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Usually, particles will start sticking to bowl or balls when 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.
Especially metal alloys can be very ductile, which will hinder a grinding success too. If magnetic forces use to be present, a fine grinding will be barely impossible.
In this case, we ground sample for 10 minutes until a light sticking of sample has been present. Afterwards, we separated the desired fraction of < 100µm particles by sieving out. Coarse fraction has been fed into the bowl again and has been ground for additional 10 minutes.
This procedure has been repeated until the volume of coarse sample has reached 15ml which will be smaller as the minimum volume of sample we recommended for using with our 250ml bowls.
Fine fraction (< 100µm) and coarse fraction (> 100µm) have been packed separately.
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