What Is a Tungsten Filament?

Tungsten wire, a filament made by forging and drawing tungsten bars.

Tungsten

Grade characteristics and uses

WB001: good winding performance, no sagging, suitable for ordinary incandescent, double spiral or triple spiral

Most of tungsten wire production uses ammonium paratungstate (APT) as raw material. The general process is to place ammonium paratungstate in air at about 500 ° C.

Including high temperature performance, room temperature performance and consistency of wire diameter.

Tungsten wire is used as a small amount

Thermal radiation from objects can produce electromagnetic waves of various frequencies (wavelengths). For tungsten wires, almost 100% of the electromagnetic waves incident on the surface are absorbed. (The absorption and radiation coefficient is 1) For tungsten wires, almost 100% of the electromagnetic waves entering the surface will be absorbed (the absorption and radiation coefficient is 1). Therefore, its thermal radiation is close to the temperature-dependent black body radiation. Therefore, its thermal radiation is close to the temperature-dependent black body radiation. ^[1]

The two poles of the energy-saving lamp are ordinary tungsten wire and tungsten wire. After heating, they can emit electrons. A relatively high voltage is applied to the two sides of the lamp to form an electric field. These electrons will be accelerated in the lamp and formed with Speed and energy

The easiest method: there are two types of lamps, which are very different. The color temperature of the lamp is about 5600, and there will be fluctuations because the bulb is aging.

model	Tungsten content	Impurity element content		Manufacturer
		total	Each
WAL1, WAL2	99.95%	0.05%	0.01%	Luoyang Mettlen
W1	99.95%	0.05%	0.01%
W2	99.92%	0.08%	0.01%
Note: Potassium is not included in the impurity content.

From the beginning, the development of the tungsten wire industry was closely linked to the lighting bulb industry. In 1878, Edison (TA Edison) invented the carbon filament light bulb. But this kind of bulb has serious shortcomings, mainly because its life is too short. Almost 20 years later (1897), carbon filaments were replaced by reed filaments and tantalum filaments, but due to lower melting points of Os and Ta, the operating temperature and light efficiency were low.

In 1879, Edison tried carbon filament and used it for hundreds of hours. Although "carbon" has a very high melting point (3550 ° C), it has a low "sublimation" temperature. At low temperatures, the solid is directly sublimated into a gaseous state, so it is easy to consume and has a short service life. It must be completely insulated from the air (it will burn in the air). At present, almost all tungsten wires with a melting point (3410 ° C) are used. The advantage is that the "sublimation" rate is lower when the melting point is lower than the melting point. Therefore, it can be heated to a higher temperature than "carbon filament". Tungsten wire also burns in the air, so the bulb needs to be evacuated.

In order to avoid the sublimation of the filament, an inert gas is injected into the bulb. These gases are mainly argon and do not contain oxygen. Partially vaporized tungsten atoms can return to the filament by collision. Although inert gas increases the life of the filament, it comes at a price. The existence of inert gas in the original vacuum bulb increases heat conduction and convection, which removes energy and reduces the equilibrium temperature. Sublimed tungsten gas forms faint particles in the inert gas and also forms black spots on the inner surface of the bulb by convection.

In 1903, according to the patents of A. Just and F. Hannaman, Hungary produced the first tungsten filament. It is the heating of carbon filaments in tungsten oxyhalide vapor containing free hydrogen to a high temperature, so that the carbon is completely replaced by tungsten. The incandescent filament prepared in this way more or less contains carbon, which is not only very brittle, but also the filament is constantly densified when the light bulb is in use, so the electrical parameters of the filament will change.

In 1904, Jester and Hannamon recognized the effect of carbon on brittleness, using a carbon-free binder mixed with tungsten compounds, extruded into filaments, and then heated to reduce to metal in hydrogen. The tungsten wire produced by this method is very brittle, but because it has a much better light efficiency, it has replaced carbon wire, hafnium wire and tantalum wire for making bulbs.

None of these methods can produce fine tungsten wires. In order to solve this problem, in 1907, a low nickel content tungsten alloy was introduced. It was prepared by mechanical processing, but its severe brittleness prevented its application. Until 1909, General Electric's Coolidge produced tungsten billets through powder metallurgy, and then used machining to produce tungsten wires with ductility at room temperature, which established the tungsten wire processing industry. The foundation also laid the foundation for powder metallurgy.

However, this "ductile" tungsten filament shows significant brittleness after the bulb is ignited. In 1913, Pintsch invented thoriated tungsten wire (ThO2 content of 1% to 2%), which greatly reduced the brittleness of incandescent filaments. At first, the sagging of the filament (see the anti-sagging performance of tungsten filament) was not a problem, because the filament at this time was a straight filament, but after 1913, Langmuir changed the straight filament to a spiral filament. In this way, when the bulb During use, the high working temperature and self-weight make the filament sag, so pure tungsten and thorium tungsten are difficult to meet the requirements of use.

In order to solve the problems of sag and short life of tungsten wire, in 1917, A. Pacz invented the tungsten wire which is "non-deformable" at high temperature. At first, he used a refractory crucible to fire WO3 when preparing pure tungsten. He accidentally found that the tungsten wire spiral made from the tungsten powder reduced by this WO3 was no longer mysteriously sagging after recrystallization. Subsequently, after 218 repeated experimental verifications, he finally found that the tungsten wire prepared by adding potassium and sodium silicate to tungstic acid (WO3 · H2O), reduced, pressed, sintered, and processed, formed a considerable amount after recrystallization. The coarse grain structure is neither soft nor sag resistant. This is the earliest non-sag tungsten wire. Perth's discovery laid the foundation for the production of non-sag tungsten wires. Until now, the United States still does not call sagging tungsten wires "218 tungsten wires" to commemorate this major discovery of Perth.

However, the earliest produced non-sag tungsten wire is more brittle than rhenium tungsten wire, so that some bulb factories insist on using rhenium tungsten wire as the filament. However, with the continuous development and improvement of the production process of non-sag tungsten filaments, people have gradually realized that the simultaneous addition of K, Si, and Al compounds to tungsten oxide can make tungsten filaments have good anti-sag performance at high temperatures. After crystallization, it has satisfactory room-temperature ductility. This is what people often call "AKS tungsten wire", that is, "non-sag tungsten wire" or "doped tungsten wire". In 1931, T. Millner referred to this improved non-sag effect as "GK effect".