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Nano Sizing Via Wet or Dry Grinding
By Becky Shemanski, Communications Director, Custom Processing Services, Inc. and
Stephen Miranda, Director of Sales, Netzsch-Condux
Nano-sized particles are desirable in many industries, from active pharmaceuticals and pigments to technical ceramics and electronics, and are used to improve reactivity, provide increased surface area, and reduce material consumption.
Traditionally, producing sub-micron sized particles has only been possible through wet media milling. Recent developments in particle reduction technology have enabled the production of nanoparticles through a dry-grinding method using steam. Considering the advantages and applications of each method, described below, will enable the client to choose the most appropriate method and equipment to achieve the desired results.
Wet media milling employs a media mill charged with small spheres or beads and activated by a high-speed agitator shaft to create mechanical hydraulic shearing and particle impact. In agitator bead mills, such as the Netzsch Zeta Mill (LMZ), and LabStar, the forces tear apart the solids suspended in a liquid (slurry) as they are pumped through the grinding chamber. The slurry is ready for use in liquid blends or if necessary is dried and separated for further use.
Depending on the material to be ground and the objective or end-use of the resulting product, one of two types of media milling processes may be chosen. In comminution, particles are ground within the slurry by high pressure shearing and impact forces to break apart the actual particles. In de-agglomeration, the small particles which are joined together are broken apart and separated. In some cases, both comminution and de-agglomeration are used on a single product.
Factors influencing the ultimate particle size are the size of the grinding media used, the material’s residence time (time spent in the grinding chamber), number of passes through the mill, and the speed of the agitation.