Tungsten is an important and prominent metal among the refractory metals due to an excellent combination of outstanding high temperature properties and high melting point (highest of all metals). Its high strength and corrosion resistance at elevated temperatures, good thermal conductivity and low thermal expansion makes it possible to use tungsten in high temperature applications. On the other hand, owing to its high hardness and wear resistance, high modulus of elasticity and compression strength, tungsten is an important constituent as an alloying element in tool steel, superalloys, stellites and hard metal industry.

Tungsten trioxide (WO3) powder has been applied in production of light filaments and tungsten carbide. As more of its characteristics have been discovered, WO3 powder has expanded its applications in devices such as electrochromic display, semiconductor gas sensors and photocatalysts due to its outstanding electrochromic, gaschromic, thermochromic and optochromic properties. A WO3 powder with nanostructure is considered to possess enhanced properties mentioned above, owing to their large surface area and unique physical properties. 

The main sources of tungsten are the high-grade concentrates of wolframite and scheelite ores. Tungsten metal powder is produced from these minerals typically through the intermediate product of ammonium paratungstate (APT). In a subsequent process, tungsten oxides are obtained from APT by calcination in an oxygen bearing atmosphere between 560 °C and 850 °C. Tungsten metal powder is then produced by reducing the oxides with H2. However, it is difficult to produce nanosized tungsten powder with conventional evaporation and condensation methods, due to the high temperature that is needed for evaporation. Nanosized tungsten powder can be produced by various methods such as the electrodeposition, sputtering, ball milling, and complicated chemical methods. But these methods involve multi-steps and have difficulty in establishing commercial application.

Vanadium oxides include V2O3, V3O5, V4O7, V5O9, V6O13, VO2 and V2O5, in which the atom ratio of oxygen to vanadium varies from 1.5 to 2.5. Among them, VO2 presents a reversible first-order metal-insulator transition (MIT) at a critical temperature (Tc). Intensive investigations have been made on the preparation of VO2 and its properties. It is generally believed that VO2 is a monoclinic structure (M), and presents semiconductive and relatively infrared transparent below Tc, whereas it transforms into tetragonal structure (R), and presents metallic and infrared reflection above Tc. These features make the VO2 suitable for the applications in intelligent energy windows coating, optical switching devices, optical data storage medium, electrodes for electrochromics, lithium batteries and supercapacitors, etc. Nevertheless, the high critical transition temperature of VO2 material (about 68 °C) limits its application.