An experimental study on the effect of surface roughness on the formation of ultra fine powders was carried out by a rotating friction mill devised to produce submicron powders by mutual friction grinding of two specimens of marble. The following results were obtained.
(1) The surface roughness of the specimen decreased with particle size of carborundums used for final finish of the specimen surface. The specimen surface changed to take a different roughness or undulation just after abrasion, but it reached a constant roughness or undulation as the abrasion approached to a steady state.
(2) By scanning electron microscopy, it was observed that the specimen surface seemed to be melting and the surface layer changed to an amorphous state from a crystalline pre-abrasion state. From the electron diffraction pattern, the similar result was obtained on the surface layer of the produced powder.
(3) The particle size of the produced powder decreased with the surface roughness of specimen. The reason is considered that the cohesion area is smaller when the surface roughness is smaller.
(4) The mass of the produced powder increased as the surface roughness decreased. This tendency arises from the fact that the number of contact point and contact area of the tiny surface protuberance is closely related with surface roughness. It is concluded that the surface roughness of the specimen is an extremely important factor in mutual friction grinding.
