一元溶剂体系HNBP结晶形貌的理论研究

本文计算了苯、甲苯、氯苯、苯甲醚4种溶剂作用下HNBP的晶面层与溶剂层的相互作用能,并对附着能进行了修正,预测了不同溶剂作用下HNBP的晶体形貌.结果表明加入不同的溶剂后,HNBP晶体的重要晶面与溶剂都呈吸引作用.苯溶剂使晶体形貌呈长形柱体状,纵横比为8.54;甲苯溶剂使晶体形貌呈片状,纵横比为7.38;氯苯溶剂使晶体形貌呈现出长方体状,纵横比为4.53;苯甲醚溶剂使晶体形貌呈菱柱状,纵横比为4.15.     

一元溶剂体系β-HMX球形化结晶形貌的分子动力学模拟

奥克托金(β-HMX)晶体形貌在很大程度上影响其安定性能、流散性和能量输出,其中溶剂对晶习的影响起着很关键的作用,因此研究溶剂对β-HMX结晶形貌影响的微观机理具有很重要的意义.运用分子动力学方法计算了五种溶剂作用下β-HMX五个重要的晶面层与溶剂层的相互作用能,对附着能进行了修正,预测了不同溶剂作用下β-HMX的晶体形貌.结果表明,β-HMX重要晶面与五种溶剂都呈吸引作用,五种溶剂都会对晶面的附着能产生很大影响,抑制晶面的生长速率,除N-甲基吡咯烷酮(NMP)外,其余四种溶剂作用下(020)面的相对生长速率都是最快的,在晶体的最终形貌中消失.二甲基亚砜(DMSO)溶剂作用下的晶体形貌相对比较好, N,N-二甲基甲酰胺(DMF)、环己酮(CH)和NMP溶剂作用下的晶体形貌次之,γ-丁内酯(GBL)溶剂作用下的晶体形貌球形度最差.     

PYX基高聚物粘结炸药界面相互作用及力学性能的分子动力学模拟

本文采用分子动力学(MD)方法,模拟计算了聚氨酯(Estane 5703),三元乙丙橡胶(EPDM),氟聚物(F2311)三种高聚物分子分别与2,6-双(苦氨基)-3,5-二硝基吡啶(PYX)(011)晶面构建的高聚物粘结炸药(PBXs)体系的结合能,内聚能密度,径向分布函数以及力学性能.结果表明,Estane 5703与PYX(011)晶面之间相互作用最强;不同粘结剂与晶体之间的内聚能密度大小顺序为PYX/F2311> PYX/Estane 5703> PYX/EPDM;径向分布函数分析可知PYX(011)晶面与高聚物分子间的相互作用主要为静电相互作用;添加3种粘结剂后PBX体系的拉伸强度和断裂强度都得到了改善,而除了F2311外,加入另外两种粘结剂后,提高了PBX体系的抗剪切应变能力.     

四种耐热含能化合物电子结构的第一性原理研究

本文模拟计算了2,2’,4,4’,6,6’-六硝基联苯(HNBP)、2,2’,4,4’,6,6’-六硝基二苯乙烯(HNS)、2,5-二苦基-1,3,4-噁二唑(DPO)和5,5''-双(2,4,6-三硝基苯基)-2,2''-双(1,3,4-噁二唑)(TKX-55)四种耐热含能化合物的分子结构、Mulliken电荷布居、分子静电势(MEP)和Hirshfeld表面, 通过研究其分子特性、电子特性以及分子间相互作用, 以了解高耐热性含能化合物的耐热机理. 结果表明, 桥连接结构的复杂性以及分子间强氢键相互作用会增强含能化合物的稳定性. 此外, 本研究还发现中间基团的加入会对四种含能化合物分子两侧芳香环上碳原子的电荷分布以及分子表面正负静电势区域面积产生一定的影响.     

锂电池正极材料LiFePO4的电子结构和晶形模拟研究

分别运用Materials Studio软件的CASTEP和Morphology模块对磷酸铁锂(LiFePO4)的结构和晶形进行计算模拟研究，获得其优化构型、电子结构、晶体形貌、晶面面积和晶面相对生长速率等特征参数。研究结果表明，PBE方法的计算精度明显高于CA-PZ方法，化合物中的Fe—O配位键本质上是共价键。LiFePO4的理论模拟晶形为柱状晶体，与其块状的实测晶体形貌存在较大差异，这归因于理论模拟晶形是LiFePO4在真空中的生长晶习，而非真实环境下的晶习。在LiFePO4的实际晶形中，(0 2 0)晶面拥有较大的面积，这与该晶面的原子排列方式和原子占有率密切相关。此外，表面活性剂和LiFePO4各特征晶面之间可形成大量C—H…O氢键，将晶粒有效地包覆起来，降低其生长速率，从而抑制LiFePO4晶粒长大。     

3，3-二硝基氮杂环丁烷的合成

多硝基氮杂环丁烷3，3-二硝基氮杂环丁烷(DNAZ)，除用做目前最具有应用前景的含能材料之一1，3，3-三硝基氮杂环丁烷(TNAZ)的合成中间体之外，利用其呈碱性的特点与许多酸性物质反应得到含能盐。能与DNAZ形成盐的含能阴离子非常普遍，尤其以硝基取代的五元芳香杂环最为重要，主要包括3，5-二硝基-1，2，4-三唑阴离子、4，4’，5，5，-四硝基双咪唑阴离子、2，4-二硝基咪唑阴离子及3-硝基-5-羟基三唑阴离子等。这些含能盐可作为火箭推进剂的氧化剂成分。     

锂电池正极材料LiFePO_4的电子结构和晶形模拟研究

分别运用Materials Studio软件的CASTEP和Morphology模块对磷酸铁锂(LiFePO4)的结构和晶形进行计算模拟研究,获得其优化构型、电子结构、晶体形貌、晶面面积和晶面相对生长速率等特征参数.研究结果表明,PBE方法的计算精度明显高于CA-PZ方法,化合物中的Fe—O配位键本质上是共价键.LiFePO4的理论模拟晶形为柱状晶体,与其块状的实测晶体形貌存在较大差异,这归因于理论模拟晶形是LiFePO4在真空中的生长晶习,而非真实环境下的晶习.在LiFePO4的实际晶形中,(020)晶面拥有较大的面积,这与该晶面的原子排列方式和原子占有率密切相关.此外,表面活性剂和LiFePO4各特征晶面之间可形成大量C—H…O氢键,将晶粒有效地包覆起来,降低其生长速率,从而抑制LiFePO4晶粒长大.     

氯化钠/铯铅溴钙钛矿复合薄膜的原位制备及性能EI北大核心CSCD

全无机铯铅卤钙钛矿因其优异的光电性能受到广泛关注。然而,薄膜较差的稳定性和制备中大量昂贵且有毒有机溶剂的使用,严重阻碍了其商业化应用进程。在本工作中,水溶液被用作配制含氯化钠(NaCl)的钙钛矿前驱液的溶剂。通过一步溶液法获得原位生长的NaCl/CsPbBr_(3)钙钛矿复合薄膜,并在该过程中引入二甲基亚砜(DMSO)溶液来优化其晶体结构及光学性能。研究表明,NaCl和DMSO的协同作用可以调控复合薄膜中晶粒的形貌、提高相纯度并增强荧光发射。当DMSO和前驱体溶液体积比为1∶2时,复合薄膜呈现出最佳的绿光发射,荧光量子效率达48.2%。此外,得益于NaCl的有效复合及优化的晶体结构,所制备的复合薄膜具有增强的稳定性。该设计思路有利于制备柔性、大面积和高稳定性显示用荧光转换薄膜。     

通量源密度和旋涡源密度是场源吗?

《大学物理》编辑部 :贵刊 2 0 0 1年第 8期刊载了田晓岑同志的题为《“真空中的位移电流与真实电流同等地激发磁场”的传统提法并没有错》的文章 (以下简称田文 ) ,该文主要是针对我的《真空中的“位移电流”和传导电流以同样规律激发磁场吗 ?》一文的 .但田文有一重大疏漏 :就是该文引述的“亥姆霍兹定理”不适用于普遍情况 .在一般情况下 ,田文中的式 (7)和式 (8)应由以下两式取代(见该文参考文献 [5 ]中式 (1 -1 2 1 )和式 (1 -1 2 2 ) ) :Φ(ｘ ,ｙ,ｚ) =14π∫Ｖ′ ′·Ｆ(ｘ′,ｙ′,ｚ′)Ｒ ｄＶ′ -14π∮Ｓ′Ｆ(ｘ′ ,ｙ′,ｚ′)Ｒ…     

超分子结构单元研究黑索金的弹性各向异性

含能材料的弹性性质微观上体现了分子间的结合力,且与含能材料的化学分解和爆炸相关.因此,弹性性质-晶体结构的关联为设计具有特定性质的新材料和理解含能材料点火起爆提供了理论基础.本文提出超分子结构单元作为最小化学单元来定量表征黑索金(RDX)不同晶面的弹性模量.基于超分子结构单元的弹性模量模型表明,与弹性模量相关的微观因素有:超分子结构单元的分子对数量、分子对的平衡距离、分子间力常数以及分子间非键能与晶面法线的夹角;而弹性模量的各向异性来源于分子间非键能与晶面法线的夹角不同.研究结果表明, RDX的超分子结构单元包含15个RDX分子,以该超分子结构单元计算得到RDX(100),(010),(001),(210)和(021)晶面的弹性模量分别为21.7, 17.1, 20.1, 19.1和15.3 GPa.除RDX(001)晶面外,以上晶面的理论计算值与超声共振谱、脉冲激热散射、布里渊散射和纳米压痕实验值基本吻合. RDX(001)晶面的计算值(20.1 GPa)远高于实验值(15.9—16.6 GPa),原因可能是计算过程中将RDX分子看作刚性体,忽略了RDX(001)晶面在外界载荷作用下...     

Modification of UO2 crystal morphologies through hydroxylation

Atomic scale computer simulation is used to predict the surface energies of UO₂, subject to different hydroxide coverages. It was found that the {1 1 1} surface dominates dry UO₂, resulting in an octahedral morphology. However, the {1 0 0} surfaces were strongly stabilized by hydroxylation relative to the {1 1 1} surfaces. Consequently, even a modest hydroxylation of 30% substantially truncates the octahedron crystal morphology, and a fully cubic morphology is predicted at 80% hydroxide coverage.     

Preparation and growth mechanism of micro spherical ammonium dinitramide crystal based on ultrasound-assisted solvent-antisolvent method

Micro-sized spherical ammonium dinitramide (ADN) crystals are successfully prepared by a facile ultrasound-assisted solvent-antisolvent recrystallization method without introducing any additives. The influences of the volume ratio of solvent to antisolvent, the antisolvent temperature and the ultrasound power on the micro-morphologies and properties of ADN crystals are studied systematically. The changes of morphology, particle size, crystal structure and melting point of the ADN crystals are characterized through scanning electron microscopy (SEM), laser particle size analyzer (LPSA), X-ray diffraction (XRD) and differential scanning calorimetry (DSC), respectively. The results show that the optimal experimental parameters for the ADN crystal of spherical morphology are as follows: the volume ratio of solvent to antisolvent is 1:50, the antisolvent temperature is 20 ℃, and the ultrasound power is 70 W. The predicted hexagonal-flake and spherical morphologies for the ADN are close to the experimental morphologies. The growth mechanism of the spherical ADN crystal changes with supersaturation of the ADN solution. As the degree of supersaturation increases, the growth models of the spherical ADN change from the spiral growth to the rough growth, and the morphologies of ADN change from the large-sized ADN ball to the small-sized ADN ball.     

Surface structure and solidification morphology of aluminum nanoclusters

Classical molecular dynamics simulation with embedded atom method potential had been performed to investigate the surface structure and solidification morphology of aluminum nanoclusters Al_n (n=256, 604, 1220 and 2048). It is found that Al cluster surfaces are comprised of (1 1 1) and (0 0 1) crystal planes. (1 1 0) crystal plane is not found on Al cluster surfaces in our simulation. On the surfaces of smaller Al clusters (n=256 and 604), (1 1 1) crystal planes are dominant. On larger Al clusters (n=1220 and 2048), (1 1 1) planes are still dominant but (0 0 1) planes cannot be neglected. Atomic density on cluster (1 1 1)/(0 0 1) surface is smaller/larger than the corresponding value on bulk surface. Computational analysis on total surface area and surface energies indicates that the total surface energy of an ideal Al nanocluster has the minimum value when (0 0 1) planes occupy 25% of the total surface area. We predict that a melted Al cluster will be a truncated octahedron after equilibrium solidification.     

Monte Carlo simulation of surface segregation phenomena in extended and nanoparticle surfaces of Pt-Pd alloys

The surface segregation phenomena in the extended and nanoparticle surfaces of Pt-Pd alloys have been studied using the Monte Carlo (MC) simulation method and the modified embedded-atom method (MEAM) potentials developed for Pt-Pd alloys. The MEAM potentials were fitted to reproduce the experimental values of the lattice parameters, cohesive energies and surface energies of pure Pt and Pd metals, as well as the density functional theory calculation results of the lattice parameters and heat of formation of L1(2) Pt(3)Pd, L1(0) PtPd and L1(2) PtPd(3) crystal. Using the MC method and the developed MEAM potentials, we calculated the Pt concentrations in the outermost three layers of the equilibrium (111), (100) and (110) extended surfaces as well as the outermost surfaces of the equilibrium cubo-octahedral nanoparticles of Pt-Pd alloys. Our simulation results showed that the Pd atoms would segregate into the outermost layers of the extended surfaces and the Pt concentration would increase monotonically from the extended surfaces into the bulk. The equilibrium Pt-Pd nanoparticles were found to have Pd-enriched shells and Pt-enriched cores. In the shell of the Pt-Pd nanoparticles, the Pd atoms were predicted to preferably segregate to the (100) facets rather than the (111) facets.     

An atomistic surface simulation study predicting morphologies and segregation in yttrium lithium fluoride

The aim of this research on the laser material yttrium lithium fluoride (YLiF₄) is to provide the first study of its surface structure, morphology and the properties of rare-earth doped surfaces. The study utilises the METADISE computer code to model the surfaces using interatomic potentials. Equilibrium and growth morphologies are predicted and a detailed profile of segregation of rare-earth dopants to the three dominating surfaces is given. The (001), (011) and (112) surfaces dominate the morphology. Rare-earth dopants La to Sm show segregation to these surfaces, with the (112) surface being of particular interest. As this work demonstrates, it is likely to have dopants clustered towards it.     

Microwave-assisted synthesis of flower-like and leaf-like CuO nanostructures via room-temperature ionic liquids

Flower-like and leaf-like cupric oxide (CuO) single-crystal nanostructures have been successfully synthesized using ionic liquid 1-octyl-3-methylimidazolium trifluoroacetate ([Omim]TA) under the microwave-assisted approach. By controlling the concentration of [Omim]TA and reaction temperature, shape transformation of CuO nanostructures could be achieved in a short period of time. The results indicate that ionic liquid [Omim]TA plays an important role in the formation of different morphologies of CuO crystals. The crystal structure and morphology of products were characterized by X-ray powder diffraction (XRD), infrared spectrum (IR), scanning electron microscope (SEM), transmission electron microscopy (TEM), and selected-area electron diffraction (SAED). A possible mechanism for CuO nanostructure was proposed. In addition, UV-vis spectroscopy was employed to estimate the band gap energies of CuO crystals.     

Effect of Coagulation Bath DMSO Concentration on the Structure and Properties of Polyacrylonitrile (PAN) Nascent Fibers during Wet-Spinning

Polyacrylonitrile nascent fibers, as spun into the coagulation bath, were prepared by solution polymerization and wet-spinning, and a dimethyl sulphoxide (DMSO)/H ₂ O coagulation bath system was adopted. The effect of coagulation bath DMSO concentration on the structure and properties of the nascent fibers was studied in detail, and the diffusion coefficients of DMSO and H₂O for different bath DMSO concentrations were calculated by Crank's equation to explain the structural changes of the nascent fibers, including cross-section, core/shell structure, and surface morphology. The surface morphology of nascent fibers was observed by field emission scanning electron microscopy (FESEM). The results showed that as the coagulation bath DMSO concentration increased, the diffusion coefficients gradually decreased. More circular cross-section, less core/shell structure, higher degree of crystallinity, larger crystal size, larger bulk density, and higher sound velocity of the nascent fibers were obtained when thecoagulation bath DMSO concentration was 70 wt% compared to lower or higher bath DMSO concentration. Moreover, compared with the nascent fibers spun in other bath DMSO concentrations, smoother surfaces of the nascent fibers were obtained at the bath DMSO concentration of 70 wt%.     

Solvent effects on adsorption of CO over CuCl(1 1 1) surface: A density functional theory study

DFT calculations have been performed to investigate the effect of dielectric responses of the solvent environment on the CO adsorption over CuCl(1 1 1) surface by using COSMO (conductor-like solvent model) model in Dmol³. Different dielectric constants, including vacuum, liquid paraffin, methylene chloride, methanol and water solution, are considered. The effects of solvent model on the structural parameters, adsorption energies and vibrational frequency of CO adsorption over CuCl(1 1 1) surface have been investigated. The calculation results suggest that solvent effects can improve the stability of CO adsorption and reduce the intensity of C-O bond, which might mean that solvent is in favor of C-O bond activation and improve the reaction activity of oxidative carbonylation in a slurry reactor.