An experimental study on the formation of ultra fine powders was carried out by a reciprocating friction mill devised to produce submicron powders by the mutual friction grinding of two specimens of the same brittle material. The following results were obtained as the conclusion of this work.
(1) It was assumed that the production mechanism of powder by the reciprocating mutual abrasion was due to the tiny surface protuberance of the specimens by the observation of optical and scanning type electron microscope.
(2) The mean particle size of powder produced by this method was 0.2-0.3μ, which was same or rather lower than the critical size by the mechanical grinding. This particle size was nearly constant independently of the working pressure or the working time and seemed to depend on the kinds of samples.
(3) The relation of Q=cPⁿ was obtained between the working pressure P and the production rate of powder Q. Furthermore, the relation between the index n and Moh's hardness or Young's modulus was considered and the corelation of the index n and Young's modulus which seemed to be the deformation resistance of material or the grinding resistance was clarified.

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