Preparation Method of Tungsten-vanadium Dioxide Powder as Phase Change Material

As a phase change material (PCM), vanadium dioxide (VO₂) undergoes a transition from a high temperature tetragonal phase to a low temperature monoclinic phase at around 68° C. This phase change occurs on the order of nanoseconds and is reversible multiple times, accompanied by light, electrical, magnetic and other properties such as refractive index n, reflectivity R and resistivity and a series of mutations. Therefore, vanadium dioxide has broad application prospects in smart window materials, optical storage, photoelectric switches and infrared radiation detectors.

Studies have shown that the phase-change temperature of VO₂ can be adjusted by incorporating some elements (such as Mo, W, F, etc.), especially by adding high-valent metal ions by doping to reduce the VO₂ phase transition temperature and expand the use range of VO₂. The reported doped vanadium dioxide material and its preparation method mainly focus on two aspects of film and powder preparation. The preparation method of VO2 film includes chemical vapor deposition method, reaction evaporation method and magnetron sputtering method, laser pulse deposition method, sol-gel method, etc., and VO₂ powder preparation methods mainly include pyrolysis method, hydrothermal synthesis method, vacuum reduction method, spray thermal decomposition VOSO₄ and the like. However, these methods have the disadvantages that the raw materials are expensive, the process is complicated, and it is difficult to control, which leads to the low purity of the vanadium dioxide in the polymorphic form and the mixed valence state.

In order to meet the requirements of industrial production of special functional materials, some scholars have proposed a cost-effective preparation method of tungsten-vanadium dioxide powder:

5 g of V₂O₅ powder and 0.165 g of C powder were mixed and mixed on a mixer for 4 hours, and then placed in a pre-cleaned Al₂O₃ reaction vessel, which was then placed in a tube sintering furnace. The tubular sintering furnace is connected to N2 gas at one end and connected to clarified lime water through a rubber tube at the other end. First open the venting valve, after 30min, open the tube type sintering furnace heating switch, start heating, the heating rate is about 40 °C, heat at 700 °C for 3h, then continue to heat up to 850 °C, after 5h holding, with the furnace cooling, when the furnace temperature Close the vent valve when it is near 100 °C. XRD analysis showed that the reduced product was monoclinic VO2 with high purity. The phase transition point of the product is around 67.04 ° C, which is in good agreement with the phase transition temperature of the monoclinic phase VO₂ of 68 ° C.

The raw materials of the above process are V₂O₅, C and WO₃, which are inexpensive, easy to obtain, and convenient for transportation, storage and use. The equipment used is a resistance sintering furnace which can pass a protective gas. Process parameters such as gas flow rate and heating rate can be intelligently operated by flowmeters and temperature control instruments, so the whole process is simple, requires low equipment, low investment, low energy consumption, and is easy to mass-produce, which is beneficial to commercialization.

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