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排序方式: 共有231条查询结果,搜索用时 875 毫秒
81.
D. Valiev O. Khasanov E. Dvilis S. Stepanov E. Polisadova V. Paygin 《Ceramics International》2018,44(17):20768-20773
MgAl2O4 ceramics doped with rare earth ions (Eu2+ and Ce3+ ions) were fabricated by spark plasma sintering technique. A complex characterization of the crystalline and defect structure of the ceramic by XRD was carried out. Absorption, excitation, photo- and cathodoluminescence spectra were studied. The photoluminescence spectrum shifts to the blue region with a maximum at λem =?475?nm for the MAS:0.1Ce ceramics. The nature of this luminescence can be caused by the radiative transitions in the cerium ion 5d–4f. The emission spectrum of MAS:0.1Eu has a “green” band emission in range of 400–700?nm centered around 500?nm, which can be ascribed to the allowed 4f65d1→4f7 (5d–4f) transition of Eu2+. In the millisecond time range, simultaneously with the emission of the complex host centers, the impurity luminescence bands of the chromium ion are recorded. It was shown that cathodoluminescence spectra in nanosecond time range can be decomposed into several emission bands at 2.72, 3.01, 3.37, 3.63–3.82?eV caused by F-type centers. It was demonstrated that the Eu2+ and Ce3+ ions lead to change the intensity ratio of the luminescence bands. The luminescence decay kinetics of synthesized spinel ceramics in nano- and millisecond time range were investigated in detail. 相似文献
82.
Alberto Moreira Jorge Jr. Egor Prokofiev Maria Regina Martins Triques Virginie Roche Walter José Botta Claudio Shyinti Kiminami Georgy I. Raab Ruslan Z. Valiev Terence G. Langdon 《International Journal of Hydrogen Energy》2017,42(34):21822-21831
This investigation was conducted to evaluate the effect of cold rolling on the structure and hydrogen properties of two magnesium alloys, AZ91 and AM60D, after processing by equal-channel angular pressing (ECAP). The results show that the use of cold rolling after ECAP significantly increases the preferential texture for hydrogenation and increases the potential for the use of these alloys as hydrogen storage materials. The ECAP was performed through two different numbers of passes in order to give different grain sizes and both materials were subsequently cold-rolled through the same numbers of passes for a comparison of the hydrogenation absorption. It is shown that the hydriding properties are enhanced by an (0001) texture which improves the kinetics primarily in the initial stages of hydrogenation. The results demonstrate that optimum sorption properties may be acquired through a combination of fine grains and appropriate texture. 相似文献
83.
Specific features of Eu~(3+) and Tb~(3+) magnetooptics in gadolinium-gallium garnet (Gd_3Ga_5O_(12))
Uygun V. Valiev John B. Gruber 付德君 Vasiliy O. Pelenovich Gary W. Burdick Mariya E. Malysheva 《中国稀土学报(英文版)》2011,(8)
We reported magnetooptical properties of Eu3+(4f(6)) and Tb3+(4f(8)) in single crystals of Gd3Ga5O12 (GGG), Y3Ga5O12 (YGG), and Eu3+(4f(6)) in Eu3Ga5O12 (EuGG) for both ions occupying sites of D2 symmetry in the garnet structure. Absorption, luminescence, and magnetic circular polarization of luminescence (MCPL) spectra of Tb3+ in GGG and YGG and absorption and magnetic circular dichroism (MCD) of Eu3+ in EuGG were studied. The data were obtained at 85 K and room temperature (RT). Magnetic susceptibility of... 相似文献
84.
Ruslan Z. Valiev Terence G. Langdon 《Metallurgical and Materials Transactions A》2011,42(10):2942-2951
The processes of equal-channel angular pressing (ECAP) and high-pressure torsion (HPT) are now established for the fabrication
of ultrafine-grained metals having superior properties by comparison with their coarse-grained counterparts. This article
examines the recent developments designed to improve the processing technology of ECAP and HPT and to establish these techniques
as viable procedures for use in industrial applications. Based on these developments, it is reasonable to anticipate these
processing procedures will experience increasing use in the fabrication of commercial products. 相似文献
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88.
B. Radiguet A. Etienne P. Pareige X. Sauvage R. Valiev 《Journal of Materials Science》2008,43(23-24):7338-7343
In order to get information about radiation resistance of ultrafine grained austenitic stainless steels, a 316 steel was deformed by high pressure torsion. The mean diameter of the grain after deformation was 40 nm. This material was annealed at 350 °C for 24 h or irradiated with 160 keV iron ions at 350 °C. Changes in the microstructure during annealing or irradiation were characterised by transmission electron microscopy (grain size) and laser assisted tomographic atom probe (solute distribution). Results indicate that this annealing has no influence on the grain size whereas the grain diameter increases under irradiation. Concerning the solute distribution, atom probe investigations show evidence of radiation-induced segregation at grain boundaries. Indeed, after irradiation, grain boundaries are enriched in nickel and silicon and depleted in chromium. On the contrary, no intragranular extended defects or precipitation are observed after irradiation. 相似文献
89.
O. A. Kogtenkova A. A. Mazilkin B. B. Straumal G. E. Abrosimova P. Zięba T. Czeppe B. Baretzky R. Z. Valiev 《Journal of Materials Science》2013,48(13):4758-4765
The structure, phase composition, and their thermal evolution were studied in case of ternary Al–Zn–Mg alloys before and after high-pressure torsion (HPT) in Bridgman anvils. The as-cast non-deformed alloys contained the fine particles of Mg32(Al,Zn)49 (τ phase), MgZn2 (η phase), AlMg4Zn11 (η′ phase), and Mg7Zn3 phases embedded in the matrix of Al-based solid solution. During heating in differential scanning calorimeter (DSC), all these phases dissolved around 148 °C. The τ nanoparticles coherent with (Al) matrix-formed instead around 222 °C. HPT of the as-cast alloys strongly refined the grains of (Al) solid solution from 500 μm to 120–150 nm. The particles of τ, η, η′, and Mg7Zn3 phases fully dissolved in the (Al) matrix. During the following DSC-heating, particles of η phase appeared and grew. Their amount became maximal around 166 °C. The growth of η phase in the fine-grained HPT-treated alloys instead of τ phase in the coarse-grained ones is explained by the shift of the (Al) + η/(Al) + η + τ/(Al) + τ lines in the Al–Zn–Mg ternary phase diagram due to the grain boundary (GB) adsorption. At 166 °C the η phase formed the continuous flat layers in numerous (Al)/(Al) GBs. This corresponds to the complete GB wetting by the η phase. Other (Al)/(Al) GBs contain separated lenticular η particles (incomplete GB wetting). Increasing the temperature from 166 to 320 °C led to the disappearance of the completely wetted (Al)/(Al) GBs. In other words, the transition from complete to the incomplete wetting of (Al)/(Al) GBs by the η phase proceeds between 166 °C and 320 °C. 相似文献
90.
Davydov S. Ya. Valiev N. G. Shestakov V. S. Domozhirov D. V. 《Refractories and Industrial Ceramics》2019,60(2):139-141
Refractories and Industrial Ceramics - Sources of powdered waste in processing clay and other ceramic raw materials for crushing and screening complexes are crushers, screens, and transfer units. A... 相似文献