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The bulk density of sample use to be so fine, that only 75 grams of sample can be filled into the 500 ml bowl. After adding water, the volume of sample collapsed, so additional 25 grams of sample could be fed.
We started grinding with a total of 100 grams of sample and 80 ml of total amount of water.
A d50 < 5 µm as desired is reachable within 5 minutes of grinding.
We proceeded grinding for a total of 15 minutes by programming pausing times (factor 1:2 of grinding times and pausing times to avoid over pressure; bowl temperature should remain < 80 °C; else, pausing times should be enlarged).
After 15 minutes of grinding, the present d50 was < 1,79 µm with d90 < 4,56 µm.
With a second sample and ~ 120 ml of water, we tried grinding for a longer time (30 minutes), but fineness did not change significantly. To achieve a better grinding result, we recommend changing grinding balls after 15 minutes of grinding with 5 mm Ø grinding balls to e.g. 1 mm diameter.
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