COLLOIDAL GRINDING PRODUCING NANO PARTICLES BY COLLOIDAL GRINDING
So-called colloidal or nano grindings are usually carried out as wet grindings. To reduce already small parti- cles further in size by using mechanical force, a h h ener
RETSCH’s Emax and planetary ball mills. Further important tools and optimum grinding ball fi llings.
high energy input is required. This input is prov nt cri
riteri ria for na nano grindings ar grindings are sui abuitable grindin
ovided by grinding
PRELIMINARY GRINDING
Depending on the size of the initial sample material and desired fi nal fi neness, a preliminary size reduction step can be useful. A dry grinding process with grinding balls of >3 mm Ø is usually carried out by fi lling one third of the jar with grinding balls and one third with sample material. The obtained sample is then used for the actual colloidal process.
Grinding jar “comfort” for PM series with safety closure, aeration cover
Grinding jar “comfort”for PM series with HOW TO CARRY OUT COLLOIDAL GRINDING IN A BALL MILL
With the planetary ball mills and the new Emax, RETSCH offers two types of ball mills which provide the required energy input for colloidal grinding down to the nanometer range. Grinding jars and balls made of an abrasion-resistant material such as zirconium oxide are best suited for this type of application. 60 % of the grinding jar volume is fi lled with grinding balls of 0.5 to 3 mm Ø, providing a large number of frictional points. The actual sample fi lls about one third of the jar volume. By adding a suitable dispersant (e. g. water, isopropanol, buffer), the consistency of the sam- ple should become pasty thus providing ideal preconditions for colloidal grinding. If a very high fi nal fi neness is required,
it is recommended to proceed with a second colloidal grind- ing with 0.1 to 0.5 mm Ø grinding balls, particularly if 2 to 3 mm balls were used in the fi rst process (the balls need to be 3 x bigger than the particle size of the initial material). To separate the sample from the grinding balls, both are put on a sieve (with aperture sizes 20 to 50 % smaller than the balls) with a collecting pan. For the subsequent colloidal grinding 60 % of the jar is fi lled with small beads. The sus- pension from the previous grinding is carefully mixed with the grinding beads until a pasty consistency is obtained.
CONSISTENCY
If a sample tends to swell during wet grinding, the consis- tency of the sample-grinding ball mixture should be checked during the process to add more dispersant if required. If the
material is known to swell easily, it should be diluted more strongly before the grinding is started.
REMOVAL OF GRINDING JAR
Care must be taken when removing the grinding jar from the planetary ball mill as it can have a temperature of up to 150 °C due to the heat generated during the grinding pro- cess. Moreover, pressure builds up inside the grinding jar. Therefore, it is recommendable to use the optional safety closure for the “comfort” grinding jars of the PM series which allows for safe removal of the jar. After the grinding
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www.retsch.com
process the jar should cool down for a while. The Emax jar already has an integrated safety closure. Moreover, the
effective cooling system of the Emax prevents the jars from
heating up too much. Both jars can be equipped with option- al aeration covers which allow working under inert atmo- sphere.
Direct contact: 866-473-8724
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