What Is Tungsten?
Tungsten (element symbol: W) is a transition metal element with an atomic weight of 183.85.
Tungsten is used in various fields such as automobiles, tools, lighting, home appliances, semiconductors, and medicine by being processed into various product forms such as powder, ingot, wire, bar, and plate.
Uses of Tungsten
Tungsten is used in the following applications, taking advantage of its properties:
- Highest melting point among metals
Exposed to high temperatures, such as electrodes for generating electron beams for electron microscopes, discharge wires, discharge lamp electrodes, etc. - Relatively high electrical resistance
Filaments used in light bulbs, heaters in furnaces, etc.
Tungsten is also used for lighting purposes, but its use is declining with the spread of LEDs.
Other applications include the use of tungsten as an alloy with carbon, which is an alloy of tungsten and carbon, and tungsten as an alloy with carbon, which is an alloy of tungsten and carbon.
Tungsten carbide, an alloy with carbon, is a typical example. It is one of the cemented carbides and is used as an additive in cutting tools and steel. Tungsten carbide is used not only for cutting tools but also as an abrasive because it does not soften at high temperatures, maintains high hardness, and has high strength.
Characteristics of Tungsten
Tungsten has a silvery-white surface on polished lumps and a gray powder with a specific gravity of 19.3. It has the highest melting point of any metal (3,380℃) and boiling point of 5,800℃. It is also characterized by a low coefficient of thermal expansion, and is used as a raw material for containers and parts used at high temperatures, such as crucibles and furnaces.
Although Tungsten is not the main ingredient, KS steel, an alloy of iron containing cobalt, tungsten, chromium, and carbon, was called the strongest permanent magnet when it was developed in Japan in 1917.
Tungsten ore is mixed with other metals such as wolframite, ferberite, manganese hubnerite, and scheelite (chemical formula: CaWO4). Among these, wolframite and scheelite are the most important ores.
More than 80% of the ores are produced in China, and others are produced in Russia, Australia, Canada, and other countries.
Despite the uneven distribution of its production, it is an element of high importance, and as a security measure, a stockpile of at least 60 days’ worth of tungsten for domestic consumption has been established.
Other Information on Tungsten
1. Types of Tungsten Alloys
A number of alloys have been developed that are mainly composed of Tungsten. Tungsten-based sintered alloys in which the binder phase is composed of nickel, copper, iron, etc., are called heavy alloys. Heavy alloys include the tungsten-nickel-copper (W-Cu-Ni) and tungsten-nickel-iron (W-Fe-Ni) systems.
The Tungsten-Nickel-Copper system is not magnetic but has high thermal conductivity. On the other hand, the Tungsten-Nickel-Iron system is weakly magnetic and has excellent mechanical properties such as tensile strength and elongation. Heavy alloys are produced by powder metallurgy because Tungsten has a very high melting point.
After the metal powder is uniformly mixed, it is pressed and formed under high pressure, and then sintered at high temperatures to produce it.
The physical properties of the alloy can be differentiated by adjusting the particle size of the Tungsten used in the manufacturing process, the type of metal used for the binder, and the quantity ratio.
2. Toxicity of Tungsten
Tungsten ingots themselves are not toxic, so they are used in applications where they come into direct contact with tools and accessories.
As for the toxicity of tungsten compounds, it has been reported that the half lethal dose LD50 (an index of acute toxicity) in rats by oral intake is 3,300 mg/kg for phosphoric tungsten acid, 1,190 mg/kg for sodium tungstate, and 840 mg/kg for tungsten oxide (VI). All of these compounds are toxic and poisonous.