| Effects of reduction temperature, hydrogen flow rate, water content of hydrogen, and amount of the charge on the particle size of the reduced tungsten powder from APT or WO₃ were investigated. The size distribution of the reduced powder was measured with sedimentation balance and the shape and particle size of the powder was observed with electron microscope. It is considered that the growth of the reduced metallic tungsten particle was occurred the evaporation and condensation reaction of WO₃ in wet hydrogen atmosphere and the reaction was accelerated with the increase of reducing temperature, amount of charge, and water vapor content of hydrogen. The evaporation and condensation reaction, however, was retarded by two step reduction of APT with hydrogen since preliminary reduction at 600℃ transforms APT to fine WO₂ which has the highest sublimation point among the tungsten oxides. And the subsequent final reduction of WO₂ at 800℃ provided the fine metallic tungsten powder. The portion of the fine metallic tungsten powder under 2μ obtained by the two step reduction process was amounted to 78%. |
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