scholarly journals Estimation of the Na Insertion/Extraction Reaction Rate as the Na Chemical Diffusion Coefficient in Low-Temperature-Fired Soft Carbon

2018 ◽  
Vol 86 (3) ◽  
pp. 116-121
Author(s):  
Junji SUZUKI ◽  
Narumi KUBOTA ◽  
Yukikazu OMURA ◽  
Keisuke SUGATA ◽  
Kento KISA ◽  
...  
Keyword(s):  
Diffusion Coefficient ◽  
Low Temperature ◽  
Reaction Rate ◽  
Chemical Diffusion ◽  
Chemical Diffusion Coefficient ◽  
Extraction Reaction ◽  
Soft Carbon

Dynamics of Hydrogen in the Hexagonal (C14) Laves Phase Compounds TiCr1.8-xMnx

2009 ◽  
Vol 283-286 ◽  
pp. 231-237
Author(s):  
Giovanni Mazzolai
Keyword(s):  
Activation Energy ◽  
Diffusion Coefficient ◽  
Low Temperature ◽  
Chemical Diffusion ◽  
Laves Phase ◽  
Chemical Diffusion Coefficient ◽  
Diffusion Of Hydrogen ◽  
Laves Phase Compounds

The diffusion of hydrogen has been investigated in the AB2 Laves phase Compounds TiCr1.78 and TiCr1.4Mn0.4, by absorption techniques. It has been found that H at temperatures higher than 700 K diffuses through the classical over-barrier mechanism, while at low temperature (around 100 K) the diffusion is governed by phonon-assisted tunnelling. The activation energy for classical hopping is rather high and increases with the substitution of Mn for Cr. In the range of H contents nH investigated (nH=H/Me0.03) the chemical diffusion coefficient does not depend on the H concentration.

scholarly journals Boundary layer analysis for a 2-D Keller-Segel model

2020 ◽  
Vol 18 (1) ◽  
pp. 1895-1914
Author(s):  
Linlin Meng ◽  
Wen-Qing Xu ◽  
Shu Wang
Keyword(s):  
Boundary Layer ◽  
Diffusion Coefficient ◽  
Approximate Solution ◽  
Chemical Diffusion ◽  
Singular Perturbation Theory ◽  
Energy Estimates ◽  
Chemical Diffusion Coefficient ◽  
Boundary Layer Problem ◽  
Classical Energy ◽  
Layer Analysis

Abstract We study the boundary layer problem of a Keller-Segel model in a domain of two space dimensions with vanishing chemical diffusion coefficient. By using the method of matched asymptotic expansions of singular perturbation theory, we construct an accurate approximate solution which incorporates the effects of boundary layers and then use the classical energy estimates to prove the structural stability of the approximate solution as the chemical diffusion coefficient tends to zero.

Diffusion und Korrelation in goldreichen Gold—Zinn-Mischkristallen / Diffusion and Correlation in Gold-Rich Gold—Tin Solid Solutions

1972 ◽  
Vol 27 (7) ◽  
pp. 1109-1118 ◽  
Author(s):  
Chr. Herzig ◽  
Th. Heumann
Keyword(s):  
Diffusion Coefficient ◽  
Impurity Content ◽  
Chemical Diffusion ◽  
Correlation Factor ◽  
Coarse Grained ◽  
Pure Gold ◽  
Large Temperature ◽  
Chemical Diffusion Coefficient ◽  
Self Diffusion ◽  
Different Temperatures

Abstract The diffusion of Sn-113 and Au-195 in pure gold and dilute tin -gold alloys has been measured at different temperatures and tin concentrations in coarse-grained specimens. In addition the dependence on concentration of the chemical diffusion coefficient and the diffusion of tin in gold at very low impurity concentrations has been determined using the electron microprobe. It was found, that the self-diffusion coefficient of tin as well as that of gold increased strongly with in-creasing impurity content. The thermodynamic factor is equal to one up to ca. 0.5 at.-% tin. For the correlation factor of the diffusion of tin in gold, calculated by the relation of Lidiard, an essentially temperature independent value is obtained. A comparison of the experimental results with the model of Le Claire concerning the impurity diffusion in metals shows, that this model seems to require a too-large temperature dependence of the correlation factor

Oxidation Kinetics of Nitrogen Doped TiO2-δ Thin Films: Analysis on the Basis of Oxygen Activity Dependence of the Chemical Diffusion Coefficient

2018 ◽  
Vol 383 ◽  
pp. 147-152
Author(s):  
Misha Sinder ◽  
Jian Min Shi ◽  
Klaus Dieter Becker
Keyword(s):  
Thin Films ◽  
Diffusion Coefficient ◽  
Electron Concentration ◽  
Chemical Diffusion ◽  
Oxygen Activity ◽  
Chemical Diffusion Coefficient ◽  
Recombination Reaction ◽  
Nitrogen Doped ◽  
Pressure Profiles ◽  
Concentration Step

The model explaining the occurrence of the electron concentration step front during oxidation of nitrogen-doped TiO2-δ thin films is presented. This model is based on ambipolar chemical diffusion coefficient analysis, for which immobile and uniformly distributed nitrogen component is assumed. The diffusion species and oxygen activity (pressure) profiles are obtained by numerical and approximate analytical simulation of the chemical diffusion. The profiles indicate the presence of two separate singularities: the electron concentration step front, and the electron-hole recombination reaction front. The electron concentration step front relates to the singularity of the ambipolar diffusion of three types of charged species with essentially different diffusion coefficients.

Oxygen Chemical Diffusion Coefficients of (U, Pu)O2-x

2017 ◽  
Vol 375 ◽  
pp. 84-90 ◽  
Author(s):  
Masashi Watanabe ◽  
Takeo Sunaoshi ◽  
Masato Kato
Keyword(s):  
Activation Energy ◽  
Diffusion Coefficient ◽  
Diffusion Coefficients ◽  
Surface Reaction ◽  
Chemical Diffusion ◽  
Chemical Diffusion Coefficient ◽  
Thermo Gravimetry ◽  
Metal Ratio

The oxygen chemical diffusion coefficient in (U, Pu)O2-x was determined by thermo-gravimetry as functions of the Pu content, oxygen-to-metal ratio and temperature. The surface reaction was considered in the diffusion coefficient determination. The activation energy for the chemical diffusion coefficient was 60 kJ/mol and 65 kJ/mol, respectively, in (U0.8Pu0.2)O2-x and (U0.7Pu0.3)O2-x.

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