Powder Structure Control

While the last period of work was focused on the implementation of structure descriptors
this year was about the determination of physical parameters of model granules and their
correlation to structure parameters.
Model granules were generated containing different size distributions of primary particles
to achieve different internal structures. A bimodal particles size distribution of fine and
coarse limestone particles was chosen and combined with a polyethylene glycol binder.
Three dimensional X-ray micro tomography images of the model granules were recorded
and used for further calculations of structure descriptors. The structure descriptors that
were evaluated include volume and surface fraction, star volume, chord length distribution
and covariance function.
For the determination of physical properties three different methods were chosen. The
mechanical strength is measured by single particle crushing and the dissolution or disintegration
behaviour by conductivity measurements and online particle sizing respectively.
To achieve statistically relevant results for the single particle crushing, a high number of
single granules has to be measured. An experimental set-up was designed that scans
positions of granules on a sample container and crushes these granules consecutively.
Regarding dissolution and disintegration behaviour of the structured granules, the conductivity
of granules containing salt within the binder phase can be determined in a standard
beaker test. The second method to measure dissolution behaviour contains the
measurement of particles size distribution over time in a laser diffraction system. The
granules are dispersed in an optical glass cuvette and measured continuously.
The structural as well as the physical parameters provide results that are suitable to distinguish
between differently structured granules.
The combination of both kinds of measures to evaluate if there are any significant correlations
between structural and physical measures is the next step that was performed.
In the last part of this first period the two aspects of structure description and property
measurement will be combined on an significant set of granules, representing a variation
of granule structures.