大尺寸纳米晶磁环的动态磁性能测量

 在感应型速调管调制器中使用了纳米晶磁性材料制作大尺寸磁环，使用伏安向量法对材料试样的磁性能进行测量，得到频率为20.03 kHz和50 kHz时的动态磁化曲线、磁导率、磁场损耗等参数。使用脉冲法对成型的大尺寸磁环动态磁性能进行测量，励磁方式和工作中完全一致，在测量脉冲脉宽3.5~4.0 μs，重复频率50 Hz，初次线圈均为1匝，外径220 mm，内径80 mm，高60 mm，截面积4 200 mm²时，得到磁环实际能够达到的伏秒数为0.007 V·s，此时所需的偏磁电流大小为8 A。     

Layered LiCo1?xMgxO2 (x = 0.0, 0.1, 0.2, 0.3 and 0.5) cathode materials for lithium-ion rechargeable batteries

Layered LiCo_1−x Mg _x O₂ (x = 0.0, 0.1, 0.2, 0.3 and 0.5) oxide materials were synthesized using LiNO₃, Co(NO₃)₂, Mg(NO₃)₂ as the precursors, and the effect of the dopants on the electrochemical properties was investigated. thermogravimetric/differential thermal analysis was carried out to observe the phase transformations of LiCo_0.9Mg_0.1O₂. The phase purity and cation environment of the synthesized oxides were characterized using X-ray diffraction and Fourier transform infrared spectroscopy. The particle size, nature, morphological properties and composition of the synthesized oxides were examined by TEM and SEM with energy dispersive X-ray spectroscopic analysis. Finally, the electrochemical behavior of the prepared layered materials was studied using cyclic voltammetry and charge–discharge cycling. LiCo_0.8Mg_0.2O₂ has good cycling results when compare to other doped and undoped materials. These results have been also supported by cyclic voltammograms.     

Synthesis and luminescence properties of nanocrystalline Gd2O3:Eu by combustion process

The nanocrystalline Gd₂O₃:Eu³⁺ powders with cubic phase were prepared by a combustion method in the presence of urea and glycol. The effects of the annealing temperature on the crystallization and luminescence properties were studied. The results of XRD show pure phase can be obtained, the average crystallite size could be calculated as 7, 8, 15, and 23 nm for the precursor and samples annealed at 600, 700 and 800 °C, respectively, which coincided with the results from TEM images. The emission intensity, host absorption and charge transfer band intensity increased with increasing the temperature. The slightly broad emission peak at 610 nm for smaller particles can be observed. The ratio of host absorption to O²⁻-Eu³⁺ charge transfer band of smaller nanoparticles is much stronger compared with that for larger nanoparticles, furthermore, the luminescence lifetimes of nanoparticles increased with increasing particles size. The effects of doping concentration of Eu³⁺ on luminescence lifetimes and intensities were also discussed. The samples exhibited a higher quenching concentration of Eu³⁺, and luminescence lifetimes of nanoparticles are related to annealing temperature of samples and the doping concentration of Eu³⁺ ions.     

Silica-coated Y2O3:Eu nanoparticles and their luminescence properties

Crystalline Y₂O₃:Eu is of paramount significance in rare earth materials and research on luminescence spectra. In this work, the nanocrystalline Y₂O₃:Eu was coated with silica by a facile solid state reaction method at room temperature. The transmission electron microscope (TEM) photographs showed that the prepared Y₂O₃:Eu particle is polycrystalline with the size of 20 nm, the size of silica-coated particle is about 25 nm. The XPS spectra indicated that the silica layer is likely to interact with Y₂O₃:Eu by a Si-O-Y chemical bond. The luminescence spectra showed that the intensity of ground samples is lower than that of unground ones, the intensity of silica-coated phosphors is higher than that of the ground samples, while almost the same as that of the unground ones. Therefore, the silica coating decreases the surface defects of nanoparticles of the nanocrystalline Y₂O₃:Eu, thus increasing their luminescent intensity.     

Electronic structure,magnetic properties,and microstructural analysis of thiol-functionalized Au nanoparticles: role of chemical and structural parameters in the ferromagnetic behaviour

The present work describes the field emission characteristics of nanocrystalline metal clusters decorated multi walled carbon nanotubes (MWNT) field emitters fabricated over flexible graphitized carbon cloth. MWNT have been synthesized by catalytic chemical vapour decomposition (CCVD) of acetylene over Rare Earth (RE) based AB₂ (DyNi₂) alloy hydride catalyst. Fine powders of RE based AB₂ alloy hydride catalysts have been prepared by hydrogen decrepitation technique. The as-grown carbon nanotubes (CNTs) are purified by acid and heat treatments and characterized using XRD, SEM and TEM. Purified MWNT have been decorated with nanocrystalline Pd, Pt and Pt–Ru metal clusters using a simple chemical reduction method. The characterization of metal decorated CNTs were done by using XRD, SEM, TEM, HRTEM and EDX. Nanocrystalline Pd, Pt and Pt–Ru metal clusters decorated MWNT field emitters have been fabricated over graphitized carbon fabric using spin coating method. The field emission characteristics have been studied using an indigenously fabricated set up and the results are discussed. The samples show excellent emission properties with a fairly stable emission current over a period of 4 h. As the presence of the graphitic layer provides strong adhesion between the nanotubes and carbon cloth, the use of graphitized carbon cloth as substrate opens new possibilities for CNT field emitters.     

Structural characterisation of the silica and alumina Zener pinning phases in nanocrystalline CeO2 by 29Si and 27Al nuclear magnetic resonance

Nanocrystalline CeO₂ samples have been manufactured using sol-gel techniques, containing either 15 % silica or 10 % alumina by weight to restrict growth of the ceria nanocrystals during annealing by Zener pinning. ²⁹Si and ²⁷Al MAS NMR have been used to investigate the structure of these pinning phases over a range of annealing temperatures up to 1000 °C, and their effect on the CeO₂ morphology has been studied using electron microscopy. The silica pinning phase resulted in CeO₂ nanocrystals of average diameter 19 nm after annealing at 1000 °C, whereas the alumina pinned nanocrystals grew to 88 nm at the same temperature. The silica pinning phase was found to contain a significant amount of inherent disorder indicated by the presence of lower n Qⁿ species even after annealing at 1000 °C. The alumina phase was less successful at restricting the growth of the ceria nanocrystals, and tended to separate into larger agglomerations of amorphous alumina, which crystallised to a transition alumina phase at higher temperatures.     

Photoelectrochemical Characteristics Of α-Fe2O3 Nanocrystalline Semiconductor Thin Film

-Fe₂O₃ single crystal thin films have been prepared from 45nm diameter colloid. These thin nanocrystalline films exhibit a typical behavior of n-type semiconductor material because of the anodic photocurrent generation. The anodic photocurrent response upon illumination and the reversal spike of cathodic current upon the light switched off suggests that the electrons can flow in both directions and no space charge layer exists at the thin film/electrolyte interface. The decreased photocurrent responses of thicker films can be explained by the electric resistance effect and recombination effect. Moreover, the thicker film will lead to a poor photocurrent response for short wavelength light. Considering the use of sunlight, the thin film thickness should be controlled to an optimal value.     

Phase Transformation Mechanism of Graphite-Turbostratic Graphite in the Course of Mechanical Grinding

IntroductionSome industrially- widely- used carbon materi-als,such as Pan- based carbon fiber,glassy car-bon,carbon black and carbon film,have a tur-bostratic graphitic structure[1— 4] . This structure isbased on the same hexagonal plane of the carbonatoms as graphitic crystalline. The difference be-tween atoms lies in the random translations and ro-tations which destroy the character of three dimen-sional ordering. Turbostratic graphite materials aremostly composed of non graphitic carbon. …     

Time‐Resolved Phase Transitions of the Nanocrystalline Cubic to Submicron Monoclinic Phase in Mn2O3‐ZrO2

The nanocrystalline cubic phase of zirconia was found to be thermally stabilized by the addition of 3 to 40 mol % manganese. The nanocrystalline cubic, tetragonal and monoclinic phases of zirconia stabilized with manganese (III)oxide (Mn‐Stabilized Zirconia) were prepared by thermal decomposition of carbonate and hydroxide precursors. Both the crystallization and isothermal phase transitions associated with Mn‐SZ were studied using high temperature x‐ray diffraction and x‐ray diffraction of quenched samples. Cubic Mn‐SZ initially crystallized and progressively transformed to tetragonal, and monoclinic structures above 700°C. The nanocrystalline cubic Mn‐SZ containing 25 mol % Mn was found to have the greatest thermal stability, retaining its cubic form at temperatures as high as 800°C for periods up to 25 hours. Higher than 40 mol %, cubic Mn₂O₃ was found to coexist with cubic Mn‐SZ. The crystallite sizes observed for the cubic, tetragonal and monoclinic Mn‐SZ phases ranged from 50 to 137, 130 to 220, and 195 to 450 Å respectively, indicating, for ZrO₂, that particle size was a primary factor in determining its polymorphs. The classical Avrami equation for nucleation and growth was applied to the observed phase transformations.