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Dissolution of Metal Ions

Certainly a thermodynamically stable oxide layer is more likely to generate passivity. However, the existence of the metastable passive state implies that an oxide him may (and in many cases does) still form in solutions in which the oxides are very soluble. This occurs for example, on nickel, aluminium and stainless steel, although the passive corrosion rate in some systems can be quite high. What is required for passivity is the rapid formation of the oxide him and its slow dissolution, or at least the slow dissolution of metal ions through the him. The potential must, of course be high enough for oxide formation to be thermodynamically possible. With these criteria, it is easily understood that a low passive current density requires a low conductivity of ions (but not necessarily of electrons) within the oxide. [Pg.135]

The corrosion current due to diffusion of metal ions through the passivating film, and dissolution of metal ions at the oxide-solution interface. Clearly, the smaller this current, the more protective is the oxide layer. [Pg.814]

For some metallic electrodes, such as transition metals, metal ions dissolve directly from the metallic phase into acidic solutions tiiis direct dissolution of metal ions proceeds at relatively low (less anodic) electrode potentials. The direct dissolution of metal ions is inhibited by the formation of a thin oxide film on metallic electrodes at higher (more anodic) electrode potentials. At still higher electrode potentials this inhibitive film becomes electrochemically soluble (or apparently broken down) and the dissolution rate of the metal increases substantially. These three states of direct dissolution, inhibition by a film, and indirect dissolution via a film (or a broken film) are illustrated in Fig. 11-9. [Pg.381]

Corrosion is an electrochemical process that occurs when metal is immersed in water and a difference in electrical potential between different parts of the metal causes a current to pass through the metal between the region of lower potential (anode) and the region of higher potential (cathode). The migration of electrons from anode to cathode results in the oxidation of the metal at the anode and the dissolution of metal ions into the water. [Pg.590]

In eutectic-based ionic liquids, the chloride ions act as strong ligands for the oxidized metal ions, forming a range of chlorometallate anions. The free chloride ions are present in very low concentrations as they are complexed with the Lewis acidic metal ions and so the dissolution of metal ions must lead to a complex series of equilibria such as... [Pg.288]

Option 3. Direct Addition of Lime to the Pile. Direct addition of hydrated lime Ca(0H)2 to the pile has the same effect as Option 10, to be discussed later. Los Alamos leaching studies have shown that as little as 5% lime added to finely divided waste prevents acid formation and dissolution of metal ions. However, there is some question about the uniformity of dispersion and about directly adding solid powdered lime to the pile at the time the waste is spread and bulldozed. Field experiments are required to prove this technology. Until the minimum effective dosage is demonstrated in the field, a conservative figure of 25% of the lime theoretically required to neutralize the total sulfuric acid has been used in the cost calculations. [Pg.621]

The current (z) measured during the growth of the porous film can be taken as the sum of the ionic current, due to the oxidation of the metal at the metal/oxide interface, and the electronic current, 4i, due to faradaic processes occurring at the oxide/electrolyte interface. The former can be described as the sum of the formation current density, associated to oxide formation, and the dissolution current, zmetal ions into the electrolyte at the pore bottom. Then,... [Pg.135]

The catalytic liquid-phase oxidation of aqueous phenol solution, carried out in a variety of reactor systems, demonstrates that phenol can be transformed to nontoxic compounds at milder reaction conditions than used in the thermal processes. The present study indicates that it is advantageous to conduct the reaction in a trickle-bed reactor with partial wetting of catalyst particles, perhaps with cyclic operation, since a direct contact between the catalyst surface and gas-phase increases the concentration of active sites for phenol oxidation. Furthermore, the reaction selectivity in a trickle-bed reactor is higher than that in a slurry reactor. The main drawback of the investigated process is dissolution of metal ions into the liquid-phase, which calls for more stable catalysts. [Pg.642]

Electrolytical reduction of Tc-pertechnetate has been investigated (Benjamin 1969, 1970 Dworkin and Gutkowski 1971 Eckelman et al. 1971a Gil et al. 1976). When using zirconium or tin electrodes, anodic dissolution of metal ions produced in situ reduction of pertechnetate (Steigman et al. 1974). Electrolysis has been used as a reliable method for laboratory production of Tc pharmaceuticals. [Pg.60]

Acidification of a body of water is generally accompanied by dissolution of metal ions from the underlying bedrock. These may include toxic metals ions such as Cd " ", and In each case, the metals are solubilized because of the reaction... [Pg.101]

Halide ions, according to the adsorption theory of passivity, tend to break down passivity by competing with the passivator for adsorption sites on the metal surface. Should a halide ion find a vacant site and closely approach the surface, hydration and dissolution of metal ions are favored, and the anodic reaction can proceed with low activation energy, in contrast to the high activation energy required when a passivator is adsorbed. The anode reaction, if it persists, is confined to localized areas where the competitive process first succeeds, because surrounding metal immediately becomes cathode of an electrolytic cell, and is protected by flow of current from further anode activity, a process called cathodic protection. This attack at specific sites leads to corrosion pitting typical of metals otherwise passive that are actually corroded by their environment. [Pg.389]

Most pickling inhibitors function by forming an adsorbed layer on the metal surface, probably no more than a monolayer in thickness, which essentially blocks discharge of H+ and dissolution of metal ions. For example, both iodide and quinoline are reported to inhibit corrosion of iron in hydrochloric acid by this mechanism [19]. Some inhibitors block the cathodic reaction (raise hydrogen overpotential) more than the anodic reaction, or vice versa but adsorption appears to be general over all the surface rather than at specific anodic or cathodic sites, and both reactions tend to be retarded. Hence, on addition of an inhibitor to an acid, the corrosion potential of steel is not greatly altered (<0.1 V), although the corrosion rate may be appreciably reduced (Fig. 17.3). [Pg.310]

Electrolytic polishing is a convenient way to polish metallic samples in the fine grinded (600 grit) or machined surface states. This method requires formation of an electrical circuit in which the sample is the anode (Fig. 3). A suitable electrolyte flows across the surface of the sample. The current density is adjusted for the type of material and size of the polished sample to facilitate suitable dissolution of metal ions from the to-be-polished surface. As the electrolyte washes over the sample, any perturbations in the surface (high energy sites) are selectively dissolved. The result is a flat surface with no mechanical damage. [Pg.69]

Figure 9.22 Multiplexed detection of pathogens using NC antibody conjugates and MWCNT-PAH/SPE. Step I antibody immobilization Step 2 immunocapture Step 3 NC-an-tibody conjugates immunobinding Step 4 dissolution of metal ions from NC and Step 5 SWSV analysis (Reproduced from [143], with permission from Elsevier)... Figure 9.22 Multiplexed detection of pathogens using NC antibody conjugates and MWCNT-PAH/SPE. Step I antibody immobilization Step 2 immunocapture Step 3 NC-an-tibody conjugates immunobinding Step 4 dissolution of metal ions from NC and Step 5 SWSV analysis (Reproduced from [143], with permission from Elsevier)...
This section on film growth will be restricted to direct film formation processes in which passivation is the result of the direct reaction between the metal surface and the aqueous solution. Other processes of film formation, such as dissolution/precip-itation (dissolution of metal ions and subsequent precipitation of an oxide, oxi-hydrox-ide, or hydroxide) and anodic deposition processes (anodic oxidation of metal ions in the solution and deposition on the surface), are not treated here. [Pg.150]

The late transition and main group metals follow the anodic oxidation pathway analogous to that in aqueous solutions. The minimal oxidation potentials in these cases can in fact be very low (up to max. 3.0 V), whUe higher ones are readily applied to accelerate the process. The anodic reaction consists of dissolution of metal ions in the form of anionic halide complexes, which are later transformed into insoluble alkoxides by reaction with alkoxide anions generated at the cathode, for example (Lehmkuhl, 1975) ... [Pg.5]

Eiectrodeposition runs parallel with the process of electrolysis. Redox reactions taking place in the bath solution simultaneously result in the metal deposition on the cathode, also known as the working electrode. Various steps involved in the eiectrodeposition include (i] oxidation at anode on the application of external current, (ii] dissolution of metal ions in electrolyte solution, (iii] metal ion transportation from electrolytic solution to the cathode surface, (iv] reduction of ions at the cathode, and (v] continuous metal layer formation on the cathode surface. The amount of metal deposition depends on deposition time and other parameters determined by Faraday s law, described by the following equation ... [Pg.702]


See other pages where Dissolution of Metal Ions is mentioned: [Pg.85]    [Pg.821]    [Pg.98]    [Pg.285]    [Pg.336]    [Pg.81]    [Pg.136]    [Pg.311]    [Pg.208]    [Pg.32]    [Pg.850]    [Pg.50]    [Pg.138]    [Pg.414]    [Pg.17]    [Pg.271]    [Pg.557]    [Pg.268]    [Pg.644]   
See also in sourсe #XX -- [ Pg.138 ]




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