Particle comminution in a centrifugal air classifier was experimentally investigated. Six different scale classifiers with rotor blades ranging in diameter from 270 to 2000 mm were used. Powders tested were Si 3 N 4 , Al 2 O 3 , limestone and cement. It was observed that new particles were produced by comminution in the classifier in two size ranges: one in a coarser range and the other in a range from submicron to several microns. Comminution was promoted by increases in the rotation speed of the rotor blades, classifying air flow rate and shear gradient. The size ranges of the new particles produced by comminution shifted toward finer regions with increases in rotation speed of the rotor blades and shear gradient.