Cathodic activation

The usual practice in old wells of only partially cementing the outer pipe can lead to cell formation (steel in the cement-steel in the soil) in the transition regions to the uncoated sections (see Sections 4.2 and 4.3). In contrast to the well-known cathode steel-soil in the vicinity of the ground surface, the cathodic activity of the... 

The addition of cathodically active elements to pure lead was the main objective of investigations to improve its corrosion resistance to H2SO4 [42,44]. Best known is copper-lead with 0.04 to 0.08% Cu. By adding combinations of alloying elements, it was possible to produce lead alloys that not only had much better corrosion resistance, but also had greater high-temperature strength. Lead alloy with 0.1% Sn, 0.1% Cu and 0.1% Pd is an example [45]. 

Both silicon and aluminium are added to zinc to control the adverse effects of iron. The former forms a ferro-silicon dross (which may be removed during casting). Aluminium forms an intermetallic compound which is less active as a cathode than FeZn,] . Similarly in aluminium and magnesium alloys, manganese is added to control the iron . Thus in aluminium alloys for example, the cathodic activity of, FeAl, is avoided by transformation of FeAlj to (Fe, Mn)Al/. This material is believed to have a corrosion potential close to that of the matrix and is, therefore, unable to produce significant cathodic activity . 

Mn02 is used for the same purpose as the cathode active material in lithium-manganese dioxide (Li - Mn02) batteries it has been used for a long time in zinc-carbon and alkaline-manganese dioxide batteries, which are aqueous-electrolyte systems. 

The Li-SOCl2 battery consists of a lithium-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 lithium tetrachloro-aluminate. Thionyl chloride serves as both the cathode active material and the elec-... 

Nickel hydroxides have been used as the active material in the positive electrodes of several alkaline batteries for over century [1], These materials continue to attract much attention because of the commercial importance of nickel-cadmium and nickel-metal hydride batteries. In addition to being the cathode active material in nickel-metal hydride batteries, Ni(OH)2 is an important corrosion product of the anode during cycling. There are several reviews of work in the field [2-10],... 

In plain tinplate cans for acid foods, tin provides cathodic protection to steel (3,4). The slow dissolution of tin prevents steel corrosion. Many investigators (5-1I) have defined this mechanism in detail and have shown that the tin dissolution rate is a function of the cathodic activity of the base steel, the steel area exposed through the tin and the tin-iron alloy layers, and the stannous ion concentration. Kamm et al. showed that control of the growth of the tin—iron alloy layer provides a nearly continuous tin-iron alloy layer and improves the corrosion resistance of heavily coated (over 45 X 10"6 in. tin) ETP for mildly acid food products in which tin provides cathodic protection to steel (12). The controlled tin-iron alloy layer reduces the area of steel exposed to the product. ETP with the controlled alloy is designated type K, and since 1964, 75 type K ETP has been used to provide the same protection as 100 ETP provided previously (13). 

B. Cathodic Activation of Unsaturated Systems by Sulphonyl Groups. . 1019... 

Crystalline chemical and electrochemical manganese dioxides are employed in billions of cells of Leclanche type which remain today probably the most popular and inexpensive power sources for wrist watches, cameras, flashlights, portable electronic products, etc. Worldwide annual output of power sources is estimated at 40 bln. pieces more than 70% of them are those operating with Mn02 chemistry as a cathode active material or a... 

A form of electrolytic manganese dioxide obtained by us from fluorine-containing electrolytes was seen to produce the best cathode active material for Zn/Mn02 and Li/Mn02 types of power sources. 

INVESTIGATION OF THIN-FILM ELECTRODE MATERIALS AS CATHODIC ACTIVES FOR POWER SOURCES... 

An enormous amount of work has been done in this wide field and a number of excellent reviews on different aspects of sulfur electrochemistry has been published [1-7], so here we confine our attention to some principal reactions and interesting apphcations of both anodic and cathodic activation of sulfur-containing molecules. Compared to other chalco-genides, sulfur has frontier orbitals that have volume, symmetry, and energy more suitable for efficient interaction with adjacent carbon atoms. The ionization of molecular sulfur requires about 10 eV. Conjugation of the pz orbitals of sulfur with a 7T-system lowers the ionization potential by ca. 2 eV. For this reason, compounds of divalent sulfur undergo oxidation rather easily often giving rise to cation radicals or dications. The stability of this species is in line with the... 

Figure 9-2 shows the potential energy curves of metallic ions both in transfer equilibrium and in anodic polarization. The anodic and cathodic activation energies Ag and 4 are given as functions of overvoltage t (positive in the anodic and n ative in the cathodic direction), respectively, in Eqn. 9-3 ... 

Expressing the anodic and the cathodic activation energies in the standard state as 4 4. o) respectively, and the standard equilibrium potential... 

The evaluation of catalysts for FEMFCs in recent years has been well defined experimentally and numerically. In particular, studies have correlated that observed in liquid electrolytes to that observed in MEAs (e.g., for cathode activity, see Gasteiger et al. ). 

For DMFC systems, Pt cathodes are also used as the catalyst of choice however, given Pt s ability to reduce oxygen and oxidize methanol, this lack of selectivity makes them sensitive to methanol crossover from anode to cathode via the membrane. This methanol crossover can have a depolarizing effect on cathode performance, reducing overall cathode activity. To combat this, an extensive effort has been made to identify and develop selective oxygen/reduction catalysts unaffected by MeOH crossover. 

One further degradation mode related to catalysis is a consequence of operating at low current densities typical of portable power application. Under these conditions, overoxidation of the Pt cathode catalyst occurs, reducing cathode and overall MEA performance. Zelenay has shown that starving the cathode of air flow lowers the cathode potential to low values, causing reduction of Pt oxides and restoring cathode activity. ... 

Antoine, O., Bultel, Y, Ozil, P, and Durand, R. Catalyst gradient for cathode active layer of proton exchange membrane fuel cell. Electrochimica Acta 2000 45 4493 500. 

Trasatti, S. (1992) Electrocatalysis of hydrogen evolution progress in cathode activation, in Advances in Electrochemical Science and Engineering (eds H. Gerischer and C.W. Tobias), VCH Verlag GmbH, Weinheim. 

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