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Metals diffusion through

In the anoxic zone, heterotrophic respiration of particulate Mn02 and Fc203 or FeOOH causes manganese and iron to be reduced to Mn (aq) and Fe (aq). As dissolved ions, these trace metals diffuse through the pore waters. The ions that diffuse upwards will reenter the oxic zone, where they react with O2 to reform the oxyhydroxides. This produces a metal-enriched layer that lies just above the redox... [Pg.319]

Volumetric steady-state gas permeation tests at elevated temperatures are typically used to characterize the performance of paUadium membranes. Electrochemical methods are also effective, even at high temperatures [90, 166]. Permeation through palladium depends on a solution-diffusion mechanism, including the steps of chemisorption and dissociation into atoms, absorption into the metal, diffusion through the metal lattice, transfer from the bulk metal to the opposite side, and recombination into molecules for desorption [167, 168]. Difiusion of molecular hydrogen through boundary layers adjacent to the surface is also necessary. [Pg.84]

Boscov, M.E.G, OHveira, E., Ghilardi, M.P. and Silva, M.M. (1999). Metal diffusion through a lateritic compacted clay. Proceedings 4th Brazilian Conference on Geo-Environmental Engineering (REGE099). Sao Jose dos Campos, Brazil, (in Portugese)... [Pg.308]

III. This mechanism can take place only at metallic electrodes that allow diffusion of oxygen through the metal. Oxygen is adsoibed and dissociates on the metal, diffuses through the metal as a neutral species and at the interface with the SE it reacts with two electrons and then enters the SE. This was suggested to be the mechanism for Ag electrodes on YSZ and Ag on doped CeOj. However, it was also suggested that Ag on doped Ce02 follows model r. ... [Pg.279]

The protein fraction is responsible for a major part of membrane function Non polar materials can diffuse through the bilayer from one side to the other relatively eas ily but polar materials particularly metal ions such as Na" K" and Ca " cannot The... [Pg.1078]

FIGt 22-48 Transport mechanisms for separation membranes a) Viscous flow, used in UF and MF. No separation achieved in RO, NF, ED, GAS, or PY (h) Knudsen flow used in some gas membranes. Pore diameter < mean free path, (c) Ultramicroporoiis membrane—precise pore diameter used in gas separation, (d) Solution-diffusion used in gas, RO, PY Molecule dissolves in the membrane and diffuses through. Not shown Electro-dialysis membranes and metallic membranes for hydrogen. [Pg.2025]

The oxidation of a particular metal in air is limited by the outward diffusion of metallic ions through an unbroken surface film of one species of oxide. Assume that the concentration of metallic ions in the film immediately next to the metal is Cj, and that the concentration of ions in the film immediately next to the air is C2, where and C2 are constants. Use Tick s First Law to show that the oxidation of the metal should satisfy parabolic kinetics, with weight gain Am given by... [Pg.287]

Reference electrodes are used in the measurement of potential [see the explanation to Eq. (2-1)]. A reference electrode is usually a metal/metal ion electrode. The electrolyte surrounding it is in electrolytically conducting contact via a diaphragm with the medium in which the object to be measured is situated. In most cases concentrated or saturated salt solutions are present in reference electrodes so that ions diffuse through the diaphragm into the medium. As a consequence, a diffusion potential arises at the diaphragm that is not taken into account in Eq. (2-1) and represents an error in the potential measurement. It is important that diffusion potentials be as small as possible or the same in the comparison of potential values. Table 3-1 provides information on reference electrodes. [Pg.85]

Additionally, hydrogen atoms diffuse through metals and coalesce to form hydrogen molecules at certain preferred locations such as inclusions. [Pg.895]


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