| Structure and dynamics of tetrahedral ionic glass-forming liquids Pierre Lucas1; 1UNIVERSITY OF ARIZONA, Tucson, United States; PAPER: 75/Molten/Invited (Oral) SCHEDULED: 14:50/Sat. 26 Oct. 2019/Ambrosia A (77/RF) ABSTRACT: 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. |
