Chalk

Sample starts sticking right after a dry grinding time of 10 minutes. A longer dry grinding is not recommended.

Fineness has been determined by our Laser Particle Sizer ANALYSETTE 22 NanoTec. Desired Endfineness of d90 < 20µm has been achieved.

When 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.

If a better endfineness should be achieved, a grinding in suspension will be possible. Also anti sticking agents can be used to lower the dry grinding endfineness (see result 2).

Comments of result 1 use to count for this trial as well.

Found fineness in result 1 has already been quite fine. By adding ~2,5% of Aerosil (used as anti-sticking agent), sticking of sample has not been delayed as desired.

Detected fineness use to be comparable to the measurement we did with our Laser Particle Sizer ANALYSETTE 22 NanoTec in result 1.

If better endfineness should be achieved, we recommend changing ball diameter after 10 minutes of dry grinding to e.g. 3mm Ø and proceed grinding in suspension (e.g. with alcohol).

In our last trial, we wanted to show the grinding result of smaller quantities with Mini-Mill PULVERISETTE 23. Only particles < 5mm has been used as start size; else, pieces might stay intact.

With this trial, sample use to start sticking after 4 minutes of dry grinding. By measuring the fineness with our Laser Particle Sizer ANALYSETTE 22 NanoTec, a d90 < 32µm has been detected.

Desired endfineness could not be achieved with our Mini-Mill PULVERISETTE 23.