Production Method of Tungsten Powder by Direct Reduction

At present, the common method for producing tungsten powder with high green strength is by: using ammonium paratungstate (APT) as raw material, APT is sintered to form tungsten oxide (WO3, WO2.9), and then tungsten oxide is reduced by hydrogen to form tungsten powder. Finally the high-green-strength tungsten powder is obtained by screening and removing impurities.

A method for producing high-green-strength tungsten powder by directly reducing APT is omitted, which eliminates the APT sintering, and APT is directly place within hydrogen atmosphere. The direct reduction treatment is carried out to prepare a tungsten-containing powder, and the finished product is obtained by screening and removing impurities.

The main procedures of the process are as follows:

1) Hydrogen reduction:

APT with bulk density of 2.8g/cm3 and particle size of 40μm is placed in a high-temperature stainless steel boat according to the thickness of the layer of 35mm and the loading capacity of 800g/boat. The boats are subjected to furnace with fifteen tubes and three conveyor belts to carried out a reduction treatment for 8 hours; the temperature bands were 800 °C, 880 °C and 950 °C, the boats are pushed at a speed of  20 mm/min, the hydrogen dew point was below -40 °C, and the flow rate was 8 m³/ hour. The boats are reversely pushed into the furnace tube, the material is cooled and the primary tungsten powder is obtained; the hydrogen after the reduction treatment is input into the recovery device to be filter and dried and then reused;

2) Screening and impurity removal:

The reduced tungsten powder is sent into a rotary vibrating screen with a pore diameter of 120 μm to be screened to remove large particles and falling pieces of boats, and a high-green-strength tungsten powder with average particle size of 3.05 μm is obtained. The tungsten powder has a green strength of 2.32 MPa without adding any molding agent. It has a good strength and high purity.

Due to the direct reduction treatment of APT in hydrogen atmosphere, the first temperature zone in the primary stage of the reduction reaction mainly forms a large amount of volatile WO3 or WO2.9 and causes the two to adhere to each other after deposition, forming a loose aggregate structure and bridging structure. The tungsten powder formed by the rapid reduction of tungsten oxide in these structures in the high temperature region destroys the bonding strength of the tungsten oxide, and still retains the original loose aggregation or bridging structure, avoids the deposition of tungsten powder, and makes the particle development incomplete, forming an irregular particle morphology, thereby facilitating press molding. The process has the advantages of short production process, convenient and reliable operation control, high purity of tungsten powder, high bonding strength and stable quality; powder particle size of 1.8-3.5 μm, compaction strength of up to 2.0-3.6Mpa, sintering The product has high density and high temperature resistance, and can be widely used in the manufacture of flamethrowers and rocket flight rudders in aviation and aerospace.

• < Prev
• Next >