【作者】 王芳；

【导师】 贡雪东；

【作者基本信息】 南京理工大学 ， 材料科学与工程， 2013， 博士

【摘要】 高氮高能化合物作为新一代高能量密度材料(HEDM),广泛应用于高能钝感炸药、推进剂、以及气体发生剂等方面,几乎涉及含能材料的各个领域。对其结构和性能开展较为系统和深入的研究有重要意义。本文运用当代理论和计算化学方法,对新型高氮化合物(氮杂环化合物、氮杂笼状化合物、全氮化合物和三嗪胍盐)的几何结构、电子结构、爆轰性能以及晶体结构等进行计算研究。论文主要包括三部分内容：1.通过分子设计,采用氮原子取代典型硝胺HMX(环四甲撑四硝胺)、双环HMX(顺式-2,4,6,8-四硝基四氮杂双环[3.3.0]辛烷)、TNAD(反式-1,4,5,8-四硝基四氮杂双环[4.4.0]癸烷)环上的CH基团,并增加硝基数目,提高分子的氮含量和氧平衡。研究分子结构、稳定性和能量变化规律,并兼顾稳定性和爆轰性能的要求,从上述衍生物中筛选出10种具备研制潜力的HEDM候选物。基于密度泛函理论方法和分子力学方法,获得了2,4,6,8-四硝基-1,3,5,7-四氮杂立方烷(TNTAC)的优化构型、生成焓、晶体结构、以及爆速和爆压等性质；采用不同密度泛函理论方法比较了两种可能的热分解引发键(骨架C-N键和侧链C-N02键)的离解能,探讨其热解引发机理。与著名的高能化合物CL-20(六硝基六杂氮异伍兹烷)和ONC(八硝基立方烷)相比,TNTAC稳定性略低,但爆轰性能更加优越,是有较高合成价值和应用潜力的HEDM目标物。对4,4’,6,6’-四叠氮偶氮基-1,3,5三嗪(TAAT)和4,4’,6,6’-四叠氮-肼基-1,3,5-三嗪(TAHT)等一系列桥连三嗪化合物结构和性能的计算研究表明,叠氮基能够大幅度提高桥连三嗪化合物的生成焓；-NF2、-NO2、-N=N-和-N=N(O)-基团能有效地提高爆轰性能。桥基和三嗪环之间的p→π共轭作用有利于分子稳定。将分子稳定性或感度与电子结构和静电势参数相关联,发现当强吸电子基团-NF2和-NO2引入三嗪环时,分子表面正负静电势平衡程度降低,分子稳定性降低。综合考虑爆轰性能与稳定性,在系列衍生物中筛选出三种具有优良爆轰性能与较低感度的潜在HEDM.采用密度泛函理论方法,对已合成的9种N5+盐的几何结构、电子结构、稳定性和能量性能等进行了研究。结果表明(N5)2SnF6、N5PF6、N5BF4和N5SO3F盐在室温下不但具有一定的稳定性,而且爆炸时释放的能量比Pb(N3)2大,是具有开发和应用前景的HEDM候选物。另外对一系列多叠氮胺N-(N3)n (n=1-6)的结构和性质进行了研究,为实验合成新的全氮化合物提供理论指导。2.选择偶氮三嗪TAAT和TAHT为研究对象,首次对它们的晶体能带结构和性能进行周期性量子化学计算,并探讨了压力的影响。运用CASTEP程序包中的固体密度泛函方法优化晶体结构,计算能带结构。发现LDA/CA-PZ方法较GGA/PW91和GGA/RPBE方法更适用于研究TAAT和TAHT晶体；首次报道了TAAT和TAHT的前沿能带、带隙和态密度及其与感度等性能的关系。计算结果表明晶体的带隙随压力的升高整体上降低,在100GPa时,带隙几乎降低到0eV,预示分子晶体由半导体变为金属态体系。晶体的能带波动幅度随压力的增加而增大,态密度图谱越来越平滑和分散；分析Fermi能级附近导带和价带的组成,预示桥基-N=N-和-NH-NH-上的N原子是化学反应的活性中心；当静水压从0增加到100GPa时,TAAT和TAHT晶胞内分子均发生叠氮基-四唑环异构反应,并出现新的分子结构。3.应用色散校正的密度泛函方法(DFT-D),在B97-D/AUG-cc-PVDZ水平下对一系列三嗪胍盐的分子内氢键作用进行了深入的理论研究。通过自然键轨道理论(NBO)、分子中的原子理论(AIM)和能量分解分析(EDA)手段对氢键进行表征、并分析氢键的作用形式和本质；比较了不同阳离子如胍盐、氨基胍盐、二氨基胍盐、三氨基胍盐和胍基甲酰胺和阴离子上的取代基对氢键作用和其它能量性质的影响。计算结果表明分子内氢键来源于阴阳离子中LP(N或O)→σ*(N-H)轨道相互作用,这些氢键与其它原子构成七元或八元环,有利于分子的稳定。阴阳离子之间的相互作用能主要由静电相互作用和轨道作用贡献,色散能贡献很小。胍基甲酰胺阳离子比其它阳离子更有利于提高分子内氢键相互作用,对分子稳定性贡献较大。阴离子不同取代基对稳定性的贡献顺序为：-N02<-NF2<-N3(-ONO2)<-NH2。更多还原

【Abstract】 The nitrogen-rich energetic compounds, well known as the fourth generation of high energy density materials (HEDM), have been widely used in almost all fields of energetic materials, such as insensitive explosives, propellants, and gas generating agents. Therefore, it is necessary to perform systematic and in-depth studies on their structure and properties. In this thesis, we used several theoretical methods to study the geometric structure, electronic structure, detonation performance, crystal structure, and other properties of nitrogen-rich energetic materials, including aza-heterocyclic compound, aza-cage compounds, all-nitrogen compounds, and triazine guanidinium salts. The contents of the dissertation can be divided mainly into three parts:The first part concentrates on molecular design for HEDM. By molecular modification, the CH groups in the ring of typical nitramine HMX (1,3,5,7-tetranitro-1,3,5,7-tetraazacyclooctane), bicyclic-HMX (cis-2,4,6,8-tetranitro-1H,5H-2,4,6,8-tetraazabicyclo[3.3.0]octane), and TNAD (trans-1,4,5,8-tetranitro-1,4,5,8-tetraazadecalin) are replaced by nitrogen atoms, and more nitro groups are introduced. As a result, the increment of nitrogen content and oxygen balance lead to higher density and more internal energy. The variation trends of structure, stability, and energy are discussed. Considering the requirements of HEDMs, we find ten promising HEDM candidates with good explosive performances and stability.Based on density functional theory (DFT) and molecular mechanics (MM) methods, the fully optimized structure, heat of formation (HOF), density, crystal structure, detonation velocity, and detonation pressure of cage compound2,4,6,8-tetranitro-1,3,5,7-tetraazacubane (TNTAC) are reported. Pyrolysis mechanism is investigated and ascertained by comparig the bond dissociation energy (BDE) of two possible trigger bonds (C-N in cage and C-NO2on side chain. In comparison with the famous cage explosives CL-20(2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane) and ONC (octanitrocubane), TNTAC exhibits better detonation performance and meets the stability requirement. Therefore, TNTAC is expected to be a novel candidate of HEDM with high exploitable values.Computational studies on a novel series of bridged triazines such as4,4’,6,6’-tetra(azido)azo-1,3,5-triazine (TAAT) and4,4’,6,6’-tetra(azido)hydrazo-1,3,5-triazine (TAHT) show that HOF can be increased largely by-N3group, and-NF2,-NO2,-N=N-, and-N=N(O)-groups are effective structural units for improving the detonation performance. p→π conjugation interaction is found between the nitrogen-bridge group and the triazine ring, which makes the bridged triazine molecule stable as a whole. Taking the detonation performance and thermal stability into account, three bridged triazines are recommended as energetic insensitive explosives.DFT calculations have been performed on the geometrical structure, electronic structure, stability, and energetic properties of nine synthesized N5+-containing salts. The results show that (N5)2SnF6, N5PF6, N5BF4, and N5SO3F have medium stability and release much more energy than Pb(N3)2and HMX during thermal decomposition. They can be considered as potential candidates of very energetic explosives. In addition, similar studies are carried out on a series of azidamines N-(N3)n (n=1-6). The results provide some useful information for the research of novel all-nitrogen compounds.The second part focuses on the periodic quantum mechanics studies on TAAT and TAHT. The influence of pressure on the structures and properties has also been investigated.The solid DFT method in the CASTEP program is used to optimize the crystal structure and calculate band structures. The results demonstrate that LDA/CA-PZ is more reliable than GGA/RPBE and GGA/PW91for studying the polyazide crystals. Frontier band structure, band gap, and density of states (DOS) of TAAT and TAHT are reported for the first time. The correlations between them and their sensitivity are discussed in detail. The band gaps decrease generally with the increasing of pressure, and drop to nearly zero at100GPa. This indicates the molecular crystals undergo an electronic phase transition from a semiconductor to metallic systems. The band fluctuation increases with the increment of pressure, and DOS becomes more dispersed and smoother. An analysis of the valence and conduction bands near Fermi level shows that the N atoms of the bridges-N-N-and-NH-NH-act as an active center. What is more, the azide-tetrazole transformation in TAAH and TAHT molecules are observed as the pressure increases, and new structures have formed.The third part centers on the dispersion corrected DFT method (DFT-D) studies of the intramolecular hydrogen bonding interactions and properties of a series of nitroamino[1,3,5]triazine-based guanidinium salts at the B97-D/AUG-cc-PVDZ level. By means of natural bond orbital (NBO), atoms in molecules (AIM), and energy decomposition analysis (EDA), the hydrogen bonds are characterized, and the origin of hydrogen bond and the interaction energies are analyzed. The effect of different substituents and cations (including guanidinium, aminoguanidinium, diaminoguanidnium, triaminoguanidinium, and guanylurea cations) on the hydrogen bonding interactions and other properties are also discussed. LP(N or O)→σ*(N-H) orbital interactions are found between the cations and anions, and they are associated with a seven or eight-membered pseudo ring which enhances the molecular stability. The electrostatic and orbital interactions contribute mainly to the stability, and the dispersion energy has very small contributions. Results show that the guanylurea cation is better for improving the thermal stabilities of the ionic salts than other cations. The contributions of different substituents to the thermal stability increase in the order of-NO2<-NF2<-N3(-ONO2)<-NH2更多还原