Hydrogen diffusion and effect of grain size on hydrogenation kinetics in magnesium hydrides

2008 ◽  
Vol 23 (2) ◽  
pp. 336-340 ◽  
Author(s):  
X. Yao ◽  
Z.H. Zhu ◽  
H.M. Cheng ◽  
G.Q. Lu
Keyword(s):  
Experimental Data ◽  
Activation Energy ◽  
Grain Size ◽  
Diffusion Coefficients ◽  
Hydrogen Diffusion ◽  
Metal Hydrides ◽  
Grain Size Effect ◽  
Temperature Dependent ◽  
Hydrogenation Kinetics ◽  
Work First

Hydrogenation and dehydrogenation of metal hydrides are of great interest because of their potential in on-board applications for hydrogen vehicles. This paper aims to study hydrogen diffusion in metal hydrides, which is generally considered to be a controlling factor of hydrogenation/dehydrogenation. The present work first calculated temperature-dependent hydrogen diffusion coefficients by a theoretical model incorporated with experimental data in a Mg-based system and accordingly the activation energy. The grain size effect on diffusion in nanoscale was also investigated.

Diffusion Coefficients of Interest for the Simulation of Heat Treatment in Rare-Earth Transition Metal Magnets

2012 ◽  
Vol 727-728 ◽  
pp. 163-168 ◽  
Author(s):  
Marcos Flavio de Campos
Keyword(s):  
Experimental Data ◽  
Heat Treatment ◽  
Activation Energy ◽  
Rare Earth ◽  
Transition Metal ◽  
Impurity Atom ◽  
Diffusion Coefficients ◽  
Arrhenius Equation ◽  
Atom Diffusion ◽  
Essential Input

In the case of the modeling of sintering and heat treatments, the diffusion coefficients are an essential input. However, experimental data in the literature about diffusion coefficients for rare-earth transition metal intermetallics is scarce. In this study, the available data concerning diffusion coefficients relevant for rare-earth transition metal magnets are reviewed and commented. Some empirical rules are discussed, for example the activation energy is affected by the size of the diffusing impurity atom. Diffusion coefficients for Dy, Nd and Fe into Nd2Fe14B are given according an Arrhenius equation D=D0exp (-Q/RT). For Dy diffusion into Nd2Fe14B, Q 315 kJ/mol and D08 . 10-4m2/s.

Quantitative Modelling of Nucleation Kinetics in Experiments for Poly-Si Growth on Sio2 by Hot-Wire Chemical Vapor Deposition

2001 ◽  
Vol 664 ◽  
Author(s):  
Maribeth Swiatek ◽  
Jason K. Holt ◽  
Harry A. Atwater
Keyword(s):  
Activation Energy ◽  
Grain Size ◽  
Chemical Vapor Deposition ◽  
Vapor Deposition ◽  
Chemical Vapor ◽  
Nucleation Density ◽  
Hot Wire ◽  
Nucleation Kinetics ◽  
Temperature Dependent ◽  
Cluster Density

ABSTRACTWe apply a rate-equation pair binding model of nucleation kinetics [1] to the nucleation of Si islands grown by hot-wire chemical vapor deposition on SiO2 substrates. Previously, we had demonstrated an increase in grain size of polycrystalline Si films with H2 dilution from 40 nm using 100 mTorr of 1% SiH4 in He to 85 nm with the addition of 20 mTorr H2. [2] This increase in grain size is attributed to atomic H etching of Si monomers rather than stable Si clusters during the early stages of nucleation, decreasing the nucleation density. Atomic force microscopy (AFM) measurements show that the nucleation density increases sublinearly with time at low coverage, implying a fast nucleation rate until a critical density is reached, after which grain growth begins. The nucleation density decreases with increasing H2 dilution (H2:SiH4), which is an effect of the etching mechanism, and with increasing temperature, due to enhanced Si monomer diffusivity on SiO2. From temperature-dependent measurements, we estimate the activation energy for surface diffusion of Si monomers on SiO2 to be 0.47 ± 0.09 eV. Simulations of the temperature-dependent supercritical cluster density lead to an estimated activation energy of 0.42 eV ± 0.01 eV and a surface diffusion coefficient prefactor of 0.1 ± 0.03 cm2/s. H2-dilution-dependent simulations of the supercritical cluster density show an approximately linear relationship between the H2 dilution and the etch rate of clusters.

scholarly journals Computer-Aided Arrhenius-Evaluation of Kinetic Data

1995 ◽  
Vol 50 (6) ◽  
pp. 549-554
Author(s):  
P. Hugo ◽  
J. Leonhardt ◽  
S. Wagner
Keyword(s):  
Experimental Data ◽  
Activation Energy ◽  
Kinetic Data ◽  
Evaluation Method ◽  
Arrhenius Law ◽  
Temperature Dependent ◽  
Dependent Part ◽  
Computer Aided ◽  
Temperature Programmed ◽  
Temperature Dependance

Abstract A new evaluation method is presented to analyse the temperature dependance of reactions with rates that can be separated into a temperature dependent and a concentration dependent part. The proposed method allows to evaluate isothermal, adiabatic, isoperibolic and temperature programmed measurements in an unified manner. To determine the activation energy an Arrhenius law but no explicite kinetic model has to be assumed. The application of the method is demonstrated using experimental data of different reactions from former investigations.

Effects of Microstructure on the Electrical Conductivity of SrCo0.8Fe0. 2O3_δ

1999 ◽  
Vol 575 ◽  
Author(s):  
K. Zhang ◽  
M. Miranova ◽  
Y. L. Yang ◽  
A. J. Jacobson ◽  
K. Salama
Keyword(s):  
Activation Energy ◽  
Electrical Conductivity ◽  
Grain Size ◽  
Size Effect ◽  
Temperature Region ◽  
Grain Size Effect ◽  
Average Grain Size ◽  
Lower Temperature ◽  
Lower Temperature Region ◽  
Test Temperature Range

ABSTRACTThe effect of microstructure on the electrical conductivity of SrCO0.8Fe0.2O3_δ (SCFO) was investigated in air using a four-point dc method. In the test temperature range of 200 to 900 °C, the electrical conductivity of this material was observed to increase with the increase of the average grain size in the lower temperature region where the conductivity increases with the increase of the temperature. The activation energy is decreased with the increase of the grain size in this region, 0.04 ± 0.004 ev for 4.1μm sample and 0.01 ± 0.001 ev for 14.8 μm sample. When temperature is further increased, the conductivity of this material decreases with the increase of the temperature, and the grain size effect becomes less noticeable.

Simulation of the Temperature Dependence of Hall Carriers in Al Doped 4H-SiC

2012 ◽  
Vol 717-720 ◽  
pp. 237-240 ◽  
Author(s):  
Anindya Nath ◽  
Raffaele Scaburri ◽  
Mulpuri V. Rao ◽  
Roberta Nipoti
Keyword(s):  
Experimental Data ◽  
Activation Energy ◽  
Electrical Properties ◽  
Energy Level ◽  
Weighted Least Squares ◽  
High Dose ◽  
Global Minima ◽  
Temperature Dependent ◽  
Wide Range ◽  
Scattering Factor

A global minima search weighted and non-weighted least squares algorithm has been employed for a comparative study of various possible models to describe electrical properties of high dose Al implanted 4H-SiC. A wide range of experimental data has been taken from literature to demonstrate validation of the model. It was found that a single activation energy level, a temperature dependent Hall scattering factor and a degeneracy factor equal to 4 lead to a satisfactory fitting of experimental Hall data up to an Al substitutional density of 1020cm 3 in 4H SiC.

Hydrogen Diffusion in Quartz: A Molecular Dynamics Investigation

1995 ◽  
Vol 408 ◽  
Author(s):  
A. Bongiorno ◽  
L. Colombo
Keyword(s):  
Activation Energy ◽  
Molecular Dynamics ◽  
Diffusion Coefficient ◽  
Hydrogen Diffusion ◽  
Diffusion Path ◽  
Arrhenius Law ◽  
Hydrogen Diffusivity ◽  
Temperature Dependent ◽  
Crystalline Quartz ◽  
Wide Range

AbstractWe present a molecular dynamics investigation on hydrogen diffusivity in crystalline quartz by computing the diffusion coefficient over a wide range of temperatures (700K < T < 1500K) and by characterizing the diffusion path and mechanism. Our main findings are: (i) hydrogen diffusion is anisotropically confined along the c-axis in α- and β-quartz; (ii) hydrogen diffuses through a jump-like mechanism; (iii) the temperature-dependent diffusivity follows an Arrhenius law with activation energy of 0.56 eV and 0.27 eV for α-and β-quartz, respectively.

Grain size effect on activation energy in spinel CoFe2O4 ceramic

2016 ◽  
Author(s):  
Sweety Supriya ◽  
Sunil Kumar ◽  
Manoranjan Kar
Keyword(s):  
Activation Energy ◽  
Grain Size ◽  
Size Effect ◽  
Grain Size Effect

DFT Calculations to Study Hydrogen Localization and Diffusion in Disordered Bcc Ti-V-Cr Alloys

2019 ◽  
Vol 289 ◽  
pp. 205-211 ◽  
Author(s):  
Olga O. Bavrina ◽  
Marina G. Shelyapina ◽  
Daniel Fruchart ◽  
Nikola Novaković
Keyword(s):  
Experimental Data ◽  
Activation Energy ◽  
Diffusion Coefficient ◽  
Hydrogen Diffusion ◽  
Theoretical Study ◽  
Metal Species ◽  
Tetrahedral Sites ◽  
Diffusion Parameters ◽  
And Diffusion ◽  
Good Agreement

Here we report on the results of our theoretical study of hydrogen localization and motion in disordered bcc Ti-V-Cr alloys. The calculations have been carried out within a DFT supercell approach for a certain composition, namely Ti0.33V0.27Cr0.4 for H/M = 1/32. It was found that hydrogen is localized in highly distorted tetrahedral sites formed by different metal species. H atoms are displaced towards titanium. The estimation of the hydrogen diffusion parameters provides the activation energy value of 0.126 eV and the diffusion coefficient at 294 K equal to 1.9 10-10 m/s2 that is in good agreement with available experimental data.

Landau-Ginzburg-Devonshire Theory of the Grain Size Effect on the Ferroelectricity in BaTiO 3 Nanoceramics

2020 ◽  
Author(s):  
Kum-Ok Jang ◽  
Il-Hwan Kim ◽  
Il-Hun Kim ◽  
Kye-Ryong Sin ◽  
Chol-Jin Kim
Keyword(s):  
Grain Size ◽  
Size Effect ◽  
Grain Size Effect

Effect of ionizing radiation on the kinetics of hydrogenation on the Ni-MgO mixed catalyst

1982 ◽  
Vol 47 (7) ◽  
pp. 1780-1786 ◽  
Author(s):  
Rostislav Kudláček ◽  
Jan Lokoč
Keyword(s):  
Experimental Data ◽  
Activation Energy ◽  
Liquid Phase ◽  
Ionizing Radiation ◽  
Oxide Catalyst ◽  
Absorbed Dose ◽  
Hydrogenation Rate ◽  
Solution Composition ◽  
Mixed Catalyst ◽  
Kinetics Of

The effect of gamma pre-irradiation of the mixed nickel-magnesium oxide catalyst on the kinetics of hydrogenation of maleic acid in the liquid phase has been studied. The changes of the hydrogenation rate are compared with the changes of the adsorbed amount of the acid and with the changes of the solution composition, activation energy, and absorbed dose of the ionizing radiation. From this comparison and from the interpretation of the experimental data it can be deduced that two types of centers can be distinguished on the surface of the catalyst under study, namely the sorption centres for the acid and hydrogen and the reaction centres.

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