Parasitic corrosion

Aluminum Batteries. Aluminum is another attractive anode material with a high theoretical energy density, but problems such as polarization and parasitic corrosion have inhibited the development of a commercial product. It, too, is being considered for a number of applications, with the best promise as a reserve or mechanically rechargeable battery (see Chaps. 9 and 38). 

This parasitic corrosion reaction, or self-discharge, degrades the coulombic efficiency of the anode and must be controlled to minimize this loss of capacity. 

Lithium metal, atmospheric oxygen, and water are consumed during the discharge, and excess LiOH is generated. The cell can operate at high coulombic efficiencies because of the formation of a protective film on the metal that retards rapid corrosion after formation. On open-circuit and low-drain discharge, the self-discharge of the lithium metal is rapid, due to the parasitic corrosion reaction... 

The parasitic corrosion reaction is highly undesirable as it produces no electric energy but consumes lithium. This highly exothermic reaction (-53.3 kcal/g-mol of lithium) can accelerate corrosion detrimentally. Efficient minimum-weight batteries require that this parasitic reaction be minimized. 

In addition to producing electrical energy in this reaction, a parasitic corrosion occurs at the metal anode that contributes to the dissolution of aluminum, generating minute quantities of hydrogen gas and also heat ... 

A number of researchers have begun to prepare poly-mer/superconductor composites with the hope of improving the processibility and properties of the hybrid materials (see Table 37.1) [1-8], For example, polymeric matrices loaded with ceramic superconductor components have been used in a plastic extrusion process to prepare superconducting wires and filaments [5,6]. Moreover, hydrophobic polymers have been used as environmentally protective layers [7,8] to slow the parasitic corrosion reactions that occur when cuprate compounds are exposed to water, acids, carbon dioxide, and carbon monoxide. 

In normal battery operation several electrochemical reactions occur on the nickel hydroxide electrode. These are the redox reactions of the active material, oxygen evolution, and in the case of nickel-hydrogen and nickel-metal hydride batteries, hydrogen oxidation. In addition there are parasitic reactions such as the corrosion of nickel current collector materials and the oxidation of organic materials from separators. The initial reaction in the corrosion process is the conversion of Ni to Ni(OH)2. 

The problems connected with the TeClt (C) and C1(C) cells are low capacity and parasitic currents, and of the S, Se and CI2 cells corrosion of the seals and insulators. All these cells were (in 1973) in the early stages of development. The cells have ED of about 200 Wh/kg (70). 

The corrosion inhibitor can be a complexing agent that stops the metal redeposition reaction (reduction) by eliminating free metal ions from the solution. Theoretically, this would consecutively stop the associated oxidation reaction. Due to parasitic reduction reactions, however, the metal oxidation can continue, even enhanced by the complexing agent effect. 

The main practical problem of this type of battery is the tendency of the anode to corrosion, according the following parasitic reaction ... 

Related to the corrosion problems was a recent SECM study, which demonstrated the possibility of eliminating typical experimental problems encountered in the measurements of heterogeneous electron transfer at semiconductor electrodes (27). In this experiment, the redox reaction of interest (e.g., reduction of Ru(NH3)s+) is driven at a diffusion-controlled rate at the tip. The rate of reaction at the semiconductor substrate is probed by measuring the feedback current as a function of substrate potential. By holding the substrate at a potential where no other species than the tip-generated one would react at the substrate, most irreversible parasitic processes, such as corrosion, did not contribute to the tip current. Thus, separation of the redox reaction of interest from parallel processes at the semiconductor electrode was achieved. 

Compact design No busbars required Low-cost electrical equipment Higher operating voltage Lower operating current Parasitic electrical bypass currents Consequent reduced electrical efficiency Inhomogeneous current distribution Increased corrosion rate of electrodes... 

Actions and ITses.—Internally —In large doses, irritant and corrosive poison seldom administered medicinally, although, in doses of from five to ten grains, it has been recommended in glanders and farcy. Externally —Caustic to indolent ulcers, fistulas, and bony tumours as a stimulant in scab, mange, and similar affections also as an anti-parasitic for the destruction of pediculi, acari, < c. 

The reason that we gave the nitrate precedence over other salts is that we expect it to reduce the corrosion of the walls and also because it does not give products under radiation which may gum the system. The sulfate which has negligible absorption may precipitate sulphur although it is not clear that this cannot be avoided by the addition of peroxide. The parasitic absorption of the fluoride, the use of which was propsed by Allen, is also negligible but there is a strong opinion (Hiskey) that it will be difficult to avoid precipitation of the peroxide at such concentrations of the hydrofluoric acid which are tolerable from the point of view of corrosion. If the uranium is used in the form of a solution in Bi or fluorocarbons it may be necessary to eliminate the products of nuclear reactions of these substances along with the fission products. 

High surface passivation, based on energetics and/or kinetics, needs to be established to mitigate corrosion and aU other parasitic reactions. 

Effective PEC interfaces activated for the gas evolution reactions and passivated for corrosion and other parasitic reactions need to be engineered, using, for example, heterojunction and/or catalytic coating and/or dispersions. 

Higher parasitic currents that lower current efficiency and cause corrosion Malfunction of a unit cell can be difficult to locate No flow measurements to the individual cells... 

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