How can macroscopic powder characterization be realized?
The determination of the macroscopic, physical properties of a powder sample is essential for its all-encompassing characterization. This provides a fundamental understanding of the behavior of a powder in its entirety and especially with regard to processing, packaging and the transport, as well as for the storage and application of the powdered material. The macroscopic behavior of a powder depends very much on the particular conditions. For example, the bulk density or the angle of repose of a powder heap depends on the height of fall and the resulting compaction. Therefore, the measurement conditions for determining such parameters are defined in various standards. The most widespread and most frequently used standard for macroscopic powder characterization is ASTM D6393. While many standards usually define the measurement of only one parameter (e.g. ISO 3953 – Tapped density of metal powders, ISO 3923 – Bulk density of metal powders), the ASTM D6393 standard defines the conditions for the determination of 10 different parameters, so-called Carr indices:
- Measurement of Carr Angle of Repose
- Measurement of Carr Angle of Fall or Carr Angle of Collapse
- Calculation of Carr Angle of Difference
- Measurement of Carr Angle of Spatula
- Measurement of Carr Loose Bulk Density
- Measurement of Carr Packed Bulk Density or Tap Density
- Calculation of Carr Compressibility
- Measurement of Carr Cohesion
- Measurement of Carr Uniformity
- Measurement of Carr Dispersibility
Depending on the application, each of these parameters can be used for an evaluation of the powder or allow a statement on the powder quality in the further process. For example, the angle of repose and the collapse angle should be considered for the design of a conical storage silo. For the dimensioning of packaging bags and drums, or for the production of tablets from powder raw materials, tapping and bulk densities are decisive parameters.
Innovative measuring instruments such as the PowderPro A1 enable fully automatic determination of Carr indices thanks to angular measurements by means of a CCD camera and an image processing routine, automatic control technology and state-of-the-art software with implemented, standardized measuring procedures (SOPs). The immediate data communication with an electronic scale enables the automatic and direct transmission of the weighing data to the measuring system.
In the following videos measurements are shown as examples:
For the determination of the tapped density of powders and granules, optionally with one, two or three stations to increase the sample throughput, we have the BeDensi T1, T2 and T3 in our product range, optionally with a sound insulation box as well as our standard material 3P-SRF-F6 for bulk density and tapped density measurements.