Porosity of freeze-dried γ-Al2O3 powders

The porosity, inter-particulate and inter-agglomerate, of γ-Al2O3 nanopowders obtained by the freeze-drying method has been studied. Homogeneous spherical granules with diameters ranging from 1 to 100 μm have been obtained. These granules are constituted by soft agglomerates of nanoparticles. The pore volume and size distribution are a function of the freezing kinetics and the processing parameters. Mercury intrusion porosimetry results show that the powders exhibit a multimodal porosity. A mesoporosity with mean size of 10 nm, attributed to the inter-particulate porosity, is practically constant, whereas the inter-agglomerate porosity (100–600 nm), strongly depends on the salt concentration, freezing rate and thermal treatment of the powders.