Journal of the Society of Powder Technology, Japan

The present paper deals with the filtration performance of needle felt filters prepared from various kinds of materials. Single fiber collection efficiency was correlated experimentally with Reynolds number and the direct interception parameter, taking into account both volume fraction and needle punching density. Although the difference in the collection efficiency stemming from electrostatic charges on the fiber surface was observed, its dependence on the interception parameter showed the same tendency for all the materials.
It was verified that the drag coefficient of felt filters varied inversely with Reynolds number and depended strongly on the volume fraction. Also an empirical expression of the drag coefficient applicable was obtained in a wide range of the volume fraction.

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Using the mechanical processing method called MECHANOFUSION to prepare composite particles, the authors reported on a study about the preparation of metal-ceramic composite particles in a vacuum. The major principle in forming composite particles is to apply some mechanical forces to the mixed powder in the apparatus used. The measurement of the forces, however, has seldon been attemped. Here, an attempt was made to measure the forces quantitatively acting on a powder bed using several strain gauges.
From the experiment using glass beads as the raw material, it was found that (1) if the rotational speed of the drum was high with high loading amount of the powder, the generated compressive and frictional forces are large, and (2) the compressive force is several times larger than the frictional force. During the preparation of composite particles using Cu-Al₂O₃ mixed powder under reduced pressures, their forces were measured. As a result, both forces appeared to be higher under lower atmospheric pressure.

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A generating process for oxide ultra fine particles (UFP), particulary SiO₂ and In₃O₃ is studied using an arc discharge method with a shield gas nozzle as an electrode. The arc is generated between the tungsten electrode cathode and a bulk material anode in an argon-oxygen atmosphere and an argon gas flowing in the shield gas nozzle. Pure Si and In are used as the bulk materials.
The results obtained are as follows:
(1) SiO₂ UFP of high purity are obtained by shielding the tungsten electrode with argon gas.
(2) Oxygen content in the mixed gas, to obtain In₂O₃ UFP of high purity, is about 10vol% at 125g/h of the generation rate with a 100A current.
(3) A composition of In₂O₃-SnO₂ complex UFP that can be obtained using this method is definitely affected by the vapor pressure of the bulk metal oxides.

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