掺杂钛催化机理及其再结晶石墨导热性能的研究

用煅烧石油焦作填料、煤沥青作粘结剂、钛粉作添加剂,采用热压工艺制备了一系列不同质量配比的掺杂钛再结晶石墨.考察了不同质量配比的添加钛对再结晶石墨的热导率、抗弯强度的影响以及微观结构的变化.实验结果表明,与相同工艺条件下制备的纯石墨材料相比较,掺杂钛再结晶石墨的热导率、抗弯强度均有较大的提高.室温下,RG-15再结晶石墨的层面方向热导率可达424W/(m·k),抗弯强度可达50.2MPa.微观结构分析表明,少量的掺杂钛,即可使材料达到很高的石墨化度;过多的钛掺杂量不利于材料的热导率以及抗弯强度;原料中掺钛量为15wt％时,再结晶石墨的微晶发育以及排列程度最好,此材料的石墨化度为96.4％,微晶参数La为306nm.XRD物相分析表明,钛元素在再结晶石墨中以碳化钛的形式存在.钛对再结晶石墨制备过程的催化作用可以用液相转化机理来解释.     

以中间相沥青为粘结剂的低密度高导热炭纤维网络体的研究

以中间相沥青为粘结剂, 采用500 ℃低温炭化炭纤维, 经低压模压成型、炭化和石墨化后得到低密度高导热炭纤维网络体。与以1300 ℃炭化炭纤维为原料和以酚醛为粘结剂制备的炭纤维网络体进行了比较。对粘结剂炭收率(热重分析)、样品微观形貌(扫描电子显微分析)、石墨化度及微晶尺寸(X射线衍射分析)等进行了表征。研究结果表明: 由于高炭收率和高片层取向度的中间相沥青与500 ℃低温炭化处理炭纤维共同经历后续热处理时呈现出相近的热收缩率, 因而具备良好的相互粘结性和石墨片层铆接效应, 其制备的炭纤维网络体经石墨化后密度为0.317 g?cm ^-3, 由此制备的相变复合材料的面内热导率为19.30 W·m ^-1·K ^-1, 较纯相变材料(石蜡)提升了80倍, 明显高于以1300 ℃炭化炭纤维为原料, 以中间相沥青和酚醛分别为粘结剂制备样品的面内热导率(17.03和14.47 W·m ^-1·K ^-1)。     

Characteristics of an artificial graphite anode material for rapid charging: manufactured with different coke particle sizes

An artificial graphite anode material (10–15 μm) is produced using coke at two sizes (10–15 μm, 2–5 μm) and the electrochemical properties are compared and discussed. We produce and measure an artificial graphite anode material using coke with a particle size of 10–15 μm, limited lithium ion insertion–desorption pathways, increased migration pathways, and low-speed charge–discharge characteristics. When a block is manufactured using coke at a particle size of 2–5 μm and an anode material is created with a particle size of 10–15 μm, voids capable of storing lithium ions between the coke particles form inside the anode material. These spaces are utilized and the capacity was measured. In addition, the lithium ion insertion-deintercalation path and lithium ion diffusion distance are controlled and the high-speed discharge properties were measured (78.3%) at low temperatures (5C/0.1C, ? 10 °C). At the same time, the high specific surface area due to the small size of the coke was controlled by the binder pitch used in the block, leading to excellent initial efficiency performance.

     

浸银炭石墨复合材料的密封摩擦特性

采用超细石油焦粉为主要成分,添加复合氧化物陶瓷粉末,制备一种高强、耐磨的炭石墨基体;选择适当的热处理工艺控制石墨化程度;采用热等静压浸银新方法达到密实增补强度。M209G浸银炭石墨复合材料具有碳的高硬度,石墨的自润滑,陶瓷相的耐磨,银的导热与塑性等综合优点,体现了刚度和塑性的完美结合,利用X-衍射仪、光学显微镜、扫描电子显微镜等分析了材料的显微组织结构和摩损表面形貌,并探讨了其磨损机理与密封摩擦特性,结果表明：M209G浸银炭石墨配气阀座在密封摩擦表面上形成了一层具有抗摩性质的润滑膜,使摩擦处于边界润滑状态,金属银在高温、高压、高速下产生熔化析出和塑性流动形成了大面积连接,不仅降低了摩擦,而且有利于密封。     

Structure and electrochemical applications of boron-doped graphitized carbon nanofibers

Boron-doped graphitized carbon nanofibers (CNFs) were prepared by optimizing CNFs preparation, surface treatment, graphitization and boron-added graphitization. The interlayer spacing (d???) of the boron-doped graphitized CNFs reached 3.356 ?, similar to that of single-crystal graphite. Special platelet CNFs (PCNFs), for which d??? is less than 3.400 ?, were selected for further heat treatment. The first heat treatment of PCNFs at 2800?°C yielded a d??? between 3.357 and 3.365 ?. Successive nitric acid treatment and a second heat treatment with boric acid reduced d??? to 3.356 ?. The resulting boron-doped PCNFs exhibited a high discharge capacity of 338 mAh g?1 between 0 and 0.5 V versus Li/Li? and 368 mAh g?1 between 0 and 1.5 V versus Li/Li?. The first-cycle Coulombic efficiency was also enhanced to 71-80%. Such capacity is comparable to that of natural graphite under the same charge/discharge conditions. The boron-doped PCNFs also exhibited improved rate performance with twice the capacity of boron-doped natural graphite at a discharge rate of 5 C.     

Electrochemical characterizations of Li2.6Co0.4N/Graphite anodes for lithium ion batteries

Li_2.6Co_0.4N anode material was prepared by solid-state reaction. The material was used to prepare Li_2.6Co_0.4N/natural graphite composite anode materials with the aim to improve the electrochemical performance of natural graphite. Natural graphite showed a low initial columbic efficiency of 69%, which was improved to ~ 100% by adding 20 wt.% of Li_2.6Co_0.4N into the material. On the other hand, the composite materials showed better capacity retention than both pure Li_2.6Co_0.4N and natural graphite. The material containing 20 wt.% of Li_2.6Co_0.4N exhibited a reversible discharge capacity of 243 mAh g^? 1 after thirty cycles, as compared to a capacity of 212 mAh g^? 1 for natural graphite.     

Zinc oxide quantum dots for textile dyes and real industrial wastewater treatment: Solar photocatalytic activity,photoluminescence properties and recycling process

Three samples of ZnO quantum dots (ZQDs) were synthesized by a modified sol–gel method at different temperatures for 3 h. The first sample (S1) was prepared at room temperature 27 °C, while second and third samples (S2) and (S3) were prepared by the calcination process at 500 and 900 °C, respectively. A study of XRD and TEM determines the purity, high crystallinity and the presence of elongated shape of the prepared catalysts. On using TEM, DRS and EBT analysis, the crystallite size values, bandgap energy, and active surface area were (7.1 nm, 3.49 eV, and 150.1 m²/g), (9.8 nm, 3.45 eV and 112.2 m²/g) and (13.5 nm, 3.39 eV and 78.94 m²/g) for S1, S2, and S3, respectively. The Photoluminescence properties showed that the fluorescence rate for S1 was doubled the observed one in the S2 sample. The photodegradation results of both methyl orange as an industrial raw material and real industrial wastewater of S1 sample showed the finest activity when compared with the rest samples. It was cleared from the collecting data that the photocatalytic performance decreases with the crystallite size increases The mineralization efficiency of the real industrial wastewater that exposed to sunlight for six months were evaluated according to the allowed COD limit for Egyptian Environmental Law, In addition the recycling process for reusable for ZnO prepared samples for 8 times investigated and evaluated.     

腐殖酸基石墨化材料的制备及其电化学性能

以腐殖酸为前驱体,通过高温热处理制备锂离子电池负极材料。采用扫描电子显微镜(SEM)、X射线衍射(XRD)和电化学测试系统对该材料的形貌、微晶结构和电化学性能进行表征。结果表明,腐殖酸基石墨化材料呈现出较为规整的石墨片层结构,且随着石墨化温度的升高,所得材料的石墨化度也越来越高。腐殖酸基石墨化材料均表现出良好的电化学性能,石墨化温度为2 800℃所制备的石墨化材料的首次放电比容量为356.7 mAh/g,充电比容量为277.6 mAh/g,首次充放电的库仑效率为77.81%,在1C和2C倍率下50次充放电循环后的容量保持率分别高达99.4%、95.9%,是一种理想的锂离子电池负极材料。     

纳米碳管用于锂离子电池负极材料的研究

采用氧化法提纯了煤焦化工业副产品中的纳米碳管,采用X射线衍射法对纳米碳管的结构进行了研究,透射电镜研究了纳米碳管的形貌。提纯的纳米碳管d002为0.3496nm,具有类似石墨的结构和较高的石墨化度。研究了纳米碳管的电化学性能,其首次放电比容量达584.3mAh/g;添加石墨粉组成了20％的纳米碳管和80％的石墨粉的体系作为锂离子电池负极材料,其首次放电比容量为490.1mAh/g,并有较好的循环性能。     

Physical properties of multiwalled carbon nanotubes

Multiwalled carbon nanotubes (MWNTs), which were prepared by hydrogen arc discharge, were purified by using an infrared radiation heating system. The morphology, structure, vibrational modes and crystalline perfection of purified MWNTs were investigated by using scanning electron microscopy, high-resolution transmission electron microscopy, an X-ray diffractometer and a Raman spectrometer. Moreover, the electrical conductivity of individual purified MWNTs was measured using a two-probe method using a micro manipulator system. It turned out that the MWNTs had a high degree of graphitization, an electrical conductivity of about 1.85×10³ S cm⁻¹ along the long axis, and an enormous current density of more than 10⁷ A cm⁻².     

Preparation of porous SnO2 helical nanotubes and SnO2 sheets

We report a surfactant-free chemical solution route for synthesizing one-dimensional porous SnO₂ helical nanotubes templated by helical carbon nanotubes and two-dimensional SnO₂ sheets templated by graphite sheets. Transmission electron microscopy, X-ray diffraction, cyclic voltammetry, and galvanostatic discharge–charge analysis are used to characterize the SnO₂ samples. The unique nanostructure and morphology make them promising anode materials for lithium-ion batteries. Both the SnO₂ with the tubular structure and the sheet structure shows small initial irreversible capacity loss of 3.2% and 2.2%, respectively. The SnO₂ helical nanotubes show a specific discharge capacity of above 800 mAh g⁻¹ after 10 charge and discharge cycles, exceeding the theoretical capacity of 781 mAh g⁻¹ for SnO₂. The nanotubes remain a specific discharge capacity of 439 mAh g⁻¹ after 30 cycles, which is better than that of SnO₂ sheets (323 mAh g⁻¹).     

X-ray diffraction line profile analysis of nanocrystalline graphite

The structure evolution to nanocrystalline graphite produced by ball milling in n-dodecane has been studied by Fourier analysis of broadened X-ray diffraction line profiles according to double-Voigt method. The Fourier analysis gave size and strain distributions of the coherently diffracting domains (X-ray crystallite size) and root-mean-square-strain (rmss) and their average values. The precursor graphite was defined by average crystal sizes of about hundreds of nanometers, measured along the in-plane and out-of-plane directions, and low rmss value of 0.38 × 10⁻³. During milling, the average crystallite sizes of graphite decreased to about 6 and 43 nm along the out-of-plane and in-plane directions, respectively. Correspondingly, the rmss of milled graphite increased to 6.54 × 10⁻³. Analysis of the out-of-plane to in-plane crystallite size ratios showed that the crystallites became progressively thinner and flatter. A linear relationship between rmss and reciprocal crystallite size along the stacking axis revealed that size of disordered boundary regions gradually increased at the expense of ordered crystalline regions. A model describing crystalline–nanocrystalline transformation of graphite along different crystallographic axis was formulated and used to discuss the experimental data. It was concluded that a distortion-controlled process is responsible for the crystalline–nanocrystalline transformation of graphite milled in n-dodecane.     

微氧化处理对球形石墨结构及电化学行为的影响

研究了微氧化处理对球形石墨的晶体结构、表面形貌和电化学行为的影响. 采用XRD、Raman光谱和SEM等手段分析了样品的结构和形貌, 并采用恒电流充放电测试、粉末微电极技术和慢速扫描循环伏安法(SSCV)研究了微氧化前后石墨负极的电化学行为. 结果表明, 微氧化后石墨颗粒中的结构缺陷增多, 近表面区域的无序度增大, 面内平均晶粒尺寸L_a减小, 且菱形相含量降低, 石墨呈不规则的鳞片状, 部分层面的边缘有卷曲与刻蚀现象. 微氧化后石墨负极的第三次脱锂容量从345.5 mAh/g增加至381.4 mAh/g, 且其循环性能得到有效改善. 同时, 微氧化后锂离子较容易从石墨中脱出, 脱锂过程中一阶Li-GICs(lithium-graphite intercalation compounds, 简称Li-GICs)向二阶Li-GICs的阶转变可在较低的电位下发生.     

球磨CeMg12+100%Ni合金热力学及电化学贮氢性能

用球磨工艺制备CeMg12+100%Ni电极合金,研究了球磨工艺对合金结构及电化学性能的影响。结果表明球磨CeMg12+100%Ni合金具有非晶纳米晶结构,由Mg2Ni相以及Ni相组成,其含量随球磨时间的延长而增加,这在一定程度上改善了合金的电化学放电性能。球磨非晶纳米晶具有较好的结构稳定性,在吸氢后形成的氢化物相仍保持非晶纳米晶尺度,这有利于降低氢化物的热稳定性,改善电化学放电性能。     

Tribological property of onion-like fullerenes as lubricant additive

Onion-like fullerenes (OLFs) were generated by arc discharge in water between pure graphite electrodes. The size and crystalline morphology of the generated OLFs were characterized by means of the high-resolution transmission electron microscopy and X-ray diffraction. Furthermore, OLFs were added to base lubricant and the tribological property of OLFs was investigated by using a four-ball type tribometer. The results indicated that the OLFs with diameter about 25 nm were of high degree graphitization. Good friction-reduction property at different additive concentration and applied load as lubricant additive was obtained. The scratches on the worn surfaces become slighter and more uniform with addition of OLFs to the base lubricant. In addition, the tribological mechanism of the sliding-bearing system was proposed.     

Silicon,flake graphite and phenolic resin-pyrolyzed carbon based Si/C composites as anode material for lithium-ion batteries

Si/C composites, based on nano-Si, flake graphite and phenolic resin-pyrolyzed amorphous carbon, were synthesized by liquid solidification and subsequent pyrolysis. The performances of the prepared Si/C composites are investigated by means of thermogravimetric analysis (TG–DTA), X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscope (TEM) and galvanostatic cell cycling, as well as cyclic voltammograms. The results indicate that the initial charge capacity of the composites is 640.51 mA h g^?1 at a current density of 100 mA g^?1 and the initial coulombic efficiency is 73.82%. The Si/C composites also exhibit excellent cycling performances when cycled at different discharge/charge rates.     

微扩层鳞片石墨负极材料的制备及电化学性能研究

研究了微扩层鳞片石墨的制备工艺、晶体结构、表面形貌以及电化学行为之间的关系。采用XRD和SEM等手段分析了石墨样品的结构和表面形貌; 采用比表面积分析仪、振实密度仪分别测试了样品的BET比表面积和振实密度等指标; 并应用恒电流充放电测试、循环伏安技术和电化学阻抗法(EIS)研究了微扩层处理前后石墨负极的电化学行为。结果表明, 经微扩层处理后, 石墨的平均层间距d₀₀₂略微增大, 平均晶粒尺寸Lc、La减小, 颗粒的表面更光滑。微扩层石墨的首次库伦效率从91.6%提高至92.7%, 可逆容量由345.5 mAh/g提高至379.8 mAh/g。且其循环性能与倍率放电性能均得到有效改善, 同时石墨的嵌锂电位略有提高, 锂离子从石墨中脱出更容易, 电化学可逆性提高。分析是由于微扩层后石墨负极材料脱嵌锂反应的活化能降低所致。     

Hydrogen storage of a mechanically milled carbon material fabricated by plasma chemical vapor deposition

Abstract

Carbon materials were prepared by plasma chemical vapor deposition at different pressures without catalyst, and the structure and hydrogen storage characteristics of milled and unmilled samples of the materials were evaluated. Using this approach, we were able to fabricate graphite microcrystals with a crystallite size of several nanometers, and the crystallite size and surface area could be controlled by changing the pressure during plasma chemical vapor deposition. The hydrogen storage capacity of the unmilled materials was 0.3?wt%, but milling increased this value to 1.0?wt% by reducing the crystallite size and increasing the crystallite surface area.     

Graphite and boron carbide composites made by hot-pressing

Composites consisting of graphite and boron carbide were made by hot-pressing mixed powders of coke carbon and boron carbide. The change of relative density, mechanical strength and electrical resistivity of the composites and the X-ray parameters of coke carbon were investigated with increase of boron carbide content and hot-pressing temperature. From these experiments, it was found that boron carbide powder has a remarkable effect on sintering and graphitization of coke carbon powder above the hot-pressing temperature of 2000° C. At 2200° C, electrical resistivity of the composite and d(002) spacing of coke carbon once showed minimum values at about 5 to 10 wt% boron carbide and then increased. The strength of the composite increased with increase of boron carbide content. It was considered that some boron from boron carbide began to diffuse substitutionally into the graphite structure above 2000° C and densification and graphitization were promoted with the diffusion of boron. Improvements could be made to the mechanical strength, density, oxidation resistance and manufacturing methods by comparing with the properties and processes of conventional graphites.     

Influence of crystallite size on the hardness and fatigue life of steel samples coated with electrodeposited nanocrystalline Ni-W alloys

The present work deals with the effect of crystallite size on the hardness and fatigue life of steel samples coated with electrodeposited nanocrystalline Ni-W alloys. The Ni-W alloys were electrodeposited on steel samples at four different current densities (0.05, 0.10. 0.15 and 0.20 A/cm²) and at a temperature of 75 °C. The crystallite size of the deposit reduced (from 40 to 13 nm) with an increase in current density (from 0.05 to 0.20 A/cm²) due to an increase in the tungsten content (from 0.72 to 9.33 at.%). Ni-W alloy containing 9.33 at.% W and having a crystallite size of 13 nm exhibited the maximum hardness of 638 HV. The alloys, with the crystallite size in the range 40-13 nm, followed the direct Hall-Petch relation, i.e. hardness increased with a reduction in the crystallite size. The coated samples exhibited inferior fatigue lives compared to uncoated samples. This may be attributed to the presence of tensile residual stresses and inherent microcracks in the coatings. Among the specimens coated with Ni-W alloys, as the crystallite size decreased, the fatigue life of the specimen increased owing to the increase in hardness values.