Microcellular Al2O3 ceramics from wood for filter applications

Microcellular biomorphous Al2O3 was produced by Al-vapor infiltration in pyrolyzed rattan and pine wood-derived biocarbon preforms. At 1600 degrees C the biocarbon preforms reacted with gaseous aluminum to form Al4C3. After oxidation in air at temperatures between 1550 degrees and 1650 degrees C, for 3 h, the biocarbon preforms were fully converted into alpha-Al2O3. Owing to the high anisotropy of biomorphous Al2O3, the compressive strength behavior was strongly dependent on the loading direction. The compressive strength of the specimens (0.1-11 MPa) is strongly dependent on their overall porosity and their behavior could be explained using the Gibson-Ashby model. The Darcian permeability (k(1)), as well as the non-Darcian permeability (k(2)), increased with an increase of the total porosity. The Darcian permeability of biomorphous Al2O3 was found to be in the range of 1-8 x 10(-9) m(2), which is in the order of magnitude of gas filters, and, therefore, suitable for several technological applications.