A Method to Prepare Tungsten Sponge with Uniform Pores

The tungsten sponge is the major carrier of the impregnated ruthenium tungsten cathode. The pores in the sponge are used to store the emissive material and at the same time serve as a transport channel for the emissive material. So far, the major difficulty in preparing the uniform distribution of tungsten sponges is that the particle size of tungsten powder is not uniform.

Screening methods, blowing methods, froth flotation methods, and low-temperature sintering methods do not perfectly solve the problem of tungsten powder uniformity and its high production cost. Therefore, researchers have innovated a method that can solve the problem of uneven particle size of tungsten powder at low cost. The method of the experimental process is as follows:

1) The tungsten powder is charged into a vacuum furnace, and calcined at a low temperature of 450 ° C to remove the gas in the tungsten powder and reduce the oxidized tungsten powder;

2) Use high-speed jet grading equipment to classify tungsten powder, firstly adjust the speed of the impeller rotating at high speed in the classifier to 500-1000 rpm, and effectively separate the tungsten powder with smaller particle size (below 2 microns). Secondly, the speed of the impeller rotating at a high speed in the classifier is adjusted to 100-200 rpm, and the coarse tungsten powder is effectively separated, so that a graded tungsten powder having a very concentrated particle size distribution can be obtained;

3) Fill the graded tungsten powder into the latex tube and tightening the nozzle; placing the latex tube filled with tungsten powder into the pressure chamber of the cold isostatic pressing device for pressing, the pressure is 20 MPa×10-20 min. , obtaining a pressed tungsten billet;

4) Place the pressed tungsten ingot into a hydrogen furnace and performing low temperature sintering at 950 °C;

5) The low temperature sintered tungsten billet is roughed to obtain a straight and neat shape, and the porosity value of the low-burning tungsten billet is calculated by calculation: (tungsten gravity specific gravity - tungsten specific gravity) / tungsten specific gravity;

6) The low temperature sintered tungsten billet is placed in a hydrogen furnace, and subjected to high temperature sintering at 1850 ° C to 2150 ° C to obtain a desired tungsten sponge, and a high burnt porosity value is calculated (in general, the porosity value is The final pore size of the tungsten sponge);

7) The tungsten sponge obtained by high temperature sintering is difficult to be turned. For this reason, the tungsten sponge is used to improve the turning performance. The copper immersion is generally carried out in a hydrogen furnace, the copper immersion temperature is 1400 ° C, and the copper immersion copper ends to obtain a tungsten copper rod. ;

8) Produce the tungsten-copper rods according to the drawings, and obtain the tungsten-copper parts.

9) Immerse the tungsten-copper parts in a nitric acid solution, and then ultrasonically cleaning to remove the copper in the tungsten-copper parts, repeated several times until the color of the nitric acid solution does not change significantly, and then the parts are cleaned with distilled water;

10) In order to completely remove the residual copper in the parts, the parts are subjected to hydrogen heating by means of high-frequency heating, and the temperature is 1500 ° C to 1600 ° C. Thus, the desired tungsten sponge parts can be obtained.

Compared with the conventional method for preparing a tungsten sponge, the above method can effectively prevent the ultrafine particles from blocking the pores between the tungsten particles, and the ultrafine particles are connected with the large particles to form larger tungsten particles, thus the tungsten sponge with uniform pores is obtained. 

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