POROSITY TAILORING IN SYNTHETIC ALUMINO-SILICATE MATERIALS

Aqueous based process for the production of alkali-bonded ceramic foams allows to tailor the porosity in a wide dimensional range to fulfill the porosity requirements for many scientific and industrial applications (biomaterials, catalysis, filtration, thermal insulation, etc.) [1]. Porous 3D networks (foams) were prepared by inducing an interconnected ultra-macro-porosity, up to millimeter range, exploiting an in situ foaming process, involving direct foaming and simultaneous chemical consolidation. The use of metal silicon powder in alkaline condition, leads to the evolution of gaseous H2, that generates foamed architectures when the viscosity of the slurry contemporary increases and the material, consequently, consolidates. Alkali bonded ceramics technology allows to produce ceramic-like materials and high-temperature resistant composites by using simple and low temperature (lower than 80 °C) processes. During the inorganic in situ foaming (i.e. without to employ polymeric templates) it is necessary to consider many variables, such as the amount of foaming agent, the viscosity of the slurry, the process temperatures and the geometry of the die, because the size and the distribution of the pores depend on the experimental conditions. Alkali-bonded ceramic foams were thoroughly studied in order to optimize the consolidation process and to obtain the desired porosity. Ceramic foams were also fully characterized in term of microstructure and intrinsic and induced porosity. The experimental findings highlighted the versatility of these foams that may be properly tailored as a function of the possible final application.