ORALS

Molten halide salts are of interest for applications as heat transport fluids (HTF) in concentrated solar power plants due to their excellent resilience at high temperatures. Application as HTF requires a combination of properties including high heat capacity, low vapor pressure and low viscosity to optimize fluid flow through heat-exchanger networks. A fundamental understanding of viscous behavior in halide salts in relation to their structure is therefore of interest for optimizing HTF formulations. Here we perform a combination of modeling (ab-initio molecular dynamics) [1] and spectroscopic analysis (Raman) [2] of tetrahedral zinc chloride melts as a function of temperature. It is found that the ratio of edge- to corner-sharing tetrahedra varies with temperature and that it can be correlated with the viscous behavior through configurational entropy considerations. More interestingly, it is observed that a fragile-to-strong transition occurs at high temperature which can also be correlated with a change in structural behavior [3]. This behavior is compared with that of other tetrahedral melts and found to be related to changes in multiple physical properties such as heat-capacity, density, compressibility etc.

References:
[1] A.Q. Alsayoud, M. Venkateswara Rao, A.N. Edwards, P.A. Deymier, K. Muralidharan, B.G. Potter, K. Runge, P. Lucas, Structure of ZnCl2 Melt. Part I: Raman Spectroscopy Analysis Driven by Ab Initio Methods, J. Phys. Chem. B, 120 (2016) 4174-4181.
[2] P. Lucas, G.J. Coleman, M. Venkateswara Rao, A.N. Edwards, C. Devaadithya, S. Wei, A.Q. Alsayoud, B.G. Potter, K. Muralidharan, P.A. Deymier, Structure of ZnCl2 Melt. Part II: Fragile-to-Strong Transition in a Tetrahedral Liquid, J. Phys. Chem. B, 121 (2017) 11210-11218.
[3] P. Lucas, Fragile-to-Strong transitions in Glass Forming Liquids, J. Non-Cryst. Solids, (2019) in print.