Preparation and thermal insulation performance characterization of endothermic opacifier doped silica aerogel

Doping classical opacifiers will restrain silica aerogel's thermal radiation at high-temperature but cannot further improve its short-term thermal insulation performance. The phase change material (PCM) could absorb heat while maintaining a nearly constant temperature when melting, thus effectively controlling the heat transferred inside insulators. So, combing the classical opacifiers and PCM was a reasonable solution to the thermal insulation of silica aerogels at high-temperature. In the paper, dual-sized Al–[email protected]2O3 (1–3 μm/4–8 μm) with a shell of Al2O3 against infrared radiation and a core of Al–Si alloy for heat absorption during a solid-liquid phase change was prepared. This endothermic opacifier (EO) presents the melting point (Tm) of 846.25 K or 846.75 K and latent heat of 277.9 J·g−1 or 318.2 J·g−1, respectively. Subsequently, the EO was doped into silica aerogel to prepare an endothermic opacifier interspersed with silica aerogel (EOSA) and the temperature response of the hot surface (Thot) of the EOSA was tested at temperature differences (ΔT) to evaluate its thermal insulation performance. The results demonstrated that the effective thermal conductivity of the two EOSAs (1–22 wt%) was 0.02463–0.03066 W m−1 K−1 or 0.02636–0.03154 W m−1 K−1 at small ΔT (<15 K, Tcold = 288 K), respectively. The transient heat transfer of EOSA was delayed at large ΔT (Thot > Tm & Tcold = 288 K) during the solid-liquid phase change process, meaning that the short-term thermal insulation performance was improved. The thermal insulation performance of pure silica aerogel is the best at small ΔT but the worst at large ΔT, whereas the EOSA with 1–3 μm EO has the best thermal insulation performance at large ΔT.