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【Chinatungsten Online News Net- Tungsten News】

In 1904 a company tried to apply the drawing process they had developed for tantalum to the production of filaments of the more refractory metals, tungsten, thorium, etc. The brittleness and lack of ductility of tungsten prevented their attaining success by this method, although later, in 1913-1914, it was demonstrated that fused tungsten could be rolled and drawn at very high temperatures, using very small reduction steps. By striking an arc between a tungsten rod and a partially sintered tungsten pellet in a graphite crucible, coated on the inside with tungsten metal powder and containing an atmosphere of hydrogen, small pieces of fused tungsten, about 10 mm. diameter and 20-30 mm. long, were produced, which could be worked with difficulty. It was found that working properties could be improved to some extent by the addition of thorium oxide, which reduces the tendency to develop a columnar type of structure during cooling of the fused mass. This process was never used commercially. In the same year Just and Hannaman patented a process for producing tungsten filaments by mixing the finely divided metal powder with an organic binder, extruding through dies, and heating in suitable gases to remove the binder, leaving a pure tungsten filament. During 1906-7, the well known extrusion process, which was the method by which the majority of tungsten filaments were made for the next four or five years, was developed.