glass (2 samples; short & long; both are moistened)

After 3 minutes of dry grinding (dry, as requested), sample starts to stick strongly to the bowl . Fineness has been checked with our Laser Particle Sizer ANALYSETTE 22 NanoTec plus. No particles use to be found > 150µm, d50 < 27µm has been detected.

We detached sticking sample and proceeded grinding for a further minute until sample is sticking again.

One last time, sample has been detached and proceeded grinding a further minute for totally 5 minutes.

Again fineness has been checked (see meas. no. 61710 on separate page), d50 could only be reduced to < 23µm all particles use to be < 100µm.

This is a typical result for dry grinding of brittle, fibrous material. Ground particles become compressed to clusters. These clusters will also contain bigger particles which will not be ground any further. Also moisture will improve sticking tendency. A dried sample might be able achieving a finer grinding result. (see result 4)

A longer dry grinding time is not recommended.

For achieving a better endfineness, we recommend dry grinding until sample starts sticking and proceed grinding in suspension until desired endfineness will be reached (see result 2).

Sample has been pre ground analogous result 1.

In general, an optimum grinding result will be achieved by grinding in motor oil like viscosity. For this, we added ~ 250ml of Ethanol (EtOH) after 5 minutes of dry pre grinding.

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 70°C); grinding time or programmed pausing time might be readjusted afterwards.

After 30 minutes of grinding, fineness has been checked with our Laser Particle Sizer ANALYSETTE 22 NanoTec plus (see meas. no.61754 on separate page).

Fineness has been small enough to change ball size to 1mm Ø for a further improvement in grinding result. For this, see result 3.

General comments of result 2 also use to count for this trial.

Balls had been changed to 1mm Ø after 30 minutes of grinding in result 2.

Also 50ml of ethanol have been added to maintain an motor oil like viscosity again.

After only 15 further minutes of grinding, d50 became lowered to < 1,88µm; no particles > 12µm could be found (see meas. no. 61780 on separate page). A small sample has been taken after totally 45min (15min with 1mm Ø) for demonstration.

By further grinding, fineness will improve not as fast. After totally 120 minutes of grinding a d50 of < 1,08µm has been reached (see meas. no. 61860). This result reaches almost the desired endfineness of d50 < 1µm. A longer grinding is still possible for further improvement.

The present result has been calculated without the necessary Mie parameters which will be needed to evaluate submicron particles. For this, true d50 should be smaller as listed and desired fineness might be achieved.