Wood (dried; natural and previously treated)

Majority of sample was ground within 30 seconds. Afterwards, no significant amount felt into the collecting vessel. A bit of sample remains loose on top of the sieve cassettes openings and in the area of the first fixed knife. This is a typical residue inside the grinding chamber.

All residues have been removed easily by vacuuming with a soft brush.

Some fragments have been able to pass the trapezoidal openings longitudinal. For this, up to 3-4 mm long fragments can be found in the ground sample. Also smaller sieve cassettes can be used, but a powder fine kind of sample will not be achieved with a cutting mill.

Grinding set and sample got placed into the optional cryo-box and got fixed on the vibrating plate of the Vibratory Micro Mill. The complete inside of the cryo-box was chilled with liquid N2. Afterwards, we started the grinding process.

Because of evaporation of N2, liquid nitrogen has to be refilled constantly to the feeding funnel during the grinding process. We recommend maintain a level of nitrogen about 1/3 of the filling of the mortar.

For about 10 minutes of grinding, about 1,5 – 2 liters of liquid nitrogen have been used. Afterwards, the sample has been brushed out of the cold grinding set.

Sample is lightly sticking to the grinding set, so a cleaning step with sand and water has been performed afterwards to remove all residues properly.

We are guessing that a simultaneous grinding with a bit of sand or aluminum oxide might improve the grinding process (achievable fineness).

The grinding bowl has been placed into the sleeve for external nitrogen chilling and the sleeves got placed into the holder on the main disk. Now the clamping screw got tightened, followed to the lock nut which makes sure the system will stay in position during operation.

Now the sleeve got filled with a couple of ml of nitrogen to chill the bowl. After the nitrogen evaporated, the machine was started for a programmed grinding time of 2,5 minutes.

After 2,5 min of grinding, the bowls is still chilled (< 20°C); We pre chilled the bowl externally with nitrogen and proceeded this way until 10 minutes of grinding time got reached.

After 10 minutes, the sample is sticking lightly to the bowl and grinding balls. This usually happens when a d50 < 30 µm is reached.

Because of light diffraction, the ground particles appear lighter compared to the original sample.

Pretreated sample was pre ground analogue result 1; afterwards, about 3 grams of aluminum oxide have been fed to the grinding set as well.

We are guessing that the sharp particles of corundum will be helpful to comminute fibrous materials.

After a total grinding time of ~ 15 min, the sample is fine ground. Still a few fibrous particles can be spotted, the amount of longer particles is lesser compared to the result 2.

Also the pre cut sample of pre treated sample of spruce was used with a Planetary Micro Mill PULVERISETTE 7 classic line.

As shown in result 3, this sample was ground to a fine powder within 10 minutes of grinding. Longer particles could not been spotted without using a magnifying glass.

To hinder a cross contamination, we recommend a cleaning step by short time grinding with sand and water before the equipment should be used again.