Graphite-assisted structural design of hierarchically porous SiC(rGO) PDCs with excellent capacity in thermal protection/insulation and load bearing for hypersonic vehicles

Abstract

High flight speed of hypersonic vehicles will push thermal insulation composites to achieve balanced enhancement of high porosity with increasing load-bearing capability. Herein, hierarchically porous SiC(rGO) polymer-derived ceramics (PDCs) with lightweight, heat-insulating, anti-ablative and tough engineered merits, are designed from polycarbosilane-vinyltriethoxysilane-graphene oxide precursors by re-pyrolysis/graphite-assisted decarburization. Graphite pore-forming agents tightly coupled with SiOxCy/Cfree(rGO) by C-dangling bonds, can inhibit SiOxCy decomposition, increase ceramic network disorder and expedite concurrent removal of Cfree. SiO2 generated from Si-dangling oxidation bonding, efficiently densifies framework to retain mechanical performances, and meanwhile creates more interfaces to enhance phonon scattering. Such structure similar to nodular cast iron confers low thermal conductivity (0.11 W·m-1·K-1), particularly, fully preserves good compressive strength (5.4 MPa) for SiC(rGO)40%. Under both cyclic butane flame ablation (∼1300 °C) and long-term oxidation for 7200 s, self-healing effect of SiO2 imbues products with good structural integrity, shedding light on the opportunity to apply any thermal protection system.