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After totally 10 minutes of grinding, sample starts sticking to bowl and balls strongly.
This uses to happen after the majority of particles reached a fineness of < 20-30µm. Interacting forces between fine ground particles will become bigger as their own g-force. Therefore, particles will stick to each other and just become compressed by the used grinding balls. These clusters of particles also contain bigger particles which will not be ground any further too.
Fineness has been determined with our Laser Particle Sizer ANALYSETTE 22 MicroTec afterwards. About 95,66% of ground particles use to be < 25µm as desired.
Probably sticking might become delayed by adding anti sticking agents (like stearin), or a grinding in suspension (e.g. in isopropyl alcohol) will be capable to achieve 100% < 25µm.
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