HRTEM studies of cobalt-filled carbon nanotubes

Cobalt-filled carbon nanotubes were synthesized at high temperature and high gas pressure. A high-resolution transmission electron microscopy study demonstrates that the product of the synthesis contains cylindrical carbon nanotubes whose cores are filled with cobalt nanoparticles or nanorods. It is shown that cobalt appears inside the nanotubes in three basic modifications: face-centered cubic (fcc) lattice, hexagonal close-packed (hcp) lattice and disordered polytypic structure. The fcc lattice is often twinned, with two or more non-parallel twinning planes being observed. The orientations of the fcc and hcp cobalt particles with respect to the nanotubes were investigated. The authors believe that the variety of cobalt modifications inside the nanotubes is due to the process of segregation of the closely packed structures from the melt.     

HRTEM and EELS study of aluminum nitride in nanostructured Al 5083/B4C processed via cryomilling

The presence of aluminum nitride in nanostructured aluminum metal matrix composites was studied by high resolution transmission electron microscopy, electron energy loss spectroscopy, energy dispersive X-ray spectroscopy analysis and electron microscopy simulations. Three types of aluminum nitride structures were identified; predominantly, one layer of N atoms occupies the tetrahedral interstitial positions in the Al lattice, the frequency of which varies as a function of spatial location. The second and third were in the form of hexagonal and possibly cubic aluminum nitride particles with particle sizes on the order of 15–20 nm. The results suggest that the aluminum nitride phase evolves from intermediate transitional structures that involve N atoms in the Al lattice. The aluminum nitride phases frequently contained O and Mg, which preferentially segregate in close proximity to the reinforcement particles. First-principle calculations were used to describe the influence of O and Mg on the adsorption of N.     

球磨和催化反应球磨制备的镁基复合贮氢材料及其性能

以ZrFe1.4 Cr0.6或TiO2作为催化相,利用球磨和催化反应球磨的方法制备了Mg基复合贮氢材料,研究了其吸放氢动力学特征、循环性能和抗氧化性能.即使在较低的温度下,该复合材料也具有优良的动力学性能.利用扫描电镜、能谱分析和X射线衍射分析对该复合材料吸放氢前后的变化进行了表征.研究表明,覆盖在Mg颗粒表面的细小的ZrFe1.4 Cr0.6或TiO2粒子起到快速通过的作用,球磨引入了大量缺陷,并使部分合金粉末进入Mg基体内部,这都提高了复合材料的吸放氢速率.     

Synthesis and studies of properties of graphite oxide and thermally expanded graphite

Graphite oxide is synthesized using various reaction parameters. Stagewise evaluation of graphite oxidation dynamics in the course of synthesis is carried out using the method of sample collection and thermogravimetric analysis. Thermally expanded graphite with high texture characteristics was obtained from graphite oxide. Properties of graphite oxide and thermally expanded graphite were determined using scanning electron microscopy, X-ray diffraction, thermogravimetry, differential scanning calorimetry, energy dispersive spectroscopy, and low-temperature adsorption of nitrogen. The values of capacity of supercapacitors based on graphite oxide and expanded graphite are found.     

Irradiation induced creep of graphite

The status of graphite irradiation induced creep strain prediction is reviewed and major creep models are described. The ability of the models to quantitatively predict the irradiation induced creep strain of graphite is reported. Potential mechanisms of in-crystal creep are reviewed as are mechanisms of pore generation under stress. The case for further experimental work is made and the need for improved creep models across multi-scales is highlighted.     

HRTEM study of Co7W6 and its typical defect structure

The tetrahedrally close-packed structure of Co₇W₆ (μ-phase) was studied by HRTEM. A massive presence of random sub-unit cell twins was detected. These planar defects were characterized in detail and the twinning probability at potential mirror planes was established. High-precision image simulation of the bulk structure and defect region was performed, using a simulated evolution optimization strategy to refine the imaging conditions. Ab initio calculations were carried out in order to determine the energy involved in twinning, as well as the distortion induced in the structure.     

First-principles studies of defects,mechanical properties and electronic structure of Cr-based Laves phases

First-principles calculations have been performed to investigate the defects, mechanical properties and electronic structure of MCr₂ (M = Nb, Ti and Zr) Laves phases. The results show that the ternary additive of V preferentially substitutes the Cr site and Zr the Nb site in NbCr₂. W has a weak site preference on the Cr site in NbCr₂. The ternary site substitutions are related to the electronic structure of NbCr₂. Further calculations of the densities of states and charge density distribution of TiCr₂ show that a strong covalent bonding between the small atoms (Cr) along the Kagome net forms a tetrahedral electronic network, which is a common feature for the electronic structure in Laves phases. Mechanical properties, such as elastic constants, elastic moduli and stacking fault energies of ZrCr₂, were calculated additionally. The intrinsic and extrinsic stacking fault energies of ZrCr₂ are found to be 112 mJ m⁻² and 98 mJ m⁻², respectively.     

球磨对Zr-Cu-Al-Ni金属玻璃粉末结构与吸放氢性能的影响

本文研究了球磨对气雾化法所制备的Zr50.7Cu28Al12.3Ni9金属玻璃粉末结构与吸放氢性能的影响。气雾化的金属玻璃粉末在经过80 h的球磨后,仍呈现为非晶态。球磨对金属玻璃粉末吸放氢性能的影响在一台全自动Sieverts装置上进行了测量。球磨之后,金属玻璃粉末的吸氢性能获得提升,粉末的饱和吸氢量从雾化态的0.96 wt.% (H/M≈0.7)提升至了球磨后的2.66 wt.% (H/M≈1.9)。然而,由于吸氢后金属玻璃粉末内部生成稳定的氢化物相,使得球磨后的金属玻璃粉末的放氢性能未能获得提升。     

Quantitative analysis of microstructure of carbon materials by HRTEM

The main object of the present research is to make a quantitative evaluation on the microstructure of carbon materials in terms of microcrystal. The digitized images acquired from finely pulverized carbon materials under HRTEM at a high magnification were processed by the image processing software so as to extract the fringes of （002） lattice of graphite crystal from the background image, and an FFT-IFFT filtering operation was performed followed by processes as binarization for the image and skeletonization for the fringes. A set of geometrical parameters including position, length and orientation was set up for every lattice fringe by calculating the binarized image. Then, the above obtained fringe parameters were put into an algorithm, which was especially developed for such fringe images so as to find fringes that could be regarded as those belonged to one single graphite microcrystal. The fringe was subjected sequentially to comparing procedures with every other fringe on aspects as parallelism, relative position and spacing, and the above comparisons were repeated till the last fringe. Eventually, the microcrystal size, its stacking number, and the distribution of the microcrystal in the whole sample, as well as other related structure information of such microcrystal in carbon materials were statistically calculated. Such microstructure information at nanometer level may contribute greatly to the interpretation of the properties of carbon materials and a better correlation with the same macrostructure.     

Hybrid control of graphite cast iron structure by partial melt treatment process

The Modified Inmould Process, which forms a cast iron-graphite hybrid alloy with a spheroidal/flake graphite structure (SG/FG), has been developed by the author.^1-3 Though this process can easily control the transitional structure of SG/FG, there are some mild restrictions caused by rapid collision during the mixing of molten metals in the mould on pouring. In this study, a new experimental process was designed to solve this difficulty. The plate-like mould cavity was separated into a reaction chamber (RC) and a product cavity by a thin dam. An alloy of FeSiMg for spheroidization of base molten metal was prepared in the reaction chamber. Molten metal was poured up from the bottom of the product cavity and a part of it flowed over the dam into the reaction chamber. After being spheroidized in the reaction chamber, spheroidal graphite (SG) iron melt flowed backward into the product cavity. The density of SG molten iron with a higher carbon equivalent value is generally lower than that of flake graphite (FG) molten metal. Thus SG molten metal moved into the upper end of the product cavity by replacement of the base metal, while the base metal remained stationary at the lower end of the cavity. As a result of the phenomena of flow, movement and replacement between mutual melts, a SG/FG transitional layer structure was formed, downward, throughout the cast product.     

铌表面初始氧化行为的EELS和AES研究

利用电子能量损失谱(EELS)和俄歇电子能谱(AES)研究室温下铌的初始氧化过程，研究表明：清洁表面铌的EELS的实验值与理论值较为符合；随着氧化程度的加剧，其体等离子体(BP)、表面等离子体(SP)以及价带间跃迁所造成的电子能量损失峰发生了明显的偏移和强弱的变化，也解释了Nb→NbO→NbO2的初始氧化过程；另外，铌在潮湿空气里氧化1周，在其表面只生成很薄一层的Nb2O5氧化层。     

Nanoscale studies of the oxidation and hydrogenation of graphite surface

Nanoscale studies of the thermal oxidation and hydrogenation of graphite surfaces have been investigated using scanning tunnelling microscopy and scanning tunnelling spectroscopy. These techniques have been used to study the electronic states of the islands located at the edges of thermally oxidized and hydrogen-etched graphite surface. Spectroscopy results have shown the presence of Q_2g⁻(π), Q_2u⁻(π), Q_2u⁻(π^*), Q_2g⁻(π^*), IS and negative differential resistance electronic states recorded over islands of such treated graphite. However, these states vanish on various regions on the thermally oxidized graphite islands. This is ascribed to the disappearance of π/π^* bands when the graphite surface oxidizes and indicates the presence of oxygenated groups on the graphite surface.     

Limits of the Mg–Al γ-phase range by ball-milling

In the present work, the homogeneity range of the Mg–Al γ-phase was studied by ball-milling with post-annealing. In order to estimate the limit of its domain range, several Mg_XAl_100−X compounds from X = 47.5 to 70 by incremental steps of 2.5 were prepared. Different experimental measurements (XRD, SEM, EDX, DSC) were performed and are in mutual agreement with the properties of the existing phases. They show that deviation from the ideal composition of the intermetallic Mg₁₇Al₁₂ structure (X = 58.62) leads to a decrease of the homogeneity (morphological and chemical compositions). Rietveld refinements on XRD patterns show that the single γ-phase range is extended at room temperature and is identified for 55 ≤ X ≤ 62.5 at.% of nominal Mg powder.     

焊接缺陷引起汽车轮辋断裂的失效分析

轮辋断裂失效是汽车运输和维修时常见的现象.造成轮辋断裂有许多原因,其中,轮辋存在焊接缺陷是造成汽车轮辋早期疲劳断裂的一个主要原因.因此,对轮辋生产企业来说不仅轮辋材料、结构、尺寸要符合要求,更重要的是改进焊接工艺,提高焊接质量,加大焊后检验力度,以减少轮辋断裂失效的发生.     

液相球磨法由氧化铋制备次碳酸铋的动力学

为解决传统次碳酸铋生产过程中成本高和环境污染问题,提出采用液相球磨法由氧化铋制备次碳酸铋的新工艺,研究用碳酸氢氨和氧化铋制备次碳酸铋反应过程的动力学,考察反应温度、氧化铋粒度、液固比以及碳酸氢氨浓度对氧化铋转化率的影响。结果表明,在9-30°C的范围内,升高反应温度、减小氧化铋粉末的粒度、扩大液固比以及提高碳酸氢氨浓度均有利于氧化铋转化率的提高。对反应产物的表征分析表明,产品的纯度较高、杂质少;SEM结果显示产品次碳酸铋主要呈针棒状形态。反应过程受产物层的扩散控制,可用未反应收缩核模型描述,反应的表观活化能为9.783 kJ/mol,同时获得了描述反应过程的半经验动力学方程。     

球磨改性处理对Ti46V44Fe10合金相结构和吸放氢性能的影响

研究了不同条件下机械球磨改性处理对Ti46V44Fe10储氢合金相结构和吸放氢性能的影响.X射线衍射及扫描电镜分析表明:Ti46V44Fe10铸态合金由单一的体心立方(BCC)结构的固溶体组成;经过1 h的干法球磨(未添加四氢呋喃THF)后,合金中出现了微量的α-Ti第二相,主相晶胞体积减小,合金颗粒明显减小并发生团聚;经过0.5、1、20 h的湿法球磨(添加THF)后,合金中分别出现了含量不等的α-Ti第二相,主相晶胞体积逐渐减小,颗粒尺寸明显减小.储氢性能测试表明:球磨改性处理能有效地改善合金的活化性能,活化次数由球磨前的4次降至球磨后的1～2次;短时间(0.5 h,1 h)湿磨还能改善Ti46V44Fe10合金的吸放氢容量;但1 h干磨和20 h湿磨则会明显降低合金的吸放氢容量.     

球磨纳米NiCr/WC复合粉的微观组织

采用低温液氮高能球磨技术制备了（Ni-20％Cr）／35％WC（质量分数）纳米复合体系,研究了纳米材料的微观组织和热稳定性。结果表明,随着球磨时间的增加,粉末晶粒度在12h前下降较明显,然后呈缓慢下降的趋势;球磨21h后,NiCr合金粉末晶粒度达到10．02nm,WC粉末晶粒度达到20．2nm,且粉体粒度均匀,形状近似于球形,每个颗粒仍然是多晶结构;经过长时间球磨后,纳米粉末的结构没有发生变化,热稳定性良好;在1000℃保温0．5h后,NiCr合金粉末长大至74nm,WC粉末长大至28nm。