scholarly journals Chemical oxygen diffusion coefficient measurement by conductivity relaxation—correlation between tracer diffusion coefficient and chemical diffusion coefficient

2004 ◽  
Vol 24 (6) ◽  
pp. 1265-1269 ◽  
Author(s):  
F. Mauvy ◽  
J.M. Bassat ◽  
E. Boehm ◽  
P. Dordor ◽  
J.C. Grenier ◽  
...  
Keyword(s):  
Diffusion Coefficient ◽  
Oxygen Diffusion ◽  
Chemical Diffusion ◽  
Tracer Diffusion ◽  
Chemical Diffusion Coefficient ◽  
Conductivity Relaxation ◽  
Tracer Diffusion Coefficient ◽  
Oxygen Diffusion Coefficient ◽  
Coefficient Measurement

Elektrochemische Untersuchung der chemischen Diffusion in Wüstit mit Hilfe eines oxidischen Festelektrolyten/ Electrochemical Investigation of Chemical Diffusion in Wüstite Using a Solid Oxide Electrolyte

1974 ◽  
Vol 29 (12) ◽  
pp. 1849-1859 ◽  
Author(s):  
H. Rickert ◽  
W. Weppner
Keyword(s):  
Diffusion Coefficient ◽  
Chemical Potential ◽  
Coulometric Titration ◽  
Chemical Diffusion ◽  
Tracer Diffusion ◽  
Correlation Factor ◽  
Galvanic Cell ◽  
Constant Current ◽  
Chemical Diffusion Coefficient ◽  
Small Constant

Chemical diffusion measurements in wüstite were carried out with the help of the solid state galvanic cell pO₂, Ptl |ZrO2(+Y2O3)| Fe1 - δ(ϰ)O| Pt2, N2 with doped ZrO2 as a solid electrolyte which exhibits practically pure conduction for oxygen ions. Starting from an initial homogeneous stoichiometry as given by δ, the voltage E of the cell, i. e. the chemical potential of oxygen (or δ) in Fe1 - δO at the phase boundary with the electrolyte, was changed in small steps, corresponding to 3,5 - 15% of the whole stoichiometric range. The re-equilibration of the compound was observed by the current as a function of time. Alternatively, a small constant current was applied to the galvanic cell and the voltage between the wüstite and a reference electrode was measured. From the relaxation behaviour the chemical diffusion coefficient can be determined in several ways. The values are consistent with those calculated from tracer diffusion coefficients, the thermodynamic factor, which could be estimated from coulometric titration measurements, and a correlation factor of the order of 1. In contradiction to previous results with thermogravimetric methods the chemical diffusion coefficient increases with growing deviation from the ideal stoichiometry.

Oxygen Diffusivity of La0.6Sr0.4Co0.2Fe0.8O3-δ Perovskite Oxide

2012 ◽  
Vol 616-618 ◽  
pp. 633-637
Author(s):  
Yan Wei Liu ◽  
Zhe Lü
Keyword(s):  
Thermal Expansion ◽  
Diffusion Coefficient ◽  
Chemical Diffusion ◽  
Lattice Oxygen ◽  
Perovskite Oxide ◽  
Chemical Diffusion Coefficient ◽  
Conductivity Relaxation ◽  
Fixed Temperature ◽  
Expansion Curve ◽  
Maximum Conductivity

La0.6Sr0.4Co0.2Fe0.8O3-δ composite oxide was prepared and characterized. Dilatometer and four-probe DC were exploited to investigate the thermal expansion and electrical conductivity, respectively. The thermal expansion curve was linear, but it became steeper at the high temperature region, as a result of the loss of lattice oxygen and the formation of oxygen vacancies. The conductivity increased with temperature up to about 600oC, and then decreased due to the loss of lattice oxygen. The maximum conductivity was more than 300 S cm-1. The chemical diffusion coefficient in La0.6Sr0.4Co0.2Fe0.8O3-δ was estimated by analyzing the conductivity relaxation behavior. The relaxation process of the conductivity change for La0.6Sr0.4Co0.2Fe0.8O3-δ was traced as a function of time, at a fixed temperature. It was found that the chemical diffusion coefficients measured at temperatures 720-770oC vary from 710-8 to 110-7 cm2 S-1. The activation energy for oxygen diffusion in La0.6Sr0.4Co0.2Fe0.8O3-δ, derived from the chemical diffusion coefficient is 40.8±3.6 kJ mol-1.

Use of a dynamic gassing-out method for activity and oxygen diffusion coefficient estimation in biofilms

1998 ◽  
Vol 37 (4-5) ◽  
pp. 171-175
Author(s):  
Artem Khlebnikov ◽  
Falilou Samb ◽  
Paul Péringer
Keyword(s):  
Diffusion Coefficient ◽  
Oxygen Uptake ◽  
Oxygen Diffusion ◽  
Fixed Bed ◽  
Biofilm Reactor ◽  
Strictly Aerobic ◽  
Comamonas Testosteroni ◽  
Respiration Activity ◽  
Oxygen Diffusion Coefficient ◽  
Biofilm Development

p-toluenesulphonic acid degradation by Comamonas testosteroni T-2 in multi-species biofilms was studied in a fixed bed biofilm reactor. The polypropylene static mixer elements (Sulzer Chemtech Ltd., Switzerland) were used as a support matrix for biofilm formation. Biofilm respiration was estimated using the dynamic gassing-out oxygen uptake method. A strong relation between oxygen uptake and reactor degradation efficiency was observed, because p-toluenesulphonate degradation is a strictly aerobic process. This technique also allowed us to estimate the thickness of the active layer in the studied system. The mean active thickness was in order of 200 μm, which is close to maximum oxygen penetration depth in biofilms. A transient mathematical model was established to evaluate oxygen diffusitivity in non-steady-state biofilms. Based on the DO concentration profiles, the oxygen diffusion coefficient and the maximum respiration activity were calculated. The oxygen diffusion coefficient obtained (2 10−10-1.2 10−9 m2 s−1) is in good agreement with published values. The DO diffusion coefficient varied with biofilm development. This may be, most likely, due to the biofilm density changes during the experiments. The knowledge of diffusivity changes in biofilms is particularly important for removal capacity estimation and appropriate reactor design.

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.

Electronic/Ionic Conductivity and Oxygen Diffusion Coefficient af the Sr-Fe-Co-O System

1995 ◽  
Vol 393 ◽  
Author(s):  
B. Ma ◽  
J.-H. Park ◽  
C. U. Segre ◽  
U. Balachandran
Keyword(s):  
Diffusion Coefficient ◽  
Ionic Conductivity ◽  
Oxygen Diffusion ◽  
Ionic Conductivities ◽  
Transference Number ◽  
Transference Numbers ◽  
Oxygen Diffusion Coefficient ◽  
Ionic Transference Number ◽  
Local Fitting ◽  
Oxide Ion

ABSTRACTOxides in the Sr-Fe-Co-O system exhibit both electronic and ionic conductivities. Recently, the Sr-Fe-Co-O system attracted great attention because of its potential to be used for oxygen-permeable membranes that can operate without electrodes or external electrical circuitry. Electronic and ionic conductivities of two compositions of the Sr-Fe-Co-O system, named SFC-1 and SFC-2, have been measured at various temperatures. The electronic transference number is much greater than the ionic transference number in SFC-1, whereas the electronic and ionic transference numbers are very similar in SFC-2. At 800°C, the electronic and ionic conductivities are ≈76 and ≈4 S•cm−1, respectively, for SFC-1; whereas, for SFC-2, the electronic and ionic conductivities are ≈10 and ∼1 S•cm−1, respectively. By performing a local fitting to the equation σ • T = Aexp(-Ea / kT), we found that the oxide ion activation energies are 0.92 and 0.37 eV, respectively, for SFC-1 and SFC-2. The oxygen diffusion coefficient of SFC-2 is ≈ 9 x 10−7cm2/sec at 900°C.

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