L. Dong
,
L.G. Zhou
,
H. Ding and C.B. Zhang(Laboratory of Atomic Imaging of Solids
,
Institute of Metal Research
,
The Chinese Academy of Sciences
,
Shenyang 110015
,
China)(Departmeot of Material Science
,
Northeastern University
,
Shenyang 110006
,
China)
金属学报(英文版)
The ebct of hydrogenation-dehydrogenation on the microstructure of forping Ti-24Al14Nb-3V-0.5MO alloy was investigated by TEM and X-ray ddection. The resultsshowed that the microstructure consists of O and B2 phases as received materials, and tmoprmation of B2 phase to O phase can be eNctively promoted 6y hydrogenation. The lamellate γ hydride was found in O phase with more hydmpen content, and this γ hydride could be decomposed by dehydmpenation treatment. The sole fine Ophase could be obtained 6y hydmpenation-dehydmpenation treatment, and two possible mechanisms for the microstructure improvetnent have been discussed on the basis of experimental results.
关键词:
Ti_3Al-based alloy
,
null
,
null
Semiconductor Science and Technology
From the high-order perturbation formulae based on the two spin-orbit coupling parameter model, the electron paramagnetic resonance (EPR) parameters D, Deltag(//) (= g(//) - g(s)) and Deltag(perpendicular to) (= g(perpendicular to) - g(s)) for four Co2+ centres in Co2+-doped cubic (3C), hexagonal (2H) and 4H polytype ZnS crystals are studied using the parameters related to the structural data and the optical spectra of the studied systems. From the studies, the defect structures (characterized by the atomic positions, i.e. the relative atomic displacements delta(i) and epsilon(i) of Co2+ and S2- from the ideal positions) for Co2+ in 2H- and 4H-ZnS are obtained (for 3C-ZnS, Co2+ in the regular cubic position). The EPR parameters of various Co2+ centres in 3C-, 2H- and 4H-ZnS are also reasonably explained.
关键词:
superposition model;polymorphic zns;crystal;semiconductors;spectra;site
Journal of the American Ceramic Society
A HfAlC composite composed of HfAl4C4 and Hf2Al4C5 was successfully synthesized by the hot-pressing method. The atomic-scale microstructure was investigated through high-resolution transmission electron microscopy (TEM) and Z-contrast scanning transmission electron microscopy (STEM) imaging. The TEM observations revealed that the HfAlC grains had elongated morphologies. There was no amorphous phase in the grain boundary. The microstructure of the composite was characterized by the stacking faults resulted from the insertion of (Al4C3) units, which led to the formation of a new phase Hf4Al12C13 and intergrowth structure between HfAl4C4 and Hf2Al4C5. In addition, the antiphase grain boundary in the ternary-layered ceramics was first observed and the formation mechanism was discussed.
关键词:
transmission electron-microscope;theoretical elastic property;crystal-structure;grain-boundaries;ternary ceramics;carbides;oxidation;zr2al3c4;zr3al3c5;antiphase
J.L. Huang
,
X.G. Cao
,
E. Sukedai
,
S. Yamasaki
,
and H.C.Gu(Department of Materials Engineering
,
Luoyang Institute of Technology
,
Luoyang 471039
,
China)(Department of Mechanical Engineering
,
Okayama University of Science
,
1-1 Ridai-Cho
,
Okayama City
,
Okayma 700
,
Japan)(Institute of Materials Science and Engineering
,
Xi'an Jiaotong University
,
Xi'an 710049
,
China)
金属学报(英文版)
The direct observations of the atomic arrangements in both conventional furnace annealed and electric pulse rapid annealed Fe78B13Si9 amorphous alloy have been conducted by the lattice imaging technique in a higt resolution electron microscope. The results showed that the embrittlement of the alloy was related to the extent of atomic rearrangements during the annealing processes. The embrittlement of the alloy after 1hour conventional furnace annealing at about 270℃ is caused by the sufficient atomic rearrangements which are characterized by the growth of some bct Fe3B-like atomic short range ordering regions already existed in the as-quenched structure. Electric pulse rapid annealing can effectively retard the above-mentioned atomic rearrangements and thus restrain the embrittlement. The embrittlement only occurs when certain amount of bcc α-Fe nanocrystals are precipitated in the amorphous matrix during electric pulse rapid annealing.
关键词:
Fe_(78)B_(13)Si_9 amorphous alloy
,
null
,
null
,
null
Acta Materialia
The microstructures of bulk Zr(2)Al(3)C(4) and Zr(3)Al(3)C(5) ceramics have been investigated using transmission electron microscopy and scanning transmission electron microscopy. These two carbides were determined to have a point group 6/mmm and a space group P6(3)/mmc using selected-area electron diffraction and convergent beam electron diffraction. The atomic-scale microstructures of Zr(2)Al(3)C(4) and Zr(3)Al(3)C(5) were investigated through high-resolution imaging and Z-contrast imaging. Furthermore, intergrowth between Zr(2)Al(3)C(4) and Zr(3)Al(3)C(5) was identified. Stacking faults in Zr(3)Al(3)C(5) were found to result from the insertion of an additional Zr-C layer. Cubic ZrC was occasionally identified to be incorporated in elongated Zr3Al3C5 grains. In addition, Al may induce a twinned ZrC structure and lead to the formation of ternary zirconium aluminum carbides. (c) 2006 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
关键词:
TEM;carbides;layered structures;STEM;transmission electron-microscope;mechanical-properties;crystal-structure;ternary-systems;behavior;ti3sic2;al;carbide;ti2alc;phases
Composites Science and Technology
The thermal expansion of the reference sample, pure copper film in the temperature range of - 120 to 200 degrees C was first measured using the newly improved CCD imaging technique for measurement of thermal expansion of thin films. The results showed good accordance with the recommended data given by TPRC (Thermophysical Properties Research Centre, USA) handbook, verifying that the present method is valid for measuring thermal expansion of films. Then, the thermal expansion TE (Delta L/L-0) of silica/polyimide composite films with different SiO2 fractions i.e. 0, 1, 3, 5, 8, 10 and 15 wt% prepared using the sol-gel technique was obtained in the temperature range of - 120 to 200 degrees C using the newly improved CCD method and the differential coefficient thermal expansion (CTE) can be deduced by Delta L/L-0 similar to temperature relation. The CTE Of SiO2/PI Composite films decreased with the increase Of SiO2 content and the decrease of temperature. An empirical equation of CTE of SiO2/PI with SiO2, content has been given in this paper. (C) 2007 Elsevier Ltd. All rights reserved.
关键词:
silica/polyimide composite film;thermal expansion;CCD imaging;technique;low temperature;elevated temperature;mechanical-properties;cryogenic properties;nanocomposite films;polyimide films;low-temperature;silica
刘奕新
,
杨书全
,
张丹丹
,
黎光旭
,
韦文楼
,
郭进
无机材料学报
doi:10.3724/SP.J.1077.2009.00813
利用机械合金化方法制备了Li-N-H络合氢化物,并研究B、C作为催化剂对其储氢性能的影响.结果表明:LiNH2、Li2NH为Li-N-H络合氢化物的主要储氢相,随B的加入,储氢相的非晶化程度提高.虽然B、C的添加均使储氢量下降,但n(B):n(C)=1:2的混合添加提高了有效储氢量,同时也提高吸放氢动力学性能;B的添加可有效降低可逆吸放氢温度,适当增加球磨时间,有利于提高可逆吸放氢量.
关键词:
Li-N-H络合氢化物
,
储氧性能
,
机械合金化
Physica B-Condensed Matter
First-principles calculations based on DFT-GGA method have been performed on Rb adsorption on C(100)(2 x 1) surface. The optimized geometries, adsorption energies have been obtained and the preferred binding sites have been determined for the coverage (Theta) of one monolayer and half a monolayer. The calculated results have shown that Rb adsorbate preferred to occupy valley-bridge sites at the coverage of 0.5 ML. At higher coverage of 1 ML, two Rb adsorbates were found to reside in pedestal site and valley-bridge site, respectively. It was also found that when Rb was adsorbed on C(100)(2 x 1) surface the work function decreases linearly with increasing coverage and reaches a minimum at Theta = 0.5 ML, at higher coverage, the work function is increased again, which may be caused by depolarization effect of the adsorbate: The adsorption behavior was found to be similar to that of Rb on Si(001) and Ge(001) surface. (c) 2006 Elsevier B.V. All rights reserved.
关键词:
first-principles calculations;diamond;rubidium;work function;diamond c(100) surfaces;ab-initio;si(001)2x1-k surface;adsorbed;states;x-1) surface;double-layer;adsorption;potassium;metals;pseudopotentials
Journal of Spacecraft and Rockets
An amorphous silicon carbonitride (Si(1-x-y)C(x)N(y), x = 0.43, y = 0.31) coating was deposited on polyimide substrate using the magnetron-sputtering method. Exposure tests of the coated polyimide in atomic oxygen beam and vacuum ultraviolet radiation were performed in a ground-based simulator. Erosion kinetics measurements indicated that the erosion yield of the Si(0.26)C(0.43)N(0.31) coating was about 1.5 x and 1.8 x 10(-26) cm(3) /a tom during exposure in single atomic oxygen beam, simultaneous atomic oxygen beam, and vacuum ultraviolet radiation, respectively. These values were 2 orders of magnitude lower than that of bare polyimide substrate. Scanning electron and atomic force microscopy, X-ray photoelectron spectrometer, and Fourier transformed infrared spectroscopy investigation indicated that during exposures, an oxide-rich layer composed of SiO(2) and minor Si-C-O formed on the surface of the Si(0.26)C(0.43)N(0.31) coating, which was the main reason for the excellent resistance to the attacks of atomic oxygen. Moreover, vacuum ultraviolet radiation could promote the breakage of chemical bonds with low binding energy, such as C-N, C = N, and C-C, and enhance atomic oxygen erosion rate slightly.
关键词:
atomic oxygen;films;radiation;polymers;beam;sicn
