07.05.2025 by Dr. Chiara Baldini, Aileen Sammler
Characterization of NaNO₃–KNO₃ Salt Mixture Using NETZSCH Thermal Analysis Instruments and X-ray Diffraction
Salts and salt systems serve a broad spectrum of applications across numerous industries and in everyday life — from food preservation and flavoring to pharmaceuticals, medicine, agriculture, and water treatment. In addition, a significant variety of salts is essential in industrial sectors such as chemical manufacturing, metallurgy, and energy production, including nuclear and solar technologies.
New Insights into NaNO₃-KNO₃ Phase Stability for Thermal Energy Storage
Our latest study focuses on the NaNO₃-KNO₃ system, a widely used heat-transfer fluid and thermal energy storage material in concentrated solar power (CSP) plants. Despite its extensive application, discrepancies in equilibrium phase diagrams persist due to metastable phase formation influenced by experimental conditions.
By integrating differential scanning calorimetry (DSC), thermomechanical analysis (TMA), laser flash analysis (LFA), and high-temperature X-ray diffraction (HTXRD), we gained deeper insights into the system’s thermal and structural properties. Notably, HTXRD confirmed the formation of metastable solid solution phases, reinforcing the need for a combined thermal and structural approach to fully understand material behavior.
The recent scientific paper"Comprehensive analysis of metastable phase formation in the NaNO₃-KNO₃ system by thermal analysis and high-temperature X-ray diffraction", published in the Journal of Materials Research and Technology, directly addresses these discrepancies.
In this study, a multi-technique approach was used including differential scanning calorimetry (NETZSCH DSC 204 F1 Phoenix® ), thermomechanical analysis (NETZSCH TMA 402 F1 Hyperion® ), laser flash analysis (NETZSCH LFA 467 HyperFlash®) and high temperature X-ray diffraction (HTXRD - Empyrean Series 3).
The results show significant differences in transition temperatures and volume changes between the first and the second heating cycles. In addition, high-temperature XRD studies confirmed the formation and persistence of metastable phases, resolving previously unresolved inconsistencies in the reported data.
Integrating advanced experimental techniques in thermal analysis significantly enhances the reliability of thermophysical properties, which are crucial for the development of reliable thermodynamic databases. This integration supports the development of innovative materials optimized for diverse temperature ranges, thereby improving the efficiency and sustainability of industrial processes and energy storage solutions.
For a more detailed exploration of the methods and results, the full research paper is available online:
Acknowledgments
This study was conducted through the collaborative efforts of researchers from NETZSCH-Gerätebau GmbH (Selb, Germany), Malvern Panalytical B.V. (Almelo, 7602 EA, The Netherlands), and Forschungszentrum Jülich GmbH, IMD-1 (Jülich, Germany). We gratefully acknowledge the authors' valuable contributions and the support provided by their respective institutions.
Watch also our webinar: Salt Systems Exploring Experimental Limits
Salt systems form a distinct group of materials alongside oxides and metals. Their extensive use as heat transfer media or chemical reactants in key industries such as metallurgy, nuclear and solar energy is due to their unique thermophysical properties oupled with their relatively low cost and availability. The combination of salts with different cations and anions greatly increases the variety of applications. Accurate determination of thermophysical properties such as DensityThe mass density is defined as the ratio between mass and volume. density, heat capacity and Thermal DiffusivityThermal diffusivity (a with the unit mm2/s) is a material-specific property for characterizing unsteady heat conduction. This value describes how quickly a material reacts to a change in temperature.thermal diffusivity is highly dependent on sample preparation and choice of crucible materials. Information on the Thermal StabilityA material is thermally stable if it does not decompose under the influence of temperature. One way to determine the thermal stability of a substance is to use a TGA (thermogravimetric analyzer). thermal stability and evaporation/Decomposition reactionA decomposition reaction is a thermally induced reaction of a chemical compound forming solid and/or gaseous products. decomposition behavior of salts is also important for the interpretation of experimental results. Some salt mixtures can form metastable phases, which may depend on the temperature program or other parameters of the experimental equipment.
All these problems and possible solutions for the investigation of salt systems with TG/DTA/DSC/TMA/LFA instruments will be discussed in our webinar.
