Leucit

For pre grinding of sample, we 10 mm Ø grinding balls. After 1 minute of dry grinding, the sample started sticking to bowl and grinding balls.

This uses to happen after the majority of particles reached a fineness of < 20-30 µm. Interacting forces between fine ground particles will become bigger as their own g-force. Therefore, particles will stick to each other and become compressed by the used grinding balls. These clusters of particles also contain bigger particles which will not be ground any further.

We added 2,5 ml of isopropyl alcohol and ground for further 9 minutes. We checked the particles size by optical microscopy and only found particles < 30 µm. For this, now a change to 1 mm Ø grinding balls can be performed (see result 2).

After the change of grinding balls to 1 mm Ø, we added further 2 ml of Isopropyl alcohol to maintain a motor oil like slurry (for an optimum grinding result).

To avoid over pressure, 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. This is counting for all following trials in suspension too.

After a total grinding time of 60 minutes, the present size is fine enough to use 0,1 mm Ø grinding balls (see result 3). With such small grinding balls, a maximum of fineness can be achieved.

We changed the grinding balls to 0,1 mm Ø and added further 7 ml of Isopropyl alcohol. Afterwards, the sample has been ground further. The achieved fineness has been checked after a total grinding time of 90 minutes with our Laser Particle Sizer ANALYSETTE 22 NanoTec plus; a result of d50 < 95 nm has been determined. By proceeding of grinding, we found a d50 < 116 nm after a total of 180 minutes.

Most likely the nano sized particles started to flocculate in the slurry again.

This uses to be a typical behavior of nano size particles when the slurry will not be stabilized with a proper additive. Several kind of additives come into question to improve such a grinding result; always depends on the solvent which will be used for grinding and the kind of material which should be ground, a huge amount of tensides, as well as acids, alcohols, salts etc. can be used to hinder a flocculation of particles.

Because of the determined results, the grinding process has been aborted at this point.

It is also possible that used Mie-Parameters to determine the fineness do not fit properly; a more reliable result can be recalculated when proper Mie-Parameters can be provided.