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-Si@Al2O3 (1-3 mu m/4-8 mu m) 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 (T-m) 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 aemgel (EOSA) and the temperature response of the hot surface (T-hot) of the EOSA was tested at temperature differences (Delta T) 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 AT (<15 K, T-cold = 288 K), respectively. The transient heat transfer of EOSA was delayed at large Delta T (T-hot > T-m & T-cold = 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 Delta T but the worst at large Delta T, whereas the EOSA with 1-3 mu m. EO has the best thermal insulation performance at large T.