Tungsten is a metallic element. The chemical symbol of tungsten is W, its atomic number is 74, its relative atomic mass is 183.85, its atomic radius is 137 picommeters, and its density is 19.35 grams per cubic centimeter. It belongs to the VIB group of the sixth period (the second longest period) in the periodic table. Tungsten is a hexavalent cation in nature, and its ionic radius is 0.68×10-10m. Due to the small radius of W6+ ion, high electricity price and strong polarization ability, it is easy to form a complex anion. Therefore, tungsten is mainly in the form of complex anion [WO4]2-, which combines with Fe2+, Mn2+, Ca2+ and other cations in the solution to form wolframite or scheelite precipitation. After smelting, tungsten is a silver-white shiny metal with high melting point, great hardness, low vapor pressure, low evaporation rate and relatively stable chemical properties. It is mainly used for manufacturing filament and high-speed cutting alloy steel and super hard mould, and also used for optical instruments, chemical instruments, tungsten electrodes and tungsten rods for argon arc welding. China is the largest tungsten storage country in the world.
Tungsten is the refractory metal with the highest melting point. Generally, metals with melting point higher than 1650℃ and a certain amount of storage and metals with melting point higher than zirconium melting point (1852℃) are called refractory metals. Typical refractory metals are tungsten, tantalum, molybdenum, niobium, hafnium, chromium, vanadium, zirconium, and titanium. As a refractory metal, the most important advantages of tungsten are good high temperature strength, good corrosion resistance to molten alkali metals and vapors, used in high temperature resistant parts, military products, tungsten electrode, tungsten crucible. The oxide volatilization and liquid phase oxide of tungsten only appear above 1000℃. However, it also has the disadvantages of high plasticity-brittle transition temperature and difficult plastic processing at room temperature. Refractory metals represented by tungsten have been widely used in metallurgy, chemical industry, electronics, light source, welding materials, medical treatment, tungsten rod, tungsten electrode machinery industry and other sectors.
Tungsten is a non-ferrous metal. Metals are usually divided into two groups according to their color and properties: ferrous and non-ferrous. Ferrous metals mainly refer to iron, manganese, chromium and their alloys, such as steel, pig iron, ferroalloy, cast iron and so on. Metals other than ferrous metals are called non-ferrous metals. Tungsten is a non-ferrous metal. The strength and hardness of non-ferrous alloy are generally higher than that of pure metal, the resistance is larger than that of pure gold, the resistance temperature coefficient is small, and it has good comprehensive mechanical properties. Therefore, as a non-ferrous metal, tungsten has very high strength and hardness. Due to this characteristic, tungsten carbide with high hardness and strong wear resistance is widely used in cutting tools, rotary burrs, grinding tools, mining tools.
