Synthesis and Performance of Silicon-Encapsulated NaNO3-KNO3 Eutectic Salt Microcapsules Via Emulsion-Templated Methods

To address the leakage issue of inorganic molten salt phase change materials (PCMs) in high-temperature applications, this study successfully synthesized novel microencapsulated phase change materials (MPCMs) with a sodium nitrate-potassium nitrate (NaNO3-KNO3) eutectic salt core and a silica (SiO2) shell via a water-in-oil (W/O) emulsion-templated sol-gel method. The synthesis process was systematically optimized by investigating the effects of surfactant concentration and reaction time. The results indicate that a surfactant (Span 80) concentration of 2.5 wt% and a reaction time of 15 hours are the optimal conditions for producing MPCMs with a uniform spherical morphology, a compact and intact shell structure. Characterization through scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FTIR), and X-ray diffraction (XRD) confirmed the successful encapsulation of the eutectic salt within an amorphous silica shell, preserving the core material’s crystalline structure. Differential scanning calorimetry (DSC) analysis revealed that the optimized MPCMs possess a melting temperature of 228 °C and a latent heat of 77 J/g, with an encapsulation ratio reaching 63.6%. Crucially, leakage tests demonstrated that the MPCMs exhibit excellent thermal stability and effectively prevent leakage of the molten salt core at temperatures up to 280 °C, highlighting their great potential for high-temperature thermal energy storage applications.