Enrico Bernardo, Multifunctional Silicates from Silicone Resins filled with Oxide Nano-particles
Date: Fri 26 Apr 2013, 12:00 - 13:00
Location: Nanoforce Seminar Room
Dipartimento di Ingegneria Meccanica, University of Padova, Padova, Italy
Keywords: nanocomposites, precursors, nanoparticulates.
Many silicates are of great interest due their remarkable mechanical properties at high temperatures, low thermal expansion and high thermal shock resistance, optimum dielectric properties, biocompatibility etc. The characteristic poor interdiffusion due to partially covalent bonding, however, greatly complicates conventional sintering. A novel solution is represented by polymer-derived ceramics, in which a silicate article is obtained by direct thermal treatment in air of nano-composites consisting of silicone resins filled with suitable oxide nano-particles. The desired silicate is synthesized by the reaction of the oxide with the silica from the oxidative thermal decomposition of the silicone polymers; both residual porosity and glassy phase are very limited, and the grain size is typically below 200 nm. Fundamental examples concern pure mullite (3Al2O3.2SiO2) and zirconia toughened mullite, to be used as dielectric or high temperature structural materials, and wollastonite-based materials, including wollastonite-hydroxyapatite composites, to be used as biomaterials, mainly with a cellular morphology. More recent researches have been focused on the development of forsterite (2MgO.SiO2), to be applied as biomaterial or as dielectric, yttrium silicates (Y2O3.SiO2 and 2Y2O3.SiO2) and zircon (ZrO2.SiO2), to be applied as thermal barrier coatings and refractory components; if thermal treatments in air are avoided, and the ceramic conversion of the polymer is obtained in nitrogen atmosphere, several types of oxynitrides (i.e. SiAlON ceramics) are feasible from the same approach of nano-filled silicones, with many possible applications in ceramic composites and in the structural joining.