基于正烷铵盐二元体系相变行为精准构筑固-固相变储能材料的热力学研究

It has been one of the hot topics in the field of energy materials to find the green solid - solid phase change energy storage materials with stable structure, high phase transition enthalpy and moderate phase transition temperature. However, how to achieve the precise construction of this material is the bottleneck in the research. Under the guidance of the principle of phase chemistry, this project intends to make a series of long-chain n-alkane ammonium salts into binary compounds with significant solid-solid phase change behavior, and to cultivate single crystal, and to assist to the spectroscopy characterization.The enthalpy of dissolution and the enthalpy of combustion are determined by microcalorimeter and oxygen bomb calorimeter. molar enthalpy of dissolution at infinite dilution, solvation enthalpy and standard molar enthalpy of formation are analyzed and obtained. The thermodynamic parameters such as phase transition temperature, phase change enthalpy and phase change entropy are obtained by using the precise adiabatic calorimeter to determine the low temperature heat capacity and the low temperature DSC thermal spectrum is used. Guided by molecular dynamics simulation, with variable temperature FTIR method, correlation of structure, thermodynamic properties and energy storage effect of target compound is investigated, the nature of solid - solid phase change is revealed, the inherent law to adjust the phase change temperature and enhance the phase change enthalpy is explored. An accurate evaluation index of the solid - solid phase change materials with stabile structure, big enthalpy of phase change and moderate phase transition temperature will be established and some good green solid-solid phase change energy storage materials are selected for in-depth study and application.The results can lay a thermodynamic foundation for the precise construction of a new solid-solid phase change energy storage material with high efficiency, non-toxic, environmental protection and practicability.

寻找结构稳定、相变焓大、相变温度适中的绿色固-固相变储能材料一直是能源材料领域的前沿热点之一。然而，如何精准构筑这种材料却是研究中的瓶颈。本项目拟在相化学原理指导下，合成系列具有显著固-固相变行为的长链正烷铵盐二元体系化合物，培养单晶，辅以谱学表征；利用微热量计和氧弹热量计测定其溶解焓和燃烧焓，获得无限稀释摩尔溶解焓、溶剂化焓、标准摩尔生成焓；利用精密绝热热量计测定低温热容，佐以低温DSC热谱，获取相变温度、相变焓和相变熵等热力学参数；在分子动力学模拟指导下，佐以变温FTIR等方法，关联目标物结构、热力学性质和储能效果，揭示固-固相变本质，探寻调节相变温度和提高相变焓的内在规律；建立精准构筑结构稳定、相变焓大、相变温度适中固-固相变储能材料的评价指标，筛选出优秀的可供深入研究和应用的绿色固-固相变储能材料。研究结果可为精准构筑高效、无毒、环保和实用的新型固-固相变储能材料奠定热力学基础。

本项目基于长链正烷胺无机和有机酸盐具有显著的固-固相转变现象，可作为一种潜在的相变储能材料，在太阳能储存、工业余热储存和室内保温等方面得到广泛的应用。本项目通过努力，完成了以下四项工作：.1.合成了30余种五个系列具有显著固-固相变行为的长链正烷铵盐化合物，培养单晶，通过谱学表征，确定了化合物的分子结构、晶体结构和原子空间排布方式；.2.利用微热量计和等温环境溶解-反应热量计测定其溶解焓，设计合理的热化学循环，解析获得无限稀释摩尔溶解焓、溶剂化焓、标准摩尔生成焓；.3.利用精密自动绝热热量计测定了化合物的低温热容，佐以低温DSC热谱，获取一级相变温度、相变焓和相变熵等相变热力学参数；.4.在以量子力学为理论基础的分子动力学模拟指导下，佐以变温FTIR等方法，关联目标物结构、热力学性质和储能效果，揭示固-固相变本质，探寻调节相变温度和提高相变焓的内在规律；. 最终，本项目通过深入细致的研究，建立了准确构筑固-固相变材料的评价指标，研究结果可为精准构筑高效、无毒、环保和实用的新型固-固相变储能材料奠定热力学基础。. 在研究中, 我们试图在相化学的指导下，通过“烷胺相同酸根不同和酸根相同烷胺不同”两种模式，在低共熔相图的低共熔点处，合成出长链正烷铵盐二元体系的复合物，通过我们的努力发现，此处组成的复合物不能培养出晶体，是一种无序的混合物，而且此混合物的相变焓没有预期的那么大，主要是由于这种材料的固-固相转变是一种典型的有序到无序的转变，相变前越有序，相变后越无序，则相变焓越大。纯粹通过固-固相转变来提高相变焓遇到了瓶颈，而且长链正烷铵盐的固-固相变过程是有2到3个分立或不连续的吸热峰构成，使得它的实际应用受到了很大的限制。我们已经通过合理有效的分子设计，调整了分子结构，让固-固相转变和固-液相转变融为一体，形成一个完整连续的吸热峰，从而增大相变焓，这样使得相变储能材料的实际应用得以实现。