The focus of the recent work was on the generation of different types of structure. Random
close structured granules as presented in previous years were investigated more
detailed regarding the packing density and primary particle distance distribution inside
a granule. Additional random loose structures were generated allowing porosity as additional
phase. Porous systems were generated using two different methods: fluid bed
granulation and a sintering method. Layered systems or core/shell systems were generated
using a fluid bed; a fine particle suspension was sprayed on larger core particles.
Additionally the particle-particle distance of coarse primary particles that was presented
as suitable structure measure last year was investigated more detailed. The goal was to
develop a theoretical calculation of particle-particle distance based on the known primary
particle size distribution. Results show a good agreement between values calculated
from X-ray micro-tomography images and values from theoretical calculations. Therefore
this theoretical particle-particle distance was used as structure measure in random close
structured granules.
The dissolution measurements of different sets of experiments showed that the dissolution
speed is dependent on two factors: amount of soluble material (fraction of surface
occupied by soluble material) and pore size or phase width of soluble materials. These
two factors are strongly connected and it is difficult to investigate one without the other.
Together a high fraction of soluble material and a high phase width leads to a faster dissolution
compared to granules with smaller phase width (or pore size) and fraction.
The mechanical strength of random close structured granules showed no explicit results
and was difficult to evaluate. Random loose structured granules on the other side showed
a higher strength for lower effective porosities. These results were as expected, the development
of a network of solid bridges between primary particles leads to stable granules
if more and thicker bridges are build.