Effect of emulsion composition on gel strength and porosity in the preparation of macroporous alumina ceramics by freeze gelcasting

The freeze gelcasting of hydrogenated vegetable oil-in-aqueous alumina slurry (HVO-in-AAS) emulsions of HVO to AAS volume ratios in the range of 1.34–2.69 prepared from slurries of various alumina concentrations were studied to prepare macroporous ceramics of high porosity. The compressive strength (20–150 kPa) and Young's modulus (120–1550 kPa) of the gelled emulsion bodies increased with an increase in alumina slurry concentration and HVO to AAS volume ratio. Easy HVO removal from gelled emulsion bodies by extraction at room temperature with petroleum ether, a less toxic solvent, was achieved. The highest porosity achieved at a HVO to AAS volume ratio of 2.69 increased from 84 to 92.5% when the alumina concentrations in the slurry decreased from 30 to 10 vol.%. The cell size and cell interconnectivity of the ceramics depended on the alumina slurry concentration and HVO to AAS volume ratio. The Young's modulus of the macroporous ceramics modelled using the equation proposed by Gibson and Ashby showed large deviation in the model parameters, n and C, from the proposed values.