机械球磨对石墨结构的影响

对石墨进行了150h机械球磨,发现石墨原有的晶体结构被破坏,引入各种晶格缺陷的同时,生成了巴基洋葱、三脚架形碳纳米结构和纳米弓形等具有高度弯曲石墨面的碳纳米结构材料.还研究了其结构特征,并讨论了其形成机理 关键词：     

Ar+轰击石墨表面生成碳纳米管和碳纳米多面体

报道了一种用60keV Ar⁺轰击石墨生成碳纳米管和纳米碳壳层多面体颗粒的方法.高分辨透射电子显微镜研究指出，这些纳米多层结构物的尺寸约在20nm到0.4μm之间，碳原子层之间的距离为0.34nm.基于高分辨透射电子显微镜图像，建议了一个关于“组合碳多面体”的生长模型. 关键词：     

石墨和纳米碳中缺陷和电子动量的研究

用正电子湮没技术研究了石墨和纳米碳中的缺陷和电子动量. 结果表明, 纳米碳中缺陷的开空间和缺陷浓度分别大于和高于石墨晶体. 纳米碳中存在开空间小于单空位的自由体积以及开空间相当于约10个空位聚集体的微孔洞. 石墨晶体中的自由电子动量分布表现出显著的各向异性: 沿石墨晶体的\[0 001\]晶向的自由电子(即2Pz电子)的动量最大; 偏离该方向越大, 自由电子的动量越小; 垂直于\[0 001\]晶向的自由电子的动量最小. 而纳米碳中自由电子动量的分布表现出各向同性. The defects and electronic momenta in graphite and nanocrystalline carbon have been studied by positron annihilation techniques. The results show that the concentration and open volume of defects in nanocrystalline carbon are higher/larger than that in graphite. Two kinds of microdefects were found in the nanocrystalline carbon: free volume (with a size of smaller than that of a monovacancy) and microvoids (with a size of about ten monovacancies). The anisotropic distribution of electronic momentum was found in single crystalline graphite, the momentum of free electron shows a maximum value in \[0001\] direction, and decreases with the increase of the angle deviation from \[0001\] direction and then reaches a minimum value in the direction perpendicular to \[0001\]. However, this phenomenon was not found in nanocrystalline carbon since the distribution of electronic momentum is isotropic.     

石墨和纳米碳中缺陷和电子密度随温度的变化

测量了石墨和纳米碳在不同温度下的正电子寿命谱,研究了石墨和纳米碳中缺陷和电子密度随温度的变化.结果表明,纳米碳中缺陷的开空间和缺陷浓度分别大于和高于石墨晶体;纳米碳的平均自由电子密度低于石墨晶体.当温度从25K升至295K时,石墨和纳米碳中的平均自由电子密度随温度的升高而下降:石墨晶体中的自由电子密度随温度的升高变化较小;纳米碳的自由电子密度随温度的升高变化较大.随着温度的升高,石墨和纳米碳中的热空位数量增多,而且这些空位可迁移至微孔洞的内表面使微孔洞的开空间增大.     

一些新颖碳纳米结构的高分辨率透射电子显微镜研究

在双阳极电弧放电的阴极沉积物中已发现扁平碳纳米壳、碳纳米棒和棒-管相连的碳纳米结构.高分辨率透射电子显微镜(HRTEM)确认了碳纳米管直接生长在纳米棒之上,因而碳纳米管生长开端的来龙去脉清晰可见.另外,HRTEM图像显示,多壳层碳纳米棒有一条中心线.有可能这是一种基于单键和三重键交替“sp”杂化的炔链碳同素异形体. 关键词：     

石墨上纳米尺度金岛的形成

用扫描隧道显微镜研究了真空蒸镀在高定向热解石墨上金岛的形成和形状．随着蒸镀量的增加及时间的推移，金原子在表面通过扩散而逐渐合并成越来越大的原子团，以至岛，甚至岛群．虽然几个纳米大小的原子团仍十分可动，但在蒸镀量大于20单层时的岛或岛群已十分稳定．研究发现，同一蒸镀量下，各个金岛具有非常接近的宽度和高度，用薄膜成核的圆柱状模型计算岛的宽度与高度之比表明，金岛非常接近热力学平衡状态．这些形状各异的通过生长而自组装形成的纳米尺度金岛可用来进行介观物理的研究 关键词：     

一种新的纳米结构--管状石墨锥

文章作者利用微波等离子体辅助化学气相沉积的方法在铁针尖上合成了一种新的纳米结构，并称之为管状石墨锥．管状石墨锥在外形上由多面锥体组成，其内部是同心的圆柱形石墨层，其空心的直径为几个纳米到几十个纳米．这些管状石墨层从内到外地逐渐变短，从而使得它们呈现出锥形外观．锥的顶角一般为6-7度左右，锥的尖端只有几个纳米大小，而锥的底部可达到微米量级．值得注意的是，组成管状锥体的石墨层具有惟一的手性，都表现为锯齿型。     

双空位缺陷石墨纳米带的电子结构和输运性质研究

基于第一原理电子结构和输运性质计算,研究了585双空位拓扑缺陷对锯齿（zigzag）型石墨纳米带（具有椅型（armchair）边）电子结构和输运性质的影响.研究发现,585双空位缺陷的存在使得锯齿型石墨纳米带的能隙增大,并在能隙中出现了一条局域于缺陷处的缺陷态能带,双空位缺陷的取向也影响其能带结构.另外,585双空位缺陷对能隙较小的锯齿型石墨纳米带输运性质的影响较大,而对能隙较大的锯齿型石墨纳米带影响很小,缺陷取向并不显著影响纳米带的输运性质. 关键词： 石墨纳米带 585空位缺陷 电子结构 输运性质     

离子辐照与碳纳米结构体的合成

阐述了在离子辐照下生成各种碳纳米结构体研究的发展现状,探讨了相应的生长机制和一些相变机理 ,提出了一些有待解决的问题 ,并对其发展方向作了展望. The synthesis of carbon nanostructures, such as fullerenes, nanotubes, onions and diamond, by using ion irradiation, has been reviewed and the growth mechanisms of these carbon nanostructures as well as their phase transitions are simply discussed. It shows that high density plasma engendered by ion irradiation plays an important role in the growing of carbon nanostructures. In addition, it indicates that ion irradiation, due to its great flexibility of experimental parameters, is enormously convenient in...     

Zigzag型石墨纳米带电子结构和输运性质的第一性原理研究

采用第一性原理电子结构和输运性质计算研究了zigzag型单层石墨纳米带(具有armchair 边缘)的电子结构和输运性质及其边缘空位缺陷效应. 研究发现,完整边缘的zigzag型石墨纳米带是具有一定能隙的半导体带,边缘空位缺陷的存在使得纳米带能隙变小,且缺陷浓度越大,能隙越小,并发生了半导体-金属转变. 利用这些研究结果,将有助于在能带工程中实现其电子结构裁剪. 关键词： 石墨纳米带 空位缺陷 电子结构 输运性质     

Determining quality of graphite electrodes for electric arc furnaces by measuring ultrasonic velocity

Measuring ultrasonic velocity is an efficient means of determining electrode quality for electric arc furnaces. Close correlation between ultrasonic velocity and the physico-mechanical characteristics of the electrodes was obtained by statistical analysis.The variation of ultrasonic velocity is shown for different fabrication stages of graphite electrodes as a function of their mechanical characteristics and structure. We also present some aspects of the experimental work and apparatus used.     

Template function of liquid membranes in the assembly of tube-in-tube carbon nanostructures

Tube-in-tube carbon nanostructures (TTCNTs) have been successfully constructed on liquid membranes via a hydrogen-bonding linkage of small graphene sheets around normal carbon nanotubes (CNTs). The effects of solvent (water, tetrahydrofuran (THF), ethanol, n-hexane and N,N-dimethylformamide (DMF)) and membrane thickness on the assembling process were investigated. Results show that the formed cavity of TTCNTs becomes large with the increase of viscosity of solvent and pressure. The formed liquid membrane on CNTs surface plays a key role in this process, and it can be controlled by adjusting the membrane thickness and solvent nature. Moreover, TTCNTs show excellent catalytic reduction NO ability at low temperatures.     

Molecular dynamic simulation of amorphous carbon and graphite interface

Amorphous carbon/graphite interface is modeled by molecular dynamic simulation using a Tersoff-type potential function with the Brenner parameters for in-plane interaction combined with the pair potential function for the interplanar bonding. The interface is created by compressing the amorphous carbon produced in a separate simulation with perfect crystalline graphite terminated to expose (1120) planes. The planar structure and weak interplanar bonding allow the graphitic planes to deform in order to accommodate the bonds formed at the interface, which is consistent with the HRTEM study of the interface. The simulation indicates that the generated interface mostly consists of nearly sp₂ hybridized bonding connecting the two sides. The bonds across the interface when formed are likely to maintain their equilibrium configurations. Due to the large interplanar spacing, many atoms both on the graphite and a-C sides are left unbonded leaving the interface energetically unfavorable with respect to the bulk. These unbonded radicals probably weaken the structural rigidity of the interface providing a fracture path under stress.     

Structural transformation of graphite by arc-discharge

The formation of novel structures by the passage of an electric current through graphite is described. These structures apparently consist of hollow three-dimensional graphitic shells bounded by curved and faceted planes, typically made up of two graphene layers. The curved structures were frequently decorated with nano-scale carbon particles, or short nanotubes. In some cases, nanotubes were found to be seamlessly connected to the thin shells, indicating that the formation of the shells and the nanotubes is intimately connected. Small nanotubes or nanoparticles were also sometimes found encapsulated inside the hollow structures, while fullerene-like particles were often seen attached to the outside surfaces. With their high surface areas and structural perfection, the new carbon structures may have applications as anodes of lithium ion batteries or as components of composite materials.     

氩气电弧等离子体炬提纯大鳞片石墨研究

石墨材料作为一种工业原料,特别是纯度在99.9%以上的高纯石墨被应用在各大高科技领域,现有物理法和化学法的石墨提纯技术成本高、酸碱对设备和环境破坏严重、工艺流程复杂,因此开发一种优良有效的石墨提纯技术,已成为近年来国内外研究的热点。建立了一种利用非转移电弧等离子体炬提纯大鳞片石墨的方法,利用电弧可快速产生高温的特性,对黑龙江省鸡西市纯度为94.18%的大鳞片石墨样品进行高温处理。研究显示在本文电弧装置下提纯石墨的最佳放电参数范围气流量为25 L/min、电流为400 A、功率为10 kW,此时的电弧表面温度高达3350 ℃,利用扫描电子显微镜等对电弧处理前后石墨样品的微观结构对比发现石墨样品出现粉碎、断裂等特点,根据石墨化学分析方法国家标准GB/T 3521 2008对石墨纯度及其杂质进行研究分析,经电弧处理后石墨纯度提高到99.21%。     

Raman spectrum study of graphite irradiated by swift heavy ions

Highly oriented pyrolytic graphites are irradiated with 40.5-Me V and 67.7-Me V ^112Sn-ions in a wide range of fluences： 1×10^11 ions/cm^2–1×10^14ions/cm^2. Raman spectra in the region between 1200 cm^-1 and 3500cm^-1 show that the disorder induced by Sn-ions increases with ion fluence increasing. However, for the same fluence, the amount of disorder is greater for 40.5-Me V Sn-ions than that observed for 67.7-Me V Sn-ions, even though the latter has a slightly higher value for electronic energy loss. This is explained by the ion velocity effect. Importantly, ～ 3-cm^-1frequency shift toward lower wavenumber for the D band and ～ 6-cm^-1 shift toward lower wavenumber for the 2D band are observed at a fluence of 1×10^14 ions/cm^2, which is consistent with the scenario of radiation-induced strain. The strain formation is interpreted in the context of inelastic thermal spike model, and the change of the 2D band shape at high ion fluence is explained by the accumulation of stacking faults of the graphene layers activated by radiation-induced strain around ion tracks. Moreover,the hexagonal structure around the ion tracks is observed by scanning tunneling microscopy, which confirms that the strains near the ion tracks locally cause electronic decoupling of neighboring graphene layers.     

Preparation and physical/electrochemical characterization of carbon nanotube-chitosan modified pencil graphite electrode

In this work, preparation and characterization of single-walled carbon nanotube-chitosan (SWNT-chitosan) modified disposable pencil graphite electrode (PGE) was carried out. Firstly, commercial single-walled carbon nanotube was purified and characterized using thermal gravimetric analysis (TGA), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM) and energy dispersive analysis of X-ray (EDX) for this purpose. Purified SWNT was mixed with chitosan polymer for preparing their composite. Then, PGE was modified with this composite. The characterization of the modified electrode was carried out using atomic force microscopy (AFM). The electrochemical behaviour of the obtained electrode was investigated and compared with the electrochemical behaviour of chitosan modified and unmodified PGEs using cyclic voltammetry (CV), differential pulse voltammetry (DPV) and alternative current (AC) impedance spectroscopy. In order to obtain more sensitive electrochemical signals, the effect of SWNT concentration was studied. This modified electrode also showed electrocatalytic effect for hydrogen evolution.     

高定向热解石墨表面局域导电增强现象的扫描探针显微学研究

基于导电型原子力显微镜和扫描隧道显微镜的对比观察,研究高定向热解石墨表面上残留石墨片的导电增强现象.根据样品电阻的测量数据,将这种现象归结为导电针尖与石墨表面的点接触问题,并且发现接触电导和接触点处局域的电子密度成正比,从而确定石墨表面的局域导电增强现象的原因在于残留在石墨表面的石墨片具有较高的电子密度. 关键词： 扫描隧道显微镜 导电原子力显微镜 高定向热解石墨 导电性     

The influence of the initial structural state of armco iron on the ultrasonic treatment effect

Methods of diffraction electron microscopy have been used to examine the types of dislocation substructures formed in the surface layer of armco-iron specimens subjected to ultrasonic treatment. It is shown that banded or equiaxed ultrafine-grained structure can be generated in the material depending on its initial structural state. The special features of the plastic deformation and fracture of the ultrafine-grained surface layers of the specimens under uniaxial tension are described. The extent to which the mechanical properties of the examined material are improved by ultrasonic treatment has been found to depend on its initial state. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 1, pp. 74–82, January, 2009.     

"点石成金?"--碳结构超高压物理力学

文章介绍了石墨和碳纳米管在超高压和／或纳米压痕下的层间sp^2-sp^3键转化、软硬相转换、纳米硬度等研究进展．通过量子力学和分子动力学建模分析研究，发现超高压下石墨和碳纳米管存在软相向硬相转变的双相机制，给出了超高压获取石墨和碳纳米管超硬相的条件．理论计算与实验结果吻合很好，并能合理地解释有关石墨和碳纳米管超高压实验中看似矛盾的各种实验现象．提出了碳结构超高压物理力学概念，可为超高压碳相关物质相变、物化性质调控提供理论方法．