Evaluation of compaction behaviour of spray-dried alumina by Hg porosimetry and SEM

Compaction is a widely used fabrication process for ceramics due to its low cost and high productivity. The majority of defects are formed at this stage and, consequently, the evaluation of the process parameters is extremely important. Alumina spray-dried powders were pressed varying pressure, temperature and humidity conditions. Scanning electron microscopy (SEM) analysis was performed to observe the micro-structural evolution of the fractured surfaces in different compaction conditions. The Hg porosimetry analysis showed the decrease of intra and intergranular porosities until complete elimination of the intergranular porosity, as the pressure increased. The glass transition temperature of the binder (Tg) affects the microstructure of green bodies significantly: powders pressed at higher temperatures than Tg presented more intergranular porosity elimination at the same compaction pressure, through plastic deformation and fracturing of granules. Hg porosimetry analysis was suitable for measurement of the pressure in which total elimination of intergranular porosity occurs, join point (Pjoin): this result was confirmed by SEM.