Mechanical characterization of micro- and nano-porous alumina

Advanced membrane concepts are based on thin layers that require a mechanically robust porous substrate material. Aiming at the use in pre-combustion systems, alumina substrate with different pore sizes were characterized with respect to their mechanical properties. Elastic moduli and fracture stresses were assessed using ring-on-ring bending tests. Furthermore, elastic moduli were compared to data obtained from indentation tests. Although porosity of the micro- and nano-porous materials were equal, elastic moduli and fracture stress values revealed significant differences, indicating that based on mechanical considerations the nano-porous material is far superior, although initial permeation test indicate difficulties in using it as porous substrate. Elastic moduli showed good agreement with a model based on the load-bearing contact area. Microstructural investigations supported that the higher strength of the nano-porous material is a result of a larger contact area between grains.