Fly Ash (dry - mostly SiO2)

0,1 mm Ø grinding balls need to be used for finest grinding results. Because the present particle size is too big for such small grinding balls, a pre grinding step with e.g. 3 mm Ø grinding balls needs to be performed previously.

For this, we filled 100 g of 3 mm Ø zirconium oxide grinding balls plus 10 g of sample into the 80 ml grinding bowl and added 30 ml of water for grinding.

To avoid over pressure, we ground the sample in steps of 3 minutes, followed by a programmed pausing time of 9 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.

We checked the particle size during the grinding process after 15 minutes of grinding and 30 minutes of grinding. Fineness did not improved in last 15 minutes with a present d90 < 2,7 µm. For this, grinding balls can also be changed to 0,1 mm Ø for fine grinding (see result 2) after 15 minutes of grinding time.

After pre grinding with 3 mm Ø grinding balls, the balls had been changed to 0,1 mm Ø.

We needed to add 14 ml of water to maintain a motor oil like slurry again (necessary to achieve an optimum grinding result). Mixture became too pasty during the grinding process of result 1.

Because fineness of particle size uses to be in a range where Mie parameters use to be required for a more precise result, we used the Mie parameters of silica for calculation. If proper Mie parameters for your kind of sample are known, a recalculation of grinding results is possible.

After a total grinding time of 60 minutes, the d90 sunk to 0,46 µm. With 90 minutes of grinding time, the d90 sunk to < 0,25 µm. By longer grinding in water, the grinding result did not changed significantly. For this, the grinding process has been aborted after a total grinding time of 120 minutes.

It might be possible to improve the grinding process when grinding agents like tensides, salts, acids, bases or water mixable solvents will be added.

Because 20 g of sample will not fit into one bowl (80 ml max. volume), we recommend using the second bowl holder of the machine simultaneous with equal equipment (we used the optional counter weight on that position).