Synthesis of porous hierarchical geopolymer monoliths by ice-templating

• DOI: 10.1016/j.micromeso.2015.05.043
• Publication Date: 2015-06-13T01:00:00Z
• Authors: Elettra Papa; Valentina Medri; Patricia Benito; Angelo Vaccari; Simone Bugani; Jakub Jaroszewicz; Wojciech Swieszko...; Elena Landi
• Keywords: Alkali-bonded ceramics; 0103 physical sciences; Freeze-casting; Ice-templating; Freeze-casting; Geopolymer; Alkali-bonded ceramics; Porosity; Geopolymer; Ice-templating; Porosity; 01 natural sciences

Hierarchical geopolymers with mesoporous matrices and lamellar macro-porosities were produced for the first time by ice-templating (freeze-casting) technique in a water-based sol-gel system. Starting from an aqueous solution of metakaolin and potassium silicate, geopolymerization was triggered through a maturation step without reaching complete consolidation. Different amounts of water (20, 50, 70 vol.%) were then mixed with the geopolymer paste to induce lamellar ice growth by unidirectional freezing. The consolidation was completed during freeze-casting and drying. Ice-templated hierarchical geopolymers had 53-83% total porosity and N2 BET specific surface area values from 4 to 46 m2 g-1, depending on the amount of water added. A broad mesopore Barret Joyner Halenda distribution was detected between 4 and 100 nm with maxima from 5 to 7 nm, while macropores in the 1-to-100 ?m range were identified by Hg intrusion porosimetry. Lamellar monoliths (height 25 mm) were produced with a selected composition (50 vol.% of additional water) in order to assess the reproducibility of the ice-templating technique combined with geopolymerization.