六硝基菧（HNS）的光分解研究

【作者】 孙毅；

【导师】 舒远杰； 汪信； 徐涛；

【作者基本信息】 中国工程物理研究院 ， 材料学， 2013， 博士

【摘要】 六硝基菧(C14H6N6O12,2,2’4,4’,6,6’-六硝基均二苯基乙烯)具有耐热性能好,爆轰感度高,电爆阀值低,临界直径小等众多优点,已广泛应用于柔爆索,传爆药,耐热炸药等。同时,HNS也是一种典型的光敏炸药,在光作用下存在着明显的分解现象。目前国内外对于HNS的研究主要集中在其制备方法、粒径控制、热分解行为、点火和燃烧性能以及传爆能力等方面,有关HNS的初始光解机理,光解动力学,以及光解产物的确定等相关研究-直少见详细报道,然而这些信息对于有效了解炸药的贮存和使用性能起着关键作用。同时,深入了解炸药光解机理和动力学相关信息对于较好的控制、提高炸药的燃烧和爆轰性能也具有十分重要的意义。因此,本论文从炸药HNS分子在光作用下的稳态结构变化与瞬态结构产生机理入手研究炸药的光解反应,为炸药在光学场中的反应机理提供科学、合理的解释,为如何科学、合理、安全地实现光学技术在炸药中的应用提供依据。为此,论文主要开展了以下研究工作：采用紫外-可见吸收光谱(UV-Vis spectra)研究了HNS在不同极性溶剂中的吸收光谱,获得了炸药HNS在不同溶剂的波长吸收范围,发现溶剂化效应对吸收波长有显著影响,随着溶剂极性的增加HNS分子的吸收光谱向长波方向移动。利用紫外-可见光谱(UV-Vis spectra),X-射线光电子能谱(XPS),电子自旋共振谱(ESR),液质联用(LC-MS)技术考察了炸药HNS在紫外光作用下分子结构的变化信息,分析HNS可能发生的光解机理,结果表明C—NO2键断裂和-NO2基团异构化为业硝基基团之后脱去NO的过程均发生在HNS的紫外-可见光解反应过程中,但紫外-可见光的作用对HNS的热稳定性并没有明显影响。利用X-射线光电子能谱(XPS),傅里叶-红外光谱(FT-IR)以及异步二维相关红外谱图,比较了不同激光波长(包括紫光263nm,绿光527nm和红光1053nm)和功率密度对炸药结构的影响,分析了HNS在不同激光波长作用下可能发生的机理,结果表明：HNS的激光分解反应机理受激光波长影响较大,并且随着功率密度增加,激光产生的热效应作用逐渐明显。在263nm和527nm波长作用下,反式C=C双键断裂和硝基-亚硝基异构化反应为光解主要反应机理；在1053nm波长作用下,仅仅反式C=C双键发生了断裂。充分利用XPS分析室的超高真空(10-9mbar)和高洁净度,精心设计了一种原位XPS-激光-四级杆质谱联用技术,使激光束在样品表面的照射区域应与XPS仪器的X-射线光照射区域重合,研究了532nm波长10ns脉宽激光照射固态HNS引起的原位分解反应,对HNS在激光分解过程中产生的固体产物和气体产物同时进行探测,探讨了HNS可能发生的光热分解机理,结果表明-NO2基团异构化为亚硝基基团之后脱去NO的过程为反应主要过程。用纳秒激光光解技术、时间分辨荧光磷光光谱等方法,研究了HNS乙腈溶液在不同气体饱和条件下受到355nm激光激发后产生的瞬态产物种类和寿命,计算了各吸收峰的生成衰减速率和半衰期,分析了HNS被激发后瞬态发射中间体的种类及寿命,结果表明：有三种不同寿命的瞬态中间体存在,340nm的瞬态吸收峰归属于反式HNS的激发瞬态体,520nm的吸收峰应归属于HNS分子的激发态异构化后产生的顺式瞬态产物,另外一种三线态由于寿命太短且浓度很低,被旁边的吸收所掩盖。采用量子化学理论,借助于Gaussian程序对HNS的分子进行几何结构优化,计算了分子和电子结构,并从微观结构角度对其重要的光分解和热分解机理等进行预估,认为C-N02键断裂、NO2→ONO异构化反应和反式C=C双键断裂均具有相对较低的反应能垒,较容易发生,从理论上对光解实验结果进行了验证。更多还原

【Abstract】 HNS (2,2’,4,4’,6,6’-hexanitrostillbene, C14H6N6O12) is a heat-resistant explosive, which is widely used in booster charge, mild detonating fuse, and heat-stable explosive due to its excellent thermal stability, high detonation sensitivity and low critical diameter and so on. HNS has also been considered as a typical photosensitive explosive for the photodecomposition appears to be easily occurred. However, past studies of HNS are mostly focused on the preparation, particle size controlling, thermal decomposition behaviour, ignition and combustion performance and propagation capability and so on. No related investigation about the photodecomposition of HNS has been reported in detail. Determination of the photodecomposition mechanism, photolytic degradations kinetics, and the degradation products and identification of intermediates are very important for a better understanding of explosive lifetime prediction. Additionally, understanding the photodecomposition mechanisms and dynamics will allow for better control and improvement of the performance of energetic materials for combustion and explosion. Therefore, in this paper the photodecomposition of HNS is investigated both experimentally and theoretically. The main contents are listed as follows:The absorption wavelength of HNS is obtained in the range of full wavelength in different solvents. The solvate effect on the absorption wavelength is investigated. The selectivity of HNS molecule on the light source is determined.An experimental analysis has been subjected to study the UV-induced photodecomposition of HNS. The UV-Vis spectra, X-ray photoelectron spectroscopy (XPS) and electron paramagnetic resonance spectra (EPR) measurements are used to study the structure changes of HNS before and after UV-irradiation. The possible decomposition channel upon UV irradiation is discussed. Results show that C-NO2broken and nitro-nitrite isomerization with subsequent release of NO would be both existed in the photodecomposition of HNS. The differential scanning calorimetry (DSC) experiments have shown that there is no influence on the thermal stability of HNS powders as the effect of UV irradiation.The effects of laser irradiation on HNS, especially at the irradiation of different laser wavelengths (including263nm wavelength,527nm wavelength and1053nm wavelength) and different laser power density are studied by X-ray photoelectron spectroscopy (XPS), FT-IR spectroscopy and asynchronous two-dimensional correlation FT-IR spectra and so on. The possible decomposition channels are discussed. Results showe photodecomposition mechanism of HNS is wavelength-dependent. In the case of263nm and527nm irradiated, the nitro-nitriteisomerization and the fragmentation of trans-C=C bond are the main decomposition steps, while in the case of1053nm, only the fragmentation of trans-C=C bond is observed.A novel approach to study the photo-thermal decomposition of HNS (2,2’,4,4’,6,6’-hexanitrostillbene) at532nm induced by a10-nanosecond (ns) laser was described. In this method, an in-situ X-ray photoelectron spectroscopy (XPS)-laser-quadrupole mass spectrum on-line equipment was designed elaborately. The ultra high vacuum (10-9mbar) and high cleanliness of XPS analyzer chamber was fully exploited. The HNS film was directly irradiated by532-nm laser during XPS and MS spectra collection, thus enabling the accurate analysis of the photo-thermal decomposition. XPS and MS results showed that the nitro-nitrite isomerization with subsequent release of NO is the primary reaction in the laser-induced decomposition of HNS.Laser photolysis of HNS in acetonitrile solution is investigated with the excitation wavelength of355nm under different saturated conditions. The transient absorption spectra of HNS are investigated using nanosecond laser photolysis technique. The half-life of formation and decay rate of the transient absorption are calculated. In order to know how many kinds of transient species arised when HNS is excited by355nm laser, fluorescene and phosphorescen spectra are measured by time-resolved fluorescene and phosphorescen spectrometer. Results show that there are three kinds of transient species.In quantum chemistry calculation, all molecular structures are optimized by using Density Functional Theory (DFT) at B3LYP/6-311G (d, p) level. The charge distribution, the interaction of orbits, the electronic structure, the photodecomposition mechanism and the thermal performance are estimated. The calculation results could explain the experimental resultd preferably.更多还原