NaNO3/anorthite–mullite ceramic composites derived from steel slag and secondary aluminum dross for thermal energy storage

Against the backdrop of rapid economic development, the demand for composite phase change materials (C-PCMs) in thermal energy storage has been steadily increasing. However, the widespread application of C-PCMs has been severely constrained by high raw material costs, the poor thermal conductivity of ceramic matrices, and substantial molten salt leakage. In this study, the phase composition was designed using thermodynamic software, and C-PCMs with an anorthite-mullite ceramic matrix were successfully fabricated from steel slag (SS) and secondary aluminum dross (SAD) as primary raw materials. This study revealed the synergistic regulatory mechanisms of anorthite and mullite on the pore size of porous ceramics, the infiltration efficiency, and the mass loss rate of C-PCMs. The experimental results demonstrated that the relative contents of anorthite and mullite could be effectively controlled by adjusting the SS/SAD ratio. An increase in anorthite content reduced the average pore size of the porous ceramic and suppressed the migration rate of molten salt within the pores, thereby decreasing both infiltration efficiency and mass loss rate. Meanwhile, the mullite phase in the C-PCMs contributed to the enhancement of thermal conductivity. Under optimized conditions, the prepared C-PCMs achieved a thermal conductivity of 1.81 W/(m·K), which was 262% that of pure NaNO 3 . The latent heat reached 77.2 J/g, and the degree of supercooling of C-PCMs decreased to 0.6 °C. After 100 thermal cycles, the mass loss rate was only 3.21%. This work provides theoretical support for the high-value-added utilization of metallurgical solid wastes and the rational design of medium-to-high-temperature C-PCMs.