Cathodes, aluminum composite

G.E. Jabbour, S.E. Shaheen, M.M. Morrell, B. Kippelen, N.R. Armstrong, andN. Peyghambarian, Aluminum composite cathodes a new method for the fabrication of efficient and bright organic light-emitting devices, Opt. Photon. News, 10 (4), 24, 1999. 

Corrosion Properties. In addition to corrosion problems such as pitting and exfoliation ced by conventional (monolithic) aluminum alloys, galvanic corrosion caused by the potential difference between the graphite fibers and the aluminum matrix is a reason for concern in these composites. As shown in Table 1, graphite appears at the cathodic (noble) end of the galvanic series while aluminum is at the anodic (active) end of the series. Graphite/aluminum composites have been shown to corrode 80 times faster than monolithic aluminum alloys in an aerated 3.15 wt% sodium chloride (NaCl) at room temperature (Ref 8). 

Anthracite. Anthracite is preferred to other forms of coal (qv) in the manufacture of carbon products because of its high carbon-to-hydrogen ratio, its low volatile content, and its more ordered stmcture. It is commonly added to carbon mixes used for fabricating metallurgical carbon products to improve specific properties and reduce cost. Anthracite is used in mix compositions for producing carbon electrodes, stmctural brick, blocks for cathodes in aluminum manufacture, and in carbon blocks and brick used for blast furnace linings. 

There is no question that the development and commercialization of lithium ion batteries in recent years is one of the most important successes of modem electrochemistiy. Recent commercial systems for power sources show high energy density, improved rate capabilities and extended cycle life. The major components in most of the commercial Li-ion batteries are graphite electrodes, LiCo02 cathodes and electrolyte solutions based on mixtures of alkyl carbonate solvents, and LiPF6 as the salt.1 The electrodes for these batteries always have a composite structure that includes a metallic current collector (usually copper or aluminum foil/grid for the anode and cathode, respectively), the active mass comprises micrometric size particles and a polymeric binder. 

A typical example is aluminum, which is used as a current collector for cathodes in lithium batteries [53], The stability of aluminum in many Li salt solutions at potentials as high as 4.5 V versus Li/Li+ is due to the formation of highly insoluble Al-halides on the aluminum surface which remain stable and thus protect this active metal from corrosion [53], In any event, in the evaluation of metals as electrode materials in nonaqueous systems, each case needs to be dealt with separately because the level of passivity and stability of most of the transition metals in polar aprotic systems depends on the solution composition. 

The aluminum industry consumes much more carbon, as baked anode composites, than the total of all other industrial uses for baked and graphitized carbon products. The free world s total annual aluminum production capacity is approximately 16 million short tons, about one-third being produced in the United States. World aluminum production involves the consumption (oxidation) of about eight million tons of anode carbon. Production occurs by electrolytic deposition from cryolite-alumina melts using a process patented simultaneously, but independently, in 1886 by Hall in America and Heroult in France. While minor process modifications have been made in the intervening years, and productivity greatly increased, substantially the same process is still used. The industrial electrolytic cell consists of a shallow carbon vessel about 10 ft. wide by 30 ft. long, and 1-2 ft. deep, which acts as the cathode and contains the fused salt bath and molten aluminum product. The carbon anodes are supported above the cathode and lowered into the cell at the rate of... 

Corrosion resistance of metallic coatings is dependent on the composition and nature of the electrolyte, oxygen concentration, polarization characteristics, ratio of cathodic to anodic area and the surface contaminants. If the corrosion potentials of two metals such as iron and aluminum are close to each other in a particular environment there may be reversal of the galvanic couple. 

In the early 1980s Kaiser Aluminum investigated the use of titanium di-boride as a wettable cathode material for Hall-Heroult cells [47]. Similar investigations by Reynolds Metals Co. continued until that company s recent merger with Alcoa [107]. The Reynolds work, and earlier research and development by Martin Marietta Aluminum [108], involved TiB2-C composites. Approaches to the... 

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