基于原位气相质谱的硝酸盐热分解反应过程研究

The molten nitrate salt has been widely used as thermal energy storage (TES) medium, heat transfer fluid (HTF) and electrolyte for its excellent physical and chemical properties. However the breadth and depth of its application is limited by the thermal decomposition of nitrate. The process and mechanism of the thermal decomposition of molten nitrate salt are still under great debate. By using a home-made in situ salt vaporization oven combined with time of flight mass spectrometer (TOF-MS), we found some different but interesting results about the evolution of gases during the decomposition of molten nitrate salt. Based on these results, we deduced that there are intermediate state existing during the thermal decomposition process of nitrate salt. This project is to figure out the thermal decomposition mechanism of molten nitrate salt using the solar salt (40%wt KNO3-60%wt NaNO3) as a model. The gas phase, liquid phase and solid phase decomposition products will be acquired separately with in situ high temperature mass spectrum, in situ high temperature absorption spectroscopy and X-ray diffraction spectroscopy. Combined with thermodynamics theory calculation the mechanism of thermal decomposition of solar salt will be studied too. This work is important for exploring better way to improve thermal stability of the molten nitrate salt at high temperatures.

硝酸盐因其优异的热物理化学性质，被用作优良的传热、蓄热介质和熔盐电解质。已有的研究发现硝酸盐具有因热分解反应导致的高温不稳定性，这极大限制了其应用的广度和深度，而对其热分解温度以及反应过程的认识目前仍然存在着很大争议。本课题组在前期硝酸熔盐热分解气相质谱研究中，发现了不同以往研究所得的热分解产物，推测反应存在着中间态过程，且环境气氛是影响对其分析检测的重要因素。本项目拟以二元硝酸盐Solar salt（40%wt KNO3-60%wt NaNO3）为模型，采用高温原位气相质谱技术，高温原位吸收光谱和X射线衍射光谱技术，从气相、液相和固相三个方面定性定量的测定硝酸盐热分解产物，并结合热力学理论计算，研究硝酸盐热分解反应机理，探索提升硝酸盐高温热稳定性的途径。

在本项目支持下，我们对基于飞行时间质谱技术的高温原位气相质谱仪进行了优化和改进，开展了硝酸盐热分解气相质谱分析，并获取了不同温度条件下的硝酸盐热分解过程中所产生的气相组分含量的变化信息；结合原位熔融盐吸收光谱分析和电子顺磁共振等多种分析技术，建立了一套切实可行的、具有普适性的硝酸盐热分解反应过程和机理的研究方法，并结合化学热力学理论计算，揭示了多元硝酸盐热分解反应过程和机理；通过对硝酸盐热分解机理的研究发现，硝酸盐的热分解过程中存在着超氧根离子O2-的中间态过程，其初始分解产物主要是N2和含N氧化物等，并没有通常认识的氧气生成；基于这一机理，通过添加合适的添加剂能够有效提高硝酸盐的热稳定性，进而提升了硝酸盐的应用价值。