氮杂笼型硼烷离子液体设计合成及燃烧性能调控

Hypergolic ionic liquids can overcome the shortcomings of hydrazine-based propellants such as high volatility and strong carcinogenicity, and have become a new kind of energetic materials for aerospace power. Currently, the ignition delay times for some hypergolic ionic liquids are as low as 8 ms so as to meet requirements of the engine design. However, specific impulses of ionic liquids are all below 200 s, which can’t reach the energy requirement of propellants. In this project, according to the specific properties including high density of closo-boranes, rapid combustion for B-H groups, and high energy for N-B bonds, ionic liquids based on closo-azaborane are proposed. Their energy density and combustion speed may be largely improved with specific impulse >230 s and ignition delay time < 4 ms. Valence bond structures, ionic synergistic effects and structure-property relationships of closo-azaboranes are mainly studied. Spontaneous combustion processes are fully characterized by In-situ IR, Micro Reaction Calorimetry, TG-MS, and Quantum Chemical Calculation. Kinetics and mechanisms of the hypergolic reactions are revealed at molecular level. With the above knowledge, theoretical system is constructed for the structural design and performance adjustment of closo-azaborane based ionic liquids, which could promote the leaping developments of novel green propellants.

自燃离子液体可弥补肼类化合物易挥发、强致癌的不足，成为新一代航天动力燃料。目前，离子液体的自燃延迟时间达到了发动机设计要求（< 8 ms），但其比冲均 < 200 s，无法满足推进剂的能量指标。本项目利用笼硼烷密度高、B-H燃速快和N-B键能量高等特性，设计合成氮杂笼型硼烷离子液体，实现能量密度和燃烧性能的大幅提高（比冲: > 230 s, 自燃延迟时间: < 4 ms）；通过研究氮杂笼型硼烷离子液体的价键结构和离子协同效应，揭示结构对性能的影响规律；利用原位红外、微反应量热、热重-质谱联用等分析手段和量化计算，从分子水平上解析该类离子液体自燃反应的动力学和机理。通过本研究，建立氮杂笼型硼烷离子液体结构设计和性能调控的理论体系，为新型绿色推进剂的发展提供科学基础。

推进剂是火箭和空间飞行器的动力核心，是决定武器装备能否达到预定目标的关键，其中自燃推进剂是航天器顶级发动机设计的重要选择。目前，自燃推进剂的主要燃料是肼类物质，具有沸点低、毒性高、强致癌等不足，急需开发无毒、高能、绿色自燃推进剂燃料。自燃离子液体具有蒸汽压低、密度高、结构性质可调、毒性低等特点，恰好可以弥补肼类推进剂的不足，是绿色自燃推进剂燃料研究的重要方向。. 本项目针对硼笼类自燃离子液体比冲亟待提升的问题，开展氮杂笼型硼烷类高能自燃离子液体的设计合成研究，利用笼型硼烷密度高、B-H燃速快和N-B键能高的特性，在笼型硼烷阴离子中引入氮杂原子提高生成焓，进而大幅提高比冲。设计合成了氨基取代的硼笼阴离子，氮杂碳硼笼阴离子和[B6H7]-基阴离子三个系列18种自燃离子液体，通过1H NMR、13C NMR、IR、ESI和EA等表征手段确定了化合物的结构，进一步通过量化计算和实验对合成的18种氮杂硼笼类离子液体的密度、生成焓、热稳定性、比冲进行了深入研究，揭示了两种阴离子体系的性能参数随不同阳离子的变化规律。通过对获得的18种物质的理化性能的综合分析表明制备的1-炔丙基-3-甲基咪唑1-氨基-十二硼酸盐（Tm，198.3 ℃；HOF，299.37 kJ/mol；Isp，276.8 s）和[3-炔丙基-1-甲基咪唑][B10H13CH3CN]（Tm，-14.19 ℃ 、HOF，-54.48 kJ/mol， Isp，272s）具有较高的比冲和热稳定性，有作为推进剂高能添加剂或双组元推进剂燃料的应用潜力。