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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粘度、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、低粘度、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 high-efficiency thermal storage material for advancing 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, the measurements of properties for nitrates are not convenient at high temperature melting state for long time period, which can cause the corrosion of storage vessel made by stainless steel by nitrates salt, and the theoretical simulations are also faced to large challenge of complicate models and long computing period for optimizing the performance of nitrate molten salts. 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 mechanism of these properties. The calculated bond lengths, cohesive energy, and melting points of nitrate molten salt agree with the experimental ones. The study reveals the strongly dependence of physical properties upon the valence electron structure. The bonding strength and ability strongly depend upon the covalent electron pairs nα. The cohesive energy exhibits a positive correlation with the number of valence electrons nc. The melting mechanism is originated from the melting broken of M-O (M = Li, Na, K) bond by the vibrating of thermal phonon at melting temperature, it is suggested the atomic cluster of NO3 is still stabilized during 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 of number of covalent electron pairs (nM-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 calculations of EET and thermodynamic simulations, the binary nitrates molten salts are optimized with compositions of 0.5LiNO3-0.5NaNO3、0.5LiNO3-0.5KNO3 and 0.6NaNO3-0.4KNO3, which are suggested as good candidates for advanced molten salts with high thermal and 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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