanadium temperature, reaction time and reaction temperature were studied by redox process method with V₂O₅ as raw material, zinc as reducing agent. V（OH）₃ precursors was prepared under the optimum conditions, and the yield of V₂O₃（98.8%） was 95.4% after high temperature calcination. XRD analysis shows that the product was excellent crystallinity and exalted purity of V₂O₃.