We reported previously that copper and silver chalcogenides were formed by interparticle collisions induced by ultrasonic irradiation. Here the formation of Cu3Se2 and alpha-Ag2Se is reported in more detail. The elemental mixture with stoichiometric ratio immersed in methanol was irradiated with ultrasound at 28 kHz at room temperature using a commercial ultrasonic cleaner. Scanning electron microscopy (SEM) observations for (3Cu + 2Se) and (2Ag + Se) systems showed that the reactions proceeded from the surface to the inside of each particle of Cu (or Ag) and Se, exhibiting a clear boundary between reacted and pure elemental region. (C) 2004 Elsevier B.V. All rights reserved.