U.S. Department of Energy

Thermally-Stable Ionic Liquid Carriers for Nanoparticle-Based Heat Transfer in CSP Applications

SRNL logo Illusrtation of various colored circles connected by lines.

Illustrated is the chemical structure of the cations and anions proposed by SRNL for ionic liquid based heat transfer fluids.

Savannah River National Laboratory, under an ARRA CSP Award, is performing research to better understand the thermal stability of low-temperature organic molten salts, which are commonly referred to as ionic liquids (ILs).

Approach

They will select an appropriate IL using a constant method of determining thermal stability for both the neat IL and the NEILs. Currently, there is not a complete understanding of the thermal stability of ILs in the literature. IL thermal decomposition temperature can vary depending on the static and dynamic decomposition temperature. There are several cases where the onset of an IL's decomposition is reported to be four or five different temperatures, because of different techniques and synthesis routes (compounded by the possible presence of ionic impurity such as halide or silver used in the metathesis). Once the initial physical properties are collected, Savannah River is evaluating whether binary mixtures of different ILs lead to more promising physical properties. From the initial screening of IL thermal stabilities, the best candidates are being further investigated with the addition of nanoparticles.

Innovation

During the last two decades, ILs have gained momentum as a possible replacement for either traditional organic solvents or high-temperature inorganic molten salts. These ILs are a distinct sub-set of organic compounds that are fundamentally different than traditional molecular solvents and inorganic molten salts because of their low melting temperature and ionic nature. ILs have a melting point below 100C° by definition, and many are liquid at room temperature. ILs are composed of discrete ions that allow for remarkable tunability in designing and controlling their chemical and physical properties. In just two sub-classes of ILs, azolium and pyridinium, there are hundreds of different salts that can be synthesized.

At the end of this project, Savannah River intends to have developed a fluid capable of operation at 500°C in a parabolic trough system.

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