Size classification of submicron particles has been carried out by use of a small cyclone, the diameter of which is about 100mm∅. JIS Kanto loam powders are successfully classified at about 0.5μm. cut sizes. However, calcium carbonate has some difficulties because of its strong cohesion force. Fine silica sand and JIS flyash, the undersizes of which are less than a few percentages at 1μm, cannot be classified because of bouncing and re-entrainment of coarse particles and of the adhesion of fine particles to coarse ones in cyclone.
Precise size measurements of submicron particles are very difficult using present instruments. It is neccessary to develop more reliable measuring methods than the present techniques in order to obtain accurate partial separation efficiencies in the submicron size range.