Mechanically Alloyed Heat Treatment to Prepare The Tungsten Silicide Powder

Tungsten silicide (W5Si3) is also known as a tetragonal silicon, which is a kind of tetragonal crystal. It is a very promising high-temperature structural material and electrode material.

W5Si3 has a melting point of up to 2320 ° C, but the adiabatic temperature is only 966 K, which cannot be synthesized by normal temperature self-propagation ignition. It is usually synthesized by mechanical alloying. The mechanism of the mechanical alloying method is: by the collision between the grinding ball and the grinding ball, between the grinding ball and the material tank, the powder is plastically deformed and hardened by work hardening, and the broken powder is in the subsequent ball milling process. Cold welding occurs, and then it is broken again, and thus repeated crushing and mixing, the atoms of different components infiltrate each other, thereby achieving the purpose of alloying.

The biggest disadvantage of the traditional mechanical alloying method is that the ball milling time is long, it takes up to 300 hours, and it is prone to amorphous transformation. It is necessary to vacuum high temperature annealing the powder after mechanical alloying to obtain the final material. In view of the problems existing in the prior art, some scholars have used the method of mechanical alloying combined with heat treatment to rapidly obtain tungsten trisilicate powder, and the preparation process includes:

a) the tungsten powder and the silicon powder are uniformly mixed according to a molar ratio of 5:3;

b) The tungsten-silicon mixed powder is placed in a sealed ball-milling tank, vacuumed, and then filled with argon gas for a period of ball milling;

c)the ball milled powder is allowed to stand for a period of time in an argon atmosphere at room temperature;

d) The powder after standing in an argon atmosphere is heated in a certain range for a certain period of time to protect the atmosphere, or annealed in a vacuum of a certain pressure to obtain a powder of tungsten silicide.

The tungsten powder has a purity greater than 98% and a particle size less than 10 microns; the silicon powder has a purity greater than 98% and a particle size less than 74 microns; the vacuum pressure is -0.1 to -0.001 MPa; The time is 50-150 min, and the annealing treatment is carried out in a vacuum, and the vacuum is -0.1 to -0.001 MPa, and the time is 30 to 60 min.

Compared with the traditional mechanical alloying technology, the tungsten powder and silicon powder are used as raw materials, and the mechanically alloyed heat treatment method is used to rapidly prepare the tungsten silicide powder, which not only shortens the ball milling time, but also has low annealing temperature and avoids amorphous transformation. And the method is simple, time-saving and energy-saving.

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