Freeze-casting of highly porous cellulose-nanofiber-reinforced γ˗Al2O3 monoliths
H. Hudelja,
T. Konegger,
B. Wicklein,
J. Čretnik,
F. Akhtar,
A. Kocjan
Affiliations
H. Hudelja
Department for Nanostructured Materials, Jožef Stefan Institute, Jamova 39, 1000, Ljubljana, Slovenia; Jožef Stefan International Postgraduate School, Jamova 39, 1000, Ljubljana, Slovenia; Corresponding authors. Department for Nanostructured Materials, Jožef Stefan Institute, Jamova 39, 1000, Ljubljana, Slovenia.
T. Konegger
Institute of Chemical Technologies and Analytics, TU Wien, Getreidemarkt 9/164-CT, A-1060, Vienna, Austria
B. Wicklein
Instituto de Ciencia de Materiales de Madrid (ICMM), Consejo Superior de Investigaciones Científicas (CSIC), Calle Sor Juana Inés de la Cruz, 3, Madrid, 28049, Spain
J. Čretnik
Slovenian National Building and Civil Engineering Institute, Dimičeva ulica 12, 1000, Ljubljana, Slovenia
F. Akhtar
Division of Material Science, Luleå University of Technology, SE-97187, Luleå, Sweden
A. Kocjan
Department for Nanostructured Materials, Jožef Stefan Institute, Jamova 39, 1000, Ljubljana, Slovenia; Jožef Stefan International Postgraduate School, Jamova 39, 1000, Ljubljana, Slovenia; Corresponding authors. Department for Nanostructured Materials, Jožef Stefan Institute, Jamova 39, 1000, Ljubljana, Slovenia.
Freeze-casting is a powerful consolidation technique for the fabrication of highly porous and layered-hybrid materials, including ceramic-metal composites, and porous scaffolds for catalysis, bone substitutes and high-performance membranes. The aqueous suspensions to be freeze-casted usually contain dense particles facilitating macroporous, layered ceramics with dense (nonporous) struts. In the present study, hierarchical macro-mesoporous alumina (HMMA) monoliths were successfully prepared by freeze-casting of aqueous suspensions containing hierarchically-assembled, mesoporous γ‒Al2O3 (MA) powder and cellulose nanofibers (CNF). As-prepared monoliths were ultra-porous (93.1–99.2%), had low densities (0.01–0.25 g/cm3), and displayed relatively high surface areas (91–134 m2/g), but were still remarkably rigid with high compressive strengths (up to 52 kPa). Owing to the columnar porosity and mesoporous nature of the struts the freeze-casted HMMA monoliths exhibited high permeability and high thermal insulation, the latter ranging from 0.039 W/m∙K to 0.071 W/m∙K, depending on pore orientation.
