LiF-BeF2熔盐微观结构及扩散特性的分子动力学研究

doi:10.11949/0438-1157.20200350

化工学报 ›› 2020, Vol. 71 ›› Issue (8): 3565-3574.DOI: 10.11949/0438-1157.20200350

• 催化、动力学与反应器 • 上一篇下一篇

LiF-BeF₂熔盐微观结构及扩散特性的分子动力学研究

贺国达^1,^2,³(),汤睿^1,²(),段学志⁴,谢雷东¹,傅杰^1,²,戴建兴¹,钱渊^1,²,王建强^1,^2,⁵

^1.中国科学院上海应用物理研究所，上海 201800
^2.中国科学院微观界面物理与探测重点实验室，上海 201800
^3.中国科学院大学，北京 100049
^4.华东理工大学化学工程联合国家重点实验室，上海 200237
^5.中国科学院洁净能源创新研究院，辽宁大连 116023

收稿日期:2020-04-03 修回日期:2020-05-13 出版日期:2020-08-05 发布日期:2020-08-05
通讯作者: 汤睿
作者简介:贺国达（1994—），男，硕士研究生，heguoda@sinap.ac.cn
基金资助:
中国科学院战略性先导科技专项(XDA02010000);中国科学院青年人才专项(Y929021031)

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

Guoda HE^1,^2,³(),Rui TANG^1,²(),Xuezhi DUAN⁴,Leidong XIE¹,Jie FU^1,²,Jianxing DAI¹,Yuan QIAN^1,²,Jianqiang WANG^1,^2,⁵

^1.Shanghai Institute of Applied Physics, Chinese Academy of Sciences, Shanghai 201800, China
^2.Key Laboratory of Interfacial Physics and Technology, Chinese Academy of Sciences, Shanghai 201800, China
^3.University of Chinese Academy of Sciences, Beijing 100049, China
^4.State Key Laboratory of Chemical Engineering, East China University of Science and Technology, Shanghai 200237, China
^5.Dalian National Laboratory for Clean Energy, Chinese Academy of Sciences, Dalian 116023, Liaoning, China

Received:2020-04-03 Revised:2020-05-13 Online:2020-08-05 Published:2020-08-05
Contact: Rui TANG

摘要/Abstract

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

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

中图分类号:

O 645.4

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.

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.

图/表 12

图1 不同离子对的RDF曲线

Fig.1 RDF curves of different ion pairs

图2 不同温度对配位数的影响

Fig.2 Effect of different temperature on coordination number

表1 各离子对的平均第一峰半径和第一配位数

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

图3 离子对的平均力势

Fig.3 PMF of ion pairs

图4 不同温度下的Cageout函数

Fig.4 Cageout function at different temperatures

图5 LiF-BeF2熔盐在873 K下的网络结构蓝色球—F原子；绿色球—Be原子；紫色球—Li原子

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

图6 系统中各种结构中F原子的百分比随温度的变化(“Be3F104-等”是指Be原子数大于等于3的团簇)

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

表2 模拟体系中各种游离结构的数量百分比

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

图7 Li2BeF4(a)、Li3Be2F7(b)和Li4Be3F10(c)的中性结构蓝色球—F原子；绿色球—Be原子；紫色球—Li原子

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

表3 式（7）中的系数

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

图8 自扩散系数的模拟结果和实验结果随温度的变化

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

图9 LiF-BeF2熔盐的电导率

Fig.9 The conductivity of LiF-BeF2 melt

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LiF-BeF₂熔盐微观结构及扩散特性的分子动力学研究

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

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