Effect of aluminum on performances of cordierite-SiCw composite ceramics for high-temperature sensible thermal storage

Abstract

High-temperature thermal storage is essential for advanced solar power and energy saving systems. Cordierite-SiCw (SiC whiskers) composites as candidate sensible thermal storage materials were prepared for high-temperature (above 900 °C) applications by an in-situ synthesis method. The effects of aluminum (Al) on the phase composition and performances of the composites and the growth behaviors of SiC whiskers were studied. XRD analyses results showed that Al addition promoted SiC production whereas lowered cordierite content. The in-situ synthesis of SiC whiskers followed the vapor-solid mechanism rather than the solid-state reaction between silicon and graphite. Al addition was favorable for the production of SiC whiskers with a smooth morphology by increasing the partial pressure of SiO gas. TEM analyses results indicated that the introduced Al changed the growth behavior of the coarse whiskers (>30 nm in diameter) from the self-assembly one to the enlarged nuclei-based one and increased the diameter of the whiskers from 50 nm to 165 nm by enlarging the SiC nuclei. Aluminum could strengthen the composites and enhance the thermal storage capacity by in-situ forming corundum. The high-temperature (900 °C) heat capacity values were improved from 1.28 J g−1 K−1 to 1.4 J g−1 K−1 by introducing 0–20 wt% Al. The lowest thermal expansion coefficient of 3.14 × 10−6 °C−1 (room temperature-1000 °C) was achieved for sample AS1 sintered at 1440 °C due to its highest cordierite content.