One-step synthesis of Al2O3–β-Sialon nanowhiskers ceramics for fluid-bed thermal storage system of solar energy

Sensible thermal storage ceramics in the form of the fluid-bed show good competency on dealing with the intermittency of renewable energy and improving energy utilization efficiency by integration the functions of thermal absorption and storage. In-situ nano-sized β-Sialon whiskers reinforced Al₂O₃-based ceramic materials for fluid-bed thermal storage system were one-step synthesized by aluminothermic reduction method, using solid waste coal-series kaolin and Al powder as main raw materials and firing at 1500 °C in N₂ atmosphere. The effects of Al content and firing temperature on phase evolution, microstructure and properties of fired samples were researched by XRD, SEM, TEM, etc. The results showed that nano-sized β-Sialon whiskers could be in-situ synthesized at 1300 °C, which effectively enhanced the bending strength of fired samples. The highest β-Sialon content and the optimal properties could be achieved at 1500 °C while coal-series kaolin and Al mass ratio was equal to 70∶30, which were listed as follows: 30.7 % β-Sialon content, 74.9 MPa high-temperature bending strength (at 1400 °C), 6.17 × 10^-6·°C^-1 thermal expansion coefficient (room temperature-1000 °C), 0.74 J·(g·K)^-1 specific heat capacity (at room temperature), 873.90 kJ·kg^-1 theoretical thermal storage density (ΔT=900 °C), which is suitable as the thermal storage material for the fluid-bed thermal storage system.