Dr. Peter R. Laity
School of Applied Sciences, University of Huddersfield,

During compaction, the volume of the powder bed is reduced through various mechanisms, including granular movements, rearrangements, fragmentation and deformation.  Although it is generally assumed that the first two only play a significant role at relatively low packing densities (i.e. while there is still room for granular rearrangements), it is very difficult to quantify the contribution of each mechanism.

Small-angle X-ray scattering (SAXS) is sensitive to changes in the nanometre-scale morphology, which is predominantly associated with the internal structure of granules.  Consequently, it is possible to extract quantitative estimates of granule deformation from SAXS measurements, which can be made at different stages during compaction or locations within compacted specimens.  SAXS can also reveal the principal compressive strain direction, which can vary due to location or the effects of tooling geometry (i.e. non-planar contact surfaces and embossed features).

Results using this relatively new methodology will be presented for two materials (spheronised microcrystalline cellulose and magnesium aluminium silicate clay), which demonstrate how granule deformation increases during powder compaction.  The effects of tooling geometry on local compaction behaviour, compressive strain and stress will also be explored.