High Purity Tungsten Powder Metallurgy Preparation Method

Tungsten has good electrical conductivity, escaping work near the silicon band gap and excellent thermal stability. It has become the first choice material and is widely used in grid materials and wiring materials of integrated circuits.

Some scholars have proposed a new tungsten powder metallurgy preparation method, the main process is as follows:

A. Pre-reduction, APT-0 grade ammonium paratungstate was selected, and conventional technology was used in four band temperature reduction furnace and hydrogen was reduced to produce blue tungsten oxide with oxygen content of 19 ~ 20%.

B. Hydrogen reduction, the blue tungsten oxide with conventional reduction through the five band temperature reduction furnace, the reduction temperature of 600 ~ 950 °C, hydrogen flow rate of 4.0 ~ 6.0m3/h, hydrogen dew point ≤ -60 °C, under the pushing speed of 20~25 minutes the loading capacity was adjusted to 280±5g, 330±5g, 380±5g, 430±5g, and 480±5g respectively, and the Fisher ​​particle size was 2.0±0.2μm and 2.5±0.2μm respectively, tungsten powder of 3.0±0.2μm, 3.5±0.2μm, 4.0±0.2μm.

C. Pickling and impurity removal, the above tungsten powders were washed with deionized water with a specific resistivity>1.0×105Ω·cm for 30 to 35 minutes. After stirring and clarification were stopped, the supernatant was withdrawn and 4 to 5% of hydrochloric acid was added. , Stir and wash for 45-50min, stop stirring and clarification, extract the supernatant, and then rinse with deionized water with resistivity>1.0×105Ω•cm until pH>3. Tungsten powder is vacuum filtered and placed at 70-90°C. The vacuum drying box is dried for 24 to 30 hours and sieved through 160 to 200 mesh.

D. The size of the tungsten powder after the acid cleaning and impurity removal is from 8~10:18~20:36~40:18~20:8~10, in the order from small to large, and the tungsten powder Fisher particle size is 2.9 to 3.2μm, mixed in the mixer for 25-30min. 

E. The powder obtained in the above procedure is molded under the pressure of 15 to 25 MPa by the conventional technique, and the obtained pure tungsten billet size is 15~16×15~16×600 mm.

F. The pure tungsten bar is placed in a molybdenum boat and sintered at a hydrogen dew point ≤ -70°C and at temperature of 1200 to 1400°C for 30 to 50 minutes.

G. After high-temperature sintering, the pre-sintered pure tungsten billet is placed in a vertical melting hood and sintered at a dew point ≤ -70°C under high temperature hydrogen protection. The sintering system is two-step heating, two-step heating preservation, and the current/time parameter is: (0 ‐3200A)/15min, heat preservation: 3200A/15min, temperature rise: (3200‐4150A)/2min, heat preservation: 4150A/20min, output density ≥17.80g/cm³, size 12~13×12~13×510mm pure tungsten bar.

H. Cut off the degassing treatment, and cut the pure tungsten strip from high temperature sintering into 20-50mm, and put it into a molybdenum boat. Place it in a corundum tube electric furnace with temperature of 1600±50°C. In the hydrogen dew point ≤ -70°C, the holding time is 3～5h after degassing treatment, high-purity tungsten materials for VLSI circuits are obtained. W≮ 99.99%, Fe<0.0008%, O<0.001%, C<0.0005% in tungsten materials.

This method reduces Fe and other metal impurities that are soluble in acid and water, and Fe drops below 0.0008%. The binder does not contain carbon-containing organics during the compaction process, avoiding carbon contamination and ensuring that the carbon content is <0.0005%; In the vertical melting and high temperature sintering stage, according to the difference in the melting point of different impurity elements, a vertical melt sintering system for the purpose of further purification of tungsten is established, after the tungsten strip is cut off, it is degassed in a hydrogen atmosphere, reducing the content of gas impurities in the metal gap. Its oxygen content can be reduced to less than 0.0010%, thus achieving the effect of producing high-purity tungsten materials.

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