A Brief Introduction to The Preparation of Spherical Tungsten Powder

In recent years, with the continuous development of science and technology, spherical tungsten powder is widely used in thermal spraying, porous materials and powder metallurgy industry, and its demand is also increasing. In the field of thermal spraying, the spherical tungsten powder is not only well fluidity, but also the coating is more uniform and compact, so the product has better wear resistance.

Compared with ordinary tungsten powder, spherical tungsten powder has two salient features. First, the appearance of a spherical powder, good fluidity; Second, high tap density. Spherical tungsten powder preparation process at home and abroad mainly in the following ways:

1.Physical method

A.Arc spray gun method: ordinary DC arc welding machine in series for power, sent by a simple SCDP-3 arc spray gun control the intersection of two consumable electrode tungsten arc melting, with compressed air atomized into spherical tungsten powder. The method has the advantages of simple equipment and low cost, but the production efficiency is low.

B.Microwave single film cavity method: the tungsten powder is loaded into the quartz glass tube, and the tungsten powder is spheroidizing in the single cavity sintering furnace under the action of microwave. This method is simple, but the microwave heating of tungsten powder is limited. The particle size of tungsten powder is large, and its spheroidization temperature is high. The particle size of tungsten powder is small and its spheroidizing temperature is low, which makes the tungsten powder with different particle size appear in the spherical process.

C.Plasma method: the ordinary tungsten powder is added into the plasma ejection fluid to melt the surface (or the whole) of the tungsten powder particles to form a droplet. The droplet surface tension and contraction due to the formation of globular, then through the rapid cooling, the spherical fixed, so as to obtain the spherical tungsten powder, in the practical application of this method requires a larger powder cooling chamber and a large number of argon tungsten powder for cooling after heating, the cost is high.

2.Chemical method

A.Gas phase deposition: a process for obtaining large size (40~65 mu m) spherical tungsten powder from WF6 by vapor deposition. The process involves strong corrosiveness of HF, poor working conditions, and high requirements for environmental protection.

B.Tungsten oxide heavy oxidation - reduction method: tungsten powder by a certain temperature, oxidation time and the local oxidation of air atmosphere to form a special tungsten oxide, special tungsten oxide secondary reduction by the same process, the cost is high.

C.Ammonium paratungstate recycling redox method: the pure ammonium paratungstate as raw material, calcined in argon into purple tungsten, purple tungsten reduction of tungsten powder in the air is oxidized to tungsten trioxide, tungsten trioxide and then reduced in hydrogen. This method has long process route, difficult process control and large ammonia pollution.

At present, the research and development of spherical tungsten powder is still at the stage of development. All the above physical and chemical methods are representative at this stage, but in general, they have their own shortcomings. Comparatively speaking, although the technology of preparing spherical tungsten powder by plasma method is not very mature, the spherical tungsten powder prepared by this method has good quality, high purity and even particle size distribution. Therefore, plasma method will be one of the main directions of the development of spherical tungsten powder.

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