Montmorillonite

Because in dry grinding, each sample starts sticking to bowl and balls after a special fineness is reached (usually d50 < 20µm, when interacting forces will become bigger as particles own g-force), a grinding in suspension is required.

For this, we had to add ~ 120ml of water to maintain motor oil like viscosity for an optimum grinding result.

To avoid overpressure, we ground the sample in steps of 5 minutes, followed by a programmed pausing time of 10 minutes. After several cycles, the outside temperature of the bowl should be checked (remain below 80°C); grinding time or programmed pausing time might be readjusted afterwards.

After 60 minutes of grinding, desired fineness of d50 < 1,5µm has been reached. For a better endfineness, longer grinding times or a change to smaller ball diameter (e.g. 1mm Ø) is still possible.

Comments of result 1 use to count for this trail too.

For the second sample (natural mineral), only 70ml of water are required to achieve a motor oil like viscosity.

This sample reached a d50 of < 1,5µm after ~ 60min. After a total grinding time of 120min, d50 has been lowered to < 1,1µm.

A change of ball diameter to e.g. 1mm Ø after 60 minutes of grinding should be able to achieve the sample d50 value in much less time (probably totally 90 minutes of grinding).