Nano Tungsten Powder of Tungsten Copper Electrode Preparation II

Compared with traditional powder metallurgy (PM), tungsten copper electrode nano composite material including powder milling, compacting and sintering process, but due to the characteristics of nano particles, there are some differences between traditional powder metallurgy and nano tungsten powder preparation.

1. Phase transfer synthesis

According to the principle of phase transfer synthesis, uses unique ion exchange technology to produce ultra fine ammonium wolframate grains. And then put it to a common rotary tube furnace calcining and reduction at four tube furnace, with a high purity hydrogen -70 ℃ and powder passivation techniques to prepare nano scale tungsten particles. The specific area BET of this kind of nano tungsten powder is 6-10㎡/g (the granularity of BET is 30-50nm), the granularity of nano tungsten powder is 40-70nm, the chemical composition and properties meets a criterion of national standard.

2. Electroreduction

It uses tungsten or tungsten scraps as anode for electrolysis to produce methoxy-tungsten in methanol, which can be easily purified by sublimation and crystallization. Then uses hydrogen (H₂) to reduce methoxy-tungsten and fabricate high purity tungsten powder at 1000℃. In addition, it can use CO reduction to produce high purity tungsten carbide powder and fabricate tungsten powder in regular size by increasing reduction temperature.

3. Hybrid plasma

Thermal plasma plays an important role in the preparation of ultrafine powder by ultra-high temperature and high speed quenching. The ideal quenching rate is higher than 10℃_n^-1, DC plasma quenching rate is prompt and higher than 10℃_n^-1. Therefore, In the quenching plume of super-saturation quickly produce nucleation, which produce ultra-fine powder. By using the mixed plasma obtained from tungsten metal and ultrafine tungsten powder, the average particle size of 10μm can be obtained.

4. Laser irradiation

Related researchers from Japan develops a kind of system that uses low energy Nd : YAG as laser device to manufacture refractory metal nano grain, such as WTA, Mo. According to laser irradiation causes the liquid sputtered tungsten target to generate nano-particles of tungsten, tungsten nano particle size depends on the density and pressure of the laser energy, under different conditions can produce two types of particles, namely the large size of nano tungsten particles and small nano-size particles of tungsten.

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