Aluminum fluoride

Description

Aluminum fluoride is in the form of white crystalline solid or a white powder. It occurs naturally as minerals rosenbergite and oskarssonite.1 It can also be prepared synthetically.

Synthesis

Aluminum fluoride are produced by methods in the following:
1) Fluosilicic acid with aluminum hydroxide2
H2SiF6 + 2 Al(OH)3 → 2 AlF3 + SiO2 + 4 H2O (I) 
The reaction is exothermal and proceeds in several steps. It can be described by the following three reactions:
3H2SiF6 + 2 Al(OH)3 → Al2(SiF6)3 + 6 H2O (II)
Al2(SiF6)3 + 6 H2O → 2 AlF3 + 3 SiO2 + 12 HF (III) 
12 HF + 4 Al(OH)3 → 4 AlF3 + 12 H2O 
The reaction is carried between 70°C and 100°C. The concentration of fluosilicic acid can be as high as 35 wt% in a water solution. As the produced aluminum fluoride solution is metastable and the trihydrate begins to crystalize out quickly at temperature around 90°C, precipitated solid silica must be removed as quickly as possible.
2) Al2O3 with aqueous hydrofluoric acid3

Hydrofluoric acid is added dropwise under vigorous stirring at room temperature into Al2O3 suspension. Subsequently the solid oxide is completely dissolved. The resulting clear solution is stirred for days at room temperature. During this period, the white solid precipitates are separated from the solvent, washed with water, and consequently dried. After treatment in a muffle furnace at the desired calcination temperature, aluminum fluoride is obtained.
3) Aluminum alkoxide with non-aqueous HF solution4
Aluminum alkoxide, Al(OR)3 (R = Me, Et, iPr, or tBu), reacts with non-aqueous HF solution in an organic solvent. The reaction is carried in a sol-gel state.  After aging, a solid is formed which settles. The solid is separated by centrifugation and dried under vacuum. Gas phase fluorination of the dried gel is then applied to obtain aluminum fluoride.

Application

Aluminum fluoride is one of the most important additives in the industrial production of aluminum. The usage of aluminum fluoride can lower the melting point of cryolite and better the physical and chemical properties of the electrolyte. In the aluminum production, aluminum oxide is dissolved in a solution of cryolite. By passing an electrical current through the solution, aluminum is produced. Nevertheless, cryolite solution melts at about 1000°C. When aluminum fluoride is added, electrolysis can happen in the cryolite solution at a temperature 40-60°C lower, reducing the required amount of energy to produce aluminum.5 Aluminum fluoride is used as a barrier layer to retard oxidation of aluminum mirrors.6 It is used as a flux in ceramic glazes and enamels, in the manufacture of aluminum silicate, and as a catalyst.
Aluminum fluoride complexes with proteins can be used to study the mechanistic aspects of phosphoryl transfer reactions in biology, which are of fundamental importance as phosphoric acid anhydrides such as ATP and GTP control most of the reactions involved in metabolism, growth and differentiation.8  
Aluminum fluoride, together with zirconium fluoride, is used to produce fluoroaluminate glasses. In agriculture, aluminum fluoride can be used to inhibit fermentation. Physical vapor deposited aluminum fluoride can be used as a low index optical thin film in situations when far UV transparency is required.1 

Toxicological studies

Oral animal lethal dose (LD50) of aluminum fluoride is 0.1 g/kg. Aluminum fluoride is less toxic than most fluorides due to its slight water solubility. Exposure to high concentration of aluminum fluoride causes hypocalcemia. Inhalation and ingestion of aluminum fluoride result in typical symptoms of fluoride poisoning. Symptoms of severe poisoning include shortness of breath, congestion of the lungs, muscle spasm, and convulsions.8 Acute (short-term) toxic effects may include the death of animals, birds, or fish and death or low growth rate in plants. Acute effects are observed in 2 to 4 days after exposure of animals or plants to aluminum fluoride. Chronic (long-term) toxic effects may include shortened life span, reproductive problems, lower fertility, and changes in appearance or behavior in exposed animals.

Safeties

Aluminum fluoride is a non-combustible solid. But it is incompatible with many other commodities including chemically active metals (e.g. potassium and sodium), acid, and acid fumes. Contact can cause fire or explosion. Upon heating, toxic fumes of fluoride, including extremely toxic hydrogen fluoride, can be emitted.

References

1. https://en.wikipedia.org/wiki/Aluminium_fluoride
2. John Karlström, Reactor Model for Production of Aluminum Fluoride
3. W. Kleist, C. Häßner, O. Storcheva, K. Köhler, A simple aqueous phase synthesis of high surface area aluminum fluoride and its bulk and surface structure, Inorganica Chimica Acta, 2006, vol. 359, pp. 4851-4854
4. S. K. Ruediger, U. Groß, M. Feist, H A. Proscott, S. C. Shekar, S. I. Troyanov, E. Kemnitz, Non-aqueous synthesis of high surface area aluminum fluoridea mechanistic investigation, Journal of Materials Chemistry, 2005, vol. 15, pp. 588-597
5. https://info.noahtech.com
6. R. Elaish, M. Curioni, K. Gowers, A. Kasuga, H. Habazaki, T. Hashimoto, P. Skeldon, Elelctrochimica Acta, 2017, vol. 245, pp. 854-862
7. Alfred Wittinghofer, Signaling mechanistics: Aluminum fluoride for molecule of the year, 1997, vol. 7, pp. R682-R685
8. Jeffrey Wayne Vincoli, Risk Management for hazardous Chemicals, Bund 1, 1996, ISBN 1-56670-200-3

Chemical Properties

Aluminum fluoride is a white, odorless powder or granule.

Chemical Properties

Aluminum fluoride, AlF3, is an anhydrous crystalline powder with a melting point of 1291 "C. Aluminum fluoride (hydrated), AlF3·3^1/2H20, is a white crystalline powder that is insoluble in water.

Uses

Production of aluminum to lower the melting point and increase the conductivity of the electrolyte, flux in ceramic glazes and enamels, manufacture of aluminum silicate, catalyst.

Uses

Aluminum fluoride is used to produce lowmelting aluminum metal, as a flux in ceramic glazes and white enamels, and as a catalyst in chemical reactions.

Uses

In ceramics, as flux in metallurgy, in aluminum manufacture, as inhibitor of fermentation, as catalyst in organic reactionsAluminum fluoride is used in the smelting process to lower the melting point of electrolytes, production of aluminum silicates, refining of aluminum scarp, production of specialty refractory products, and in glass industry as filler. It is used as flux ingredient to remove magnesium.

General Description

Odorless white powder or granules. Denser than water. Solubility in water at 25°C equals 0.559 g / 100 mL.

Air & Water Reactions

Slightly soluble in water

Reactivity Profile

Aluminum fluoride when heated to sublimation condition, emits toxic fumes of fluoride [USCG, 1999].

Hazard

Strong irritant to tissue.

Health Hazard

ACUTE: respiratory irritation; possible nose bleeding or vomiting; CHRONIC: aggravates bronchitis/asthma; increased bone density.

Fire Hazard

Special Hazards of Combustion Products: When heated to sublimation condition, emits toxic fumes of fluoride

Flammability and Explosibility

Non flammable

Safety Profile

A poison by ingestion. Moderately toxic by subcutaneous route. A severe eye irritant. Violently impact-sensitive when in contact with Na and K. When heated to decomposition it emits toxic fumes of F-. See also FLUORIDES and ALUMINUM COMPOUNDS.

Potential Exposure

Used as component of electrolyte from which aluminum metal is produced; in the manufacture of ceramics, enamels, aluminum silicate; as flux in metallurgy; as a fermentation inhibitor

Shipping

UN3260 Corrosive solid, acidic, inorganic, n.o.s., Hazard class: 8; Labels: 8-Corrosive material, Technical Name Required. UN3077 Environmentally hazardous substances, solid, n.o.s., Hazard class: 9; Labels: 9-Miscellaneous hazardous material, Technical Name Required.

Incompatibilities

Reacts violently with potassium or sodium

Waste Disposal

Neutralize with soda ash; add slaked lime; let stand for 24 hours. Transfer sludge to sewage facility.