Molecular dynamics investigation on microstructure and diffusion properties of LiF-BeF2 molten salt

doi:10.11949/0438-1157.20200350

Abstract

Abstract:

LiF-BeF₂ molten salt has been paid much attention in recent years as a coolant and nuclear fuel solvent for molten salt reactor, and its diffusion behavior is closely related to the compatibility of nuclear fuel and the corrosion of structural materials. In this paper, Car-Parrinello molecular dynamics simulation was used to investigate the microstructure and diffusion behavior of LiF-BeF₂melts. The results show that Be²⁺ has a strong complexation ability to form neutral clusters, and its number decreases with the increase of temperature. Liquid LiF-BeF₂ consists of neutral clusters and free F^-,Li⁺, BeF₃^- and BeF₄^2-, rather than completely free F^-, Li⁺and Be²⁺. The self-diffusion coefficient and conductivity obtained based on this microstructure are in good agreement with the experimental results, and the change of conductivity with temperature conforms to the Arrhenius model, rather than the linear model of infinitely diluted solutions considered in the literature.

Key words: LiF-BeF₂molten salt, molecular dynamics, microstructure, diffusion, conductivity

摘要：

LiF-BeF₂熔盐作为熔盐堆的冷却剂及核燃料溶剂近年来备受关注，其扩散行为与核燃料的相容性和结构材料的腐蚀性密切相关。采用Car-Parrinello分子动力学模拟研究了LiF-BeF₂熔盐的微观结构及基于此结构的扩散行为。研究结果表明Be²⁺具有较强的络合能力，易形成中性网络聚合体，且其数量随温度的增加而减少；液态LiF-BeF₂熔盐中除了包含聚合体，还包含游离的F^-、Li⁺、BeF₃^-和BeF₄^2-，而非完全游离的F^-、Li⁺和Be²⁺。基于此微观结构获得的自扩散系数及电导率与实验结果吻合较好，且电导率随温度变化符合Arrhenius模型，而不是目前文献认为的无限稀释溶液的线性模型。

关键词: LiF-BeF₂熔盐, 分子模拟, 微观结构, 扩散, 电导率

CLC Number:

O 645.4

Guoda HE, Rui TANG, Xuezhi DUAN, Leidong XIE, Jie FU, Jianxing DAI, Yuan QIAN, Jianqiang WANG. Molecular dynamics investigation on microstructure and diffusion properties of LiF-BeF₂ molten salt[J]. CIESC Journal, 2020, 71(8): 3565-3574.

贺国达, 汤睿, 段学志, 谢雷东, 傅杰, 戴建兴, 钱渊, 王建强. LiF-BeF₂熔盐微观结构及扩散特性的分子动力学研究[J]. 化工学报, 2020, 71(8): 3565-3574.

Figures/Tables 12

Fig.1 RDF curves of different ion pairs

Fig.2 Effect of different temperature on coordination number

Table 1 The average coordination number and the first peak radius of each ion pairs

离子对	第一峰半径/?		配位数
离子对	FPMD	文献结果	FPMD	文献结果
Be-F	1.58	1.58^①	4	4^①
Li-F	1.86	1.85^①	4.6	4^①
F-F	2.61	2.56~3.02^①	12.7	8^①
Be-Be	2.98	3.03^②	0.9	0.9^②
Be-Li	3.06	3.07^②	7.6	6.9^②
Li-Li	3.10	3.05^②	5.8	5.4^②

Fig.3 PMF of ion pairs

Fig.4 Cageout function at different temperatures

Fig.5 The network structure of molten LiF-BeF2 salts at 873 K

Fig.6 Percentage of F atoms in different species in the simulation system vs. temperature

Table 2 Percentage of various free structures in the simulation system

温度/K	数量百分比/%
温度/K	游离F^-/F^-	游离BeF₃^-/Be²⁺	游离BeF₄^2-/Be²⁺	游离Li⁺/Li⁺
773	10.09	3.00	15.00	36.67
873	10.27	3.67	16.67	39.07
973	10.42	4.67	17.67	40.83

Fig.7 The neutral configuration of Li2BeF4, Li3Be2F7 and Li4Be3F10

Table 3 The coefficient of Eq. (7)

离子	Arrhenius常数A/K	扩散活化能E_a/kJ/mol
F^-	1.52×10^-6	41.98
Li⁺	4.00×10^-7	27.40
Be²⁺	2.26×10^-6	45.21
BeF₃^-	1.33×10^-6	40.66
BeF₄^2-	1.91×10^-6	43.72

Fig.8 The simulated and experimental diffusion coefficient vs. temperature

Fig.9 The conductivity of LiF-BeF2 melt

References 38

1	蔡翔舟, 戴志敏, 徐洪杰. 钍基熔盐堆核能系统[J]. 物理, 2016, 45(9): 578-590.
	Cai X Z, Dai Z M, Xu H J. Thorium molten salt reactor nuclear energy system[J]. Physics, 2016, 45(9): 578-590.
2	Rosenthal M W, Briggs R B, Kasten P R. Molten salt reactor program semiannual progress report (ORNL-4449)[R]. USA: Oak Ridge National Laboratory, 1969.
3	Williams D F, Toth L M, Clarno K T. Assessment of candidate molten salt coolants for the advanced high-temperature reactor (ORNL/TM-2006/12)[R]. USA: Oak Ridge National Laboratory, 2006.
4	Forsberg C W, Peterson P F, Pickard P S. Molten-salt-cooled advanced high-temperature reactor for production of hydrogen and electricity[J]. Nuclear Technology, 2003, 144(3): 289-302.
5	Hargraves R, Moir R. Liquid fluoride thorium reactors: an old idea in nuclear power gets reexamined[J]. American Scientist, 2010, 98(4): 304-313.
6	Petti D A, Smolik G R, Simpson M F, et al. JUPITER-Ⅱ molten salt Flibe research: an update on tritium, mobilization and redox chemistry experiments[J]. Fusion Engineering and Design, 2006, 81(8-14): 1439-1449.
7	曾友石, 杜林, 皮力, 等. 氢在FLiNaK(LiF-NaF-KF)熔盐中的渗透行为[J]. 核技术, 2015, 38(2): 73-78.
	Zeng Y S, Du L, Pi L, et al. Hydrogen permeation behavior in FLiNaK(LiF-NaF-KF) molten salt[J]. Nuclear Techniques, 2015, 38(2): 73-78.
8	Calderoni P, Sharpe P, Hara M, et al. Measurement of tritium permeation in Flibe (2LiF-BeF₂)[J]. Fusion Engineering & Design, 2008, 83(7): 1331-1334.
9	Anderl R A, Fukada S, Smolik G R, et al. Deuterium\tritium behavior in Flibe and Flibe-facing materials[J]. Journal of Nuclear Materials, 2004, 329(part B): 1327-1331.
10	Mathews A L, Baes C F. Oxide chemistry and thermodynamics of molten lithium fluoride-beryllium fluoride solutions[J]. Inorganic Chemistry, 1968, 7(2): 373-382.
11	Iwamoto N, Tsunawaki Y, Umesaki N, et al. Self diffusion of lithium in molten LiBeF₃ and Li₂BeF₄[J]. Journal of the Chemical Society Faraday Transactions, 1979, 75(9): 1277-1283.
12	Ohmichi T, Ohno H, Furukawa K. Self-diffusion of fluorine in molten dilithium tetrafluoroberyllate[J]. The Journal of Physical Chemistry, 1976, 80(14): 1628-1631.
13	Robbins G D, Braunstein J. Molten salt reactor program semiannual progress report for period ending february 29(ORNL-4254)[R]. USA: Oak Ridge National Laboratory, 1968.
14	朱宇, 陆小华, 丁皓, 等. 分子模拟在化工应用中的若干问题及思考[J]. 化工学报, 2004, 55(8): 1213-1223.
	Zhu Y, Lu X H, Ding H, et al. Molecular simulation in chemical engineering[J]. Journal of Chemical Industry and Engineering （China）, 2004, 55(8): 1213-1223.
15	Rahman A. Structure and motion in liquid BeF₂, LiBeF₃, and LiF from molecular dynamics calculations[J]. Journal of Chemical Physics, 1972, 57(7): 3010.
16	Heaton R, Brooks R, Madden P, et al. A first-principles description of liquid BeF₂ and its mixtures with LiF: potential development and pure BeF[J]. Journal of Physical Chemistry B, 2006, 110(23): 11454-11460.
17	Salanne M, Simon C, Turq P, et al. A first-principles description of liquid BeF₂ and its mixtures with LiF₂: network formation in LiF-BeF₂[J]. The Journal of Physical Chemistry B, 2006, 110(23): 11461-11467.
18	Wilson M, Madden P A. Polarization effects in ionic systems from first principles[J]. Journal of Physics Condensed Matter, 1993, 5(17): 2687-2706.
19	Segall M D, Lindan P J D, Probert M J, et al. First-principles simulation: ideas, illustrations and the CASTEP code[J]. Journal of Physics: Condensed Matter, 2002, 14(11): 2717-2744.
20	Nam H O, Bengtson A, Vortler K, et al. First-principles molecular dynamics modeling of the molten fluoride salt with Cr solute[J]. Journal of Nuclear Materials, 2014, 449(1/2/3): 148-157.
21	宁汇, 侯民强, 杨德重. 二元混合离子液体的电导率与离子间的缔合作用[J]. 物理化学学报, 2013, 29(10): 2107-2113.
	Ning H, Hou M Q, Yang D Z. Ionic association in binary ionic liquids by conductivity[J]. Acta Physico-Chimica Sinica, 2013, 29(10): 2107-2113.
22	Klix A, Suzuki A, Terai T. Study of tritium migration in liquid Li₂BeF₄ with ab initio molecular dynamics[J]. Fusion Engineering and Design, 2006, 81(1-7): 713-717.
23	Becke A D P. Density-functional exchange-energy approximation with correct asymptotic behavior[J]. Physical Review A, 1988, 38(6): 3098-3100.
24	Lee C, Yang W, Parr R G. Development of the Colle-Salvetti correlation-energy formula into a functional of the electron density[J]. Physical Review B: Condensed Matter, 1988, 37(2): 785-789.
25	Krack M. Pseudopotentials for H to Kr optimized for gradient-corrected exchange-correlation functionals[J]. Theoretical Chemistry Accounts, 2005, 114(1/2/3): 145-152.
26	Hartwigsen C, Goedecker S, Hutter J. Relativistic separable dual-space Gaussian pseudopotentials from H to Rn[J]. Physical Review B, 1998, 58(7): 3641-3662.
27	Goedecker S, Teter M, Hutter J. Separable dual-space Gaussian pseudopotentials[J]. Physical Review B, 1996, 54(3): 1703-1710.
28	Car R. Unified approach for molecular dynamics and density functional theory[J]. Physical Review Letters, 1985, 55(22): 2471-2474.
29	Dai J X, Han H, Li Q N, et al. First-principle investigation of the structure and vibrational spectra of the local structures in LiF-BeF₂ molten salts[J]. Journal of Molecular Liquids, 2016, 213: 17-22.
30	Kleinman L, Bylander D M. Efficacious form for model pseudopotentials[J]. Physical Review Letters, 1982, 48(20): 1425-1428.
31	Chadi D J. Special points for brillouin-zone integrations[J]. Physical Review B, 1977, 16(4): 1746-1747.
32	Nose S. A unified formulation of the constant temperature molecular dynamics methods[J]. The Journal of Chemical Physics, 1984, 8(1): 511-519.
33	Zhang Q R, Han Y, Wu L C. Influence of electrostatic field on the adsorption of phenol on single-walled carbon nanotubes a study by molecular dynamics simulation[J]. Chemical Engineering Journal, 2019, 363: 278-284.
34	Madden P A, Salanne M, Corradini D. Coordination numbers and physical properties in molten salts and their mixtures[J]. Faraday Discussions, 2016, 190: 471-486.
35	Pauvert O, Salanne M, Zanghi D, et al. Ion specific effects on the structure of molten AF-ZrF₄ systems (A⁺ = Li⁺, Na⁺, and K⁺ )[J]. The Journal of Physical Chemistry B, 2011, 115(29): 9160-9167.
36	Rabani E, Gezelter J D, Berne B J. Calculating the hopping rate for self-diffusion on rough potential energy surfaces: cage correlations[J]. The Journal of Chemical Physics, 1997, 107(17): 6867-6876.
37	阎建民, 罗先金, Krishna R. 非电解质溶液扩散系数的理论研究评述[J]. 化工学报, 2006, 57(10): 2263-2269.
	Yan J M, Luo X J, Krishna R. Review on theoretical calculation of diffusion coefficients in non-electrolytic solutions[J]. Journal of Chemical Industry and Engineering （China）, 2006, 57(10): 2263-2269.
38	Burrell G L, Burgar I M, Gong Q, et al. NMR relaxation and self-diffusion study at high and low magnetic fields of ionic association in protic ionic liquids[J]. Journal of Physical Chemistry B, 2010, 114(35): 11436-11443.

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Molecular dynamics investigation on microstructure and diffusion properties of LiF-BeF₂ molten salt

LiF-BeF₂熔盐微观结构及扩散特性的分子动力学研究

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Figures/Tables 12

References 38

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