Tungsten Wire History

Tungsten wire is a filament made by forging and drawing tungsten rods. Due to its excellent properties, tungsten wire enjoys a wide range of applications. For example, tungsten filaments are used in electric light sources such as incandescent and halogen lamps. In this article we will cover the history of tungsten wire.

The development of the tungsten filament industry has been closely linked to the light bulb industry from the beginning.

In 1878, Edison invented the carbon filament light bulb. But this kind of light bulb has serious shortcomings, mainly its short life. Edison experimented with carbon wire in 1879 and used it for hundreds of hours. Although "carbon" has a high melting point (3550°C), its "sublimation" temperature is very low. It sublimates directly from the solid state to the gaseous state at low temperatures, so it is easily consumed, has a short service life, and must be completely isolated from the air (it will burn in the air).

Nearly 20 years later (1897), carbon wire was replaced by osmium wire and tantalum wire, but due to the lower melting points of Os and Ta, the operating temperature and light efficiency were lower.

In 1903, according to the patent of A.Just and F.Hannaman, the first tungsten wire was produced in Hungary. In 1904, A. Just and F. Hannaman used a carbon-free binder mixed with a tungsten compound, extruded into filaments, and then heated in hydrogen to reduce them to metal. The tungsten wire made by this method is very brittle, but because its light efficiency is much better, it has replaced carbon wire, osmium wire, and tantalum wire to make light bulbs.

None of the above methods can prepare fine tungsten wire. In order to solve this problem, in 1907, tungsten alloy with low nickel content was introduced. It is prepared by mechanical processing, but its severe brittleness hinders its application.

In 1913, Pinch invented thoriated tungsten filament (ThO2 content: 1% to 2%), which greatly reduced the brittleness of incandescent lamp filaments. Initially, filament sagging is not a problem because the filament is straight at this point. But after 1913, Langmuir changed straight wire to spiral wire. In this way, when the bulb is in use, the high operating temperature and dead weight cause the filament to sag, and it is difficult for pure tungsten and thoriated tungsten to meet the usage requirements.

In order to solve the problems of tungsten wire sagging and short life, in 1917, A. Pacz invented a tungsten wire that "does not deform" at high temperatures. But the earliest non-sag tungsten filaments were more brittle than thoriated tungsten filaments, so some light bulb manufacturers insisted on using thoriated tungsten filaments.

However, with the continuous development and improvement of the non-sag tungsten wire production process, people gradually realized that adding K, Si, and Al compounds to tungsten oxide at the same time can make the tungsten wire have good sagging resistance at high temperatures. This is what people often call "AKS tungsten wire", which means "non-sag tungsten wire" or "doped tungsten wire".