Processing of polymer-derived, aerogel-filled, SiC foams for high-temperature insulation

Abstract

Porous polymer-derived ceramics (PDCs) are outperforming materials when low-density and thermal inertia are required. In this frame, thermal insulating foams such as silicon carbide (SiC) ones possess intriguing requisites for aerospace applications, but their thermal conductivity is affected by gas phase heat transfer and, in the high temperature region, by radiative mechanisms. Owing to the versatility of the PDC route, we present a synthesis pathway to embed PDC SiC aerogels within the open cells of a SiC foam, thus sensibly decreasing the thermal conductivity at 1000 degrees C from 0.371 W center dot m(-1)K(-1) to 0.243 W center dot m(-1)K(-1). In this way, it was possible to couple the mechanical properties of the foam with the insulating ability of the aerogels.The presented synthesis was optimized by selecting, among acetone, n-hexane, and cyclohexane, the proper solvent for the gelation step of the aerogel formation to obtain a proper mesoporous colloidal structure that, after ceramization at 1000 degrees C, presents a specific surface area of 193 m(2)center dot g(-1). The so-obtained ceramic composites present a lowest density of 0.18 g center dot cm(-3), a porosity of 90% and a compressive strength of 0.76 MPa.