Experimental investigation and thermodynamic modeling of the LiNO3-RbNO3-AgNO3 system and its subsystems

Computational thermodynamics approach based on experimental values is applied to evaluation and optimization of the LiNO3-RbNO3-AgNO3 system and its subsystems in this work. The substitutional solution model (SSM) was used to describe all liquid phase. All the intermediate compounds were treated as stoichiometric of which Gibbs energies comply with the Neumann-Kopp rule. A set of self-consistent database with thermodynamic model parameters obtained for the LiNO3-RbNO3-AgNO3 subsystems and this database were used to predict thermodynamic properties of the LiNO3-RbNO3-AgNO3 ternary system. The calculated results were verified experimentally using differential scanning calorimetry (DSC) and X-ray diffraction (XRD) techniques, and the agreement between the experimental values and predicted values is satisfactory. The phase diagram of the LiNO3-RbNO3-AgNO3 ternary system contain two eutectic types: one eutectic (Liquid ↔ α-AgNO3 + LiRb(NO3)2 + AgRb(NO3)2) at 385.3 ± 1.5 K and another eutectic (Liquid ↔ LiRb(NO3)2 + AgRb(NO3)2 + AgRb2(NO3)3) at 398.8 ± 1.5 K. Through computational thermodynamics approach, a multi-component system was successfully predicted and this approach will be applied to design and develop multi-component molten salt mixtures as thermal energy storage (TES) materials.