asbestos

With a thickness > 10 µm, we recommend a pre grinding of sample with 3 mm Ø grinding balls before smallest possible grinding balls will be used.

The complete sample amount of 3,6 g use to fill the 80 ml grinding bowl almost completely. During this pre grinding trial, the volume of sample collapsed when fragments of fibers got comminuted.

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. This is also counting for the following fine grinding trial (result 2).

The present slurry was a bit watery with 32 ml of water, possibly 25 ml of water might be fulfilling to achieve an optimum grinding viscosity (motor oil like). Then a faster grinding result might be achieved and less abrasion of zirconium oxide will be expected.

After ~ 20 minutes, most fibers got ground to < 10 µm length (checked by optical microscopy). Because this fineness does not use to be improved significantly, we stopped pre grinding after a total grinding time of 60 minutes and changed grinding balls to 0,1 mm for fine grinding (see result 2).

After first hour of pre grinding with 3 mm Ø grinding balls, we changed the size of grinding balls to 0,1 mm and proceeded grinding.

For an optimum grinding result, an amount of liquid should be chosen to maintain a viscosity similar to motor oil. For this, we added further 3 ml of water after 90 minutes.

We checked the present fineness of sample with our Laser Particle Sizer ANALYSETTE 22 NanoTec plus after 90 minutes and after 3 hours of grinding.

The achieved result after 90 minutes has been d50 < 164 nm. After a total of 3 hours, a d50 < 122 nm has been achieved. To achieve a better grinding result, longer grinding times are plausible. Also adding of grinding agents (like e.g. alcohols and other water mixable solvents, acids, bases, tensides, salts etc.) can lead to a better grinding result.