Zircon (two samples)

With the Planetary Micro Mill PULVERISETTE 7 premium line, smaller quantities can be ground into nano range (always depending on the sample). A grinding of up to 100 g of sample as desired is not possible.

With 30 g of sample, the grinding bowl use to be filled to the absolute maximum. If sample will reach small nano range, only 5-10 g of sample will fit into a 80 ml grinding bowl.

To maintain a motor oil like slurry for an optimum grinding result, we recommend adding ~ 35 ml of isopropyl alcohol (IPA).

To avoid over pressure, we ground the sample in steps of 3 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.

This counts for all further grinding trials in suspension too.

Start size and grinding success has been checked with our Laser Particle Sizer ANALYSETTE 22 NanoTec plus. With this instrument, Mie parameters are required for a precise determination of present particle size. Standard Mie parameters from literature do not fit for the first sample. Probably some impurities in sample use to cause a bimodal grinding result.

As start size (calculated with Fraunhofer theory) all present particles should be < 45 µm. After the first 15 minutes of grinding with 2 mm Ø grinding balls, biggest particles use to be < 5 µm. After 30 minutes of grinding, biggest particle has been detected with < 3,5 µm.

A small portion has been sampled for demonstration (see 2 ml Eppendorf tube).

To reach a maximum grinding result, balls should be changed to 0,1 mm Ø (for this, see result 2).

After a d50 < 864 nm has been achieved in result 1, the used grinding balls has been exchanged against 0,1 mm Ø. Also 5 ml of isopropyl alcohol have been added to maintain a motor oil like slurry.

We proceeded grinding with 0,1 mm Ø grinding balls in this trial. After a total grinding time of 60 minutes, d50 < 335 nm has been detected. After 120 minutes, already d50 < 286 nm has been found.

By longer grinding time, resulting fineness does not change significantly. As mentioned in result 1 – the literature Mie parameters does not fit properly to the given sample. A more precise result can be recalculated when Mie parameters will be provided.

It is also plausible using different kind of solvent or adding grinding agents (like tensides, alcohols, salts etc.) to improve the grinding result.

Sample B2 has been used to demonstrate a grinding with a classic line ball mill. With such mills, it is possible grinding higher amounts of sample in one batch. (with up to 4 bowls of 500 ml volume with Planetary Mill PULVERISETTE 5 classic line).

For a grinding of 100 g of sample as desired, the Planetary Mono Mill PULVERISETTE 6 classic line we used in our trial will be most suitable. We recommend using a 250 ml grinding bowl with the proper amount of balls.

To maintain a motor oil like slurry, we added 20 ml of isopropyl alcohol to 50 g of sample.

After 30 minutes of grinding with 10 mm Ø grinding balls, the present fineness is small enough to change balls to e.g. 1 mm Ø (see result 4).

After 10 mm Ø grinding balls (used in result 3) have been changed to 1,0 mm Ø grinding balls, we added 17 ml of isopropyl alcohol to maintain a motor oil like slurry.

After a total of 60 minutes of grinding, a d50 < 1,339µm has been determined.

After 2 hours of grinding, d50 < 573 nm has been detected. A longer grinding (to a total of 4 hours) didn’t show a significant change in size. For this, we only recommend grinding the sample maximum for 2 hours.

Usually, with a classic line planetary mill, only grinding balls down to 1,0 mm ZrO2 use to work properly. Smaller grinding ball diameters (0,5 or 0,1 mm) might not be efficient for comminution with most kind of samples and this type of mill.