Coral-like amorphous carbon nanotubes synthesized by a modified arc discharge

A coral-like amorphous carbon nanotube was prepared by a modified arc discharging furnace in hydrogen atmosphere with a mixture of Mo-Co₂O₃-Mg powders as catalyst at 600°C. This carbon nanotube presented a microscopic coral-like by SEM observation and amorphous structure of nanotubes by HRTEM observation. The XRD diffraction and Raman pattern presented noncrystal characteristics compared to the normal graphite structure. We believed that these results may be affected by the “synergistic” effect of catalyst, atmosphere, and temperature in the synthesis process. The possible explanations to the formation mechanism of this novel carbon nanotube have also been proposed.     

Characterization of TiCr(C,N)/amorphous carbon coatings synthesized by a cathodic arc deposition process

Ternary TiCrN and nanocomposite TiCr(C,N)/amorphous carbon (a-C) coatings with different carbon contents (0-26.6 at.%) were synthesized by cathodic arc evaporation with plasma enhanced duct equipment. The structural, chemical, and mechanical properties of the deposited films were studied by X-ray diffraction, X-ray photoelectron spectroscopy (XPS), and nanoindentation measurement. The atomic content ratios of carbon/(Ti + Cr) and carbon/nitrogen increased with increasing C₂H₂ flow rate. A nanocomposite structure of coexisting metastable hard TiCr(C,N) crystallites and amorphous carbon phases was found in the TiCr(C,N)/a-C coatings, those possessed smaller crystallite sizes than the ternary TiCrN film. XPS analyses revealed the concentration of a-C increased with increasing carbon content from 8.9 at.% to 26.6 at.%. Exceeding the metastable solubility range of carbon within the TiCrN lattice, the carbon formed a-C phase in the deposited coatings. The nanocomposite TiCr(C,N)/a-C coatings exhibited higher hardness value of 29-31 GPa than the deposited TiCrN coating (26 ± 1 GPa). It has been found that the structural and mechanical properties of the films were correlated with the carbon content in the TiCr(C,N)/a-C coatings.     

Silicon nanocrystals synthesized by electron-beam co-evaporation method and their application for nonvolatile memory

In this paper, the silicon nanocrystals (Si NCs)/SiO₂ hybrid films designed for nonvolatile memory applications are prepared by electron-beam co-evaporation of Si and SiO₂. Transmission electron microscopy images and Raman spectra verify the formation of Si NCs. Metal-oxide-semiconductor capacitor structure with Si NCs embedded in the gate oxide is fabricated to characterize the memory behaviors. High-frequency capacitance-voltage and capacitance-time measurements further demonstrate the memory effect of the structure resulting from the charging or discharging behaviors of Si NCs. It is found that the memory window can be changed by adjusting the Si/SiO₂ wt. ratio in source material. The memory devices with Si NCs/SiO₂ hybrid film as floating gate yield good retention characteristics with small charge loss.     

Preparation and growth mechanism of lead telluride nanocrystals by a modified molten composite-hydroxides method

PbTe nanocrystals were prepared by a modified molten composite-hydroxides method at 180 degrees C for different times, using Pb(NO3)2 and TeO2 as starting materials and KBH4 as a reductant. The nanocrystal structure and morphologies of the synthesized products were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and high resolution TEM (HRTEM), respectively. The results showed that the reaction time has a significant influence on the size and shape of the as-prepared PbTe nanocrystals. As the reaction time increased, the as-prepared products were eventually transformed from nanomaterials (nanocubes, nanorods, and nanosheets) to microcrystals with different morphologies (microcubes, mciroprisms, and microplates). The formation mechanism of the PbTe was proposed, and a one-dimensional oriented attachment growth process combined with two-dimensional oriented attachment growth process was suggested for the growth of nanorods and nanosheets.     

Ferromagnetic and weak superparamagnetic like behavior of Ni-doped ZnS nanocrystals synthesized by reflux method

In this report we have studied the magnetism induced in the undoped and Ni-doped ZnS nanocrystals synthesized via low temperature reflux method. The average diameter of the undoped and Ni-doped nanoparticles is ~3 nm as revealed from transmission electron microscopy and X-ray diffraction (XRD) studies. From XRD studies, the structure of Ni-doped nanocrystals was observed as cubic zinc blende with lattice parameter, a = 0.539 nm. The band gap of the undoped and Ni-doped ZnS nanocrystals, analyzed with UV–visible spectroscopy, was found to be blue shifted as compared to the bulk counterpart. Quenching in photoluminescence spectra was observed at higher Ni concentrations as compared to undoped counterpart. The induced magnetization as analyzed from vibrating samples magnetometer indicated a weak superparamagnetic like behavior in 1 % Ni-doped ZnS nanocrystals, whereas; at 5 and 10 % Ni-doping concentrations, ferromagnetic behavior is indicated.     

The preparation of carbon-coated iron nanocrystals produced from Fe2O3-containmg composite anode in arc discharge

Using an Fe₂O₃-containing composite anode instead of an Fe-containing composite anode in the Kratschmer-Huffman carbon arc method, carbon-coated Fe (not Fe₂O₃) nanocrystals are produced both in the soot on the reactor walls and in the cathode deposits. The encapsulates also contain a little iron carbide, but do not contain iron oxides, as identified by transmission electron microscopy ( TEM ) and X-ray diffraction (XRD). As compared with Ni₂O₃- and Co₂O₃-containing composite anodes, the action of the Fe₂O₃-containing composite anode is unique. When the Fe₂O₃ contents in the composite graphite rod for the carbon arc nanocrystal production are increased in the range 5-33 wt.%, the effect on the structure and diameter distribution of the iron nanocrystals is investigated. The diameter distribution of iron nanocrystals is about 1–30 nm. The effect of helium pressure in the range 80–680 torr on the yield of C_60/70 in carbon soot produced from the composite graphite rod has also been examined. We present a novel result about the relationship of C_60/70 yields and helium gas pressure using a composite anode differing remarkably from the result using a homogeneous graphite anode in arc discharge.     

Sub-micrometer particles produced by a low-powered AC electric arc in liquids

The article presents the report of the production of composites of sub-micrometer metal particles in matrix consisted of the metal compounds by means of an AC electric arc in water and paraffin solutions using electrodes carbon-metal and metal-metal (metal: Ni, Fe, Co, Cu). The advantage of this method is the low electric power (from 5 to 10 W) needed in comparison to standard DC arc-discharge methods (0.8 to 3 kW). This method enables the production of particles from conductive material also in wide range of temperature and in solvent which could be either transparent to light or opaque. Moreover the solvent can be electrolyte or insulating liquid. The microstructure of the composite layer was investigated by scanning electron microscopy (SEM), Electron Probe Microanalysis (EPMA) and X-ray. During particles production in water metal oxides were created. Additionally using cobalt-copper, nickel-copper as couple electrodes, insoluble in water copper (II) hydroxide crystal grains were created additionally which crystals shape was depended on transition metal. For iron-copper couple electrodes system the copper (II) hydroxide was not formed. Experiments with sequence production of Ni and Fe particles with C electrode assisting in molten paraffin let to obtain both Ni and Fe particles surrounded by paraffin. After solidification the material was insulator but if locally magnetic field influenced on the liquid solution in that place after solidification a new composite was created which was electric current conductor with resistivity around 0.1 omega x m, was attracted by magnetic field and presented magneto resistance around 0.4% in changing magnetic field in a range 150 mT. After mixing the concentrated paraffin with normal paraffin resistivity of the mixture increased and it became photosensitive and created small voltage under light influence.     

SnO2纳米晶修饰多孔Co3O4纳米棒的制备及气敏性能研究

以CoCl2.6H2O和CO(NH2)2为原料采用水热法合成多孔Co3O4纳米棒,之后通过自组装的方法将SnO2纳米晶修饰到多孔Co3O4纳米棒上。研究了SnO2纳米晶修饰对多孔Co3O4纳米棒气敏性能的影响。气敏测试结果表明SnO2纳米晶的修饰明显增强了多孔Co3O4纳米棒对CH3CH2OH和H2S的响应,对CH3CH2OH和H2S的检出下限分别达到5.0×10-6和1.0×10-6。     

Characterization and size-dependent magnetic properties of Ba3Co2Fe24O41 nanocrystals synthesized through a sol-gel method

Ba₃Co₂Fe₂₄O₄₁ nanocrystals are synthesized through a stearic acid sol-gel method. The reaction temperatures are dramatically lower than that of the conventional ceramic method. The nanocrystalline powders obtained at 750°C were spherical in shape with grain sizes in the range 15–25 nm and become a plate-like form when the heat-treatment temperature increased. The magnetic properties of these samples are different from those of the bulk Z-type hexagonal ferrite with a lower specific saturation magnetization. This phenomenon can be attributed to the existing of a nonmagnetic layer existing on the surface of the particles. The higher value of the coercivity force is obtained when the particle sizes approximately are equal to 90 nm and assume a single-domain character. The surface composition of the nanocrystalline Co₂-Z hexagonal ferrite is different from that of the bulk counterpart material with a higher content of the Ba element and Co element.     

MoS2-ZnO多孔纳米片的光催化及其室温气敏传感性能

为开发一种高性能、可回收、低成本的光催化剂,本论文使用水热法制备了多孔结构的ZnO纳米片复合MoS₂ （MoS₂-ZnO）光催化材料。通过XRD、SEM、光致发光光谱（PL）、XPS等手段对样品的形貌、光学性质等进行了测试表征。结果表明,所制备的MoS₂-ZnO样品为多孔片状结构;这种复合结构中MoS₂不仅有助于增强ZnO中光生载流子的分离效率,而且还能增强可见光区的吸收,从而提高光催化和气敏性能。在模拟太阳光下,MoS₂-ZnO纳米复合材料对高浓度（15 mg/L）的亚甲基蓝染液（MB）表现出较高的光催化降解活性。同时,MoS₂-ZnO制备的气敏传感器对低浓度（2.05 mg/m³）NO₂还具有较高的灵敏度。本工作为制备高效太阳能驱动的光催化剂和气体传感器提供了重要参考。     

Synthesis of C60-NBN and C70-NBN(N=L, 2) by DC arc Burning Method

Abstract

Macroscopic quantities of boron-doped fullerenes, such as C_60-nB_n and C_70-nB_n(n = 1, 2), were successfully synthesized by DC arc burning method, extracted by CS₂, and characterized by field desorption mass spectra. Among them C₅₈B₂ and C₆₈B₂ were extracted for the first time. The boron-doped fullerenes were found to be less stable than their pristine fullerene analogs. When the electric current becomes too high, no boron doped fullerene, but more higher fullerenes, were formed.     

Synthesis of C60-NBN and C70-NBN(N=L, 2) by DC arc Burning Method

Macroscopic quantities of boron-doped fullerenes, such as C_60-nB_n and C_70-nB_n(n = 1, 2), were successfully synthesized by DC arc burning method, extracted by CS₂, and characterized by field desorption mass spectra. Among them C₅₈B₂ and C₆₈B₂ were extracted for the first time. The boron-doped fullerenes were found to be less stable than their pristine fullerene analogs. When the electric current becomes too high, no boron doped fullerene, but more higher fullerenes, were formed.     

A facile and general approach to polynary semiconductor nanocrystals via a modified two-phase method

Cu(2)ZnSnS(4) nanocrystals were synthesized through a modified two-phase method and characterized with transmission electron microscopy (TEM), powder x-ray diffraction (XRD) and UV-vis spectroscopy. Inorganic metal salts were dissolved in the polar solvent triethylene glycol (TEG) and then transferred into the non-polar solvent 1-octadecene (ODE) by forming metal complexes between metal ions and octadecylamine (ODA). Since nucleation and growth occur in the single phase of the ODE solution, nanocrystals could be produced with qualities similar to those obtained through the hot-injection route. Balancing the reactivity of the metal precursors is a key factor in producing nanocrystals of a single crystalline phase. We found that increasing the reaction temperature increases the reactivity of each of the metal precursors by differing amounts, thus providing the necessary flexibility for obtaining a balanced reactivity that produces the desired product. The versatility of this synthesis strategy was demonstrated by extending it to the production of other polynary nanocrystals such as binary (CuS), ternary (CuInS(2)) and pentanary (Cu(2 - x)Ag(x)ZnSnS(4)) nanocrystals. This method is considered as a green synthesis route due to the use of inorganic metal salts as precursors, smaller amounts of coordinating solvent, shorter reaction time and simpler post-reaction treatment.     

热处理对AB_3型无Co贮氢合金电化学性能的研究

用真空熔炼法制备了多种贮氢合金原样,分别经不同温度、时间热处理和保护气氛下球磨处理.改性前后样品晶体结构用SEM和XRD测试进行结构表征,结果表明合金为LaNi_5和LaMg_2Ni_9晶相的复合相,经过热处理的合金颗粒粒径变小针刺变少、分布也相对更均匀.采用LANDAN进行电化学相关测试(电流密度为150mA/g),表明经过热处理使得晶体结构优化,放电容量有显著增加,且经由Al替代Ni的合金容量达到353.7mAh/g,循环50周容量保持率为76.7%,循环100周容量保持率为62.7%,表现出更好的循环稳定性.实验结果表明,无Co替代贮氢合金经热处理后电化学性能有显著提高,有望降低合金材料成本的同时提高材料的环境友好性.     

Microstructural characterization and grain refinement of AA6082 gas tungsten arc welds by scandium modified fillers

The refinement in weld metal grain size and shape results in both improved mechanical properties (ductility and toughness) as well as a significant improvement in weldability. In the present study, the influence of scandium (Sc) additions to the fillers on the structure and mechanical properties of AA6082 gas tungsten arc (GTA) weldments were investigated. Controlled amounts of scandium as grain refiner were introduced into the molten pool of AA6082 by pre-deposited cast inserts (AA4043 and AA5356) by GTA welding. Full penetration GTA welds were prepared using alternating current (AC). It was observed that grain size decreased with increasing amounts of scandium. The grain refinement is mainly caused by the Al₃Sc particles, which act as heterogeneous nucleation of α-Al grains. It has been shown that welds prepared with AA5356 cast insert exhibited high strength and ductility when compared with other welds. The observed grain refinement was shown to result in an appreciable increase in fusion zone hardness, strength and ductility. Post-weld aging treatment resulted in improved tensile strength and hardness of the weldments and this aging response could be attributed to the weld dilution from the base metal. The slow diffusion of Sc in Al matrix and stability of Al₃Sc precipitates at elevated temperatures were suggested to be responsible for the improved high temperature yield strength of welds made from Sc modified fillers.     

Separation of C2-naphthalenes by gas chromatography x fourier transform infrared spectroscopy (GC x FT-IR): two-dimensional separation approach

A two-dimensional separation approach involving gas chromatography (GC) and Fourier transform infrared spectroscopy (FT-IR) is used to separate C2-naphthalene isomers at or near baseline resolution. In addition to GC separation, the FT-IR also plays an important role in the separation, as well as its traditional role of detection and identification. This two-dimensional separation approach for the analysis of a C2-naphthalene isomeric mixture is a good example of separation design based on molecular difference and the characteristics of an analytical instrument. The details of this two-dimensional separation are discussed, along with the advantages and limitations of this approach. While two-(or multiple-)dimensional separations have demonstrated superior capabilities in the characterization of complex, largely unknown mixtures, the development of GCxFT-IR illustrates the applicability of this analytical approach in the separation of simpler but still challenging, mixtures. The GCxFT-IR results have extended this approach toward its application to the analysis of samples of more complicated composition.     

Effect of metal ion dopants on photochemical properties of anatase TiO2 films synthesized by a modified sol-gel method

Anatase TiO₂ films were successfully synthesized by a modified sol-gel method wherein peroxo titanic acid solution was derived from TiCl₄/ethanol/water solution at room temperature. The as-prepared films were further surface-doped by photodeposited Fe₂O₃ and Cr₂O₃ to improve its physicochemical properties. The phase and structure of the films were investigated by X-ray diffraction, scanning electron microscopy and X-ray photoelectron spectroscopy. The physicochemical properties of the films were also measured. The results show that both hydrophilicity and photocatalytic activity of the films were remarkably improved by doping transition metal ion Fe³⁺. In case of Cr³⁺ doped films, hydrophilicity was also significantly enhanced but photocatalytic activity for methyl orange under UV irradiation was still comparable with the undoped films.     

CuAlO2纳米晶的水热-分解制备及表征

采用新制备的Cu2O和Al(OH)3为反应原料,利用水热-分解法制备了p型半导体CuAlO2纳米晶.采用X射线衍射(XRD)、透射电子显微镜(TEM)、X射线光电子能谱(XPS)和紫外-可见(UV-Vis)吸收光谱对其结构、形貌、表面组分和性能进行了表征分析,对反应机理进行了讨论.结果表明在水热条件下首先是Al(OH)3转化为γ-AlOOH,然后γ-AlOOH分解并与Cu2O反应生成CuAlO2纳米晶.确定了以Cu2O和Al(OH)3溶胶为反应原料,采用水热-分解法制备CuAlO2纳米晶的最佳反应条件.