particle size characterization of ultrafine tungsten powder

Ultrafine tungsten powders are of special interest today due to their ability to produce hardmetals with superior hardness and wear resistance and the researchers focused on ultrafine tungsten powder production and characterization have been performed for decades.
Recent study described the production mechanism of ultrafine tungsten powder, and Zeiler pointed out that each ultrafine tungsten carbide grain was obtained from each ultrafine tungsten grain and the fineness of ultrafine tungsten carbide particle was determined by the conventional manufacturing process, and is not produced by milling or classification process.
At the same time, the particle size charaterization of ultrafine tungsten powder had been characterization of ultrafine tungsten powder had been characterized in the above-mentioned literatures. Schubert pointed out that BET-surface area measurement can give some idea about the ultrafine tungsten carbide powder and Zeilier pointed out that due to the high sensitivity of BET-mehtod to particle roughness and "sponge-like" structure of ultrafine powder, correlations and comparisons of different products can be absolutely misleading. With ragard to ultrafine powder, Bock pointed out that the rasults of conventional particle size and particle size distribution measurements by conventional particle size measurement methods(FSSS, sedimentation,laser diffraction)are erroneous due to the high drgree of particle agglomeration and insufficient particle dispersion, giving misleading high values for median particle size and inaccurate distribution.
Production of ultrafine tungsten powder
X-ray diffracted pure yellow tungsten oxide(WO3）was prepared for hydrogen reduction. Reduction experiment was performed in a multitube push-type furnace,under"dry"reduction conditions,using cocurrent hydrogen flow, temperature and humidity were kept low to provide unfavorable condition for the formation of WO2（OH)2 in order to obtain ultrafine tungsten powder.
Milling of ultrafine tungsten powder
According to ASTM standard B430(90), reduced tungsten powder was milled in a 250 ml capacity, 140mm high,60 mm diameter wide-mouth flat-bottom centrifuge bottle at 145 rpm for 1,2,4h,respectively.