Geopolymers are produced by reacting an alumino-silicate powder with an aqueous alkali hydroxide and/or alkali silicate activating solution. Geopolymers constitute a family of materials with variable properties within those characteristic of ceramics, cements, zeolites or refractories, depending on formulation. Metakaolin based geopolymers are intrinsically mesoporous and exploiting both direct and indirect foaming techniques, a hierarchical porosity can be constructed. Water affects the intrinsic meso-porosity of the geopolymer matrix, since it acts as a pore former during the polycondensation stage. By ce-templating, water can be used as a sacrificial template and porous architectures with main unidirectional anisotropic macro-pores can be obtained. Rounded ultra-macro-porosity can be obtained by direct foaming, by using blowing agents to generate gas evolution or surfactants to entrap and stabilize air bubbles. Finally, the addition of reactive or inert fillers results in a further functionalization of the materials. Silica fume or silicon carbide can be used as reactive fillers since they contain small quantities of free metallic silicon as impurity. Porous, coarse, natural or mineral inert fillers can be selected to obtain porous composites. A wide range of applications has been and is currently under investigation (insulation, adsorption, wicking, catalysis, etc.) due to the versatility of the process in tailoring the material properties.
Insight into geopolymer porosity
V Medri;E Papa;A Natali Murri;E Landi;P Benito;A Vaccari
2016
Abstract
Geopolymers are produced by reacting an alumino-silicate powder with an aqueous alkali hydroxide and/or alkali silicate activating solution. Geopolymers constitute a family of materials with variable properties within those characteristic of ceramics, cements, zeolites or refractories, depending on formulation. Metakaolin based geopolymers are intrinsically mesoporous and exploiting both direct and indirect foaming techniques, a hierarchical porosity can be constructed. Water affects the intrinsic meso-porosity of the geopolymer matrix, since it acts as a pore former during the polycondensation stage. By ce-templating, water can be used as a sacrificial template and porous architectures with main unidirectional anisotropic macro-pores can be obtained. Rounded ultra-macro-porosity can be obtained by direct foaming, by using blowing agents to generate gas evolution or surfactants to entrap and stabilize air bubbles. Finally, the addition of reactive or inert fillers results in a further functionalization of the materials. Silica fume or silicon carbide can be used as reactive fillers since they contain small quantities of free metallic silicon as impurity. Porous, coarse, natural or mineral inert fillers can be selected to obtain porous composites. A wide range of applications has been and is currently under investigation (insulation, adsorption, wicking, catalysis, etc.) due to the versatility of the process in tailoring the material properties.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
