Effect of SiO2 nanoparticles on specific heat capacity of low-melting-point eutectic quaternary nitrate salt

In order to evaluate the effect of nanoparticles on the specific heat capacity of a low-melting-point eutectic quaternary nitrate salt, 1.0 wt% SiO2 nanoparticles with an average size of 20 nm was doped into the mixed salt Ca(NO3)2·4H2O-KNO3-NaNO3-LiNO3. A mechanical dispersion mixer was developed to prepare molten salt nanofluids. The effects of the mixing time (15, 45, 90, 120, and 150 min) and stirring rate (600, 750, and 1000 rpm) on the specific heat capacity of the nanofluids were analyzed using a differential scanning calorimeter. The results showed that the specific heat capacity of the nanofluids varied with the mixing time and stirring rate. It increased by ~ 17.0% at a mixing time of 15 min and stirring rate of 750 rpm. Microstructural characterization of the molten salt nanocomposites was performed using scanning electron microscopy, which showed that special nanostructures, which resemble chain-like nanostructures, were formed on the surface of the solid nanofluids. The special nanostructures with a large specific surface area and high surface energy could increase the specific heat capacity of the molten salt nanofluids.