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在能源结构转型背景下, 开发高效储热材料是提升太阳能热发电技术的关键. 硝酸熔盐因热稳定性优异、储热密度高而被广泛应用, 但其性能优化多依赖传统实验与模拟方法, 存在效率低、成本高等问题. 本研究引入固体与分子经验电子理论(EET), 系统分析了硝酸盐MNO3 (M = Li, Na, K)及其分解产物亚硝酸盐MNO2的价电子结构、结合能和熔点, 揭示了其物性与价电子结构之间的关联机制. 计算的键长、结合能和熔点与实验相符. 结果表明: 其结合能与价电子成正相关; 熔融源于M—O键的断键, 其价电子对数与熔点呈显著正相关. 研究了二元硝酸盐的液相线与价电子结构的关联性, 计算的液相线与实验相符. 通过优化价电子结构, 可调控液化温度. 应用热动力学理论预测二元硝酸熔盐的结合黏度、电导率和热导率. 通过物性综合优化, 筛选出0.5LiNO3-0.5NaNO3等低液化温度、低黏度、高电导率、高热导率的二元硝酸盐成分. 本研究为硝酸熔盐成分设计提供了电子结构层面的依据.Nitrate molten salt is widely used as an efficient thermal storage material for improving concentrated solar power (CSP) technology, which is due to their many excellent properties such as thermal stability, high energy density, low viscosity and liquefaction temperature. However, it is not convenient to measure the performance of nitrate for a long time in a high temperature molten state, which can cause the storage containers made of stainless steel to be corroded by nitrate salt. Simulations also face huge challenges in optimizing the performance of nitrate molten salts, with models being complex and calculation time being long. In this study, an empirical electron theory (EET) of solids and molecules is used to investigate the valence electron structure, cohesive energy, and melting points of MNO3 (M = Li, Na, K) and their decomposition byproducts (nitrites) systematically for revealing the mechanisms of these properties. The calculated bond lengths, cohesive energy, and melting points of nitrate molten salt are in agreement with their corresponding measurements. This study reveals the strong dependence of physical properties on the valence electron structure. The bonding strength and ability strongly depend on the covalent electron pairs $ {n}_{\alpha } $. The cohesive energy exhibits a positive correlation with the number of valence electrons $ {n}_{\mathrm{c}} $. The melting mechanism originates from the melting-broken M−O (M = Li, Na, K) bond by the vibrating of thermal phonon at melting temperature. It is suggested that the atomic cluster of NO3 is still stabilized in the melting process. In binary nitrate molten-salts, the calculated liquidus lines match the measured ones in their binary phase diagrams well. The liquid temperatures show significant positive correlation with the weighted average number of covalent electron pairs ($ {n}_{{{M}}-{\mathrm{O}}} $) on M−O bond. The thermodynamic simulation models are used systematically to predict the viscosity, electrical conductivity, and thermal conductivity of the binary nitrate molten-salts. Based on the calculations of EET and thermodynamic simulations, the composition of binary nitrate molten salts is optimized as 0.5LiNO3-0.5NaNO3, 0.5LiNO3-0.5KNO3, and 0.6NaNO3-0.4KNO3, which are considered as good candidates for advanced molten salts with high thermal conductivity, high electrical conductivity, low viscosity, and low liquefaction temperature.
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Keywords:
- nitrates /
- valence electron structure /
- melting point /
- cohesive energy
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MNOx $ {T}_{\mathrm m} $/K[41] $ {\overline{T}}_{\mathrm m} $/K $ \dfrac{\left|\Delta{T}_{\mathrm m}\right|}{{T}_{\mathrm m}} $/% $ {n}_{{M}-\mathrm{O}} $/atom–1 $ {E}_{\mathrm c}/ $( eV·atom–1)[42] $ {\overline{E}}_{\mathrm c}/( $eV·atom–1) $ \dfrac{\left|\Delta{E}_{\mathrm c}\right|}{{E}_{\mathrm c}} $/% LiNO3 527.5 518.56 1.6 0.1795 14.350 13.986 2.5 NaNO3 579.1 586.00 1.2 0.2009 13.833 13.821 0.1 KNO3 612.2 640.27 4.6 0.2779 13.654 12.683 7.1 NaNO2 554.0 563.54 1.7 0.1859 11.233 11.582 3.1 KNO2 713.0 691.66 3.0 0.2159 11.054 10.936 1.1 
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共晶成分 $ {T}_{\mathrm{m}}/\mathrm{K} $[41] $ {\overline{T}}_{\mathrm{m}}/\mathrm{K} $ $ \dfrac{\left|\Delta{T}_{\mathrm{m}}\right|}{{T}_{\mathrm{m}}}/{\text{%}} $ $ {E}_{\mathrm{c}}/ $( eV·atom–1)[42] $ {\overline{E}}_{\mathrm{c}}/( $eV·atom–1) $ \dfrac{\left|\Delta{E}_{\mathrm{c}}\right|}{{E}_{\mathrm{c}}}/{\text{%}} $ 0.5NaNO3-0.5KNO3 494.0 497.77 0.8 13.743 13.629 0.8 0.44LiNO3-0.56KNO3 410.5 406.49 1.0 13.948 13.179 5.5 0.537LiNO3-0.463NaNO3 473.5 439.77 7.1 14.111 13.671 3.1
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x $ {T}_{\mathrm{m}} $/K[41] $ {\overline{T}}_{\mathrm{m}} $/K $ \dfrac{\left|\Delta{T}_{\mathrm{m}}\right|}{{T}_{\mathrm{m}}} $/% $ {n}_{{M}-\mathrm{O}} $/atom–1 $ {E}_{\mathrm{c}}/ $(eV·atom–1)[42] $ {\overline{E}}_{\mathrm{c}}/( $eV·atom–1) $ \dfrac{\left|\Delta{E}_{\mathrm{c}}\right|}{{E}_{\mathrm{c}}} $/% 0.1 563 566.42 0.6 0.199 13.815 13.705 0.8 0.2 546 556.96 2.0 0.1908 13.797 12.762 7.5 0.3 528 537.35 1.8 0.1763 13.779 12.924 6.2 0.4 512 522.50 2.1 0.1522 13.761 13.687 0.5 0.5 494 497.77 0.8 0.1479 13.743 13.629 0.8 0.6 514 509.20 0.9 0.1564 13.726 13.481 1.8 0.7 540 549.02 1.7 0.1769 13.708 13.209 3.6 0.8 565 558.5 1.2 0.1865 13.690 13.022 4.9 0.9 588 558.72 5.0 0.1947 13.672 12.812 6.3
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x $ {T}_{\mathrm{m}} $/K[41] $ {\overline{T}}_{\mathrm{m}} $/K $ \dfrac{\left|\Delta{T}_{\mathrm{m}}\right|}{{T}_{\mathrm{m}}} $/% $ {n}_{{M}-\mathrm{O}} $/atom–1 $ {E}_{\mathrm{c}}/ $(eV·atom–1)[42] $ {\overline{E}}_{\mathrm{c}}/( $eV·atom–1) $ \dfrac{\left|\Delta{E}_{\mathrm{c}}\right|}{{E}_{\mathrm{c}}} $/% 0.1 514.3 493.85 4.0 0.1788 14.280 13.831 3.1 0.2 497.7 474.34 4.7 0.1766 14.211 12.952 8.9 0.3 477.9 481.83 0.8 0.1693 14.141 13.166 6.9 0.4 453.6 452.15 0.3 0.158 14.072 13.205 6.2 0.5 427.2 418.89 1.9 0.1471 14.002 13.195 5.8 0.56 410.5 406.49 1.0 0.1429 13.948 13.179 5.5 0.6 437.6 429.44 1.9 0.1472 13.932 12.678 9.0 0.7 476 458.42 3.7 0.1528 13.863 12.633 8.9 0.8 524.4 521.35 0.6 0.172 13.793 12.558 9.0 0.9 572.8 575.54 0.5 0.1964 13.724 12.878 6.2
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x $ {T}_{\mathrm{m}} $/K[41] $ {\overline{T}}_{\mathrm{m}} $/K $ \dfrac{\left|\Delta{T}_{\mathrm{m}}\right|}{{T}_{\mathrm{m}}} $/% $ {n}_{{M}-\mathrm{O}} $/atom–1 $ {E}_{\mathrm{c}}/ $(eV·atom–1)[42] $ {\overline{E}}_{\mathrm{c}}/( $eV·atom–1) $ \dfrac{\left|\Delta{E}_{\mathrm{c}}\right|}{{E}_{\mathrm{c}}} $/% 0.1 517.9 503.94 2.7 0.1773 14.298 13.97 2.3 0.2 507.1 485.17 4.3 0.1737 14.247 13.88 2.6 0.3 495.2 467.32 5.6 0.1702 14.195 13.796 2.8 0.4 482 450.07 6.6 0.1667 14.143 13.718 3.0 0.463 473.5 439.77 7.1 0.1645 14.111 13.671 3.1 0.5 482.5 469.06 2.8 0.1787 14.091 13.608 3.4 0.6 499.4 485.9 2.7 0.1827 14.04 14.255 1.5 0.7 520.1 512.96 1.4 0.179 13.988 13.799 1.4 0.8 538.7 564.38 4.8 0.1835 13.936 14.084 1.1 0.9 558.7 566.4 1.4 0.1881 13.885 13.986 0.7
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