低压长脉冲载荷下β-HMX单晶滑移系的微观物理化学响应

采用基于ReaxFF反应力场的分子动力学方法, 从炸药弹塑性微观机制出发, 研究了在低压长脉冲载荷下β-1,3,5,7-四硝基-1,3,5,7-四氮杂环辛烷(β-HMX)炸药单晶中最有可能的七组滑移系的微观物理化学响应.模拟结果表明沿着垂直于(001)、(101)、(100)、(011)、(111)、(110)、(010)晶面的长脉冲作用方向, 这七组滑移系呈现不同的物理化学响应. 体系的剪切应力、能量、温度以及化学反应与长脉冲作用方向存在明显的依赖性: 对(010)晶面, 体系的剪切应力位垒高, 能量和温度升高得快, 化学反应很快发生, 反应敏感度最高; 对(001)晶面,体系的剪切应力位垒低, 能量和温度变化缓慢, 化学反应很难发生, 因此反应敏感度低. 滑移系的反应敏感度与滑移面两侧的分子间接触程度(即空间位阻)以及接触原子或基团间的反应活性紧密相关. 对空间位阻大且相互接触的原子或基团容易发生反应的方向, 滑移系的反应敏感度就高; 对空间位阻小或相互接触的原子或基团不容易发生反应的方向, 滑移系的反应敏感度就低. 具有较高化学反应敏感度的滑移系被认为与单晶炸药中的“热点”起源有关. 本研究为进一步发展更加合理和可靠的感度评价方法提供了理论支撑.     

冲击载荷下TATB晶体滑移和各向异性的分子动力学研究

采用ReaxFF反应力场和分子动力学方法,研究了1,3,5-三氨基-2,4,6-三硝基苯(TATB)炸药晶体在沿不同方向冲击载荷下的滑移和各向异性。冲击方向分别垂直于(101)、(111)、(011)、(110)、(010)、(100)和(001)晶面,冲击强度为10 GPa。研究结果表明,各冲击方向下可能被激发的滑移系均在{001}面,而其它滑移系均因很大的剪切阻力不容易被激发,这与TATB晶体沿c轴的层状结构和平面分子结构相符。预测了七个冲击方向下最容易被激发的滑移系,分别为(101)/{001}100、(111)/{001}010、(011)/{001}010、(110)/{001}010、(010)/{001}110、(100)/{001}120和(001)/{001}010。TATB晶体的冲击响应具有各向异性,动力学过程中体系的应力、能量、温度和化学反应都依赖于冲击方向。对垂直于(100)和(001)晶面的冲击,体系在滑移过程中遭遇的剪切阻力较高、持续时间较长,使得能量和温度较快升高,化学反应较容易发生;对垂直于(101)和(111)晶面的冲击,体系在滑移过程中遭遇的阻力较小且出现次数少,使得能量和温度缓慢升高,化学反应不易发生;对其余冲击方向,体系的响应居中。据此评价了7个冲击方向的相对敏感程度:(101)、(111)(011)、(110)、(010)(100)、(001)。本研究有助于在微观层次深入认识动载荷下TATB的响应机制、结构与性能的关系,为高能低感炸药的设计和研制提供理论参考。     

有机锡化合物催化甲基苯基碳酸酯歧化反应合成碳酸二苯酯

研究了不同配位基团的有机锡化合物对甲基苯基碳酸酯(MPC)歧化合成碳酸二苯酯(DPC)反应的催化性能.探究了电子效应和空间位阻对MPC歧化反应活性的影响,结果表明,有机锡化合物作为Lewis酸,与锡原子配位基团的吸电子效应和空间位阻影响相应催化剂的酸性从而影响其反应活性,电子效应的影响大于空间位阻的影响.氧化氢氧丁基锡[BuSnO(OH)]催化剂具有最好的催化性能,在BuSnO(OH)与MPC摩尔比为0.02,180℃及反应2.5 h条件下,MPC的转化率达到89.7%,DPC选择性为99.3%.     

锰配合物催化CO2加氢生成甲酸的理论研究

采用密度泛函理论(DFT)对锰配合物催化二氧化碳加氢生成甲酸的反应进行了理论研究. 整个催化循环主要包括氢气活化和二氧化碳氢化2个阶段. 计算结果表明, 甲酸的参与明显降低了氢气活化的反应能垒; 二氧化碳的氢化过程遵循外层机理并且氢转移是分步进行的, 决速步骤为氢负离子的转移过程, 自由能垒为21.0 kJ/mol. 对配合物中硫原子上的取代基R进行了调变, 研究结果表明, 当R为吸电子基团时能降低氢气裂解和二氧化碳氢化过程中质子转移的能垒, 而当R为推电子基团时有利于氢负离子的转移,当R=CF₃时整个反应的能量跨度(80.4 kJ/mol)最小.     

非对称反铂抗癌药物反-异丙胺·间羟甲基吡啶·二氯铂水解机理的理论研究

应用密度泛函理论PBE1PBE方法及CPCM模型计算具有空间位阻的非对称反铂抗癌药反-异丙胺·间羟甲基吡啶·二氯铂的水解反应机理.结果表明,由于空间效应,水分子从垂直于Pt平面四边形配位的方向进攻,其水解反应为水的H,O原子分别与Cl,Pt原子形成平面四边形结构的协同作用结果,Pt的5d电子和Cl的3p电子分别向水的H—O反键轨道离域,O的孤对电子向Pt的价层空轨道或Pt—Cl反键轨道离域,速率决定步骤经过一个近似三角双锥的过渡态完成.随着反应的进行,离域效应增强,Pt与O作用增强,而Pt—Cl键减弱.溶剂化效应使两步水解反应的各反应物、生成物和过渡态的能量较气相时低63.6～386.3kJ/mol,单点能垒较气相反应低约17.1～36.2kJ/mol.从空间位阻较小的异丙基相反方向进攻的反应通道更易进行,其中1B和2B通道活化焓(分别为79.7和87.8kJ/mol)最小,是第一、二步水解反应的主要通道.第二步水解活化能垒远高于顺铂,两步水解活化能垒均高于对称的反铂trans-[PtCl2(i-pra)2].     

黏结剂PLA,PCL及其共聚物与CL-20/TNT共晶黏结性能的分子动力学模拟

运用分子动力学(MD)模拟方法,对绿色黏结剂聚乳酸(PLA)、聚己内酯(PCL)和聚乳酸-己内酯共聚物(P(LA-co-CL))在六硝基六氮杂异伍兹烷/三硝基甲苯(CL-20/TNT)炸药共晶4个晶面(001),(100),(010) H和(010) T上的黏结性能进行了计算研究.对高聚物PLA,PCL和P(LA-co-CL)的密度、体积和玻璃化转变温度进行模拟以验证力场的适用性,结果显示,计算值与实验值吻合较好.分子动力学模拟计算结果表明,组成界面的晶面和高分子极性较高时,润湿性能明显较好;对相关函数计算发现,晶面和黏结剂之间H-O原子对在0. 5 nm范围内数量明显增多.对于极性最小的PCL,在所有晶面上的润湿性能都明显降低.     

ZSM-5单晶生长的研究

本文研究了DEA(二乙醇胺)-Na2O-SiO2-Al2O3-H2O体系中由晶种水热生长的ZSM-5单晶形貌和线性生长速度. 晶体外部晶面为轴面(100)、(010)及坡面(101)、(011). 在互相贯穿连生的各单晶之间, 其对称轴互成倾角. 在160-220℃范围内, 晶体线性生长速度保持恒定. 观察到单晶生长的诱导期. 由线性生长速度与温度的关系计算了生长活化能. 研究了反应物组成对晶面法线生长速度的影响、母液成分变化, 并分析了晶体的化学成分. 按晶体生长的基本原理及ZSM-5结构, 构想了实际上可能存在的ZSM-5单晶的面结构, 并估算了不同晶面上生长位的密度及其分布. 从面结构及沸石生长基元角度讨论了单晶生长机理的DEA的作用, 支持了生长基元为高聚态硅(铝)阴离子团的假设.     

CePO4低指数晶面结构性质的密度泛函理论研究

采用密度泛函理论系统研究了CePO₄三个低指数晶面的几何结构、原子弛豫和表面能。通过观察表面结构以及比较表面能大小得出最优晶面。结果表明：表面原子均存在不同程度的弛豫,表面原子弛豫程度导致表面能的差异。表面能的大小顺序为(010)<(100)<(001),(010)晶面是CePO₄晶体稳定表面。稳定表面几何结构表明,终止末端暴露原子为O原子。使用Wulff结构计算的平衡形态表明(001)晶面、(010)晶面和(100)晶面面积分别占总晶体形状面积的14%,45%和41%。低能表面在Wulff结构中起主导作用,表面能越低的晶面面积占比越大。稳定的CePO₄晶面存在不饱和键,有利于气体分子的吸附。这项工作对CePO₄在其他方面的密度泛函理论(DFT)研究具有指导性意义,并将为CePO₄基催化剂上的吸附和解离提供稳定表面。     

氧空位控制BiVO4晶面异质结的磁性和光电催化性能

在铁磁光催化剂中,大多数光生电荷具有相同的自旋状态,因此可以有效抑制光生电子和空穴的复合.利用BiVO₄{010}和{110}晶面中氧空位的形成能不同,通过晶面取向和氧空位的协同作用来调控BiVO₄的铁磁性能.在N2气氛中退火后,BiVO₄晶面异质结中氧空位的比例随着{010}/{110}晶面比例的增加而降低,因为{010}晶面上氧空位的形成能低于{110}晶面.{010}/{110}晶面比例较低的BiVO₄晶面异质结的铁磁性能优于{010}/{110}晶面比例较高的BiVO₄,因为前者颗粒尺寸更小、更立体,其比表面积和界面区域更大,所以其表面未饱和自旋对总磁矩的贡献更大.{010}/{110}比例较高的BiVO₄晶面异质结具有更大的光电流密度和光电催化产氢效率,源于BiVO₄{010}晶面比{110}晶面具有更高的电荷迁移率、更好的吸附特性和更低的能垒.并且氧空位的引入也提高了BiVO₄的制氢效率.     

重质有机资源热解过程中自由基诱导反应的密度泛函理论研究

以重质有机资源热解过程中的自由基反应为背景,为了探究自由基对共价键的诱导作用及其对共价键解离能的影响,采用基于密度泛函理论的研究方法,选择ωB97XD/6-31G**级别在Gaussian 09程序上对·CH3、·OH和·H分别诱导七类共价键反应过程的能量进行了理论计算。结果表明,空间位阻效应对自由基诱导反应能垒的影响占主要地位,共价键种类的影响相对次要;不存在·OH和·H的同基团诱导交换反应时,·OH诱导能垒比·H的高约40 kJ/mol,·CH3比·OH、·H的诱导能垒分别高约为50、90 kJ/mol;存在·OH或·H的同基团诱导交换反应时,会导致能垒约有70 kJ/mol的提高,在计算时应判断诱导反应的具体情况并加以修正。可以利用上述值估算不同共价键诱导反应的能垒。     

Is osmium diboride an ultra-hard material?

We report first-principles calculations of ideal tensile and shear strength for the recently synthesized orthorhombic OsB2 that is a primary example of a new class of ultra-hard materials synthesized by combining small, light, and covalent elements with large, electron-rich transition metals. Our calculations show that the shear strength on the (001) plane is highly anisotropic with a low peak stress of 9.1 GPa in the (001)[010] shear direction but a much higher peak stress of 26.9 GPa in the (001)[100] direction. The strong resistance against (001)[100] shear deformation prevents the indenter from making a deep imprint, giving rise to a high Vickers hardness on the (001) plane, despite the weak shear strength in the (001)[010] shear direction. The calculated peak stress of 26.9 GPa in the (001)[100] shear direction agrees well with the 30 GPa Vickers hardness observed experimentally on the (001) plane in OsB2. However, the weak shear strength (9.1 GPa) in the (001)[010] shear direction severely limits its application as abrasives and cutting tools for ferrous metals as well as scratch-resistance coatings. Our results highlight the importance of understanding atomistic deformation modes under various loading conditions in designing new ultra-hard materials.     

Anharmonic vibrational properties of explosives from temperature-dependent Raman

Raman spectra from 50 to 3500 cm(-1) and 4-296 K are analyzed for molecular crystal powders of the explosives pentaerythritol tetranitrate (PETN), beta-octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX), and 1,3,5-triamino-2,4,6-trinitrobenzene (TATB) and the inert naphthalene. Temperature-dependent Raman spectroscopy is utilized for its sensitivity to anharmonic couplings between thermally populated phonons and higher frequency vibrations relevant to shock up-pumping. The data are analyzed with anharmonic perturbation theory, which is shown to have significant fundamental limitations in application to real data. Fitting to perturbation theory revealed no significant differences in averaged anharmonicities among the three explosives, all of which exhibited larger averaged anharmonicities than naphthalene by a factor of 3. Calculations estimating the multiphonon densities of states also failed to correlate clearly with shock sensitivity. However, striking differences in temperature-dependent lifetimes were obvious: PETN has long lived phonons and vibrons, HMX has long lived phonons but short lived vibrons, while TATB has short lived phonons and vibrons at low temperature. Naphthalene, widely used as a model system, has significantly different anharmonicities and density of states from any of the explosives. The data presented suggest the further hypothesis that hindered vibrational energy transfer in the molecular crystals is a significant factor in shock sensitivity.     

Theoretical studies of energy transfer rates of secondary explosives

Understanding the mechanism of shock-induced chemical reaction in secondary explosives is necessary to pursue the development and the safe use of new explosives having high performance and low sensitivity. In an effort to understand the mechanism, the energy transfer rates of such secondary explosives as PETN(I), PETN(II), delta-HMX, alpha-HMX, beta-HMX, RDX, ANTA, DMN, and NM have been evaluated based on the formula derived by Fried and Ruggiero [Fried, L. E.; Ruggiero, A. J. J. Phys. Chem. 1994, 98, 9786]. The energy transfer rates were determined in terms of the density of vibrational states and the unharmonic vibron-phonon coupling term, which were calculated by using a flexible potential containing both intra- and intermolecular terms. For the secondary explosives, a good correlation was found between the energy transfer rates and the impact sensitivity. The energy transfer rates are several times faster for the explosives with higher sensitivity such as PETN, HMX, and RDX than those with lower sensitivity such as ANTA, DMN, and NM. The calculations presented suggest the energy transfer rate in secondary explosive crystals is a significant factor in their sensitivity and introduction of double bond, or hydrogen bonds, or caged structure into secondary explosives is expected to decrease the sensitivity.     

Structural,thermochemical and detonation performance of derivatives of 1,2,4,5-tetrazine and 1,4 <Emphasis Type="Italic">N</Emphasis>-oxide 1,2,4,5-tetrazine as new high-performance and nitrogen-rich energetic materials

In this study, density functional theory calculations are used to estimate enthalpy of sublimation, enthalpy of formation and crystal density of some important derivatives of 1,2,4,5-tetrazine and 1,4 N-oxide 1,2,4,5-tetrazine. These data were used for predicting their detonation properties including heat of detonation, detonation pressure, detonation velocity, detonation temperature, spark sensitivity, deflagration temperature and power of energetic using appropriate methods. The results show that the title compounds exhibit high positive solid-phase enthalpy of formation. It is found that detonation pressure and detonation velocity of these compounds are high because of the large values of crystal density and solid-phase enthalpy of formation. Detonation temperature and spark sensitivity of some derivatives are higher than octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine as one of the high-performance explosives.     

Theoretical studies on high energetic density nitramine explosives containing pyridine

The insensitive property of explosives containing pyridine is combined with the high energy of nitramine explosives,and the concept of new nitramine explosives containing pyridine is proposed,into which nitramine group with N N bonds is introduced as much as possible.Based on molecular structures of nitramine compounds containing pyridine,density functional theory(DFT) calculation method was applied to study designed molecules at B3LYP/6-31+G(d) level.The geometric and electronic structures,density,heats of formation(HOF),detonation performance and bond dissociation energies(BDE) were investigated and comparable to 1,3,5-trinitro-1,3,5-triazinane(RDX) and 1,3,5,7-tetranitro-1,3,5,7-tetrazocane(HMX).The simulation results reveal that molecules B and D perform similarly to traditionally used RDX.Molecule E outperform RDX,with performance that approach that of HMX and may be considered as potential candidate of high energy density compound(HEDC).These results provide basic information for molecular design of novel high energetic density compounds.     

Anisotropic Reaction Properties for Different HMX/HTPB Composites: A Theoretical Study of Shock Decomposition

Plastic-bonded explosives (PBXs) consisting of explosive grains and a polymer binder are commonly synthesized to improve mechanical properties and reduce sensitivity, but their intrinsic chemical behaviors while subjected to stress are not sufficiently understood yet. Here, we construct three composites of β-HMX bonded with the HTPB binder to investigate the reaction characteristics under shock loading using the quantum-based molecular dynamics method. Six typical interactions between HMX and HTPB molecules are detected when the system is subjected to pressure. Although the initial electron structure is modified by the impurity states from HTPB, the metallization process for HMX does not significantly change. The shock decompositions of HMX/HTPB along the (100) and (010) surface are initiated by molecular ring dissociation and hydrogen transfer. The initial oxidations of C and H within HTPB possess advantages. As for the (001) surface, the dissociation is started with alkyl dehydrogenation oxidation, and a stronger hydrogen transfer from HTPB to HMX is detected during the following process. Furthermore, considerable fragment aggregation is observed, which mainly derives from the formation of new C−C and C−N bonds under high pressure. The effect of cluster evolution on the progression of the following reaction is further studied by analyzing the bonded structure and displacement rate.     

Mesoscopic Simulation of Aggregate Behaviour of Polymers in β-HMX-based PBXs

The mesoscopic structures of β-HMX (octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine)-based PBXs (polymer bonded explosives) at room temperature were investigated using dissipative particle dynamics method. The parameters and repulsive parameters of dif-ferent polymers and β-HMX, the mesoscopic structures of β-HMX-based polymer-bonded explosives at different temperatures have been studied. The results showed that the compat-ibility between β-HMX and vinylidenedifluoride (VDF), β-HMX and chlorotrifluoroethylene(CTFE), VDF and CTFE increased with increasing temperature. The temperature and mo-lar ratio of the polymers played an important role in wrapped process. And there exists the optimum temperature and molar ratio.     

X-ray crystal structure analyses and atomic charges of color former and developer. I. Color developers

The crystal and molecular structures of 2,2-bis(4-hydroxyphenyl)propane (Bisphenol A, BPA) (1), benzyl 4-hydroxybenzoate (2), 1,7-bis(4-hydroxyphenylthio)-3,5-dioxaheptane (3) and 4-hydroxyphenyl 4-isopropoxyphenyl sulfone (4) have been determined by X-ray crystal structure analysis. Theoretical calculations of the steric hindrance and semiempirical quantum chemical calculations to determine the color characteristics have been carried out. It is clear that the energy barriers for the variation of the orientation of phenol group in 1 to 4 are due to steric hindrance caused by the other moiety and the peak profiles are due to repulsive interactions of the other moiety. Net atomic charges on the hydrogen of the OH group are larger than those on the other atoms in the molecules. This high electron charge of the para orientation will cause the different thermosensitivity and stabilization.