Novel cordierite foams from preceramic polymers and reactive oxide fillers

Cordierite (Mg2Al4Si5O18) ceramic foams have been successfully prepared by a novel approach, consisting of the firing at 1350 degrees C of commercial silicone resins (Sikes (R) MK and H62C) embedding micro-sized Mg(OH)(2) and Al2O3 powders, acting as reactive fillers. The foaming was due to a preliminary heating stage, at 300 degrees C, at which magnesium hydroxide decomposed, releasing water vapor in the viscous mass offered by silicone resins before their ceramic conversion. Two different strategies were employed for the mixing of components, depending on the nature of the preceramic polymer used. For a liquid polymer, the fillers were added starting from polymer solutions; for a solid polymer, the fillers were incorporated by melting in a conventional extruder. Despite significant differences in the formulations and in the mixing, the resulting ceramics are similar, in terms of remarkable phase purity, total porosity (in the order of 64%) and mechanical properties (compressive strength approximate to 2.3 MPa).