Alumina Porous Ceramics Obtained by Freeze Casting: Structure and Mechanical Behaviour under Compression

Abstract

The aim of the work is to analyse the mechanical behaviour of anisotropic porous alumina ceramics processed by freeze casting (ice templating). The freeze cast specimens were characterised by a lamellar structure with ellipsoidal pore shape, with a size ranging from 6 to 42 µm and 13 to 300 µm for the minor and major axes, respectively, as a function of the freezing rate and the powder and binder contents. The pore volume fraction ranged from 40 to 57%. SEM analysis of the porous structures after the compression test showed a typical deformation pattern caused by the porosity gradient through the specimen, as determined by X-ray radiography. The apparent elastic modulus of the anisotropic porous alumina ranged from 0.2 to 14 GPa and the compressive strength from 6 to 111 MPa, varying as a function of the process parameters which determine the pore network characteristics. The relationships between stress-strain behaviour in compression and the microstructure and texture were established. An analytical model based on a Gibson and Ashby relationship was used and adapted from SEM microstructural analysis after a mechanical test in order to predict the compressive strength of processed anisotropic alumina.

Freeze casting process for the generation of graded porosity in Al2O3 ceramics

“…6c. These pore channels spread throughout the material in an oriented direction, which resulted in a considerable mechanical strength as presented in [35]. The morphology and pore structure of the GFC sample are shown in Fig.…”

“…The presence of the core was also harmful to the compressive strength, decreasing its value drastically. A comparison was established between the compressive strength obtained in this study and in the other studies [16,18,35,36] that used the freeze casting method as the processing route. This comparison is shown in Table IV.…”

“…Li and Li [16] also used tert-butanol as a solvent, with 65%-82% porosity. Hautecoeur et al [35] used water as a solvent with different cooling rates, which changed the pore morphology, directly impacting the compressive strength. In [36], camphene was used as a solvent and the porosity of the samples ranged from 59% to 82%.…”

The Plant-Like Structure of Lance Sea Urchin Spines as Biomimetic Concept Generator for Freeze-Casted Structural Graded Ceramics

“…The porosity of the ceramics was determined using Equation1). Instead of the density of calcite, a theoretical density of α-Al 2 0 3 of 3.97 g/cm 3 [ 39 , 40 ] was implemented in Equation (1).…”

Tailoring the Microstructure of Lamellar Ti3C2Tx MXene Aerogel by Compressive Straining

“… 13 Typical domain structural parameters illustrating (f) small pore size/sheet spacing, 7 (g) larger pore size/sheet spacing. 7 (h) unaligned sheet/domain angles, 14 (i) greater alignment of sheet/domain angles, 14 (j) small domain size, 15 and (k) larger domain size. 15 Sheet/wall structural features include (l) large wall/sheet thickness, 16 (m) smaller wall/sheet thickness, 16 (n) wall/sheet openings, 2 (o) wall/sheet bridges, 10 (p) plate-like wall composition.…”