Flow properties of ductile ceramic granules - challenges in characterization

Spray dried granules are important in the processing of ceramic components as base material for dry compaction shaping operations. During the processing steps flow behavior of the granule material is a critical property. This can influence the handling during storage and transport as well as the homogeneity of the die filling in compaction process. In the latter case inadequate material properties of the compact can result if the flow behavior does not meet the requirements. During product design of granules it is therefore necessary to pay attention on this integral processing property and analyze them with adequate methods. Because of their internal structure, which consists of small primary particles, pores and organic components, granules exhibit some special properties in contrast to systems of dense primary particles. Therefore, the evaluation of the flowability measurement methods (e.g. shear test with rotational shear cell) for the application in the field of ductile ceramic granules in size ranges 20 - 200 µm is necessary. In this context the focus is on the characterization under small loads and selectivity for granule systems with good flow properties. The results of extensive experiments with alumina press bulk in comparison with reference lime stone are presented.