Ball Mills High Energy Ball Mills for Nano-Scale Grinding

There are basically two methods of producing nano-scale particles: the “Bottom-Up” technique involves synthesizing the particles from atoms and molecules. With the “Top-Down” method the particles are reduced to nanometer size by grinding. Suitable tools for this method are planetary ball mills, such as Retsch’s new PM-series grinders, which provide the necessary energy input.

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The common rules for size reduction to micron size do not apply for the nano-scale; with decreasing particle size, electrostatic and even molecular interactions increase, leading to particle agglomerations which cannot be reduced any further in size. For this reason, the grinding process has to be carried out in a liquid medium (colloidal grinding) which disperses the particles as much as possible.

For nano-grinding in a ball mill, the grinding jar and balls have to be of a very abrasion-resistant material, such as zirconium oxide, to minimize contamination of the sample material by abrasion. Factors like the choice of dispersion medium or grinding ball size have a crucial influence on the success of the process. Generally, small ball diameters (smaller than three millimeters or 0.12 inches) and grinding times of several hours are beneficial for the production of nano-particles as substantially more energy and a greater surface are required than for dry grinding in the micron range.

German manufacturer Retsch recently presented a new series of planetary ball mills for nano-scale-grinding with sufficient energy input and ultra fine grinding balls. The new PM100, PM200 and PM400 grinders use grinding balls as small as Ø 0.1 millimeters (less than 0.004 inches). Other features of the PM-series ball mills include:

• powerful and quick grinding down to nano range

• automatic grinding chamber ventilation

• programmable starting time

• power failure backup ensures storage of remaining grinding time

• reproducible results due to energy and speed control

• ten SOPs can be stored

• perfect stability on lab bench thanks to FFCS technology

• suitable for long-term trials and continuous use

• two different grinding modes (dry and wet)

• wide range of materials for contamination free grinding

Thanks to various safety features, it is possible to run these mills unsupervised for many hours, the company says.

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