Université de Mons 0.2 Guillaume JEAN | Service de Science des Matériaux Manufacture of macroporous ceramics by spark plasma sintering G. Jean 1, V. Sciamanna 1, L. Verbelen 1, M. Gonon 1, M. Demuynck², F.Cambier² 1 UMons - Faculté Polytechnique de Mons, Service de Science des Matériaux, 56, rue de l'Epargne, 7000 Mons (Belgium) ²Belgian Ceramic Research Centre, 4, avenue du gouverneur Cornez, 7000 Mons (Belgium) Conclusions  Pressure applied on the packing induces the formation of necks between the granules.  Porous alumina ceramics with porosity up to 55 % can be obtained by spray-dried granule packing sintering.  The final material can only show intergranular porosity or intergranular and intragranular porosities.  Spark Plasma Sintering (SPS) was performed. Compared with hot pressing sintering, porous alumina ceramics can be manufactured at lower heating temperature, high heating and cooling rate and shorter sintering time. Purpose The aim of this research is to develop a new route for manufacturing macroporous ceramics (>50 nm) characterized by a porosity level greater than 30% and highly interconnected pores, with sizes between 30 µm to 80 µm. Such porous materials could find applications in the fields of fluid transfer/mixing, catalysis or filtration. Classical processing methods (replica technique, sacrificial template method, direct foaming) doesn’t meet all these requirements. The process should be sufficiently versatile in order to tailor: i)- the porosity fraction within a large range (typically 30 to 80 %); ii)- the pore size distribution (single or multimode). Methodology To “bridge” packing of basic ceramic “units” (spheres, cylinders,…) by sintering. Sintering must promote solid diffusion at interfaces between units with a limited densification to keep high porosity. Sintering Driving force: reduction of surface energy of the particles caused by decreasing their solid/vapour interfaces Powder compact T > 0.4 Tm Dense polycrystalline solid : Basic ceramic units: Industrial granules obtained by spray-drying of alumina powder with : d 50 of 0.4 µm and specific surface area of 8 m²/g The granules are spherical ; have a porous structure and a nearly unimodal size distribution (d 50 : 76 µm). Sintering of granule packing Pressureless ( Total porosity fraction is 68% (maximum porosity that can be expected by bridging the granules’ packing). A pressure during heat treatment is necessary to activate diffusion through the contact points of the granules and promote sintering. Pressure effect on granule packing Compaction curves of the heat treated granules Expected structure Packing of basic units bridged together give the negative image of the structure resulting of sacrificial methods using organic beads. This new route allows to make material with :  highly interconnected porosity  good control of the pore size distribution  porosity up to 50% with good mechanical Properties Sacrificial method Expected structure Spark Plasma Sintering (SPS) SPS is a hot pressing technique using pulsed DC current Advantages compared to conventional hot-press sintering: I n order to work with a pressure higher than 0.2 MPa, mechanical resistance of the granules sould previously be improved to avoid plastic deformation and to keep the intergranular porosity during granule packing sintering. Plastic deformation begins at much higher pressures when the temperature of the heat treatment increases. There is a reinforcement of the granule’s mechanical properties.  Promote the bridging of granules by neck growth  A very high heating and cooling rate (up to 1000 K/min)  Decrease sintering temperature  Decrease sintering time 0 Compaction pressure (MPa) Normalised density Relative density (%) 50 40