Novel Ceramic/Camphene‐Based Co‐Extrusion for Highly Aligned Porous Alumina Ceramic Tubes

Abstract

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.

Three‐dimensional Ceramic/Camphene‐based Coextrusion for Unidirectionally Macrochanneled Alumina Ceramics with Controlled Porous Walls

“…As the initial alumina content increased from 15 to 25 vol%, the overall porosity of the samples, calculated from their dimensions and weight, decreased from 84 ± 1.0 vol% to 68 ± 4.3 vol%. This was mainly attributed to a decrease in the porosity of the alumina walls, as is often the case with porous ceramics produced using freeze casting . The porosity of the alumina walls, which was roughly calculated by considering the overall porosity of the samples and the fraction of the macrochannels, decreased from 76 to 57 vol% with an increase in initial alumina content from 15 to 25 vol%.…”

“…This was mainly attributed to a decrease in the porosity of the alumina walls, as is often the case with porous ceramics produced using freeze casting. 12,14 The porosity of the alumina walls, which was roughly calculated by considering the overall porosity of the samples and the fraction of the macrochannels, decreased from 76 to 57 vol% with an increase in initial alumina content from 15 to 25 vol%. However, regardless of the initial alumina contents, all the samples showed that a commercial epoxy could completely infiltrate into the pores (data not shown here), suggesting good interconnection between the pores.…”

Freeze Casting: From Low‐Dimensional Building Blocks to Aligned Porous Structures—A Review of Novel Materials, Methods, and Applications

“…[ 107 ] However, the formation of aligned micro pores is limited in this approach. Highly oriented pores can be obtained by a 3D ceramic/camphene‐based coextrusion (3D‐CoEx) technique ( Figure A), [ 108 ] in which a continuous ceramic/camphene filament consisting of a pure camphene core and a frozen alumina/camphene shell is deposited by coextrusion. Subsequently, unidirectional macrochannels and interconnected micropores are created through removal of camphene.…”

“…Reproduced with permission. [ 108c ] Copyright 2015, Elsevier. B) Schematic of 3D printing combining freeze casting and extrusion/inkjet.…”

Fabrication of ice-templated tubes by rotational freezing: Microstructure, strength, and permeability

“…However, the difficulties demolding the tubes after solidification is drawback of this set-up that limits further industrial development. Moon et al [27] overcomes this issue combining ice-templating with co-extrusion, however the resultant porosity is not radially aligned.…”