Exploring expandable microspheres as a novel pore former in gel-cast macroporous alumina

Sammanfattning: Expandable microspheres have been explored as sacrificial templates for the production of macroporous ceramics. Concentrated alumina powder suspensions that contain expandable microspheres have been consolidated by gel-casting. The temperature range for the setting of the monomers and cross-linkers in the gel-casting system was tailored to allow the gas-filled polymer spheres to expand before the surrounding powder body became rigid. It has been demonstrated that it is possible to tune and tailor the porosity up to 86 % and the pore size distribution from 15 up to 150 micrometers by controlling the amount and size of the expandable microspheres. Scanning electron microscopy showed that the porosity became more and more open as the total porosity increased. This was corroborated by a preliminary study by X-ray µ Computed Tomography, which showed a very high connectivity between the pores, in a macroporous alumina body with a high porosity. The connectivity was reduced when alumina particles were deposited as a homogenous coating of on the expandable microspheres by a layer-by-layer coating process. The expandable microspheres has the advantage that a relatively low amount of organic material results in a large pore volume, which allow rapid and facile burn-out. It was demonstrated that the temperature induced expansion of the microspheres, and the associated increase of the suspension volume could be used as a novel casting method to yield macroporous alumina bodies with complex shapes. Ceramics produced with this method could find application ranging from bone scaffolds to low mass kiln furniture.