Quantification of internal structures of spray-dried granules

The internal structure of spray-dried granules determines the processing parameters (e.g. dosing, compacting, redispersing ... ) as well as the properties of the resulting components. The main factors which have an influence on internal structure are the process parameters as well as the properties of the raw material and suspension. For the design of granules the correlations between process parameters and granule properties are required. The characterization of granule parameters like flowability, compaction behaviour and distributions of size, shape and strength is a necessary background. But also the internal granule structure is an important influencing factor. State of the art is the characterization of structures with techniques like computer tomography, immersion liquid technique or microscopic-analysis on polished sections or fracture surfaces. Because of deficient resolution or falsification of results by preparation only a qualitative characterization is possible. In this paper an artefact free preparation technique for weak granules with ion beam technique will be presented. By taking SEM images of internal structures macroscopic (2 ... 100 µm) and microscopic (10 nm ... 5 µm) parameters in spraydried granules can be visualised. Based on these micrographs the quantitative analysis of structure parameters (porosity, porosity gradients, pores, distribution of primary particles) is demonstrated.