Investigations of the correlation between granule microstructure and deformation behaviour

For the improved handling and processing of fine and nano-sized materials in ceramic industries a granulation step is required. The processability of granulated material is characterised by flowability and compactibility. Microstructure in combination with deformation behaviour affect the residual defects and with this the quality of sintered compounds. Two alumina oxide granules with different internal structures (hollow and homogeneous) were produced by spray drying. The correlations between granule microstructure and deformation behaviour were investigated using a single granule strength tester. To interpret correlations it is necessary to characterise the internal granule structures first by an objective and quantitative method. For characterising the internal structure via total porosity several techniques (mercury intrusion porosimetry, weight and volume analysis and image analysis of cross sectional images) were compared to find the best fitting one. Additionally the promising technique of image analysis of computer tomography scans is also investigated regarding applicability for granules smaller 160 ?m. As the total porosity is not sufficient for a definite internal structure characterisation a further parameter H defining the distribution of solid material over the cross sectional area is suggested. The internal granule structures are analysed following the described method. Single granule deformation tests were done with several size classes of granules to investigate correlations between microstructure, size and deformation behaviour. Hollow granules seem to show a different deformation behaviour compared to homogeneous ones as their force increases much steeper until reaching the fracture point. Also the deformation behaviour of hollow granules after the fracture point is different than for homogeneous ones, the force drops impressive in some cases even to force zero whereas the force decreases gentler for homogeneous samples.