A urea crystal templating method for the preparation of porous alumina ceramics with the aligned pores

A novel process for the preparation of porous alumina ceramics with an aligned pore structure has been reported. The urea dissolved in the aqueous alumina slurry at higher temperature formed rod shaped crystals aligned in the direction of gravity when cooled to room temperature. The gelatin used to set the slurry, controls the crystallization of urea such that the urea crystals produced in the suspension containing the gelatin had much lower width and thickness compared to that produced in the suspension without the gelatin. The alumina powder catalyzed the thermal decomposition of urea that enabled the removal of the majority of the urea crystals from the alumina green body by isothermal heating at temperature much lower than the melting point of urea. The void space created by the removal of the urea crystals remained as pores in the sintered ceramics.