Reduction of metallic ions by molten gallium under ultrasonic irradiation and interactions between the formed metals and the gallium

Metallic gallium can reduce ions of silver, copper or gold in a slow spontaneous reaction to form the free metals. However, when the reduction is performed with molten gallium under ultrasonic irradiation, the gallium is dispersed into micrometric spheres and the reduction rate is enhanced dramatically. This is due to the large surface area of unoxidized gallium that is formed, on which the heterogeneous reduction occurs. Each of these metals formed also a certain amount of an intermetallic compound with the gallium: Ag2Ga, CuGa2 and AuGa2. Zinc has a more negative reduction potential than gallium and therefore no reduction of zinc ions was expected. Nevertheless we conducted an experiment using a solution of zinc ions to check whether the extremely high temperature that develops near the surface of the particles during cavitation can overcome the energetic barrier for such reduction. (C) 2015 Elsevier B.V. All rights reserved.