Unidirectional porous alumina ceramics fabricated by freeze-drying process with sodium alginate

Alumina porous ceramics were prepared via unidirectional freezing of alumina/sodium alginate slurry and subsequent freeze-drying and sintering. The permeability of the obtained porous ceramics with the porosity of 66.7% is more than ten times greater than that of Al₂O₃ foams prepared through a conventional process. The compressive strength of the sample with the solid loading of only 25% is 16.03 MPa. The porous ceramics with such a satisfactory strength and complex pore structure can be used in various applications such as fuel cell electrodes, catalysts support and high efficient filtering. Sodium alginate was used as a toxic-free binder for the preparation, making the process environmental friendly and increasing the green body strength. The uniformity of structure is affected by the fluidity and viscosity of alumina slurry. The addition of a dispersant can improve the viscosity of slurry and the uniformity of microstructures. In addition, the effects of solid loading and sintering temperature on the pore size distribution, compressive strength and permeability were also investigated. As the solid loading decreasing from 30% to 20%, the porosity increased from 61% to 72%, compressive strength decreased from 16.03 to 3.42 MPa, permeability increased from 0.19×10^-11 m² to 4.51×10^-11 m². Furthermore, as the sintering temperature increased from 1300 to 1500 ℃, the porosity decreased from 69.72% to 67.02%, the compressive strength increased from 4.45 to 18.66 MPa, permeability decreased from 4.51×10^-11 m² to 4.09×10^-11 m².