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The demand for clean energy production and storage has increased interest in molten salt technologies, including Molten Salt Reactors (MSR). Understanding of how molten salts properties change with respect to temperature and structure is vital to establishing efficient, cost effective MSR systems. Research into these materials however has been limited due to the difficulty in accurately measuring properties of these reactive materials at elevated temperatures and controlled environment in a time efficient way. Much research has turned to molecular dynamic (MD) modeling to alleviate these issues. This research presents a custom fabricated falling ball viscometer system for measuring molten salt viscosity quickly. A model for correlating velocity to viscosity for Re < 300 was also developed for use with this system. The viscometer is demonstrated on eutectic FLiNaK and NaF-ZrF4 (53–47 mol%) up to 150 K above the respective melting points. The results are compared to MD simulations to verify their effectiveness for predicting viscosity and previously reported measurements. 

The atomic structure of FLiNaK and its evolution with temperature are examined with x-ray scattering and molecular dynamics (MD) simulations in the temperature range 460–636 °C. In accord with previous studies, it’s observed that the average nearest-neighbor (NN) cation-anion coordination number increases with increasing cation size, going from ∼4 for Li-F to ∼6.4 for K-F. In addition, we find that there is a coupled change in local coordination geometry – going from tetrahedral for Li-F to octahedral for Na to very disordered quasi-cuboidal for K. The varying geometry and coordination distances for the cation-anion pairs cause a relatively constant F-F next-nearest neighbor (NNN) distance of approximately 3.1 Å. This relatively fixed distance allows the F anions to assume an overall correlated structure very similar to that of a hard-sphere liquid with an extended radius which is beyond the normal F ion size but reflects the cation-anion coordination requirements. Careful consideration of the evolution of the experimental atomic distribution functions with increasing temperature shows that the changes in correlation at each distance can be understood within the context of broadening asymmetric neighbor distributions. Within the temperature range studied, the evolution of F-F correlations with increasing temperature is consistent with changes expected in a hard-sphere liquid simply due to decreasing density. 

DOI: 10.1007/978-3-030-92559-8_5 The sixth Intergovernmental Panel on Climate Change report (IPCC) recently released predicts a deep reduction in emissions to meet global goals of 1.5 °C reduction in temperature. It states that concentrations of CO₂ have continuously increased in the atmosphere reaching averages of 410 ppm in 2019. Therefore, it becomes imperative to reduce CO₂ in any way possible. Silicon, which is an important material for renewable energy, electronics, and metallurgy, is primarily produced by the carbothermic reduction of quartz. This metallurgical grade silicon is then refined by the Siemens Process to solar grade silicon using hydrogen chloride. The by-product of trichlorosilane from this process is highly volatile and unstable. This work aims to achieve the above process of reduction in a single step using electrochemistry. This would eliminate multiple steps and save energy and cost and reduce emissions if a suitable inert anode is used in production. Understanding electrochemical cell characteristics therefore is needed to prove and scale this technology. Macroscopic models help engineers to design, develop, and improve the efficiency of electrochemical cells. They solve conservation equations of mass, momentum, and energy and help determine electrode current distribution, fluid flow, heat distribution, and stability of the cell. They also help in correlating experimental work and understanding measurements in cells from a lab scale to a plant scale. However, they do not predict the microstructure and plating of material on the cathode. This can be calculated using phase field models. These phase field models predict interface stability and deposition morphology in the cell. In this work, we present these models in addition to proof-of-concept experiments.