In 1907, a tungsten alloy with low nickel content came out. It was prepared by machining, but its serious brittleness hindered its application. Until 1909, an electric appliance company obtained tungsten billet by powder metallurgy, and then produced tungsten wire with ductility at room temperature by machining, which laid the foundation of tungsten wire processing industry and powder metallurgy.
However, this "ductile" tungsten alloy shows obvious brittleness after the bulb is ignited. Thorium tungsten filament was invented in 1913 (the content of ThO2 is 1% ~ 2%), which greatly reduces the brittleness of incandescent filament. At first, the sagging of the filament was not a problem, because the filament at this time was a straight filament, but after 1913, the straight filament was changed to a spiral filament. In this way, when the bulb is used, the high working temperature and the effect of self weight make the filament sag, so pure tungsten and thorium tungsten are difficult to meet the use requirements.
In order to solve the problems of tungsten wire sagging and short service life, tungsten alloy with "no deformation" at high temperature was invented. At first, when preparing pure tungsten, he roasted WO3 in a refractory crucible. He accidentally found that the tungsten wire spiral made of tungsten powder reduced by WO3 was mysteriously no longer sagging after recrystallization. Subsequently, after 218 times of repeated experimental verification, it was finally found that the tungsten wire prepared by adding potassium and sodium silicate to tungstic acid (WO3 · H2O) and reducing, pressing, sintering and processing formed a fairly coarse grain structure after recrystallization, which was neither soft nor sagging resistant. This is the earliest non sagging tungsten wire. Perth's discovery laid the foundation for the production of non sagging tungsten wire. Until the United States, it was still called "218 tungsten wire" to commemorate Perth's major discovery.
The production process of doped tungsten alloy is lengthy, including tungsten smelting, powder metallurgy blank making and plastic processing.
Ammonium paratungstate (APT) is usually used as raw material in the production of doped tungsten alloys. In addition to the traditional classical process for preparing ammonium paratungstate from tungsten concentrate, the research on extraction method and ion exchange method was carried out internationally in the 1950s, and these processes were also adopted in China in the 1970s, which simplified the process flow and improved the recovery rate of tungsten. Since the 1960s, many countries have adopted blue tungsten oxide doping process to replace tungsten trioxide doping, so as to improve the doping effect. The pickling of tungsten powder was applied to production in the 1960s. Its main purpose is to wash away the excess dopant, ultra-fine powder and some harmful impurities in tungsten powder, so as to improve the processing performance and high-temperature performance of tungsten wire. Since 1960s, pass rolling method has been applied continuously. Pass rolling is to make the blank pass through the pass of a pair of rotating rolls, and reduce the section and extend the length under the action of roll pressure.
Although only a small part of tungsten ore is finally made into lamp tungsten wire and similar products, the most important significance of tungsten in science and technology is the transformation of its research results to practical application. The acquired knowledge has immeasurable value in the new field of powder metallurgy, especially in the manufacture of cemented carbide.
