A Composite Stirring-Milling Reagentless Process for Soft Metal Micro- and Nanoparticle Production

A simple, reagentless, eco-friendly and economically viable method to produce metal micro and nanoparticles (NPs) by means of two different wet milling schemes is proposed. With this technique, metal spheroids of millimetric sizes are subject to a tribological disaggregation in liquid phase, with formation of a nanosized solid whose aggregation is damped by a proper capping agent. This procedure has been tested for elemental Bi, using both a new cross-shaped, custom-made and magnetically driven turbine in the presence of a milling medium and an autogenous vibrating miller. All processes were carried out in inert atmosphere to dampen the oxidation of the as-formed metal particles, whose average diameters and shape has been determined by Dynamic Light Scattering and Field Emission Scanning Electron Microscopy, respectively. The average particle diameters obtained by vibrating milling belong to a microsized range (237-433 nm), irrespective of the capping agent used, as are those produced by wet bead milling in the presence of polyvinyl pyrrolydone as capping agent. Instead, Bi NPs with average diameter of 75 nm have been obtained by bead milling with Na lauryl ether sulphate. Finally, a discussion about possible applications of the designed process is proposed.