High-temperature solar energy absorption enhancement of mixed-phase core–shell spherical Al-based composite particles

•Noval dry mixing extrusion method synthesizes core–shell composite particles.•Mixed-phase mental oxides increase absorptivity to 91.4 % with enhancement of 356%.•Particles remains stable in 1200 °C high temperature and violent collision environments.•Narrow bandgap characteristics effectively adjusted absorption and radiation.•Light capture efficiency of the 0.04 m PA-SⅠ particle curtain reaches 83.9 %. This study focuses on the development of heat transfer/thermal energy storage particles for direct irradiation solid particle solar receivers to improve the efficiency by enhancing solar absorption, thermal stability, thermal storage property, and mechanical strength. A novel dry-mix extrusion technique was adopted to synthesize Al-based core–shell composite particles. The research shows that particles coated with 5.5 wt% mixed-phase metallic compounds maintain over 90 % solar absorptivity after 300 h at 1200°C, 600-1200°C thermal cycling, and wear tests, with an absorptivity change negligible (±2.20 %) and a mass loss of less than 0.053 g. The cost of the particles is below 1.5€/kg with good flowability, compressive strength up to 398.6 MPa, and an energy density as high as 2675.3 kJ/(m3·K). Monte-Carlo finite element numerical results found that the absorption efficiency of a composite particle curtain with a thickness of 0.02 m and a volume fraction of 0.05 increased by 169.6 % over the original ones. The particles can operate for extended periods at higher temperatures or harsh conditions to improve energy conversion efficiency, extend service life, and reduce maintenance requirements. It demonstrates the potential application value in the field of thermal energy absorption and storage, providing highly promising candidates for future high-temperature solar thermal applications.