SiO2@Al2O3 core-shell nanoparticles based molten salts nanofluids for thermal energy storage applications

Three different sizes of the SiO2@Al2O3 core-shell nanoparticles were synthesized by tuning the silica precursor using the wet chemical route. The precise control of the outer shell diameter of SiO2 was controlled by optimum concertation of the silica precursor in the alumina solution. Gradual increment of the outer shell depth and the chain-like aggregated structure was observed from TEM while increasing the silica precursor during the synthesis of SiO2@Al2O3 core-shell nanoparticle. Respectively, the size of the SiO2@Al2O3-10 nanoparticles is 12 +/- 2 nm with no observable SiO2 diameter, SiO2@Al2O3-20 is 14 +/- 2 nm with 2 nm of SiO2 diameter and SiO2@Al2O3-35 is 17 +/- 2 nm with 5 nm of SiO2 diameter in the outer layer. The interaction and quantitative elemental properties of the core-shell nanoparticles were studied using FTIR, XRD and SEM-EDX analyses. Consequently, the potentiality of the core-shell nanoparticle was analyzed for the prospective of TES application by mixing 1 wt% core-shell nanoparticles with 99 wt% eutectic binary molten nitrate salt (nanofluids) via one-step dry preparation method. The changes in the thermophysical properties were observed with respect to the addition of silica precursor or increasing silica outer diameter in the SiO2@Al2O3 core-shell nanoparticle. From the analysis, 19% higher thermal conductivity was obtained for the nanofluid prepared with SiO2@Al2O3-35 core-shell nanoparticles. A higher viscosity also was observed for the chain-like aggregates of SiO2@Al2O3-35 core shell-based nanofluids, which was 25 to 34% higher compared to the base fluids in the temperature range between 250-400 degrees C.