Synthesis and properties of new geopolymeric foams

Geopolymers are innovative, versatile and cheap inorganic materials with a wide number of industrial applications, having, furthermore, obtained in environmentally friendly conditions [1]. In previous papers, the synthesis and thermal stability of geopolymers were deeply investigated [2,3]; the aim of this study was to develop new geopolymeric foams with tailored porosity in the nano-ultramacro range, in the view of potential applications in the thermal insulation, catalysis, filtration, biomaterials, etc. Geopolymers have been prepared starting from metakaolin and potassium silicate; the process conditions were varied to change the intrinsic nano-micro-porosity of the material and study their influence on the geopolymerization degree. Optimum geopolymerization conditions were selected to develop porous 3D networks by inducing interconnected ultra-macro-porosity (up to millimetric range) in the material, exploiting the ability of Si powder to generate H2 by reaction with H2O (Fig. 1). The in situ foaming was strongly dependent on H2O content of the precursors and the successive process of H2O elimination. The H2 formation is in fact a H2O consuming process, thus increasing the viscosity, as consolidation occurs. The geopolymeric inorganic resins and the related foams were fully characterized in term of microstructure, intrinsic and induced porosity size distribution, specific surface area, geopolymerization degree and surface accessibility. The thermal behavior of the materials was also deeply investigated. The experimental findings highlighted the versatility of these foams, that may be properly tailored as a function of the possible final application.