WANG Weihua XIAO Keqin CHU Zhaoqin DONG Yuanda Institute of Solid State Physics
,
Academia Sinica
,
Hefei
,
ChinaWANG Genmiao Centre of Structural Analysis
,
China University of Science and Technology
,
Hefei
,
China
金属学报(英文版)
Amorphous Al_(80)Fe_(20) powder which can hardly be obtained using conventional rapid quenching technique was directly prepared from crystalline Fe and A1 powders by means of mechanical alloying process.The amorphization process was examined by X-ray analysis and Mssbauer spectroscopy,and the thermal behaviour was studied by DSC.The results show that the rate of amorphization is controlled by the diffusion reaction at the interfaces and changes with the milling time.The effect of milling conditions on amorphization by mechanical alloying was al- so investigated.
关键词:
mechanical alloying
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null
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null
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null
Acta Materialia
Boron nitride nanotube (BNNT)/aluminum matrix composite nanohybrids were fabricated through magnetron sputtering of Al onto dispersed multiwalled BNNTs with average external diameters of 40-50 nm. Aluminum phase coating tightly wrapped the BNNTs after the deposition. The coating thickness in the range of 5-200 nm was controlled by changing sputtering time. Using imaging techniques and electron diffraction analysis in a transmission electron microscope, the Al phase was found to create nanocrystalline shields around individual BNNTs. The chemical states of the hybrid nanomaterials during the initial stages of sputtering were analyzed by X-ray photoelectron spectroscopy. Direct in situ bending and tensile tests on individual BNNT-Al nanocomposites were carried out by using a dedicated transmission electron microscope-atomic force microscope holder. In parallel, high-resolution TEM images and video recordings were taken for the analysis of deformation kinetics and fracture mechanisms. The nanohybrids with a suitably thick aluminum coating (similar to 40 nm) withstood at least nine times higher stresses compared to a pure non-armed Al metal. This pioneering work opens up a prospective pathway for making ultralight and superstrong "dream" structural materials for future automotive and aerospace applications. (C) 2012 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
关键词:
Aluminum;Boron nitride;Composites;Nanotubes;Transmission electron;microscopy (TEM);carbon nanotubes;youngs modulus;composites;strength;behavior
Physica Status Solidi B-Basic Research
The EPR g-factors g(\\), g(perpendicular to) and hyperfine structure constants A(\\), A(perpendicular to) for a tetragonal Co2+ centre, i.e.. Co(H2O)(2)Cl-4 centre, in NH4Cl crystal are calculated from the perturbation formulas based on a cluster approach. In these formulas, the parameters related to the contributions from the configuration interaction. the covalency effect and the low-symmetry crystal field can be obtained from the optical spectra and the structural model and data of the studied system. The core polarization constant it in the calculation formulas of hyperfine constants is used as an adjustable parameter. The calculated results are in good agreement with the observed values.
关键词:
superposition model;centers;resonance;ions;cr3+
Xisheng YE
,
Jian SHA and Zhengkuan JIAO(Dept. of Physics
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Zhejiang University
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Hangzhou 310027. China)Zifei PENG and Lide ZHANG(Institute of Solid State Physics
,
Chinese Academy of Sciences
,
Hefei 230031
,
China)
材料科学技术（英文）
Using DTA (difFerential thermal analysis) measurement on nanostructured TiO2, we find two endothermic peaks on the DTA curve. From XRD (X-ray diffraction) analysis of the original nanostructured TiO2 and its heat-treated samples, we obtain the following results: the first endothermic peak corresponds to the desorption of physical or chemical absorption, the second one is related to the structural phase transition from brookite to anatase then to rutile, and this structural phase transition is beneficial to the grain growth of nanocrystal
关键词:
Physica Status Solidi B-Basic Research
The perturbation formulae of EPR g-factors g(i) (i = x, y, z) and hyperfine constants Ai for a 3d(7) (Co2+) ion at a rhombic octahedral site in a crystal are established from a cluster approach. In these formulae, the contributions from the covalency effect, the configuration interaction and the rhombic crystal field are considered and the parameters used in the calculation of EPR parameters. except the core polarization constant x in the calculation of Al, can be estimated from the optical spectra and the structure data of the studied system. From these formulae, the EPR parameters g(i) and A(i) for the rhombic Co2+-V-Ag centre in AgCl are reasonably explained by considering suitable rhombic distortion and so the microstructure of this rhombic centre is obtained.
关键词:
superposition model;crystals
ZANG Qishan ZHOU Xiangyang LIU Kang KE Wei ** Institute of Metal Research
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Academia Sinica
,
Shenyang
,
110015
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China*** Institute of Corrosion and Protection of Metals
,
Academia Sinica
,
Shenyang
,
110015
,
China+ To whom correspondence should be addressed.
材料科学技术（英文）
From the corrosion fatigue test under intermit- tent wetting condition for offshore structural steel of A537 cl.l and data analysis,some results associ- ated with the role of pits in fatigue process have been discussed.
关键词:
pitting
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null
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null
Pramana-Journal of Physics
By calculating the optical spectrum band positions and EPR parameters (g factors, g(parallel to), g(perpendicular to) and zero-field splitting D) by diagonalizing the complete energy matrix of 3d(8) ions in trigonal symmetry, the defect structure of Ni2+ centre in alpha-LiIO3 crystal is studied. It is found that to reach the good fits of optical and EPR data between calculation and experiment, the Ni2+ ion should shift by Delta z approximate to 0.298 angstrom along C-3-axis and the O-2-ions between the Ni2+ ion and Li+ vacancy (V-Li) should be displaced away from the V-Li by Delta x approximate to 0.097 angstrom because of the electrostatic interaction. The results are discussed.
关键词:
Optical spectra;electron paramagnetic resonance;defect structure;Ni2+;alpha-LiIO3.;field;ions;cr3+;temperature;parameters;epr;pressure;model;liio3
