Aluminium fluoride is the inorganic compound which has the chemical formula of AlF3. This chemical compound is one of the popularly used chemical in many manufacturing process in various industries. The main use of aluminium fluoride is in the aluminium production.
In the production process of aluminium, producers do extract the aluminium from aluminium oxide by passing certain amount of electric current through the molten compound. We know this process as electrolysis. Producers add aluminium fluoride to the aluminium oxide to lower the reaction temperature so that the conductivity of melted compound would increase. This will make the manufacturing process more efficient.
This chemical compound plays significant role in the production of aluminium metal. You can actually see the other aluminium floruide uses in different applications including intermediates for industrial process, as fillers, as catalyst in organic synthesis and some others. This article will cover aluminium fluoride uses, its chemical characteristic and preparation methods.
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Aluminium Fluoride Properties
Aluminium fluoride has the physical form of white, solid crystalline. This chemical compound is highly stable as it can resist from the strong solvent like the high concentrated sulfuric acid. The common chemical form of aluminium fluoride is the hydrate form. This means that this compound has one or more molecules of hydration water. The common chemical formula for these hydrate forms is AlF3·3.5H2O. This means that every two molecules of aluminium fluoride in crystal form contain seven molecules of water. This chemical compound is also called as aluminium trifluoride.
As mentioned before, this compound has the chemical formula of AlF3 . It has the inorganic salt type with the solid state. Aluminium fluoride has the molecular weight of 83.98 g per mol and melting point of 1291°C (2356°F). This inorganic compound is slightly soluble in the cold water and normally soluble in the hot water. Aluminium fluoride is insoluble in the acetone, alcohol and other organic solvents. The main use of aluminium fluoride is in the aluminium metal production.
The chemical structure of aluminium fluoride adopts the structure of rhenium trioxide with the addition of distorted AlF6 octahedra. In this structure, each fluoride element is connected to two Aluminium centers. Aluminium fluoride has the 3 dimensional polymeric chemical structure, so that it has the high melting point level. In the gas form, aluminium fluoride has the form of trigonal molecules of D3h symmetry. The Al-F bond of this gas molecule has the length of 163 pm. Just like other gas metal trifluorides, this AlF3 compound adopts the planar structure at the evaporation process. However, the other aluminium trihalides in solid form has different properties. AlCl3 has single layer structure while AlBr3 and All3 are molecular dimers. Unlike aluminium fluoride, these aluminium trihalides has the low melting point and easily evaporate to release dimers.
Aluminium Fluoride Uses in Aluminium Manufacturing
Aluminium fluoride plays an important role in the aluminium manufacturing process. People use aluminium fluoride as the additive in the production process of aluminium. To get that aluminium product, they use the electrolysis process with the aluminium fluoride as the main additive. Aluminium fluoride, just like cryolite, is able to decrease the melting point of electrolytes to below 1000 °C. This chemical can also enhance the conductivity of the aluminium solution. In this electrolyte solution, the aluminium oxide is dissolved.
1. Aluminium Manufacturing
After that, the electrolysis process takes part and form up the bulk Aluminium (Al) metal. In the common aluminium manufacturing process, the producers add about 10 to 25 kg aluminium fluriode to the electrolytic cell for every 1 ton of aluminium produced. This amount will be based on the smelter technology used by the respective producers.
2. Aluminium Production
These abilities are really useful in the smelting process of aluminium as it will improve the efficiency in the aluminium production. Aluminium fluoride allows the manufacturer to lower the energy use in the manufacturing process, cut streamline production and decrease the production cost. In the same time, aluminium fluriode can form the purer aluminium product from this production process.
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Aluminium Fluoride Uses as Flux, Filler and others
Aluminium fluoride can also be used as the flux ingredient which can remove the magnesium in the refining process of aluminium scrap. Flux itself is the material which has the ability to lower the melting point of another substance which is used in the metal cleaning process. So, when the magnesium bearing aluminium alloys melt, fluoride makes reaction with the magnesium which will allow the removing process of this chemical element. With the ability, the remelters can create the aluminium alloy products which are magnesium free. The aluminium fluoride uses as flux can also be seen in some metallurgical processes. There are some other aluminium fluoride uses which you see in the following list.
- In ceramic industry. Aluminium fluoride uses can be seen also in the ceramic industry as the main compound to glaze and aluminium body mixture in the ceramic industry. They also use this aluminium fluoride to create the special refractory products.
- In glass industry as filler. Aluminium fluoride can play as a filler. You can see this use in the glass industry.
- In manufacturing aluminium silicates. People also use aluminium fluoride to manufacture the aluminium silicates.
- In glass production. Aluminium also can be utilized in another manufacturing process like fluoro aluminate glasses production. In this process, aluminium fluoride becomes the main ingredient with the zirconium fluoride.
- In the production of low index optical thin film. We can also see aluminium fluoride uses in the thin film product. With the magnesium fluoride, aluminium fluride can be the raw material for the low index optical thin film. Aluminium fluoride is more preferable if there’s higher UV transparency requirement. The physical vapor deposition of aluminium fluoride by evaporation process is a great option to get such a low index optical thin film.
- In fermentation process. Another aluminium fluoride uses is it can be used in the fermentation process. Aluminium fluoride has the capability to inhibit the fermentation process. This use is really beneficial in the beer and wine making industries.
- As catalyst. You can also see the aluminium fluoride uses as the catalyst in the organic compound synthesis process. The synthesis itself is the chemical reaction to form up the new chemical product from the simple chemical or reactants.
Preparation of Aluminium Fluoride
There’re actually some ways to produce this aluminium fluoride. Here’re some usual methods of aluminium fluoride preparation:
- In the first method, we mix alumina trihydrate or Aluminium hydroxide with chemical formula Al(OH)3 with hydrofluoric acid or HF. This kind of method usually is advisable for the preparation in the small scale laboratory
- In second method, we react aluminina trihydrate or Al(OH)3 with hydrogen fluoride in gas form. This reaction is actually similar with the first method, but this reaction takes place in the dry condition.
- The third method, we combine fluorosilicic acid or H2SiF6 with alumina trihydrate or Al(OH)3. This kind of method is extensively used in the industry as the cost is the lowest rather than the previous two methods. We can easily get the fluorosilicic acid as the main component for this reaction since this substance is the by product from the fertilizers and phosphoric acid production. This makes the cost of obtaining fluorosilicic acid is cheaper rather than hydrogen fluoride or hydrofluoric acid.
- In the next method, we treat alumina with hydrogen fluoride gas. The chemical reaction of this preparation is as follow:
- H2SiF6 + Al2O3 → 2 AlF3+ SiO2 + H2O
The above reaction is conducted in the high temperature condition of 700°C. This is also one of the most popular method to get aluminium fluoride product.
- In fifth method, we can obtain aluminium fluoride from thermal decomposition of ammonium This is the alternative method which producer may choose in the manufacturing scale.
In the nature, you can find aluminium fluoride in the form of aluminium fluoride trihydrate. This chemical element can be found in the rosenbergite, which is the rare mineral type. You can also find the non-hydrate form of aluminium floruide in the mineral like oskarssonite.
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Safety of Aluminium Fluoride Uses
As discussed before, the common use of aluminium fluoride is for the chemical industry applications. It’s also interesting to discuss the safety issue for this chemical compound. Most of the authorities state that aluminium fluoride does not contain the possible health hazard if it’s ingested in moderate amount. This is due to its low solubility properties.
However, aluminium fluoride may bring the risk if it’s inhaled or infect human skin. In modest amount, it can possibly cause the skin and eye irritation problems from the moderate level to the serious level. It can also lead to nose, throat and lungs irritation which can include nosebleeds. The risk of aluminium fluoride also includes the symptoms like coughing, short breathing or tightness in chest. These are the similar symptoms like asthma. The long exposure of this compound will impact to the bone weakness and joints stiffness.
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