Optimized processing of defect-free porous alumina by gel casting process

Abstract

Porous alumina ceramics was fabricated by direct foaming method using a natural foaming agent shikakai of Acacia Mimosaceae family. Binders affected the foam stability and stable foams were obtained with 2 wt% PVA wrt alumina. The dispersant concentration (0.5%) and the milling time (12 h) were optimized. The slurries for gel casting were prepared by varying solid loading, saponin and surfactant concentration at a constant PVA content. At low saponin content (0.07–0.4%), cracked and drained samples formed. Both cracking and drainage defects were minimized on increasing saponin to 2%. 1.5% Glycerol addition resulted in defect-free samples which could be correlated with the lowering of the shear modulus of the slurry with glycerol addition. The microstructure of the green and sintered samples show that porosity and interconnectivity improved with saponin and glycerol addition. In defect-free samples, the highest total porosity was 51.23 ± 4.25% in 30% solid loading samples. The maximum pore size was 67.16 ± 45.6 µm. Both porosity and pore size decreased with increase in solid loading and saponin content.