Cerium oxide

First we checked the level of fineness of the start size of the sample. Literature hasn’t provided proper Mie parameters, so we used a refractive index of 2,2 and an absorption coefficient of 0,01. For the start size, we determined a d50 < 1,03 µm and d90 < 1,74 µm. If proper Mie parameters can be provided, a recalculation of the start size (or our grinding results) can be performed anytime.

We recommend zirconium oxide as grinding media, because the smallest grinding balls (0,1 mm Ø) for finest grinding results are only provided in this media. A further disadvantage of metal grinding media would be a discoloration of a whitish sample.

Desired sintered corundum is designed to comminute fibrous, organic samples. This grinding media is producing much more abrasion than other ceramic grinding materials. In sintered corundum, only grinding balls down to 10 mm Ø are available.

We used 180 grams of sample material for comminution inside a 500 ml zirconium oxide bow. The bowl was filled with 800 grams of 0,1 mm Ø grinding balls. On the second bowl position, we placed a properly balanced counter weight. For a faster comminution, the sample amount can be spread into two bowls.

For an optimum viscosity, we added 180 grams of water. A motor oil like viscosity was present. To avoid over pressure, we ground in cycles of one minute (at 800 rpm) of grinding time, followed by fifteen minutes of programmed pausing time. The temperature of the bowl should remain smaller than the boiling point of the used liquid; else the programming of the mill needs to be readjusted.

After five minutes of grinding at max. speed, we checked the particle size distribution and found a d10 < 10 nm; d50 < 30 nm and d90 < 90 nm already.

Because static light scattering was not capable to determine a significant improvement in particle size distribution after 15 minutes and 30 minutes (we found a flocculation of sample), we aborted the trial at this point. Flocculation often occurs when a sample is very fine. It is possible to add stabilizing agents to hinder or slow down flocculation of particles.

We estimate that up to ~ 200 grams of sample could be added into one bowl. After separation of the grinding balls (by sieving), we packed the sample best possible. The grinding equipment was cleaned by a short time comminution of sand and water (~ 20 µm sand fraction with a proper amount). After two minutes, the equipment was flushed with fresh water and dried.