In laboratories, planetary ball mills are frequently used for powder grinding and mixing. The have an good reputation to be the best mills to grind semi-hard to brittle samples to very fine particles. However, the final fineness always depending on the sample materials, and the grinding process may take several hours.
If speed increasing, the energy input, the chance to get nano size particles increasing, but the risk of warming and rising pressure inside the grinding jars is increasing too. A solution to solve this problem(especially for temperature sensitive materials) is to interrupt the grinding process and take a break.
In addition, the energy of Planetary Ball Mills is limited, so not all materials can be ground to nanometer size.