scholarly journals MWP-fit: a program for multiple whole-profile fitting of diffraction peak profiles byabinitiotheoretical functions

2001 ◽  
Vol 34 (5) ◽  
pp. 669-676 ◽  
Author(s):  
G. Ribárik ◽  
T. Ungár ◽  
J. Gubicza
Keyword(s):  
Size Distribution ◽  
Fourier Transforms ◽  
Diffraction Peak ◽  
Hexagonal Crystal ◽  
Crystal Lattices ◽  
Microstructural Parameters ◽  
Fitting Procedure ◽  
Profile Fitting ◽  
Log Normal

A computer program has been developed for the determination of microstructural parameters from diffraction profiles of materials with cubic or hexagonal crystal lattices. The measured profiles or their Fourier transforms are fitted byabinitiotheoretical functions for size and strain broadening. In the calculation of the theoretical functions, it is assumed that the crystallites have log-normal size distribution and that the strain is caused by dislocations. Strain and size anisotropy are taken into account by the dislocation contrast factors and the ellipticity of the crystallites. The fitting procedure provides the median and the variance of the size distribution and the ellipticity of the crystallites, and the density and arrangement of the dislocations. The efficiency of the program is illustrated by examples of severely deformed copper and ball-milled lead sulfide specimens.

Hydriding kinetics of ball-milled nanocrystalline MgH2 powders

2007 ◽  
Vol 22 (11) ◽  
pp. 3144-3151 ◽  
Author(s):  
Á. Révész ◽  
D. Fátay ◽  
T. Spassov
Keyword(s):  
Grain Size ◽  
Size Distribution ◽  
Size Dependence ◽  
Nanocrystalline Powders ◽  
Fitting Procedure ◽  
Profile Fitting ◽  
Log Normal ◽  
Reaction Constants ◽  
Semiempirical Models ◽  
Kinetics Of

The kinetics of hydride formation and decomposition described by semiempirical models generally do not involve particle and grain-size dependence. However, ball-milled nanocrystalline powders usually exhibit log-normal grain-size and particle-size distribution. Considering size dependence, a total reacted function for a multiparticle system has been developed. We show that the shape of the measured reaction fraction curves do not determine unambiguously the rate-controlling mechanism of hydrogen sorption, since the kinetics are strongly affected by the microstructure. With the application the convolutional multiple whole profile fitting procedure for nanocrystalline MgH2, the parameters, e.g., the median and variance of the log-normal grain-size distribution have been determined. Taking these values into account, the reaction constants corresponding to different sorption states are considerably modified compared with values obtained from classical single-particle models.

Estimation and fingerprinting of the size distribution of non-interacting spherical particles from small-angle scattering data

2021 ◽  
Vol 54 (5) ◽  
Author(s):  
Debasis Sen ◽  
Ashwani Kumar ◽  
Avik Das ◽  
Jitendra Bahadur
Keyword(s):  
Size Distribution ◽  
Small Angle ◽  
Colloidal Particles ◽  
Nonlinear Least Squares ◽  
Small Angle Scattering ◽  
Spherical Particles ◽  
Scattering Data ◽  
Fitting Procedure ◽  
Angle Scattering ◽  
Log Normal

A new method to estimate the size distribution of non-interacting colloidal particles from small-angle scattering data is presented. The method demonstrates that the distribution can be efficiently retrieved through features of the scattering data when plotted in the Porod representation, thus avoiding the standard fitting procedure of nonlinear least squares. The present approach is elaborated using log-normal and Weibull distributions. The method can differentiate whether the distribution actually follows the functionality of either of these two distributions, unlike the standard fitting procedure which requires a prior assumption of the functionality of the distribution. After validation with various simulated scattering profiles, the formalism is used to estimate the size distribution from experimental small-angle X-ray scattering data from two different dilute dispersions of silica. At present the method is limited to monomodal distributions of dilute spherical particles only.

Processing of Ultrafine Grained Cu-30%Zn Alloy through Severe Plastic Deformation Using Accumulative Roll Bonding

2010 ◽  
Vol 667-669 ◽  
pp. 571-576
Author(s):  
Sayed Ghafar Hashemi ◽  
Beitallah Eghbali
Keyword(s):  
Dislocation Density ◽  
Size Distribution ◽  
Profile Analysis ◽  
X Ray Diffraction ◽  
X Ray ◽  
Ultrafine Grained ◽  
Average Contrast ◽  
Log Normal ◽  
Zn Alloy

In the present research, the microstructural features of ultrafine grained Cu-30 Zn alloy via ARB at room temperature were investigated by X-ray diffraction peak profile analysis. The character of dislocations was determined by analyzing the dislocation contrast factors. The average contrast factors for the different reflections obtained by determination of the type of dislocations and Burgers vectors in crystals. Also, using the modified Williamson–Hall and Warren–Averbach procedure size parameters, the effective outer cut-off radius and density of dislocations were determined. Assuming that the grain size distribution is log-normal, the median and the variance of the size distribution of sub grains were obtained. It was found that the crystallite size is reduced substantially, while the dislocation density increases up to 2 cycles of ARB. After 2nd cycle, dislocation density decreases. This is attributed to the occurrence of dynamic restoration process which takes place during next ARB cycles.

Profile Fitting by the Interference Function

1991 ◽  
Vol 35 (A) ◽  
pp. 577-584
Author(s):  
Luca Lutterotti ◽  
Paolo Scardi
Keyword(s):  
Crystallite Size ◽  
Size Distribution ◽  
Interplanar Distance ◽  
Single Peak ◽  
Bimodal Size Distribution ◽  
Interference Function ◽  
Fitting Procedure ◽  
Profile Fitting ◽  
Diffraction Angle ◽  
Number Of Cells

AbstractOn the basis of the “column-like” powder model of Warren and Averbach, a profile fitting procedure was devised to obtain microstructural disorder parameters. The interference functionwhere d is the interplanar distance, λ the wavelength, θ the diffraction angle and N the number of cells within a column, was used to model experimental profiles taking into account the column-like crystallite size and r.m.s. strain distributions. The procedure can be applied both to single peak and to two or more peaks of multiple order of reflection. The method was tested on several samples, also having a bimodal size distribution, and the results compared with those obtained by the well-established Warren-Averbach analysis.

Hydrogen Storage in Nanocrystalline Mg Powders

2008 ◽  
Vol 589 ◽  
pp. 149-154
Author(s):  
Ádám Révész
Keyword(s):  
Grain Size ◽  
Reaction Kinetics ◽  
Size Distribution ◽  
Hydrogen Desorption ◽  
Hydrogen Atmosphere ◽  
Reaction Function ◽  
Microstructural Parameters ◽  
Milling Duration ◽  
Log Normal ◽  
Kinetics Of

Conventional polycrystalline MgH2 was ball-milled under hydrogen atmosphere Afterwards 2 mol % pre-milled Nb2O5 (∼ 40 nm) was added to the MgH2 as a catalyst and the milling was continued. The effect of the milling duration and microstructure on the temperature of hydrogen desorption and on the dehydriding kinetics of the ball-milled MgH2 + Nb2O5 powders was analyzed. In addition, taking into account the microstructural parameters, e.g. the median and variance of the log-normal grain-size distribution of MgH2 powders, the reaction kinetics can be modeled by introducing a multi-particle reaction function.

Determination of particle size distribution in an Fe2O3-based catalyst using magnetometry and x-ray diffraction

1992 ◽  
Vol 7 (7) ◽  
pp. 1856-1860 ◽  
Author(s):  
Manjula M. Ibrahim ◽  
Jianmin Zhao ◽  
Mohindar S. Seehra
Keyword(s):  
Particle Size ◽  
Particle Size Distribution ◽  
Size Distribution ◽  
Line Broadening ◽  
X Ray Diffraction ◽  
X Ray ◽  
Mössbauer Measurements ◽  
Log Normal ◽  
Log Normal Distribution

In this paper, the techniques of SQUID magnetometry and line broadening in x-ray diffraction are employed for determining an important parameter for catalysts, viz. the particle size distribution. Magnetization versus temperature (5 K–400 K) and magnetization versus field (up to 55 kOe) data are reported for an α–Fe2O3 based catalyst. After determining the region of superparamagnetism, the distribution function f(r) is determined assuming a log normal distribution and Langevin paramagnetism of superparamagnetic particles. The distribution is found to be fairly symmetric with center near 65 Å and range of 35 to 115 Å. From line-broadening of Bragg peaks in x-ray diffraction, particle radii varying between 75 Å and 110 Å are obtained. These results are compared with the reported Mössbauer measurements of Huffman et al. on the same sample.

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