The microstructure of two kinds of self-made PAN-based high-modulus carbon fibers (HMCF-1, HMCF-2) was studied by scanning electron microscopy (SEM), Raman spectroscopy, X-ray diffraction (XRD) and high resolution tra...
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ISBN:
(纸本)9783037851234
The microstructure of two kinds of self-made PAN-based high-modulus carbon fibers (HMCF-1, HMCF-2) was studied by scanning electron microscopy (SEM), Raman spectroscopy, X-ray diffraction (XRD) and high resolution transmission electron microscopy (HRTEM), and was compared with that of T800 and M55J. The correlation of XRD and HRTEM in terms of graphite crystallite sizes and interlayer spacing of graphite layer was also investigated. The results show that the diameters of T800, HMCF-1 and HMCF-2 are almost the same (similar to 5.20 mu m) and all of them are lager than that of M55J (similar to 4.86 mu m). The crystal sizes and the degree of graphitization are in the order of HMCF-2>HMCF-1>M55J>T800, while the regularity of the lattice fringes of HMCF-2 is better than those of others.
Different thickness of polycrystalline ZnTe films have been deposited onto glass substrates at room temperature by vacuum evaporation technique. The structural characteristics studied by X-ray diffraction (XRD) showed...
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Different thickness of polycrystalline ZnTe films have been deposited onto glass substrates at room temperature by vacuum evaporation technique. The structural characteristics studied by X-ray diffraction (XRD) showed that the films are polycrystalline and have a zinc blende (cubic) structure. The calculated microstructure parameters revealed that the crystallite size increases and microstrain decreases with increasing film thickness. The transmittance and reflectance have been measured at normal and near normal incidence, respectively, in the spectral range 400-2500 nm. For ZnTe films of different thicknesses, the dependence of absorption coefficient, a on the photon energy showed the occurrence of a direct transition with band gap energy E-g(opt) = 2.21 +/- 0.01 eV (For ZnTe films of different thicknesses) confirming the independency of deduced energy gap on film thickness. The refractive indices have been evaluated in terms of envelope method, which has been suggested by Swanepoul in the transparent region. The refractive index could be extrapolated by Cauchy dispersion relationship over the whole spectra range, which extended from 400 to 2500 nm. It was observed that the refractive index, n increased upon increasing the film thickness up to 508 nm, lying within the experimental error for further increases in film thickness. (C) 2009 Elsevier B.V. All rights reserved.
X-ray tools are being powerful methods for qualitative and quantitative analyses of nanocrystalline materials This work is an overview of detailed X-ray investigations relative to microstructural studies applied for a...
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X-ray tools are being powerful methods for qualitative and quantitative analyses of nanocrystalline materials This work is an overview of detailed X-ray investigations relative to microstructural studies applied for a refined binary Al-based alloys thin films system as samples deposited on glass substrates. Energy dispersive analysis of X-ray (EDAX), X-ray diffraction (XRD) and transmission electron microscopy (TEM) methods were used to determine the chemical composition, the microstructure parameters and the solubility of copper in aluminum.
The snow cover model SNOWPACK includes a detailed model of snow microstructure and metamorphism. In SNOWPACK, the complex texture of snow is described using the four primary microstructure parameters: grain size, bond...
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The snow cover model SNOWPACK includes a detailed model of snow microstructure and metamorphism. In SNOWPACK, the complex texture of snow is described using the four primary microstructure parameters: grain size, bond size, dendricity and sphericity. For each parameter, rate equations are developed that predict the development in time as a function of the environmental conditions. The rate equations are based on theoretical considerations such as mixture theory and on empirical relations. With a classification scheme, the conventional snow grain types are predicted on the basis of those parameters. The approach to link the bulk constitutive properties, viscosity and thermal conductivity to microstructure parameters is novel to the field of snow cover modeling. Expanding on existing knowledge on microstructure-based viscosity and thermal conductivity, a complete description of those quantities applicable to the seasonal snow cover is presented. This includes the strong coupling between physical processes in snow: The bond size, which changes not only through metamorphic processes but also through the process of pressure sintering (included in our viscosity formulation), is at the same time the single most important parameter for snow viscosity and thermal conductivity. Laboratory results are used to illustrate the performance of the formulations presented. The numerical implementation is treated in the companion paper Part I. A more complete evaluation for the entire model is found in the companion paper Part III. (C) 2002 Elsevier Science B.V. All rights reserved.
It is well known that snow texture affects many properties of the snowpack. For example, new snow, layers of either small rounded grains or larger faceted and cup-shaped crystals, as well as wet snow, all show differe...
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It is well known that snow texture affects many properties of the snowpack. For example, new snow, layers of either small rounded grains or larger faceted and cup-shaped crystals, as well as wet snow, all show different viscous behaviors. The most direct approach to include such effects in snow-cover models is to formulate processes and properties in terms of microstructure parameters such as grain and bond size, coordination number, bond neck length, etc. Such an approach was taken for the Swiss snow-cover model SNOWPACK. Because the interdependence of properties and processes is inherent to a microstructure-based formalism, great care must be taken to properly adjust the parameters involved. Using both laboratory and field experiments, it is shown how a consistent set of parameters may be found to account for growth processes, as well as for conductivity and viscosity. (C) 2001 Elsevier Science B.V. All rights reserved.
The present work deals with the dehydration transformation of Ca-montmorillonite in the temperature range 300-500 degrees C. Thermal, infrared (IR), and X-ray diffraction (XRD) analyses were used to describe the therm...
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The present work deals with the dehydration transformation of Ca-montmorillonite in the temperature range 300-500 degrees C. Thermal, infrared (IR), and X-ray diffraction (XRD) analyses were used to describe the thermal transformation. The microstructural and layer disorder parameters like crystallite size, r.m.s. strain ([e(2)](1/2)), variation of interlayer spacing (g), and proportion of planes which were affected by the defect (gamma), have all been calculated from the (001) basal reflection using the method of variance and Fourier line shape analysis. These investigations revealed that sample underwent transformation from hydrated phase to dehydrated phase at 200 degrees C, and as a consequence, its basal spacing collapsed from 16.02 Angstrom (30 degrees C) to around 10 Angstrom (200 degrees C). This transformation occurred through a wide range of temperature, i.e. within the range 120 degrees-200 degrees C. The crystallite size was maximum at room temperature (30 degrees C), however, the size decreased with increasing temperature in the hydrated phase, whereas the size increased with increasing temperature for the dehydrated phase. The g, gamma and [e(2)](1/2) of the hydrated and the dehydrated phase increased and decreased, respectively with increase of heating temperature.
The wide angle X-ray diffraction on W0.65Mo5-xTaxSe2 (0 less than or equal to x less than or equal to 0.35) compounds have been used for calculation of the crystallite size by method of variance and Fourier technique ...
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The wide angle X-ray diffraction on W0.65Mo5-xTaxSe2 (0 less than or equal to x less than or equal to 0.35) compounds have been used for calculation of the crystallite size by method of variance and Fourier technique and for microstructural parameters purposes. The crystallite size showed the decreasing trend with increasing composition up to x=0.15 and after that it increased sharply. On the contrary, mean fractional change in interlayer spacing, fractions of the planes affected by defects, dislocation density, and root mean square strain showed the opposite trend. The crystallite size anisotropy and stacking fault probability showed 1:1 correspondence in their variation with composition. The radial distribution analysis have also been employed to find out the information about the inter atomic distances, coupling constants and mean square displacements for different pairs of atoms. These results have been interpreted in terms of difference in packing of layers in these compounds.
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