// Thermal Analysis Labs July 27, 2020

Simultaneous Thermal Analysis and Evolved Gas Analysis (STA-EGA) for Molten Salt Applications

Molten salts are increasingly applied in solar power generation and nuclear power heat management applications. In both applications, they are employed as high temperature heat-transfer fluids to enable powering of heat engines or steam turbines. Molten salts have unique advantages over other high temperature heat-transfer fluids, such as supercritical water: Lower vapor pressure decreases the risks associated with high pressure fluid, and fuels may be dissolved in the salt to create a system with built-in natural feedback loops that prevent thermal runaway of reactor cores – creating “inherently safe” reactor systems. In solar power systems, molten salts possess improved safety associated with a lack of hydrogen production and lower operating pressures as compared with supercritical water.

Figure 1. TG/DSC-MS analysis of thermal stability of a ternary Nitrate/Nitrite molten salt system in an oxygen atmosphere.

To evaluate the utility of molten salts for these applications, a good understanding of the thermal stability of the materials is needed. However, this can be challenging due to the corrosive nature of many of these materials. Rene Olivares from CSIRO in Australia illustrates full characterization of a molten salt system under multiple atmospheres in a paper published in Solar Energy.[1] An example data set under a pure oxygen atmosphere is shown in Figure 1. The data shows the oxidation of the nitrite component by the oxygen atmosphere, followed by the rapid thermal decomposition of the ternary system at approximately 712°C. Iron current density provides insight into the decomposition mechanism. In this way thermal stability can be characterized as a function of temperature as well as atmosphere. This data was collected using a SETARAM thermal analyzer.

Figure 2. SETARAM Themys thermal analyzer.

Traditionally, this kind of advanced study into corrosive systems using corrosive purge gasses has been challenging with traditional thermal analysis equipment. SETARAM’s high performance thermal analyzers are designed for easy maintenance and resilience to corrosive attack without compromise of performance, with dynamic range from ambient to 2400°C with a single furnace (no cumbersome switching of furnace systems required, with no loss of performance at lower temperatures). SETARAM’s high-precision balances offer unparalleled sensitivity and versatility, with multiple levels of precision and load available for each thermal analyzer. SETARAM’s unique Tricouple DTA technique is available for high sensitivity and high accuracy temperature measurements of phase change phenomena on the Themys thermal analysis platform (Figure 2). The corrosive gas accessory for the Themys enables TGA testing under highly corrosive environments, including flurorine and hydrogen chloride atmospheres. Additionally, testing can be performed under flammable and explosive gas mixtures with the Themys’s hydrogen safety configuration.

For greater ease of use and budget friendliness, the SETARAM Labsys (Figure 3) platform offers the ease of use and versatility of SETARAM’s proven top-loading balances, the high sensitivity 3D DSC Cp rod, and retains the versatility to swap between TGA, DSC, and STA measurement modes offered on the Themys platform. Testing under reducing and oxidizing atmospheres is available.

Figure 3. SETARAM Labsys thermal analyzer.

 SETARAM’s TGA and STA systems can be paired with MS and FTIR systems through the use of heated transfer line accessories enabling evolved gas analysis up to 2400°C. Together, this makes SETARAM systems ideal platforms to unlock the thermal stability of molten salt systems.

[1] R. Olivares. Solar Energy. 2012. 86(9). 2576-83. DOI: 10.1016/j.solener.2012.05.025


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