Aluminum fluorides

Aluminum fluoride is utilized, in addition to cryolite, as a raw material in the electrolytic manufacture of aluminum (temperature of electrolyte 950°C, composition 80-85% Na AlFft, 5-7% AIF, 5-7% CaF2, 2-6% AFO, 0-7% LiF). No fluorine should actually be consumed in this process, modern plants recovering the fluorine in its entirety. Other uses are as a flux (in welding, soldering, manufacture of casts), and as a melting point depressant in glass and enamel. The aluminum fluoride capacities in Europe are given in the table below. 

Starting material lluorspar fluorspar fluorspar fluorspar hexafluoro-silicic acid 

Most important European manufacturer is PCUK with a capacity of 96 103 t/a. 

Aluminum Fluoride Manufacture from Hydrogen Fluoride 

In the Lurgi process aluminum hydroxide is first calcined at 300 to 400°C and then reacted with hydrogen fluoride in a fluidized bed reactor at 400 to 600°C (dry process)  

Aluminum fluoride (uh-LOO-min-um FLOR-ide) is a highly stable compound that occurs as a white crystalline solid. It resists the action of even strong solvents, such as hot concentrated sulfuric acid. The compound often occurs as a hydrate containing one or more molecules of water of hydration. The most common of these hydrates has the chemical formula A1F3-3.5H20, meaning that for every two molecules of aluminum fluoride in a crystal, there are seven molecules of water. The major uses of aluminum fluoride are in a variety of applications in the chemical industry. 

Three methods are available for the preparation of aluminum fluoride commercially. In the first method, alumina trihydrate (aluminum hydroxide A1(0H)3) is treated with hydrofluoric acid (HF). A second method of preparation is almost identical except that it takes place in the dry state 

Aluminum fluoride. Red atom is aluminum and green atoms are fluorine, publishers 

The primary use of aluminum fluoride is in the production of aluminum metal. In that process, aluminum is extracted from one of its compounds (usually aluminum oxide) by passing an electric current through the molten (melted) compound. The addition of aluminum fluoride to the raw materials used in the process reduces the temperature at which the reaction occurs and improves the conductivity of the molten compound. 

Some other uses of aluminum fluoride include  

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Production of hydrogen fluoride from reaction of Cap2 with sulfuric acid is the largest user of fluorspar and accounts for approximately 60—65% of total U.S. consumption. The principal uses of hydrogen fluoride are ia the manufacture of aluminum fluoride and synthetic cryoHte for the Hall aluminum process and fluoropolymers and chlorofluorocarbons that are used as refrigerants, solvents, aerosols (qv), and ia plastics. Because of the concern that chlorofluorocarbons cause upper atmosphere ozone depletion, these compounds are being replaced by hydrochlorofluorocarbons and hydrofluorocarbons. 

Another use for cryoHte is in the production of pure metal by electrolytic refining. A high density electrolyte capable of floating Hquid aluminum is needed, and compositions are used containing cryoHte with barium fluoride to raise the density, and aluminum fluoride to raise the current efficiency. 

B. Jensen, Phase and Structure determination of a New Complex Alkali Aluminum Fluoride, Institute of Inorganic Chemistry, Norwegian Technical University, Trandheim, 1969. 

Production. Global hydrogen fluoride production capacity in 1992 was estimated to be 875,000 metric tons. An additional 204,000 metric tons was used captively for production of aluminum fluoride. Worldwide capacity is tabulated in Table 5 (38). Pricing for hydrogen fluoride in 1990 was about 1.52/kg (39). 

Anydrous HF for the production of aluminum fluoride. See also Table 6. 

North America accounts for about 38% of the worldwide hydrogen fluoride production and 52% of the captive aluminum fluoride production. Table 6 (38) summarizes North American capacity for hydrogen fluoride as weU as this captive capacity for aluminum fluoride production. In North America, HF is produced in the United States, Canada, and Mexico, but represents a single market, as weU over 90% of the consumption is in the United States. 

In the North American HF market, approximately 70% goes into the production of fluorocarbons, 4% to the nuclear industry, 5% to alkylation processes, 5% to steel pickling, and 16% to other markets (41). This does not include the HF going to aluminum fluoride, the majority of which is produced captively for this purpose. 

Aluminum Industry. Large amounts of HE are consumed in the production of aluminum fluoride [7784-18-17, AIE, and cryoHte [15096-52-3] (sodium aluminum fluoride), used by the aluminum industry. Both of these compounds are used in the fused alumina bath from which... 

Hydrofluorocarbons are also prepared from acetylene or olefins and hydrogen fluoride (3), or from chlorocarbons and anhydrous hydrogen fluoride in the presence of various catalysts (3,15). A commercial synthesis of 1,1-difluoroethane, a CFG alternative and an intermediate to vinyl fluoride, is conducted in the vapor phase over an aluminum fluoride catalyst. 

No cryolite is actually needed once the smelting process is in operation because cryolite is produced in the reduction cells by neutralizing the Na20 brought into the cell as an impurity in the alumina using aluminum fluoride. 

Thus operating cells need aluminum fluoride [7784-18-17, AIF., rather than cryoHte. Much aluminum fluoride is produced in a fluidized bed by the reaction of hydrofluoric acid gas and activated alumina made by partially calcining the alumina hydrate from the Bayer process... 

Aluminum fluoride is also made by the reaction of fluosiUcic acid [16961 -83-4] H2SiFg, a by-product from phosphoric acid production (see Phosphoric ACID AND THE PHOSPHATES), and aluminum hydroxide from the Bayer process. 

Oxyfluoride ions are discharged at the anode, forming carbon dioxide [124-38-9] and aluminum fluoride. The first oxygen can be removed more readily from Al2 02F4 than either the second or the oxygen from Al2 0Fg ... 

According to Faraday s law, one Faraday (26.80 Ah) should deposit one gram equivalent (8.994 g) of aluminum. In practice only 85—95% of this amount is obtained. Loss of Faraday efficiency is caused mainly by reduced species ( Al, Na, or A1F) dissolving or dispersing in the electrolyte (bath) at the cathode and being transported toward the anode where these species are reoxidized by carbon dioxide forming carbon monoxide and metal oxide, which then dissolves in the electrolyte. Certain bath additives, particularly aluminum fluoride, lower the content of reduced species in the electrolyte and thereby improve current efficiency. 

A third technique employs monovalent aluminum. By bringing vapors of aluminum fluoride or aluminum chloride into contact with carbothermicahy reduced aluminum ahoy at 1000—1400°C, the fohowing reaction occurs... 

After the Si02 is filtered off, the aluminum fluoride is crystallized as the tfihydrate which is then calcined at 500—550°C to yield anhydrous A1F.. 

The aluminum halides and aluminum nitrates have similar properties with the exception of the family of aluminum fluoride compounds which are discussed elsewhere (see Fluorine compounds, inorganic). Of the remaining members ia this aluminum haUde family, chloride derivatives are the most commercially important alurniaum brornide /7727-/3 -JJ AlBr, alumiaum iodide [7784-23-8] and alumiaum nitrate [13473-90-0] are of... 

Minerals and Ash. The water-soluble extract solids which iafuse from tea leaves contain 10—15% ash. The tea plant has been found to be rich in potassium (24) and contains significant quantities of calcium, magnesium (25), and aluminum (26). Tea beverages are also a significant source of fluoride (27), owing in part to the uptake of aluminum fluoride from soils (28,29). 

Gl ss-Ionomers. Glass-ionomers show fluoride release at levels that are usually higher than those found in composite materials. The fluoride is found within the aluminosihcate glass, which is melted with fluoride fluxes and ground to form powder filler. The fluoride is added as calcium fluoride [7789-75-5] aluminum fluoride [15098-87-0] and sodium fluoride [7681-49-4] in a combined proportion of approximately 20% by weight in the final powder (284,285). 

The combination of alkali metal acid fluorides and porous aluminum fluoride IS a stable, solid, and efficient substitute for anhydrous hydrogen fluoride for promoting the ring-opening reactions of simple aliphatic oxiranes to give the fluorohydrins under sonication [/5] (equations 14 and 15)... 

One of the most useful ways of introducing fluorine into organic compounds is the placement of the hydroxyl group in alcohols hydroxy compounds, and carboxylic acids Methyl alcohol reacts with anhydrous hydrogen fluoride at 100 500 °C in the presence of aluminum fluoride [60, 61], zinc fluoride [62] chromium fluonde [63], or a mixture of aluminum and chromium fluondes [64] to give a 20-78% yield of fluoromethane Attempted fluorinations of higher alcohols by this method failed [60]... 

The primar> uses for hydrogen fluoride in the United States arc in the manufacture of chlorofluorocarbons, aluminum fluoride, sodium aluminum fluoride (ciyolitc). md uranium tetrafluoride, and in petroleum alkylation. 

A side stream from the anode product mixture is passed over a hot (100-115°C) alumina bed where the fluorine reacts quantitatively to produce aluminum fluoride and oxygen. The nitrogen/oxygen ratio is... 

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