Molten salts computer simulation

In the case of molten salts, no obvious model based on statistical mechanics is available because the absence of solvent results in very strong pair correlation effects. It will be shown that the fundamental properties of these liquids can be described by quasi-chemical models or, alternatively, by computer simulation of molecular dynamics (MD). 

Molecular dynamics and Monte Carlo simulations have been extensively applied to molten salts since 1968 to study structure, thermodynamic properties, and dynamic properties from a microscopic viewpoint. Several review papers have been published on computer simulation of molten salts. " Since the Monte Carlo method cannot yield dynamic properties, MD methods have been used to calculate dynamic properties. 

Since the plume of hydrogen bubbles is so important in a fluorine electrolyser, experimental work was carried out to validate the accuracy of plume prediction by EA. KF-2HF molten salt electrolyte is so aggressive that it makes laser Particle Image Velocimetiy (PIV) measurements difficult in a large fluorine cell. We therefore designed a hydraulic set-up using water (see fig. 3) in order to simulate the two-phase hydrodynamics of the fluorine electrolyser. We present the specific experimental study performed to determine the shape of the plume and the EA computations. The experimental and CFD results are then compared. 

It is thus the aim of the present book to serve as a guide in the measurement of the physico-chemical properties of molten salts and to characterize briefly the properties and the structure of different types of molten salt systems. In this book, only direct methods of measurements and different methods of processing the measured data are discussed. Computer simulation methods are not considered. 

As the transport properties of molten salts are known to be often sensitive to their liquid structure, the analysis of ionic conductivity would be a powerful tool to attain the structural information. In this study, the ionic conductivities of a molten xZnBr2-(l-x)ABr (A = Li, Na, K) system were measured by means of a conventional ac technique. In addition, the short-range structure and connected xZnBr2 cluster structure of molten xZnBr2-(l -x)ABr (A = Li, Na, K) system was studied by a molecular dynamics simulation. The experimental ionic conductivity measurements and molecular dynamics simulation of molten xZnBr2-(l-x)ABr (A = Li, Na, K) system were undertaken at different compositions and temperatures. We will discuss the conductive behavior of ions from both computational and experimental points. 

Ionic systems, such as simple electrolyte solutions or molten salts, were successfully characterized by MC-simulations which sometimes also provide the only experimental data available in order to test the validity of various approximations employed in the respective theories when real experiments are difflcult or impossible to perform. With the advent of powerful computers and algorithms, MC-simulations are also performed successfully on polyelectrolyte solutions. Important contributions of MC-simulations to the understanding of charged systems are particularly expected for polyions with internal degrees of freedom, such as rod-like and flexible polyions, where the coupling between intra- and intermolecular correlations imposes great problems and restrictions to analytical theories. 

The Raman spectra of LnF3-KF (Ln = La, Ce, Nd, Sm, Dy or Yb) show that at mole fractions Xldfs < 0-25, LnFg octahedra are the predominant species. The value of Vi for this varies from 445 cm (Yb) to 400 cm (La). Computer simulation of the vibrational dynamics of Lads melts was used to help in the analysis of IR and Raman spectra. The Raman spectra of the molten salt systems LnBrs-KBr (Ln = La, Nd or Gd) and NdCls-ACl (A = Li, Na, K or Cs), show that at low L11X3 concentrations the predominant species are LnXg "... 

A model of the molten salt obtained by computer simulations is nowadays generally used to refine the structiwe, avoiding errors arising from incomplete knowledge of S(q) at very small and very large angles, q(r —> 0) and q r oo) required for the integration (3.3). 

Computer simulations have been applied to studies of the structure of molten salts along two lines one is the fi ee standing application of the computer simulation to obtain the partial pair correlation functions, the other is the refining of x-ray and neutron diffraction and EXAFS measurements by means of a suitable model. In both cases a suitable potential function for the interactions of the ions must be employed, as discussed in Sect. 3.2.4. Such potential functirms are employed in both the Monte Carlo (MC) and the molecular dynamics (MD) simulation methods. A further aspect that has been considered in the case of molten salts is the long range coulombic interaction that exceeds the limits of the periodic simulation boxes usually involved (for 1000 ions altogether), requiring the Ewald summation that is expensive in computation time and is prone to truncation errors if not applied carefully. 

Woodcock and Singer [117] were among the early persons who studied the structure of molten salts, in their case potassium chloride at 772 and 1033 °C, by means of Monte Carlo computer simulations. At about the same time Woodcock [118] reported the partial pair correlation functions for molten lithium chloride at 1000 °C obtained by molecular dynamics simulations. 

Table 3.7 Molten salt structural data from computer simulations Monte Carlo (MC) or molecular dynamics (MD)...

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