Aluminium oxide

With a start size of ~ 150µm, we recommend a pre grinding step with 5mm Ø balls.

To avoid overpressure, 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 80°C); grinding time or programmed pausing time might be readjusted afterwards. This is counting for all further grinding trials too.

After 60min of grinding, fineness has been checked and d50 < 820nm has been detected with our Laser Particle Sizer ANALYSETTE 22 NanoTec (see meas. no. 1297 on separate page).

This result is more than fulfilling (probably already 30 min. might be) to change the balls to smaller diameter (e.g. 1,5mm Ø – for this, see result 2).

After sample has been ground with 5mm Ø balls in result 1, ball diameter has been changed to 1,5mm Ø. After additional 7 hours of grinding, d50 result did not change that much. Especially for particles < 1µm, Mie parameters need to be provided for a proper determination.

Particles of > 10µm which has been found in result 1 have been ground. Only particles up to 3µm have been found after totally 8 hours (probably 2 hours might be fulfilling for such a result too).

For this, balls might be changed to e.g. 0,5mm Ø directly (without using 1,5mm Ø grinding balls). For this, see result 3.

In our last trial, balls have been changed from 1,5mm Ø to 0,5mm Ø. By grinding for additional 4 hours (totally 11 hours), a d50 < 307nm has been detected (see meas. no. 1340 on separate page).

Because this measurement has been performed without Mie parameters, true value could be much finer.

Longer grinding times and a further change of ball diameter are still possible to achieve a better endfineness (compare other grinding results of aluminum oxide).