Kalknatronglas, Borosilikatglas

For pre grinding of such glass samples, we recommend using 15 mm Ø grinding balls. With less dense grinding materials (e.g. silicon nitride), probably 20 mm Ø grinding balls should be used.

To avoid over pressure, we ground the sample in steps of 5 minutes, followed by a programmed pausing time of 8 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 further grinding trials too.

After 10 minutes of grinding, we checked the present particles size by optical microscopy. We didn’t spot any pieces larger than 100 µm. Now the grinding balls can be changed to e.g. 2 mm Ø (see result 2).

Because of the rising amount of particles, more water need to be added to maintain a motor oil like viscosity (suggested for an optimum grinding result). After 30 minutes, about 10 grams (corresponding to dry glass weight) of sample needed to be removed to add 16 ml more water and achieve the mentioned kind of viscosity.

Because fineness does not improve significantly after 30 and 60 minutes, a further change in grinding balls (to 0,5 mm Ø) is recommended (see result 3). Probably also a direct change to 0,1 mm Ø might be possible.

Grinding balls have been changed to 0,5 mm Ø and sample got ground for a further hour. With 0,5 mm grinding balls, 60 minutes result (total of 2 hours) resulted in a d50 < 149 nm.

Because longer grinding time did not improve that grinding result with 0,5 mm grinding balls, we recommend changing the grinding balls to 0,1 mm Ø zirconium oxide grinding balls (smallest available grinding balls in our portfolio).

Finally, we changed the grinding balls to 0,1 mm Ø size.

After an additional grinding for 3 hours, we determined the particle size distribution and found d50 < 117 nm. It might be possible to proceed the grinding process to achieve even better grinding results, but most likely additives should be added.

Nano size particles tend to flocculate rapidly in suspension. To hinder this process, a suitable additive should be added (depending on the sample properties, acids, bases, tensides {aliphatic, cationic or anionic}, salts etc.).

The second sample of borosilicate glass was ground similar to results 1-4. We summarize the different steps in for this result.

In the beginning, we added 20 ml of water and hat to add further 6 ml after one hour. At his point, no particles > 10 µm could be spotted by optical microscopy. We also changed the grinding balls to 0,5 mm Ø after one hour of grinding with 2 mm Ø grinding balls.

With the change to 0,1 mm Ø grinding balls (after a total 2 hours), we added further 3 ml of water.

Like result 1, also in this trial we might be able to change to 0,5 mm Ø right after 30 minutes too.

After 5 hours of grinding, we determined a fineness of d50 < 101 nm. Next to longer grinding time or adding of proper additives to hinder a flocculation, also different kind of solvents can be used for grinding (e.g. Benzine, Isopropyl alcohol, Hexane etc.) might come into question.