Electrolytes, aluminum

Emissions for Three Electrolytic Aluminum Reduction Cell Types Using Best Available... 

Electrolytic aluminum production is the most important process in both volume and significance. World production is about 15 megatons per year, consuming about 240 billion kilowatthours of electrical energy. Aluminum oxide (alumina), AI2O3, is subjected to electrolysis at a temperature of 950°C to this end it is dissolved in molten cryolite NujAlFg, with which it forms a eutectic melting at about 940°C. Carbon anodes that are anodically oxidized to CO2 in the process are employed. The overall electrolysis reaction can be written as... 

Mitrovic, M. and L. Knezic. 1979. Electrolytic aluminum oxide membranes -a new kind of membrane with reverse osmosis characteristics. Desalination 28 147-56. 

Charles Martin Hall produces electrolytic aluminum. Dr. H6roult made the same discovery independently at about the same time. 

In 1972, The Aluminum Company of America (Alcoa) announced a large-scale project to develop a commercial electrolytic aluminum chloride process [256], Based on extensive laboratory studies, a demonstration plant (15,000 tons per year) was built and operated for several years. Alcoa used commercial grade low calcined alumina as input material for the chlorination step, where it was reacted with chlorine and carbon to form gaseous A1C13 and C02 and CO. The... 

The Principles and Techniques of Electrolytic Aluminum Deposition and Dissolution in Organoaluminum Electrolytes... 

Electrolytic Aluminum Deposition from Nonaqueous Organic Electrolytes. 175... 

Processing Techniques for Electrolytic Aluminum Deposition from Electrolytes Containing Aluminum Alkyls. 211... 

The first attempt to electrolytically deposit an aluminum layer was carried out more than 100 years ago. Since then, other methods of electrolytic aluminum deposition were continued to be published. However, none stood up to careful scrutiny. The wish to electrodeposit a newly-to-be-erected statue of William Penn with aluminum led the city council of Philadelphia to be swindled. A charlatan claimed to be able to complete the electroplating process by using a secret recipe. The aluminum was to protect the statue from corrosion in the sea climate. The contractor had the city finance the construction of the world s largest eletroplating plant. Only subsequently would the defraud be publicized, when it became clear that zinc had been elec-trodeposited instead of eiluminum [203]. 

This section provides a survey of the electrolytic deposition of aluminum out of organoaluminum electrolytes, from its discovery to its technical applications. First, the deposition of metals from nonaqueous organic electrolytes is generally discussed, and the corresponding problems and possibilities are pointed out. In detail, concrete examples of electrolytic aluminum deposition from organoaluminum electrolytes and their fundamental complex chemistry and electrochemistry are treated. In a further section, the properties of such deposited aluminum are described, and finally an overall view is given of the development in instrumentation from the first laboratory cell to a coating plant unit with a capacity of 90 mVh. 

Most metals can be electrolytically deposited from water-free melts of the corresponding metal salts. It is well known that aluminum, lithium, sodium, magnesium, and potassium are mass produced by electrolytic deposition from melts. Industrial processes for the melt-electrolytic production of beryllium, rare earth metals, titanium, zirconium, and thorium are also already in use. Pertinent publications [74, 137, 163] describe the electrolytic deposition of chromium, silicon, and titanium from melts. Cyanidic melts are used for the deposition of thick layers of platinum group metals. It is with this technique that, for instance, adhesion of platinum layers on titanium materials is obtained. Reports concerning the deposition of electrolytic aluminum layers [17, 71-73, 94, 96, 102, 164, 179] and aluminum refinement from fused salts [161] have been published. For these processes, fused salt... 

Consequently, in early 1953, research on these complex compounds was initiated to determine whether they were suitable for electrolytic aluminum deposition. The first trials ended in disappointment, because the electrolytes, employed as melts, yielded useless aluminum coatings containing large portions of alkali metal. Besides, the electrolytes showed a very low conductivity compared to aqueous systems. Attempts to improve the quality of the aluminum deposits by adding excess triethylaluminum led to unexpected observations. Hence, a detailed investigation of alkali metal fluoride-aluminum trialkyl systems was necessary. 

Fig. 1 shows one of the first electrolytically deposited alumimun coatings to be obtained from this type of electrolyte. Since electrolytic aluminum deposition from this system has no true smoothening effect, thick layers become even rougher, as illustrated by the thickly coated cathode plate shown in Fig. 1. The cathodic deposition and the anodic dissolution of aluminum corresponded to almost 100 <7o of the amount expected according to the Faraday rule, which is an important prerequisite for even considering using this electrolysis technique for technical applications. Independently of the layer thickness, the deposited aluminum layers are found to be ectraordinarily pure. Spectroscopic investigations have revealed purities of up to 99.999%. Even when relatively impure raw aluminum with purities of 99.7% functions as the anode, very pure aluminum can be deposited. Therefore, obviously not only a technique of electroplating aluminum was discovered, but also a method of...

Already in the first year after the discovery of electrolytic aluminum deposition from solutions containing aluminum alkyls, an apparatus for the continuous plating of wire was tested [118], see Fig. 17. 

The first production plant in the world for electrolytic aluminum coating from organoaluminum complexes was put into operation by SEDEC (Berlin) in 1983. In order to shorten the processing time required by the HGA plant, this unit was designed as a rectangular cell. The production cell has an electrolyte volume of 15,000 L. The capacity of this automatic aluminum plating unit amounts to 32 m /h, with a layer thickness of 10 pm. Articles mounted on 32 frames, each 500 X 1000 mm in size, can be simultaneously coated. Fig. 19 shows the electrolysis... 

In comparing electrolytic aluminum coating with conventional aqueous plating processes, it turns out that both proceed via the following process steps to afford electroplated pieces ... 

Recent technology for electrolytic aluminum production employing aluminum chloride has also been of interest because of the about 30% power savings possible [21]. Since aluminum chloride melts at much lower temperatures and forms a much more fluid melt than the standard Hall-Heroult electrolyte matrix, much higher voltage efficiencies are possible. However, sublimation and control problems limit the utility of direct, one-component electrolytic methods. The essence of this idea is employed in the process, developed by C. Toth of Alcoa, which has the additional advantage of enabling clay sources of alumina to be tapped [22] (Fig. 12.4). 

Alcoa has developed a second electrolytic aluminum process that involves electrolysis of aluminum chloride. The aluminum chloride is obtained by chlorinating aluminum oxide. The chlorine liberated at the anode can be recycled. Also the electric power requirements of this process are less than for the Hall-Heroult process. This aluminum chloride reduction has not been used as much as the oxide reduction. 

Electrolytic aluminum was in commercial production only two years after the independent discoveries of the same process were made in 1886 by Charles Martin Hall in Oberlin, Ohio in the U.S., and by Paul Heroult in France. They had found that alumina is... 

Paper or polymer film Electrolytic (aluminum or tantalum)... 

The products were polymers of methyl methacrylate, butyl acrylate, or their copolymer. The amount of surfactant was about 9% of the monomers and for the cosurfactant the feature was only 1 %. When the same surfactant was used with pentanol as cosurfactant or with no cosurfactant, the particle size distribution was much broader, even bimodal. The latexes were shown to be stable vs. electrolyte (aluminum sulfate), and also for several freeze-thaw cycles. These features were attributed more to the nature of the surfactant than to the use of polymerizable cosurfactant. 

Electrolytic Aluminum foil electodes with electrolyte-impregnated paper dielectric O-IO" High capacitance... 

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