Fabrication of lamellar porous alumina with axisymmetric structure by directional solidification with applied electric and magnetic fields

A novel directional solidification method was used to fabricate lamellar porous alumina with an axisymmetrical structure by combining multiple cold sources, electrostatic field, and magnetic field during the freezing of aqueous alumina slurries. Multiple cold sources with mutually perpendicular directions formed by the bottom and parallel sides of rectangular copper molds induced a specific growth direction for ice crystals. The pore channels of porous ceramic are arranged parallel to the direction of electric field lines, and the axisymmetrical structure was obtained after applying the electrostatic field. The applied magnetic field can reduce pore channel size; however, the field has no effect on pore channel direction and distribution, and leads to cracking in the central region of porous ceramics. The compressive strength along the electrostatic field direction is higher than that achieved by conventional freeze casting.