Effectively Grinding and Dispersing Nanoparticles Using a Fine Bead Mill
U. Enderle, G. Kolb, S. Mende and H. Way
NETZSCH Fine Particle Technology, LLC, US
dispersing, grinding, comminution, nanoparticles
Dispersing NanoParticles into liquids can be challenging, the tremendous surface area and surface energy which provides the beneficial effects of nanomaterials also prevents easy dispersion into liquids. Conventional technology for dispersing powders into liquids is not sufficient for dispersing these tiny particles into discrete entities in a liquid.
Production of stable suspensions or dispersions of nanometer size particles is done by utilizing a comminution process, like a small media mill. Grinding coarser particles into the nanometer range or dispersion of agglomerated nano-sized primary particles, which is called dispersion method or top-down process, is done on an industrial level with a bead mill, but the bead mill process can contaminate the material or worse destroy the structure of the particle.
It has been discovered that by using very fine particle size grinding media beads, in the range of 70-125 microns, grinding materials into the nanometer range is economically feasible. Or for dispersing nanometer sized particles using beads even as fine as 30-50 microns shows a significant improvement in process efficiency.
The limitation to the process up to this point has been that scalable industrial equipment that can use these small beads on a continuous basis is not well known or well accepted due to the difficulty in handling the small beads, i.e. removing them for the suspension after dispersing the particles, or loading and discharging the small beads into the machine..
A newly developed bead mill with an improved grinding media separation system allows use of beads with diameters down to 50 m. While this may not seem significant, for dispersing NanoParticles one of the methods for preventing damage to the NanoParticles is to run the machine at a slow rotor speed. A slow rotor speed reduces the separation efficiency of conventional bead mills, limiting the use of that equipment for dispersion of NanoParticles.
The new mill also addresses the practical problems of handling the very small grinding media.
The paper will discuss the design aspects and operating modes of the new separation system. Results of the dispersion are discussed
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Nanotech 2006 Conference Program Abstract