Anodic insoluble products

On the basis of the results from XPS studies by Kanamura and co-workers that the SEI has a multilayered structure,Peled and co-workers modified their lithium electrode passivation model to include carbonaceous anodes and proposed a so-called mosaic model to describe the SEI structure on the anode, as Figure 15a shows.According to this model, multiple reductive decompositions occur between the negatively charged anode surface and the various electrolyte components simultaneously, depositing a mixture of insoluble products on the anode. This heteropolymicrophase SEI consists of many microregions that are of entirely different chemical... 

A remark has to be made that also applies to (b) anodic oxidation of a metal is often a very complex process, involving, for example, adsorption of intermediates in a multi-step mechanism, film formation of insoluble products, etc. In such cases, the impedance plots can be much more intricate and the straightforward relation to the corrosion rate can be obscured. 

In those cases where the anodic compound formed by the action of the discharged anions upon the anode metal is insoluble, i.e. lead sulphate formed by the action of sulphate ions upon a lead anode, the anode is speedily covered with the insoluble product, and further action is prevented. Luckow1 showed that this difficulty can be obviated by using a considerable quantity of a secondary salt (sodium chlorate), the anions of which attack the anode and crowd out the anions of the primary salt, so that precipitation takes place a short distance from the anode, and the product falls continuously to the bottom of the vat instead of clinging to the anode surface. 

Other anodic reactions are also of interest when there is formation of an insoluble product. Sulfide films were used (30, 31) in the case of Cu and Cu-Zn alloys. These methods can serve for the determination of the relative orientation of the grains in a polycrystalline pure metal or homogeneous solid solutions. In the case of pure metals, the color of the surface film depends on the orientation of the grains. In the case of solid solutions, their composition affects the rate of oxidation and, therefore, the color of the films. It is possible in fills way to detect composition heterogeneities in a solid solution. 

The electrochemical behaviour of the ribbed-functionalized iron(II) [65, 68] and ruthenium(II) [78] clathrochelates with alkylamine, thioaryl, thioalkyl, phenoxyl and crown ether substituents in a-dioximate fragments was characterized by E1/2 values for Fe3+/2+ and Ru3+/2+ couples (Table 37). The Tomes criterion values of most complexes exhibited reversible or quasi-reversible anodic processes. Moreover, the quasi-reversible oxidation processes are accompanied by the formation of insoluble products followed by passivation of the working electrode. The Ev2 values depend on the electron-donating properties of the substituents in the ribbed fragments. The correlations of E1/2 values for Ru3" 2+ and Fe + 2+ couples with these substituents Hammet s Opara constants were observed in Refs. 65, 68, and 78. These correlations are rather qualitative, but they enable one to conclude that ruthenium complexes are less sensitive to the change of substituents in dioximate fragments. There was no correlation between the Em values and the inductive Taft s (cr,) constants for substituents in dioximate fragments. 

This evidence of the uptake of inhibitive anions into oxide films forms the basis of the chemical or pore plugging theory of inhibition, associated originally with Evans etal. In this theory the rdle of the inhibitive anion is to promote the repair of weak points or pores in the oxide film, where corrosion has started, by reacting with dissolving iron cations to form insoluble products of separate phase, which plug the gaps. These insoluble products may contain the inhibitive anion either as a salt, e.g. phosphate, or a basic salt, e.g. azeiate , or as an insoluble oxide, e.g. CrjOj from chromate Precipitation of such solid products is favoured if the pH in the region of the pores does not become acid. Thus, on the basis of this theory, inhibition by anions such as phosphate, borate, silicate and carbonate, is enhanced by their buffer properties which serve to prevent a fall in pH in the anodic areas. Since ferric salts are usually more insoluble than... 

When the dependence of log(iiim — i) with potential is linear and the slope is RT X 2-303/ F, an insoluble product of the electrode reaction is formed. Such curves, resulting in sharp bends, were observed for some anodic waves corresponding to a formation of an insoluble mercury compound, e.g. diethylbar-bituric acid.< >... 

Under float potential conditions, a trickle current always passes between the electrodes in order to maintain a specified potential. Assuming that the SEI has a small but finite electronic conductivity, electrons leave the carbon anode, transit the SEI, and reduce one or more components of the electrolyte at the SEI/electrolyte interface at z=L(t). Here, we focus our attention on solvent reduction. In accord with experimental data and theoretical analysis presented elsewhere in this volume, we assume that a solvent component, generically labelled S , undergoes two electron reduction and neutralization by Li to produce an insoluble product P . This reaction occurs only at the SEI/electrolyte interface. Assuming the stoichiometry of the pseudo-reaction shown in Figure 3, the molar production rates /Mjjof the various species are related by... 

The Li-SOCh battery consists of a hthium-metal foil anode, a porous carbon cathode, a porous non-woven glass or polymeric separator between them, and an electrolyte containing thionyl chloride and a soluble salt, usually hthium tetrachloroaluminate. Thionyl chloride serves as both the cathode active material and the electrolytic solvent The carbon cathode serves as a catalytic surface for the reduction of thionyl chloride and as a repository for the insoluble products of the discharge reaction. 

The work of Evans on the electrolysis of ethereal solutions of Grignard reagents [118] in general confirms the view of the anodic process as a free radical process. Thus, he showed that electrolysis of Grignard reagents with an insoluble anode gives products, the formation of which can be e lained by disproportionation, dimerization of the initially formed radicals, and reaction with the... 

Electrochemical Fluorination. In the Simons electrochemical fluorination (ECF) process the organic reactant is dissolved in anhydrous hydrogen fluoride and fluorinated at the anode, usually nickel, of an electrochemical ceU. This process has been reviewed (6). Essentially all hydrogen atoms are substituted by fluorine atoms carbon—carbon multiple bonds are saturated. The product phase is heavier than the HF phase and insoluble in it and is recovered by phase separation. 

This is essentially a corrosion reaction involving anodic metal dissolution where the conjugate reaction is the hydrogen (qv) evolution process. Hence, the rate depends on temperature, concentration of acid, inhibiting agents, nature of the surface oxide film, etc. Unless the metal chloride is insoluble in aqueous solution eg, Ag or Hg ", the reaction products are removed from the metal or alloy surface by dissolution. The extent of removal is controUed by the local hydrodynamic conditions. 

Production and Economic Aspects. Thallium is obtained commercially as a by-product in the roasting of zinc, copper, and lead ores. The thallium is collected in the flue dust in the form of oxide or sulfate with other by-product metals, eg, cadmium, indium, germanium, selenium, and tellurium. The thallium content of the flue dust is low and further enrichment steps are required. If the thallium compounds present are soluble, ie, as oxides or sulfates, direct leaching with water or dilute acid separates them from the other insoluble metals. Otherwise, the thallium compound is solubilized with oxidizing roasts, by sulfatization, or by treatment with alkaU. The thallium precipitates from these solutions as thaUium(I) chloride [7791 -12-0]. Electrolysis of the thaUium(I) sulfate [7446-18-6] solution affords thallium metal in high purity (5,6). The sulfate solution must be acidified with sulfuric acid to avoid cathodic separation of zinc and anodic deposition of thaUium(III) oxide [1314-32-5]. The metal deposited on the cathode is removed, kneaded into lumps, and dried. It is then compressed into blocks, melted under hydrogen, and cast into sticks. 

Pla.tinum, Platinum plating has found appHcation in the production of platinised titanium, niobium, or tantalum anodes which are used as insoluble anodes in many other plating solutions (see Metalanodes). Plating solutions were often based on platinum "P" salt, which is diamminedinitroplatiniim (IT). A dinitroplatinite sulfate—sulfuric acid bath has been used to plate direcdy onto titanium (129). This bath contains 5 g/L of the platinum salt, pH adjusted to 2.0 with sulfuric acid. The bath is operated at 40°C at 10—100 A/m. Other baths based on chloroplatinic acid have been used in both acid and alkaline formulations the acid bath uses 20 g/L of the platinum salt and 300 g/L hydrochloric acid at 65° C and 10—200 A/m. The alkaline bath uses 10 g/L of the platinum salt, 60 g/L of ammonium phosphate and ammonium hydroxide to give a pH of 2.5—9.0. The alkaline bath can be plated directly onto nickel-base alloys acid baths require a gold strike on most metals. 

For environments in which tin is less readily corroded than lead, corrosion resistance of the alloy decreases as the lead content increases the decrease may, in some circumstances, be sharp at a particular composition. In the more corrosive media, such as nitrite solution, a sharp increase of corrosion rate is observed as the lead content increases beyond 30waters with low contents of dissolved salts, the corrosion rate increases slowly with lead content up to about 70% and then rises more steeply, but in the general run of supply waters the ability of lead to form protective insoluble anodic products is helpful to the durability of solder. Selective dissolution of tin has been... 

Depending on electrolyte composition, the metal will either dissolve in the anodic reaction, that is, form solution ions [reaction (1.24)], or will form insoluble or poorly soluble salts or oxides precipitating as a new solid phase next to the electrode surface [reaction (1.28)]. Reacting metal electrodes forming soluble products are also known as electrodes of the first kind, and those forming solid products are known as electrodes of the second kind. 

Anodic dissolution (oxidation) of the metal with the formation of soluble [reaction (16.1)] or insoluble [reaction (16.2)] products... 

Reactions of Ph" radicals (12h) formed at anodes yield styrene (30), biphenyl (31), p-terphenyl (32), insoluble hydrocarbon of high molecular weight and, in smaller amounts, benzene (33) as well as ethanol (19). 30 was the main product for substituted reagents 5q and 5r but for unsubstituted 5e only if the current efficiency, Teu was low. For higher Y i values 31 became the chief organic product. However, in contrast to aliphatic Grignard reagents, except methyl, the current efficiency was always much below 100%. In order to explain the above results the possibility of another route of anodic oxidation, different... 

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