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991.
Suppressing crystallization of a metallic melt results in a disordered solid, also known as a metallic glass. One may conclude that a metallic glass is free of defined structural length scales beyond some atomic‐scale value that characterizes short‐ and medium‐range order. While it is well known from atomistic modeling that a metallic glass is structurally heterogeneous, heterogeneities at such a small length scale can hardly be resolved in experiments. This review highlights experimental insights into elastic fluctuations and structural heterogeneities that emerge at scales between a few nanometers and tens to hundreds of micrometers. It distinguishes between structural and property fluctuations in as‐cast metallic glasses, and heterogeneities introduced by elastic and inhomogeneous plastic deformation. As‐cast glasses reveal elastic fluctuations across 3 orders of magnitude, suggesting a hierarchy of length scales that can be tuned by thermomechanical processing. Similarly, nanoscale strain localization into shear bands drives the formation of structural and elastic heterogeneities at both the nano‐ and the microscale. It is proposed that both types of fluctuations will allow one to quantitatively define structure–property relationships via measurable length scales—an approach that has largely contributed to the engineering success of crystalline metals. 相似文献
992.
Different
methods have been used by various workers to determine the activation energy
of thermal crystallization (Ec)
in chalcogenide glasses using non-isothermal DSC data. In the present work,
the crystallization kinetics of two important binary alloys Se80Te20
and Se80In20 is studied using
non-isothermal DSC data. DSC scans of these alloys have been taken at five
different heating rates. The values of activation energy of crystallization
(Ec) have been determined
by four different methods, i.e., Kissinger's method, Matusita-Sakka
method, Augis-Bennett's method and Ozawa's method, have
been used to calculate Ec.
The results obtained have been compared with each other to see the effect
of using different methods in the determination of Ec. 相似文献
993.
J. Bendisch 《Journal of statistical physics》1992,67(5-6):1209-1217
For square, triangular, and for hexagonal lattices there is numerical and theoretical support that the ground-state thresholdp
c
between ferro- and paramagnetism in random 2D Ising ±J models, withp as the concentration of antiferromagnetic bonds, is identical top
*which is characterized by minimal matching properties of frustrated plaquettes. From square lattices of size 100×100 we have got pc,sq<0.117 by simulations which produced average groundstate magnetizations per spin by means of exact minimal matchings. Moreover, from the squareL×L-lattices treated (L = 10, 20, 50, 100) we obtained the estimatep
c,sq
0.1 which is in agreement with the Grinstein estimatep
c,sq
0.099 andp
c,sq
0.105 by Freund and Grassberger. 相似文献
994.
Vinnik M. I. Vinnik R. M. Grinev V. E. Piljugaizeva S. V. 《Russian Chemical Bulletin》1993,42(5):843-850
The formation of linear epoxy-amine polymers has been studied using the calorimetry method. Catenate polymer (olympic gel) is produced in the course of linear polycondensation of aniline with resorcinol diglycidyl ether. A relation was found to exist between the kinetics of the processes and the glassy state transition temperatures for the samples obtained in the reaction. A model of glassy state formation is proposed, In accordance with latter the polymeric glasses are considered to have the dissipative structure resulting from a kinetically controlled phase transition.Deceased April 8, 1991.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 889–895, May, 1993.The authors are grateful to Prof. Z. Rigbi (Izrael) for help and support and to V. A. Rosniatovskii for participation in the discussion of results 相似文献
995.
E. Cordoncillo J.B. Carda M.A. Tena G. Monrós P. Escribano 《Journal of Sol-Gel Science and Technology》1997,8(1-3):1043-1047
The optical properties of extremely small particles of semiconductor materials provide a sensitive probe of the band structure
in the materials. The Sol-Gel process has been applied successfully to the preparation of small particle-size CdS-doped silica
glasses such that quantum size effects are significant. Transparent and colorless gels were prepared through the hydrolysis
of a complex solution of Si(OC2H5)4, (CH3)2SO, Zn(CH3COO)2·2H2O and Cd(CH3COO)2·2H2O. These gels were heated at 350, 500 and 750°C. The thermal treatments of samples were established by TDA/TGA analysis. By
means of shift in optical absorption spectra, quantum size effects could be inferred in glasses containing these calcogenide
microcrystals. 相似文献
996.
M. Vardelle C. Trassy A. Vardelle P. Fauchais 《Plasma Chemistry and Plasma Processing》1991,11(2):185-201
An experimental study of the vaporization of metallic and ceramic particles in a thermal do plasma jet has been initiated and two series of experiments have been performed: (1) measurement of the vapor concentration within the plasma jet by absorption spectroscopy. (2) Investigation of the vapor cloud surrounding a single particle in flight by emission spectroscopy. The temperature within this cloud is determined by the intensity ratio of two lines which are simultaneously measured. The cloud radius is deduced /torn measurement of the particle velocity by laser doppler anemometry, and the vapor concentration is calculated from the line intensity profile, once the temperature is known. Results on iron and alumina particles injected in argon or argon-hydrogen plasma jets are given and discussed. 相似文献
997.
HMCM‐22 catalysts modified with La2O3 (5% La) and MgO (≈0.87% Mg) were prepared respectively by impregnation method, and were characterized by scanning electron microscopy, X‐ray diffraction, N2 physical adsorption‐desorption and temperature‐programmed desorption of NH3. The effect of supported metallic oxides (La2O3, MgO) on catalytic performance in xylene isomerization of C8 aromatics (ethylbenzene, m‐xylene and o‐xylene) was investigated in detail. The experimental results showed that 5% La/HMCM‐22 catalyst had higher isomerization activity and stronger shape‐selectivity than 0.87% Mg/HMCM‐22 catalyst, owing to its more acid sites and smaller pore size. And the loading amount of La was optimized to be about 7%. Moreover, supporting metal over 7% La/HMCM‐22, respectively with 0.3% Pt, 3% Ni and 3% Mo, was carried out to prepare bifunctional isomerization catalysts. In comparison, 3% Mo/7% La/HMCM‐22 showed the best catalytic performance with both high activity and high selectivity, with the low hydrocracking of m‐xylene and o‐xylene. Besides, the optimal reaction conditions were found: 340°C, 1.5 MPa H2, WHSV 4 h?1 and H2/C8 4 mol/mol. Under the above conditions, ethylbenzene conversion was up to 20%, para‐selectivity was over 23% with low xylene loss of 2.9%. 相似文献
998.
Enhancing Charge Separation in Metallic Photocatalysts: A Case Study of the Conducting Molybdenum Dioxide
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Zhuofeng Hu Gang Liu Xingqiu Chen Zhurui Shen Jimmy C. Yu 《Advanced functional materials》2016,26(25):4445-4455
A new visible‐light responsive metallic photocatalyst, nanostructured MoO2, has been discovered. The metallic nature of MoO2 is confirmed by valance X‐ray photoelectron spectroscopy spectrum and theoretical calculations. However, MoO2 itself shows only moderate activity due to the serious charge recombination, a general disadvantage of metallic photocatalysts. The findings suggest that its effective charge diffusion length Lp is smaller than 1.0 nm while the separation efficiency ηsep is less than 10%. Therefore, only the periphery of the metallic MoO2 can effectively contribute to photocatalysis. This limitation is overcome by integrating MoO2 in a hydrothermal carbonation carbon (HTCC) matrix (mainly contains semiconductive polyfuran). This simple chemical modification brings two advantages: (i) an internal electric field is formed at the interface between MoO2 and HTCC due to their appropriate band alignment; (ii) the nanostructured MoO2 and the HTCC matrix are intertwined with each other intimately. Their small size and large contact area promote charge transfer, especially under the internal electric field. Therefore, the separation rate of photoexcited charge carrier in MoO2 is greatly enhanced. The activity increases by 2.4, 16.8, and 4.0 times in photocatalytic oxygen evolution, dyes degradation, and photoelectrochemicl cell, respectively. The new approach is helpful for further development of metallic photocatalysts. 相似文献
999.
Anthony Jouanin Jean Paul Hugonin Philippe Lalanne 《Advanced functional materials》2016,26(34):6215-6223
Basic design rules are disclosed for broadband light‐extraction colloidal films formed with disordered ensembles of plasmonic particles. They are derived through the numerical study of a test‐bed geometry consisting of a low‐refractive index slab in air. Albeit simple, the geometry encompasses many physically effects encountered in real light‐emitting devices, including the pronounced absorption at the peak of the nanoparticles resonance spectrum, the anisotropy of the radiation diagram of nanoparticles in waveguides and unavoidable coherent multiple interferences that ruin the predictive strength of first‐order scattering models. How we can simultaneously take advantage of (1) the shape or size of the individual nanoparticles, (2) their transverse position with respect to the guiding photonic structure, (3) their concentration, and (4) the structural topology of the disorder ensemble are illustrated. Following this approach, a threefold enhancement in the extraction efficiency can be reached as compared to a film without plasmonic particles. It is also predicted that the extraction rapidly saturates and then decreases as the nanoparticle density increases, suggesting that best performance is achieved at low concentrations. Spectrally broad and directionally random far‐field radiation diagrams are additionally reported, which do not suffer from deterministic interferential behaviors observed at particular wavelengths and directionalities with periodic light‐extraction structures. 相似文献
1000.