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• 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
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