高压下新型聚合氮结构的设计及合成

发布时间：2018-03-25 22:09

本文选题：聚合氮　切入点：高压　出处：《吉林大学》2017年博士论文

【摘要】：聚合氮是高压下解离双原子分子氮形成的由氮氮单键键合而成的全新网络状结构。由于氮氮三键(946 KJ/mol)与氮氮单键(159 KJ/mol)间存在巨大的能差,当聚合氮解聚恢复成分子氮时将释放巨大的能量,其能量密度是现有材料的5倍以上。因此,聚合氮是一种突破传统的高能量密度材料,在众多领域有着广泛的应用前景。目前,已经有两种聚合氮结构在实验上得到了证实(cg-N结构和PL-N结构)。这些研究极大地激发了人们对其他含氮体系的研究热情。研究含氮体系的高压相变,以及是否存在聚合相;通过高压化合手段,能否形成新的高含氮化合物,并形成聚合相;通过纳米限域方法,能否使聚合氮稳定到常温常压,是当前聚合氮研究领域中的关键科学问题。针对上述科学问题,本文中利用高压手段、理论与实验相结合的方法开展了典型含氮体系的高压相变和稳定性研究,包括叠氮化合物体系、N-H体系、Na-N体系以及纳米限域体系,得到以下主要结论:1、利用高压原位同步辐射技术、高压原位Raman光谱和高压原位红外光谱实验方法结合CALYPSO晶体结构理论预测,研究了NH_4N_3的压致相变行为,最高压力达62.3 GPa。首次在室温、15.8 GPa的温和条件下获得了由氮氮单键键合形成的螺旋孔道状N-H聚合结构(P212121),该聚合结构卸压时能够保持到4GPa左右的低压区。同时,我们还首次确定了低压区高压相Ⅰ的晶体结构(单斜结构,P2/c)。2、利用粒子群搜索方法,开展了等比例的氮氢体系的高压结构预测,在0-180GPa内预测出三种全新的聚合结构,即C2/c、N8H8-ring、Pc结构。在这三种结构中,所有的N原子通过N-N单键键合,N存在的缺陷和悬键由H原子饱和。它们的能量水平均低于已经报道的P21/m结构,是更为稳定的N-H聚合结构。这些结构可以通过N_2/H2混合物压致合成,转变压力为10 GPa左右。特别是,我们发现N8H8-ring在常压下依然保持亚稳特性,这表明,如若在实验上合成出这种聚合结构,极有希望将其稳定到常压条件。与此同时,这些聚合结构都具有非常高的能量密度。3、采用基于粒子群算法的CALYPSO软件,对Na-N体系进行了高压变组分的结构预测,除已知NaN3、Na3N外,还提出了一系列新奇的结构(NaN_2、Na2N_2、NaN5)。更为重要的是,在16.9 GPa的压力条件发现了高含氮量的NaN5聚合相,其中所有的N原子通过氮氮单键键合形成N5环。除了NaN5外,在51 GPa压力以上还在NaN_2组分中发现了另一个具有之字链构型的聚合结构(Cmmm_II)。此外,热力学稳定性计算表明,压力大于50 GPa时NaN3组分开始分解,分解产物为NaN_2和NaN5组分。4、利用基于第一性原理的DFT计算方法,开展了氮化硼纳米管(BNNTs)限域聚合氮的稳定性研究。研究表明,限域于BNNT(5,5)中的N8链聚合氮结构能够稳定存在于常温常压条件,这是由于主客体结构之间的电荷转移造成的。对于其他管径的BNNTs,稍加压力即可使N8链聚合结构稳定。与其他限域模板相比,BNNTs具有极好的热稳定性,更为重要的是在超高压高温条件下具有极强的氮惰性。我们知道聚合氮的合成往往需要高压甚至高温高压,BN纳米管优异的理化性质为实验上限域聚合氮的研究提供了可能。本课题的研究工作为聚合氮的常压截获提供了重要解决途径。
[Abstract]:The polymerization is a new nitrogen network structure under high pressure dissociation of diatomic molecules formed by the nitrogen nitrogen bond formed. Because nitrogen triple bond (946 KJ/mol) and nitrogen bond (159 KJ/mol) there is a huge difference between can, when the polymerization depolymerization to molecular nitrogen nitrogen recovery will release enormous energy the energy density is 5 times more than the existing materials. Therefore, polymerization of nitrogen is high energy density materials a breakthrough of the traditional, has a broad application prospect in many fields. At present, there have been two kinds of polymerization nitrogen in the experiment confirmed the structure (cg-N structure and PL-N structure). These studies greatly stimulate the people of other nitrogen system research enthusiasm. High pressure phase transition of nitrogen containing system, and the existence of polymerization phase; by high-pressure combined means, whether the formation of high nitrogen compounds and the formation of new phase polymerization, by nano domain method; limit, can make polymerization Stable nitrogen to normal temperature and pressure, is a key scientific problem in current research in the field of polymerization nitrogen. In view of the above problems in science, high pressure by means of this paper, method of combination of theory and experiment was carried out on typical high-pressure nitrogen transformation and stability of the system, including the azide compound system, N-H system, Na-N system and nano limited the domain system, the main conclusions are as follows: 1, the use of high pressure in situ synchrotron radiation technology, high-pressure in situ Raman spectroscopy and infrared spectroscopy in situ high pressure experimental method combined with CALYPSO crystal structure theory predicts that NH_4N_3 study of the pressure induced phase transition behavior, up to 62.3 GPa. for the first time at room temperature, 15.8 GPa under mild conditions have shaped helical pores N-H formed by nitrogen bond polymerization (P212121), the structure of polymeric structure pressure relief to maintain a low pressure area to about 4GPa. At the same time, we first determined the low pressure area The crystal structure of high-pressure phase I (P2/c.2, monoclinic structure) using particle swarm search method, the prediction of high pressure hydrogen nitrogen ratio structure system, predict the aggregation structure, three kinds of new 0-180GPa in C2/c, N8H8-ring, Pc. In the three structures, the N atom through the N-N bond, N flaws and dangling bonds by H saturated. Their energy levels are lower than those of P21/m structure have been reported, is a more stable N-H polymerization structure. These structures can be synthesized by pressure induced N_2/H2 mixture, the transition pressure is about 10 GPa. In particular, we found that N8H8-ring remains metastability under atmospheric pressure, which indicates that if in the experiment to synthesize the polymeric structure, it is very hopeful to be stable to atmospheric conditions. At the same time, has a very high energy density.3 the aggregation structure, using CALYP based on particle swarm algorithm SO software, predict the structure of high voltage variable components of the Na-N system, in addition to the known NaN3, Na3N, also put forward a series of novel structures (NaN_2, Na2N_2, NaN5). More importantly, the high nitrogen content of NaN5 polymerization phase under the pressure of 16.9 GPa, all of them the N atom by nitrogen bond formation of N5 ring. In addition to NaN5, the pressure of 51 GPa are still NaN_2 components found in the polymeric structure of another zigzag chain configuration (Cmmm_II). In addition, calculations show that the thermodynamic stability, pressure is greater than 50 GPa NaN3 group started decomposition, decomposition the products are NaN_2 and NaN5 component.4, using the first principle calculation method based on the DFT, the boron nitride nanotubes (BNNTs) on the stability of confinement of polymerization nitrogen. The study shows that the confinement in BNNT (5,5) N8 in the polymerization of nitrogen structure can stably exist in normal temperature and pressure conditions, this is due to the subjective and objective The charge transfer between the body structure. For other diameter BNNTs, a little pressure can make N8 chain polymerization stable structure. Compared with other confinement template, BNNTs has excellent thermal stability, more important is to have strong nitrogen inert in ultra high pressure and high temperature conditions. We know that the synthesis of polymeric nitrogen often even the requirement of high temperature and pressure, can provide excellent physical and chemical properties of BN nanotubes on experimental limit domain aggregate nitrogen. This study provides an important way to solve the atmospheric interception of polymerization nitrogen.

【学位授予单位】：吉林大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：O631

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