Spherical tungsten powders were synthesized by (RF) argon plasma with irregular tungsten powders. The microstructure and crystallographic phases of the synthesized powders were characterized using scanning electron microscopy (SEM) and X-ray diffractometry (XRD). The results showed that fine spherical powder composed of pure tungsten phase with favorable dispersity and its surface becomes smooth. The spheroidization efficiency of synthesized powders was almost 100 %, and the particle size distribution became narrower after spheroidization treatment. The spheroidization efficiency of the sample decreases gradually as increasing of the feeding rate. The RF plasma spheroidization of tungsten powder is an ideal route synthesis of well- spherical metallic tungsten powders which is widely used in thermal spraying and metal injection moulding process.
Powders of given sizes are often demanded for the preparation of porous wares and, therefore, the spherical tungsten powders are classified by fractions using air or liquid separation methods. In the present case, the method of sedimentation in ethyl alcohol was used to give fractions from 2 to 10um. The spherical powder has the following fraction distribution (in u and % by weight): <2, 29.92; 2 to 4, 41.4; 4 to 6, 13.2; 6 to 8, 4.75; 8 to 10, 3.4; >10, 17.3. By the same method other fraction is close to the normal distribution.
Spherical tungsten powder preparation
The spherical tungsten powder was prepared by chemical reaction with ammonium tungstate and strong acids under ultrasonic and mechanical agitation. After precipitation reaction, the precipitate was dried and grinded, and then reduced into tungsten powder with hydrogen. The effects of acid kinds and dispersant on the fine tungsten powder were studied in this paper. The result shows that the acid kinds and its addition amount have great effect on the shape of tungsten particles. The tungsten powder with uniform particle size and spherical could be prepared by adding 17ml sulfric acid into 100ml ammonium tungstate. The tungsten particles can be finer and more dispersive, and have a spherical with addition of dispersant SDS (Sodium dodecyl sulfate). The particle size is about 1.5 micrometer.
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