新型相同钠离子混合熔盐相图预测及物性测量

The phase diagram prediction and experimental study of ternary same cation systems

为了提高第三代聚光式太阳能热发电技术的效率,降低系统的运行成本,需要开发出具有更高使用温度的新型高温储热/蓄热材料。本文基于相同阳离子的原则,选取3种相同钠离子熔盐NaNO_(3)、NaCl、Na_(2)CO_(3)作为基盐,借助相图原理指导混合熔盐的配制,通过FactSage软件对NaNO_(3)-NaCl-Na_(2)CO_(3)三元体系进行相图热力学计算,利用差示扫描量热仪对预测最低共熔点附近多组共晶盐进行热物性分析。结果发现,当三元体系熔盐NaNO_(3)∶NaCl∶Na_(2)CO_(3)物质的量比例为0.92∶0.064∶0.016时熔点最低,测得最低共熔点为279.9℃,相变潜热值为194.1 J/g,与相图预测结果(291℃)基本一致,验证了相图计算的准确性。对该体系其他热物性进行测量,得到其分解温度为595℃(质量损失率为3%),比热容为1.60 J/(g·K)(500℃),平均比热容为1.62 J/(g·K),相比于Solar Salt和Hitec平均比热容分别增加了0.12 J/(g·K)和0.28 J/(g·K)。该新型三元体系熔盐具有潜热、比热容大和使用温度范围较宽的优点,在制备复合材料潜热储热方面有很大潜力,为开发新型太阳能热发电储热/蓄热材料提供了借鉴,也为借助相图理论指导混合熔盐的开发提供了参考。

New high-temperature thermal storage/storage materials with higher service temperatures must be developed to improve the efficiency of third-generation concentrated solar thermal power generation technology and reduce the system's operating costs.Based on the same-cation principle,three molten salts,i.e.,sodium nitrate(NaNO_(3)),sodium chloride(NaCl),and sodium carbonate(Na_(2)CO_(3))of the same sodium ion,were selected as base salts,and the phase diagram principle guided the preparation of mixed molten salts.The phase diagram thermodynamic calculation of the NaNO_(3)-NaCl-Na_(2)CO_(3)ternary system was carried out using the FactSage software program.The thermophysical analysis of several groups of eutectic salts near the lowest eutectic point was carried out using a differential scanning calorimeter.The results showed that when the molar ratio of the molten salts in the ternary system(NaNO_(3):NaCl:Na_(2)CO_(3))was 0.92:0.064:0.016,the melting point of the system was the lowest,the lowest eutectic point was 279.9℃,and the latent heat was 194.1 J/g.These results were essentially consistent with the theoretical calculation result(291℃),verifying the model's accuracy.Other thermophysical properties of the system at the lowest eutectic point were measured.The decomposition temperature of the system at this ratio was 648℃(the mass loss rate was 5%),and the specific heat value was 1.60 J/(g·K)(500℃).The measured specific heat value increased by 0.12 compared with Solar Salt and 0.28 compared with Hitec salt.The new ternary system had large latent heat of molten salts and a broad temperature range.It showed significant potential in the preparation of latent heat storage involving composite materials.The system can be used as a reference for developing new thermal storage/storage materials for solar power generation and as a guide for the development of mixed molten salts using phase diagram theory.