Grinding into Nanopowders for the Chemical and Pharmaceutical Industries

A new planetary ball mill PULVERISETTE 7 premium line, from FRITSCH GmbH, has been launched recently. The company provides customers with the ability to comminute small samples up into the nano range (1 nm = 10-9 m) with this comminution concept.

An example is new medications with nanoscale-active ingredients, which are of particular interest to the pharmaceutical sector. The human body absorbs active ingredients in the nano scale a lot faster than conventional compounds, reducing the dosage of medications due to better bioavailability.

As well as achieving the same therapeutic effects with less active ingredients, unnecessary side effects can also be reduced. The enlarged specific surface of nano particles which effectively illustrate new catalytic attributes is also why there is a demand for nano particles in the chemical sector.

In a planetary mill, the sample is placed together with the grinding balls into a grinding bowl. The grinding bowls are fastened onto the sun dial and counter-rotate around the center of the disc. The sample is successfully comminuted through beating, crushing, and grinding processes.

For conventional planetary mills, the maximum possible speed range is restricted to approximately 800 rpm. The clamping of the grinding bowls differentiates the premium line from a regular mill. Instead of being clamped onto the disk, the bowls are sunken into the sun disk (SelfLOCK Technology).

This arrangement increases the maximum rotational speed in the premium line to 1100 rpm, enabling a 150% increase in the kinetic energy of the grinding bodies. The comminution of nanoparticles for certain materials can be achieved because of a major reduction in the nanoscale grinding time.

The comminution of aluminum oxide (Al2O3) is illustrated as a testing system here. The d50 value of the base material is 20 µm. 0.5 mm zirconium oxide (ZrO2) balls and 5 ml Al2O3 are ground together with water to approximately 300 nm for 60 minutes.

It is essential to utilize even smaller grinding pearls to achieve the range of <100 nm. ZrO2 pearls with a diameter of 0.1 mm were used in this case.

In consideration of the corresponding Mie parameters, the illustrated grain size distribution was measured using the FRITSCH Laser Particle Sizer ANALYSETTE 22 NanoTec. If a ball mill is used for comminution, a certain abrasion on the grinding bodies is unavoidable. The resulting abrasion was measured by deducting from the original.

Comparable results can also be achieved using other hard fibrous metal oxides. With these oxides, the comminution is always in a suspension, and a dry comminution is not possible.

As nanoparticles have a very large specific surface, the suspension is unstable during the end of the comminution – the particles re-agglomerate rapidly. Special additives have to be used for stabilization. Corresponding tests are performed in the Fritsch application laboratory.

The safety of the process during comminution is enhanced as the grinding bowls are sunk utilizing the new SelfLOCK-Technology. The bowls can be clamped into the mill using two hand motions, and this clamping mechanism enhances the safety process during grinding as faulty operation is prevented.

The grinding bowls used are automatically identified by the RFID-chip integrated into the lid of the bowl. Optimal rotation speed is accomplished, and non-permissible grinding settings are eliminated. If the mill is loaded inaccurately, a balance check prevents the start-up of the mill.

Secure sealing is possible with the newly-developed special bowls. A built-in valve in the lid allows controlled discharge of any overpressure arising during grinding. Ideal conditions are guaranteed to achieve reproducible and precise grinding results in the nano range.

The premium line is capable of producing and saving a number of grinding programs. The variable parameters are grinding time, pause times, speed, and reverse mode. Standard operating procedures (SOP) can be produced and can be password-protected.

Integration of the ball mill into the IT structure of the laboratory is enabled with a USB interface. Special software allows the grinding parameters to be recorded and saved, enabling validation of the grinding process.

For the new FRITSCH PULVERISETTE 7 premium line, the grinding bowl is available in a variety of sizes, for example 20 ml, 45 ml, and 80 ml. Bowls are made in a wide range of materials to suit a broad spectrum of applications. From steel to hard metal tungsten carbide; from agate to zirconium oxide; the appropriate material exists for every application.

In addition, grinding balls are available in a range of sizes. Increasingly small grinding balls are also available in order to achieve even smaller particle sizes.

The FRITSCH PULVERISETTE 7 premium line is the new standard for the formation of nanopowders on a laboratory scale.

This information has been sourced, reviewed and adapted from materials provided by FRITSCH GMBH – Milling and Sizing.

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Post time: Apr-10-2019
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