Novel ceramic/camphene-based co-extrusion for highly aligned porous alumina ceramic tubes

We herein propose a novel way of producing highly aligned porous alumina tubes by co-extruding an initial feed rod, which comprised of a pure camphene core and a frozen alumina/camphene shell. This new and simple technique produced alumina tubes (∼4.4 ± 0.1 mm in outer diameter) having uniform alumina walls (∼1.1 ± 0.12 mm in thickness) with highly aligned pores, which were created by removing the extensively elongated camphene dendrites in the extruded alumina/camphene shell. Furthermore, the heat treatment of the extruded bodies at 33°C, which is close to the freezing point of the alumina/camphene slurry, led to a considerable increase in the size of the aligned pores formed in the alumina walls, from ∼<5 to ∼54 μm with increasing heat-treatment time from 0 to 6 h. The compressive strength also increased significantly from 21 ± 1.6 to 61 ± 11.6 MPa, which was attributed mainly to the achievement of well densified alumina walls.