Multicomponent Molten Salt Mixtures Based on Nitrate/Nitrite Anions

Molten salts are a promising medium for thermal energy transfer and storage. They have a very low vapor pressure and most are unreactive in air. Over the past 3 decades, Sandia National Laboratories has investigated a variety of molten salt mixtures of alkali nitrates and, most recently, quaternary mixtures of sodium, calcium, lithium, and potassium nitrate salts. This effort led to the discovery of mixtures with liquidus temperatures below $100°C$⁠. We have now extended this work to the mixed nitrate/nitrite anion system and found compositions with liquidus temperatures below $80°C$⁠. In this paper, we present experimental results exploring the lithium, sodium, and potassium compositional space with a 1:1 molar mixture of nitrate/nitrite. From our work, we have identified a five-component system with a liquidus temperature near $70°C$⁠. Physical properties of these salts, such as viscosity and density, are reported as well as thermal stability in air. Such a molten salt mixture, with a low liquidus temperature, has the potential to make parabolic trough collectors economically competitive with traditional power generation schemes.