Al 2 O 3 exhibits high activity for the resource utilization of potent greenhouse gases, hydrofluorocarbons via dehydrofluorination or F/Cl exchange. However, it experiences completely fluorination under corrosive HF environment, leading to thorough fluorination of F-Al-O active site into F-Al-F, accompanied with serious carbon deposition. In this work, we successfully confined Al 2 O 3 in SiC (Al 2 O 3 @SiC) via treating Al 2 O 3 /SiC under high temperatures (>800 °C). The results showed that different with simple loaded Al 2 O 3 (Al 2 O 3 /SiC), during high temperature treatment, reaction between Al 2 O 3 and SiC occurred, leading to the confinement effect. Then, contributed by the interaction, desired F-Al-O species could be stabilized on the surface of SiC. While for Al 2 O 3 /SiC, it thoroughly turned into AlF 3 under identical reactive conditions, leading to inferior stability during CH 3 CHF 2 dehydrofluorination. Furthermore, the reaction rate of 5 %Al 2 O 3 @SiC is nearly up to 4 folds higher than that of traditional AlF 3 . Facilitated by the suitable Lewis acid intensity, less carbon deposition formed on Al 2 O 3 @SiC. Thus, constructing strong interaction between F-Al-O and stable SiC provides a potential strategy to stabilize unstable active centers.
Construction of a vertically aligned and densely interconnected ordered 3D filler framework in a polymer matrix is a challenge to attain significant thermal conductivity (TC) enhancement efficiency. Fortunately, many biomaterials with unique microstructures can be found in nature. With inspiration from wood, artificial composites can be rationally designed to achieve desired properties. Herein, the authors report a facile and effective approach to fabricate anisotropic polymer composites by biotemplate ceramization technology and subsequent vacuum impregnation of epoxy resin. The hierarchical microstructure of wood is perfectly replicated in the cellular biomass derived SiC (bioSiC) framework by carbothermal reduction. Owing to the anisotropic architecture of bioSiC, the epoxy composite with vertically aligned dense SiC microchannels shows interesting properties, including a high TC (10.27 W m −1 K −1 ), a significant enhancement efficiency (259 per 1 vol% loading), an outstanding anisotropic TC ratio (5.77), an extremely low coefficient of linear thermal expansion (12.23 ppm K −1 ), a high flexural strength (222 MPa), and an excellent flame resistance. These results demonstrate that this approach is expected to open a new avenue for design and preparation of high performance thermal management materials to address the heat dissipation of modern electronics.
To meet the urgent need for thermal protection of high-temperature deformable mechanisms in the aerospace industry, a novel strategy for the preparation of ablation-resistant flexible composites is proposed. Ceramic precursor is selected and introduced to epoxy modified silicone rubber (SR) to in-situ build SiC frame at high temperature to fabricate flexible thermal protective polymeric materials with excellent ablation resistance. The static ablation and dynamic ablation behaviors of the SR composites are systematically and comparatively investigated in a tube furnace and oxyacetylene torch in an automatic ablation machine for the first time. The influence of polycarbonylsilane (PCS) content on the microstructure, strength and composition of char layer, and the ablation properties at different heat environments are discussed. When the addition of PCS reached 10 phr, for the static ablation, the maximum puncture strength of char and the residual weight increased 3233% and 48.48%, respectively. The same for dynamic ablation, with the introduction of PCS, each indicator was greatly improved. Moreover, the ablation enhancement mechanisms of PCS in different ablation environments are revealed. This work may provide a new perspective for the preparation of silicone rubber composites with excellent ablation performance, expected to be well used as a thermal protection coating for hypersonic spacecrafts.
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