B4C-based nanoenhancement on the thermophysical and stability performance of solar salt: a novel approach for high-temperature TES applications

Enhancement of the thermophysical properties of molten salt-based nanofluids is essential for improving energy density and efficiency in high-temperature thermal energy storage (TES) systems. However, the mechanisms behind the anomalous increase in specific heat capacity upon nanoparticle addition remain unclear. In this study, solar salt (60 wt% NaNO 3 -40 wt% KNO 3 ) was modified with boron carbide (B 4 C) nanoparticles at concentrations of 0.5, 1.0, 1.5, and 2.0 wt% using a wet dispersion method. The structural and thermal behaviors of the nanofluids were investigated through X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FT-IR), field emission scanning electron microscopy with energy-dispersive X-ray spectroscopy (FE-SEM/EDX), differential scanning calorimetry (DSC), and thermogravimetric analysis (TGA). The DSC results from the second thermal cycle confirmed that the addition of B 4 C significantly enhanced the Cp of the base salt. Specifically, the 2.0 wt% B 4 C sample exhibited average enhancements of 31.5 % in the solid phase (100–220 °C) and 49.83 % in the liquid phase (250–400 °C) compared to pure solar salt, with a peak value of 2.11 J/g.K at 250 °C. FE-SEM analyses revealed more uniform nanoparticle distribution at lower concentrations, while higher loadings led to particle agglomeration. Thermal conductivity increased by 142.8 %, from 1.05 to 2.55 W/m.K. Although latent heat decreased with higher nanoparticle content (from 108.7 J/g to 97.2 J/g), thermal stability improved, with the decomposition onset temperature shifting from 607 °C to 644 °C at 1.5 wt% B 4 C. These results identify B 4 C as a promising non-oxide nanoadditive for TES applications, offering balanced improvements in thermal performance and stability.