Aluminum molten

The chlorofluorocarbons react with molten alkah metals and CCI2F2 reacts vigorously with molten aluminum, but with most metals they do not react below 200°C. An exception is the dechlorination of chlorofluorocarbons with two or more carbon atoms in the presence of Zn, Mg, or A1 in polar solvents. A commercial synthesis of chlorotriduoroethylene [79-38-9] employs this reaction ... 

The electrorefining of many metals can be carried out using molten salt electrolytes, but these processes are usually expensive and have found Httie commercial use in spite of possible technical advantages. The only appHcation on an industrial scale is the electrorefining of aluminum by the three-layer process. The density of the molten salt electrolyte is adjusted so that a pure molten aluminum cathode floats on the electrolyte, which in turn floats on the impure anode consisting of a molten copper—aluminum alloy. The process is used to manufacture high purity aluminum. 

Aluminum and Hydrogen. Hydrogen [1333-74-0] is the only gas known to be appreciably soluble in soHd or molten aluminum. Hydrogen can be introduced into Hquid aluminum from reaction with moisture present in the furnace atmosphere or the refractories, or with moisture entrapped in the oxide film of the soHd aluminum before melting. The solubiUty of hydrogen in molten and soHd aluminum is shown in Table 6. 

In dry air at room temperature this reaction is self-limiting, producing a highly impervious film of oxide ca 5 nm in thickness. The film provides both stabihty at ambient temperature and resistance to corrosion by seawater and other aqueous and chemical solutions. Thicker oxide films are formed at elevated temperatures and other conditions of exposure. Molten aluminum is also protected by an oxide film and oxidation of the Hquid proceeds very slowly in the absence of agitation. 

Molten aluminum reacts violently with water [7732-18-5] and the molten metal should not be allowed to touch damp tools or containers. In finely divided powder form, aluminum also reacts with boiling water to form hydrogen and aluminum hydroxide [21645-51 -2], this reaction proceeds slowly in cold water. 

Molten aluminum is removed from the cells by siphoning, generally daily, into a cmcible. Normally the metal is 99.6—99.9% pure. The principal impurities are Ee, Si, Ti, V, and Mn, and come largely from the anode, but also from the alumina. 

Anhydrous aluminum chloride, AIQ, is manufactured primarily by reaction of chlorine [7782-50-5] vapor with molten aluminum and used mainly as a catalyst in organic chemistry ie, in Friedel-Crafts reactions (qv) and in proprietary steps in the production of titanium dioxine [13463-67-7] Ti02, pigment. Its manufacture by carbochlorination of alumina or clay is less energy-intensive and is the preferred route for a few producers (19). 

Porous carbon and graphite are used ia filtration of hydrogen fluoride streams, caustic solutions, and molten sodium cyanide ia diffusion of chlorine iato molten aluminum to produce aluminum chloride and ia aeration of waste sulfite Hquors from pulp and paper manufacture and sewage streams. 

Production of one metric ton of molten aluminum requites about 500 kg of anode carbon and 7.5—10 kg of cathode blocks which is the largest industry usage of carbon materials. Aluminum smelters generally have an on-site carbon plant for anode production. Anode technology is focused on taw materials (petroleum coke and coal-tar pitch), processing techniques, and todding practices (74). 

FIGURE 14.24 In the Hall process, aluminum oxide is dissolved in molten cryolite and the mixture is electrolyzed in a cell with carbon anodes and a steel cathode. The molten aluminum flows out of the bottom ot the cell. 

TiB2 coatings for electrodes for aluminum production (Hall-cell cathodes). TiB2 has high resistance to molten aluminum yet it is readily wetted by the molten metal and good electrical contact is assured. 

Borides are generally resistant to molten metals, at least to those that do not readily form borides, such as copper, zinc, magnesium, aluminum, tin, lead, and bismuth. TiB2 is especially resistant to molten aluminum and, as such, is used in crucibles for evaporation of the metal. 

Boron nitride is one of the most outstanding corrosion-resistant materials. It is inert to gasoline, benzene, alcohol, acetone, chlorinated hydrocarbons and other organic solvents. It is not wetted by molten aluminum, copper, cadmium, iron, antimony, bismuth, silicon, germanium, nor by many molten salts and glasses. It is used extensively as crucible material, particularly for molten metals, glasses and ceramic processing. 

Degassing is the removal of dissolved hydrogen from the molten aluminum prior to casting. Chemicals are added and gases are bubbled through the molten aluminum. Sometimes a wet scrubber is used to remove excess chlorine gas. 

Direct chill casting is the pouring of molten aluminum into a water-cooled mold. Contact cooling water is sprayed onto the aluminum as it is dropped into the mold, and the aluminum ingot falls into a water bath at the end of the casting process. 

Stationary casting is the pouring of molten aluminum into molds and allowing the metal to air cool. 

Currently, systems for measuring the hydrogen content in molten aluminum are commercially available. In the most common systems, an inert gas (usually nitrogen) flows through a probe and over the molten metal, such that chemical equilibrium between the hydrogen partial pressure in the gas and the concentration of hydrogen in the... 

Orme, M. Liu, Q. Smith, R. 2000. Molten aluminum micro-droplet formation and deposition for advanced manufacturing applications. Aluminum Transactions J. 3 95-103. 

ALCOA A process proposed for manufacturing aluminum metal by the electrolysis of molten aluminum chloride, made by chlorinating alumina. It requires 30 percent less power than the Hall-Heroult process and operates at a lower temperature, but has proved difficult to control. Developed by the Aluminum Company of America, Pittsburgh, in the 1970s and operated in Palestine, TX, from 1976 abandoned in 1985 because of corrosion problems and improvements in the efficiency of conventional electrolysis. 

Calculate the mass of aluminum produced by the electrolysis of molten aluminum chloride, if a current of 500 mA passes for 1.50 h. 

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