Nanoparticles can be produced by wet grinding in stirred-media mills. In the lower nanometer range a true grinding limit exists, where the transferred energy from the grinding media is no longer sufficient to induce further breakage of the particles even after stressing events with high stress energies. The grinding limit and its influencing factors are of great interest for nanoparticle production by top-down approaches.

Wolfgang Peukert, Friedrich-Alexander University Erlangen-Nürnberg, Germany, and colleagues concluded from the variation of process parameters, e.g., grinding media size and material, stirrer tip speed, suspension viscosity, that the grinding limit is hardly affected by most of these parameters.

At high solids concentrations and/or small particle sizes, a drastic increase in suspension viscosity occurs, which leads to a dampening of the grinding media motion and to a reduction in the transferred stress energy. Hence, the rheological behavior can limit the grinding process, and a viscous dampening-related grinding limit can be reached prior to the true grinding limit.

• Nanoparticle Production with Stirred-Media Mills: Opportunities and Limits
  C. Knieke, C. Steinborn, S. Romeis, W. Peukert, S. Breitung-Faes, A. Kwade,
  Chem. Eng. Technol. 2010, 33 (9).
  DOI: 10.1002/ceat.201000105