This preliminary study reports a simple process for the production of geopolymer porous spheres through an injection and solidification method using liquid nitrogen. Metakaolin-based geopolymer slurries were prepared in advance, using a potassium-based disilicate as alkaline activating solution, and left at room temperature for several hours (maturation step) in order to trigger the geopolymerization without reaching a complete chemical consolidation. The mixture was injected as it is or mixed with water or an organic template in order to modulate the porosity developed in the final spheres. Indeed, the production process of geopolymers in aqueous medium allows the tailoring of the porosity by tuning the water content in the starting mixture, which affects the intrinsic mesoporosity of the geopolymer matrix, being water a pore former during the polycondensation stage [1,2]. The porosity of the spheres can be further tailored adding organic polymers in the mixture that act as templates of the material skeleton. The spheres, formed after the injection, were then freeze dried in a lyophilizer to remove the solidified water and complete the chemical consolidation of the geopolymer. The polymeric template can be later removed by thermal treatment. The goal of this study was to synthetize geopolymer spheres with hierarchical porous structures differing in term of intrinsic mesoporosity and architecture, which means distribution of voids/material within the sphere. The developed materials find potential applications in fields as catalysis, filtration, adsorption, etc. Geopolymer slurries composition and maturation steps were deeply investigated in order to optimize the consolidation process and to design the porosity in the final spheres. For the same reason, the timing of the organic template addition to the geopolymer mixture was also studied. The selected geopolymer spheres were characterized in term of size, morphology, macro- and microstructure, composition-stoichiometry, porosity distribution and specific surface area.
Shaping of porous geopolymer spheres
E Papa;R Bendoni;V Medri;E Landi
2017
Abstract
This preliminary study reports a simple process for the production of geopolymer porous spheres through an injection and solidification method using liquid nitrogen. Metakaolin-based geopolymer slurries were prepared in advance, using a potassium-based disilicate as alkaline activating solution, and left at room temperature for several hours (maturation step) in order to trigger the geopolymerization without reaching a complete chemical consolidation. The mixture was injected as it is or mixed with water or an organic template in order to modulate the porosity developed in the final spheres. Indeed, the production process of geopolymers in aqueous medium allows the tailoring of the porosity by tuning the water content in the starting mixture, which affects the intrinsic mesoporosity of the geopolymer matrix, being water a pore former during the polycondensation stage [1,2]. The porosity of the spheres can be further tailored adding organic polymers in the mixture that act as templates of the material skeleton. The spheres, formed after the injection, were then freeze dried in a lyophilizer to remove the solidified water and complete the chemical consolidation of the geopolymer. The polymeric template can be later removed by thermal treatment. The goal of this study was to synthetize geopolymer spheres with hierarchical porous structures differing in term of intrinsic mesoporosity and architecture, which means distribution of voids/material within the sphere. The developed materials find potential applications in fields as catalysis, filtration, adsorption, etc. Geopolymer slurries composition and maturation steps were deeply investigated in order to optimize the consolidation process and to design the porosity in the final spheres. For the same reason, the timing of the organic template addition to the geopolymer mixture was also studied. The selected geopolymer spheres were characterized in term of size, morphology, macro- and microstructure, composition-stoichiometry, porosity distribution and specific surface area.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
