feldspar

40g of sample use to be the absolute maximum for feeding into a 80ml grinding bowl. After 5 minutes of grinding, sample is sticking strongly to bowl and grinding balls.

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.

A longer dry grinding time is not recommended.

With a 250ml grinding bowl made of sintered corundum, minimum 50g of sample should be used (≙ min. 30ml of sample).

After 5 minutes of grinding, a d50 < 6µm has been found afterwards.

Sample has to be split in 2x 20g in 2 bowls made of sintered corundum.

After 3 minutes of grinding, a d50 < 15µm has been found as desired. Grinding process has been aborted afterwards.