Nano Tungsten Powder Producing Method

China is a main tungsten producing country with more than 20 thousand exportation of coarse tungsten products every year. Over 50% of tungsten consumption in the world is supplied by China. Domestic tungsten metal products output is around 1000~1200 tons. However, high quality tungsten material producing technique and intelligent property are extremely lack in China.

With development of advanced technology, requirements for tungsten and its alloy material is getting higher. Tungsten wire, plate, foil or other tungsten based alloy material have requirements for uniform structure, fine particle size and good plasticity. It then urges to enhance tungsten powder quality. In actual application, high quality nano tungsten powder grain size has decisive function for property of metallurgical material property.

Producing 1kg nano tungsten powder needs following steps:

1. Weigh 3.6 liters of high concentration of ammonium tungstate solution, the WO3 content is 350g/L, under the condition of the air jet pressure 2.5MPa, jet speed 650m • s-1, hot air temperature 250 °C countercurrent hot air drying, using supersonic spray heat conversion method to prepare nano-sized WO3 powder. The nozzle's injection angle α=45°, focal length F=13mm, and the 1280ml/min flow delivery speed, to obtain 1.26kg nano-scale WO3 powder with an average particle diameter ≤50nm.

2. Hydrogen reduction method preparing porous blue tungsten oxide powder.

Using stainless steel tubular reduction furnace 420°C, H2 gas cross-section flow rate 20ml/cm² per minute, insulation 80 minutes, to produce loose porous blue tungsten powder, the average particle size ≤ 40nm.

3. Super High Speed Interlayer Shear Crusher Breaks Blue Tungsten Oxide Grains

According to quality ratio of blue tungsten: industrial alcohol: phenolic resin = 100: 500: 3 after the initial mixing, put into the ultra-high-speed interlayer shear crusher, cut by 20,000 rev/min, 40 min/kg, in the shear during the cutting process, the slurry is introduced into a high-speed 6,000 rpm hydrocycling classifier. The large particles are continuously separated and returned to the shearing machine to continue cutting. The time is still set by the shearer at the original setting of 40 minutes per kg. The sheared nano-blue tungsten slurry is transferred to the next process.

4. Continuous High Speed Centrifugalization

The crushing and hydrocyclization graded nano-blue tungsten suspension slurry is introduced into the continuous high-speed (10,000 rpm) centrifugal separator from the pipeline and continuously centrifuged to separate the nano-blue tungsten oxide from the industrial alcohol. The industrial alcohol is clear and transparent, but contains phenolic resin, which can be reused. Blue tungsten oxide is taken out and dried naturally, then it is transferred to the suction drainage type under low-temperature H2 reduction process.

5. Extracting and Draining Low Temperature H2 to Produce Nano-tungsten Powder

In the stainless steel single-tube reduction furnace at both ends into the H2 mid-stage suction drainage, 700 °C, heat for 90 minutes, H2 cross-section flow rate 30 ml/cm2. H2 gas inlet dew point is -40°C. After the reduction, 1 kg of nano-tungsten powder was immediately sieved through a 15 μm sieve with an industrial frequency N2 gas flow vibrating sieve. A small amount of acetone-oleic acid solution was sprayed into the tungsten powder to prevent spontaneous combustion after sieving. The average particle size of tungsten powder ≤ 80nm.

6.Processes before Leaving Factory

If the first product is shipped from the factory, it needs to be processed before leaving the factory, that is, industrial alcohol is blended at a mass ratio of nano-tungsten powder:industrial alcohol=1:5. The bridging granules are broken in a high-speed interlayer shear and subjected to a high-speed hydrocyclone fine classifier to separate the large particles back and continue to shear. The fine-grained nano-tungsten powder suspension slurry is centrifugally separated by a continuous high-speed centrifuge, and the alcohol is recovered. The nano-tungsten powder mass is taken out, dried, and sieved through a 15-μm sieve with an industrial frequency N2 gas flow to obtain 10 kg of nanometer tungsten powder. Note that a small amount of acetone-oleic acid solution is sprayed into the tungsten powder in a timely manner to prevent the tungsten powder from spontaneous combustion.

7. Property Test

BET fineness, XRD phase composition detection and X-ray small angle fineness analysis were performed. The above process produces 1 kg of nano-tungsten powder having an average particle diameter of ≤80 nm and a nearly spherical shape.

8. Use vacuum packing after testing qualified. 

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