Oxygen Transport in Oxides

Z)v is the self-diffusion coefficient of the oxygen vacancies Cv.. is the concentration of oxygen vacancies 

Following a phenomenological approach, the driving force for chemical diffusion, in oxides, is the gradient of the electrochemical potential, ri- 

The Physical Chemistry of Materials Energy and Environmental Applications 

Assuming that the chemical equilibrium can be described as follows 

Thereafter, combining Equations 5.68 through 5.70 and Equation 5.72, the flux of oxygen can be written with the help of the ambipolar diffusion equation [45] 

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J.M. Floyd, Oxygen Transport in Oxides of Fluorite Structure Ph.Dc Thesis, University of London, 1969... 

The first ceramic oxygen membranes were discovered by Nernst [2] in 1899 in the form of mixrnres of zirconia and rare-earth metal oxides. Basically, oxygen transport in oxide ceramics can be realized in three variants (Fig. 1). Materials... 

The second type of behaviour (Fig. 1.89) is much closer to that which one might predict from the regular cracking of successive oxide layers, i.e. the rate decreases to a constant value. Often the oxide-metal volume ratio (Table 1.27) is much greater than unity, and oxidation occurs by oxygen transport in the continuous oxide in some examples the data can be fitted by the paralinear rate law, which is considered later. Destructive oxidation of this type is shown by many metals such as molybdenum, tungsten and tantalum which would otherwise have excellent properties for use at high temperatures. 

Ritchie, A.I.K. 1994. Sulphide oxidation mechanisms-controls and rates of oxygen transport. In Alpers, C.N. Blowes, D.W. (eds.), Environmental Geochemistry of Sulphide Oxidation, ACS Symposium Series 550. Washington DC. 

Fig. 3. Oxygen transport in solids. 02 is dissociated and ionized at the reduction interface to give O2 ions, which are transferred across the solid to the oxidation interface, at which they lose the electrons to return back to 02 molecules that are released to the stream, (a) In the solid electrolyte cell based on a classical solid electrolyte, the ionic oxygen transport requires electrodes and external circuitry to transfer the electrons from the oxidation interface to the reduction interface (b) in the mixed conducting oxide membrane, the ionic oxygen transport does not require electrodes and external circuitry to transfer the electrons to the reduction interface from the oxidation interface, because the mixed conductor oxide provides high conductivities for both oxygen ions and electrons.

OXYGEN, OXIDES 0X0 ANIONS Oxygen, photo-induced incorporation, PHOTO-OXYGENATION OXYGEN RADICALS Oxygen transport in erythrocytes,... 

Discussion of condensed-phase diffusion must first recognize the distinction between the tracer or the chemical diffusivity and the oxygen transport rate under an oxygen potential gradient. From an oxidation standpoint, it is the latter that is most relevant. Unfortunately, to calculate the transport rate, one requires a knowledge of the structure and/or concentration of defects responsible for oxygen transport, in addition to the tracer or the chemical diffusivity. 

T. Tokuda, T. Ito, and T. Yamaguchi, Self-Diffusion in a Glassformer Melt Oxygen Transport in Boron Oxide, Z. Naturforschung, 26A, 2058-2060 (1971). 

Kilner, J.A., Fast oxygen transport in acceptor doped oxides. Solid State Ionics, 2000, 129, 13-23. 

Ritchie A. I. M. (1994) Sulhde oxidation mechanisms controls and rates of oxygen transport. In The Environmental Geochemistry of Sulfide Mine-wastes (eds. J. L. Jambor, and D. W. Blowes). Mineralogical Association of Canada, Nepean, ON, vol. 22, pp. 201-246. 

The roles of the copper enzymes in electron transport, oxygen transport, and oxidation reactions have guaranteed continued interest in their study. In addition to studies of the natural compounds, there have been many attempts to design model structures of these enzymes, particularly of the binuclear species. Many of these include both nitrogen and oxygen donors built into macrocyclic ligands, although sulfur has been used as well. ... 

Perovskite membranes are interesting systems not only for their possible applications (e.g., fuel cells, oxygen generators, oxidation catalysts) but also for the fundamental fascination of fast oxygen transport in solid-state ionic. 

S. Carter, A. Selcuk, J. Chater, R.J. Kajda, J.A. Kilner and B.C.H. Steele, Oxygen transport in selected non-stoichiometric perovskite-structure oxides. Solid State Ionics, 53-56 (1992) 597-605. 

One of the most prominent properties of metalloporphyrins is the accessibility of several oxidation states, which is crucial in electron-transfer reactions, e.g. oxygenation catalysis or oxygen transport. In most cases a larger number of these oxidation states are stable on the timescale of cyclovoltammetric experiments or even longer, an example of such multiredox behaviour can be seen in Figure 4.1. 

Carter, S. et al. Oxygen transport in selected nonstoichiometric perovskite-stmcture oxides. Solid State Ionics 53-56, 597-605, doi Doi 10.1016/0167-2738(92)90435-r (1992). 

Carter S, Selcuk A, Chater RJ, Kajda J, Kilner JA, Steele BCH (1992) Oxygen transport in selected nonstoichiometric perovskite-structiu e oxides. Solid State Ion 53-56 (Part 1) 597... 

Before moving to the details of these materials, it is instructive to examine the atomistic quantities that govern the transport of oxygen in these oxides. A simple Arrhenius-type expression describes the diffusion coefficient of oxygen, D, in oxide materials. 

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