Biomimetic porous silicon oxycarbide ceramics with improved specific strength and efficient thermal insulation

Abstract

Considering the challenge of aerodynamic heating, the development of high-performance insulating ceramic materials with lightweight and low thermal conductivity is crucially important for aerospace vehicles to achieve flight at high speed for a long time. In this work, macro-porous silicon oxycarbide (SiOC) ceramics with directional pores (DP-SiOC) (mean pore size of 88.1 μm) were prepared using polysiloxane precursors via freeze casting and photocrosslinking, followed by pyrolysis. The DP-SiOC samples were lightweight (density ∼0.135 g cm–3) with a porosity of 90.4%, which showed good shapability through the molding of polysiloxane precursors. The DP-SiOC samples also exhibited an ultra-low thermal conductivity of 0.048 W(m K)–1 at room temperature, which can also withstand heat treatment at 1200 °C for 1 h. In addition, scaffolds with triply periodic minimal surfaces (TPMS) were fabricated using digital light processing (DLP) printing, which was further filled with polysiloxane precursors for increasing the strength of DP-SiOC. The TPMS scaffolds filled with macro-porous SiOC ceramics (TPMS-DP-SiOC) showed good integration between TPMS and macro-pore structures, which had a porosity ∼75% and high specific strength of 9.73 × 103 N m kg–1. The thermal conductivity of TPMS-DP-SiOC samples was 0.255 W(m K)–1 at room temperature. The biomimetic TPMS-DP-SiOC ceramics developed in this study are likely used for thermal protection systems.