Manufacture of Highly Porous Tubular Alumina Substrates with Anisotropic Pore Structure by Freeze‐Casting

Abstract

This work investigates the production of freeze‐cast tubular alumina substrates with anisotropic pores. The freeze‐casting method allows accurate control of the radial pore structure by adjusting the solid loading and sintering temperature. High porosities of 91% are attained, which decrease inversely proportional to the solid loading. Water is used as the pore forming agent by the freeze‐cast process, producing lamellar pores with highly connected aligned structure. Substrates with solid loadings within 15–20% show maximum pore alignment and anisotropy, as higher solid loading creates more isotropic pores. The average pore size distribution decreases from 11 to 2 μm as a function of the solid loading. By increasing the sintering temperature from 1300 to 1500 °C, the crushing strength significantly increases for samples prepared with high solid loading, reaching values as high as 25.4 MPa. A plot of the mechanical stability versus porosity reveals that the substrates obtained in this study show a similar trend when compared with previously reported flat substrates. Water permeation reaches 510 L m−2 min−1, showing a strong influence of the pore size. Therefore, processing of freeze‐cast tubular substrates from aqueous suspensions proves to be a versatile technique for manufacturing advanced engineering materials with anisotropic pore structure.