A jet mill grinds the materials by means of a high-speed jet of compressed air or inert gas. This type of mill causes the particles of the substance to impact on each other, and the high-speed collisions result in the reduction of the size of the particles. The gas enters through nozzles arranged on the perimeter of the jet mill chamber, creating a spiral with tangential velocity of 30 to 150 m/sec and radial velocity of about 3 m/sec. Jet mills can be set to produce particles below a certain size, and the degree of reduction is determined by the energy supplied by the gas and by the geometry of the static classifier placed before the chamber outlet.
