Tungsten wire can vary according to its size, use, and appearance. The most common application of this wire is for lighting lamps, because tungsten is very tolerant of heat. Halogen, fluorescent, and incandescent lights use the thinnest type, usually with a diameter of .001 inches (.0254 millimeters) to .1 inches (2.54 millimeters).
Pure tungsten wire can be classified as either a Type 1A or a Type 1B. Type 1A wire has non-sagging properties, typically used in hospital devices such as LEEP electrodes, thermionic emitters, and corona generation. The Type 1B can be used for products that use glass-to-metal seals, such as vacuum tubes, reed switches, and incandescent light bulbs; these wires are usually 99.95-percent pure and are excellent heat and electrical conductors. Wires of pure tungsten are usually more than .20 inches (5.08 millimeters) thick in diameter. They are so resistant to heat that some manufactured tungsten wires can have a melting point of about 6,150° Fahrenheit (3,400° Celsius).
Another type of tungsten wire is the doped wire. This means some elements have been added to somehow modify its strength and resistance. Doping also alters its chemical structure, and the wire will have an interlocking composition that makes it stronger. Three elements are commonly used in doping tungsten: potassium, aluminum, and silicon. This type of wire ranges from .001 inches (.0254 millimeters) to .250 inches (6.35 millimeters) in thickness and is used for wire and lamp filaments.
Another chemical called thoria can also be mixed in with tungsten to produce a specialized wire. Type 2A is the thoriated filament wire with just 1-percent of thoria, while the Type 2B has 2 percent. These wires can be manufactured into thread-like thinness and used for microwave ovens and plasma wielding. This type of tungsten wire is said to be 50 percent more effective as an electric conductor.
Tungsten wire can also be mixed in with another element called rhenium. Tungsten and rhenium can effectively create efficient metal alloys because both have very high melting points of 6,192°F (3,422°C) and 5,767°F (3,186°C), respectively. This type of wire is used for when very high heat is required, such as in thermocoupling. Tungsten-rhenium wires are categorized based on the percentage of rhenium included. WR30 has 3 percent rhenium, WR200 has 20 percent, while WR250 has 25 percent. All these types are highly resilient, strong, and resistant to corrosion.
Other elements used to make alloy wires is molybdenum, as it also has a high melting point of 4,753°F (2,623°C). Both molybdenum and tungsten have very similar chemical characteristics that make them ideal for alloying. This type of tungsten wire can be use in furnaces, cars, and even aircraft, as it is also resistant to heat and corrosion.
