Thermal control materials of carbon/SiO₂ composites with a honeycomb structure

Anisotropic composite thermal control materials show efficient thermal management ability, which can not only improve the heat flow in the direction of high thermal conductivity and prevent local overheating, but also reduce the heat flow in the direction of the low thermal conductivity and improve thermal insulation. In this paper, the anisotropic microstructure of natural wood (e.g. poplar) was used as a reference template. The filling of the SiO₂ aerogel into the multi-layer pore structure and microtubule structure originally occupied by lignin was controlled by the process of the axial self-adsorption, limited sol-gel and natural drying. The anisotropic composite biomimetic thermal control materials were prepared by high temperature carbonization and the thermal control properties were evaluated. The anisotropic carbon/SiO₂ (ACS) composite biomimetic thermal control material obtained after carbonization inherits the anisotropic microstructure. The axial thermal conductivity of the ACS composite biomimetic thermal control material is mainly determined by the thermal conductivity of the carbon composite microtubule structure. The SiO₂ aerogel filled between carbon composite microtubules and the abundant axial microcracks endow the ACS composite biomimetic thermal control material with excellent radial thermal insulation performance. The maximum specific surface area of the ACS composite biomimetic thermal control material is 183 m² g^-1, and the maximum density is 517.8 ± 55.9 kg m^-3. The maximum axial thermal conductivity of the ACS composite biomimetic thermal control material is 0.73 ± 0.07 W m^-1 k^-1, and the radial thermal conductivity is 0.28 ± 0.01 W m^-1 k^-1. The maximum ratio of the axial thermal conductivity to radial thermal conductivity of the ACS composite biomimetic thermal control material is 3.3.