Molecular dynamics simulation of the effects of nitrite/nitrate equilibrium on the structure and properties of KNO2-KNO3-K2CO3 molten salt systems

J Huang and LX Sang and QF Yang and YT Wu, JOURNAL OF ENERGY STORAGE, 132, 117898 (2025).

DOI: 10.1016/j.est.2025.117898

The nitrite/nitrate balance significantly affects the physical properties of molten salt systems. In this study, the effects of nitrite/nitrate equilibrium on the microstructure and physical properties of KNO2-KNO3-K2CO3 molten salt system with KNO2 concentrations ranging from 5.9 mol% to 45.9 mol% and temperatures from 673 K to 973 K were investigated by classical molecular dynamics simulation under fixed K2CO3 content. The results revealed that increasing temperature or KNO2 concentration decreases the height of the first peak in the radial distribution functions for both cation-anion pairs, while the peak positions remain unchanged. The interaction between cations and carbonate ions was found to be almost unaffected by the nitrate/nitrite ratio. Analysis based on the potential of mean force, cage correlation function, and self-diffusion coefficients indicates that the K+-CO2-3 pair exhibits the highest potential barrier and longest cage lifetime, whereas the K+-NO-2 pair shows the lowest barrier and fastest cage escape. Density, shear viscosity, and thermal conductivity generally decreased with increasing temperature. At 673 K, density, viscosity, and thermal conductivity decreased with increasing KNO2 concentration. Interestingly, the thermal conductivity at the 45.9 mol% KNO2 concentration displayed a parabolic trend with temperature, attributed to the enhanced diffusivity facilitated by the KNO2 component. This work provides important guidance for the selection and formulation of molten salt materials for next-generation CSP plants.

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