Impurity elements in tungsten alloys include H, O, C, N, P, S, and Si. Because these elements have small atomic radii, and strong diffusivity in alloys, they are more likely to be in the grain boundaries and phases. Segregation occurs in places with higher energy such as the boundary, and the increase in value generates brittle phases, thereby reducing the performance of the alloy and influence tungsten alloys properties.

During the process of nanostructured WO3 synthesis it is found that citric acid content, system pH value before hydrothermal synthesis, hydrothermal reaction temperature and hydrothermal reaction time will have great influence on the product, therefore the following will focus on several influence factors affecting the phase and morphology of nanostructured WO3.

Tungsten electrodes tip shapes can be flat, sharpened or rounded. Flat tip is cut by grinding wheel, molybdenum wire or machining. Sharpening is much more difficult. And both shapes and welding current will influence the life time of electrodes.

Liquid phase method is the most widely used method among many methods for synthesizing nano tungsten trioxide. Its advantage is that the nano structured WO3 particles are fine and evenly distributed, the content of the chemical components can be precisely controlled, the morphology of the nanostructured WO3 can be controlled by adjusting the morphology control agent, the synthetic process is simple, economical and good to mass production. There are four main methods including hydrothermal synthesis, sol-gel method, precipitation method and microemulsion method.