摘要
熔盐是太阳能热利用领域重要的储热材料之一,熔盐使用温度上限越高,储热量就越大,能量传递效率越高。为了提高熔盐使用温度上限,以Solar Salt与HITEC两种常用硝酸熔盐为对象,将实验和量子化学计算相结合研究了影响高温稳定性的因素。首先通过静态熔融法制备了Solar Salt与HITEC熔盐,并通过DSC-TG曲线分析了二者的高温稳定性,通过XPS分析了分解产物,通过计算软件模拟了硝酸盐分解为亚硝酸盐的过程,采用的是B3LYP泛函和6-31+G~*基组。最后从反应机理的角度对影响二者高温稳定性的因素进行了讨论。研究结果表明,当熔盐升温至600℃时,Solar Salt和HITEC的失重分别为2%和1%,并且亚硝酸盐没有进一步分解为金属氧化物或反应进度较小,K^+和Na^+的半径不一致,二者比例的不同是造成这两种熔盐稳定性差异的因素之一。同时,由反应物浓度不同导致化学平衡的移动,这也使HITEC较难分解。
Molten salts play a key role in thermal energy storage of solar thermal utilization.The higher the upper limit of the usable temperature of molten salt,the greater the heat storage density and the higher the energy transfer efficiency.This work uses both experiments and quantum chemical calculations to study factors affecting the stability of two molten salts of Solar Salt and HITEC at a high temperature.Solar Salt and HITEC were firstly prepared,which involved drying of NaNO3and KNO3powder in a vacuum oven at120℃for24hours;mixing the dried NaNO3and KNO3in a mortar with60%:40%(mass ratio)followed by grinding of the mixture;heating the ground powder mixture in a resistance furnace at400℃for12hours;cooling the molten salt down and grounding the sample to a powder form.The resulting material gave the Solar Salt.The HITEC were prepared by using the same method with mass ratio of KNO3,NaNO3and NaNO2being53%:7%:40%(weight fraction).High-temperature stabilities of samples were studied by DSC-TG analyses.The decomposition of the products was analyzed by XPS.The nitrate decomposition into nitrite was simulated by a software based on B3LYP functional with a base group of6-31+G^*.Finally factors affecting the stability of the nitrate salts were discussed from the reaction mechanisms.The results showed that,when heated to600℃,Solar Salt and HITEC mass losses were2%and1%,respectively.No metal oxides were produced or the production rate is too low to be observed.The difference in the metal ion proportion and the difference in the acid radical proportion were regarded as possible factors for the difference in the stabilities of the molten salts.The radii of the metal ions were found to be different,leading to different energies of intermediates and transition states.The movement of chemical equilibrium,caused by reactant,was considered as an additional reason for the different thermal stabilities of the Solar Salt and HITEC.
作者
朱闯
铁生年
韩红静
ZHU Chuang;TIE Shengnian;HAN Hongjing(New Energy(Photovoltaic) Industry Research Center,Qinghai University, Xi'ning 810016,Qinghai,China)
出处
《储能科学与技术》
CAS
CSCD
2019年第1期173-179,共7页
Energy Storage Science and Technology
基金
青海省自然科学基金(2017-ZJ-945Q)
关键词
太阳能
储热
熔盐
稳定性
分解
solar energy
heat storage
molten salt
stability
decomposition
