aluminum
Aluminum (lat. aluminum) is a chemical element in the Periodic Table of Elements that has the symbol Al and the proton number 13. It is a low-density metal. Aluminum is the third most abundant element in the Earth's crust (8.13%). Only oxygen 46.60% and silicon 22.72% have a greater representation. Together with other elements, it creates several compounds that are significantly involved in the construction of the earth's crust. The most numerous group are silicates and aluminosilicates (kaolinite), which are also its most abundant sources. The most abundant mining raw material is bauxite Al2O3. nH2O, in addition, it occurs in the form of aluminum oxide and as the mineral corundum.
History
Aluminum was discovered in 1827 by the German chemist and physician Friedrich Wöhler. Aluminum was a rare metal at the time. It was used for decorative purposes. On the uniforms of the soldiers of Napoleon III's army. aluminum knobs were shining. Its price dropped when the first aluminum factory was built in Switzerland. For its lightness, it began to replace iron and other metals. It is most widely used where high strength and low weight are required - the aviation industry, cladding panels, die-cast parts mainly for the automotive industry...
Preparation of basic raw materials
The basic input for the production of aluminum is pure aluminum oxide Al2O3, which is obtained by cleaning bauxite, which is often contaminated with various oxides, most often oxides of titanium, iron and silicon. The bauxite purification process is carried out using sodium hydroxide under pressure. Cryolite Na3[AlF6] and fluorite CaF2 are added to the Al2O3 thus purified to lower the melting point. The amphoteric nature of aluminum hydroxide Al(OH)3 is also used to separate aluminum oxide from iron hydroxide. Ferric hydroxide does not have an amphoteric character and therefore does not dissolve in alkaline hydroxide. It follows that if we add alk. hydroxide, e.g. potassium hydroxide KOH, only Al(OH)3 will dissolve. The resulting filtrate will contain aluminum cations Al3+, which we can easily convert back into aluminum hydroxide. We obtain aluminum oxide from it by drying it.
Production
Melting takes place in an electric furnace by an electrolytic process. Direct current is used in electrolysis. Electrodes are made of a mixture of coal, coke and tar. The cathode is the plates that line the walls of the furnace, the anode is a bundle of 6 to 12 carbon electrodes (graphite rods). The bath consists of a 20% Al2O3 solution, which is subjected to electrolysis. A chemical reaction occurs: electrolysis of the melt.
- Al2O3 → 2Al3+ + 3O2−
- Anode
- O2− - 2e− → O20
- O2 + C → CO2
- Cathode
- Al3+ + 3e− → Al0
At the carbon electrodes, oxygen is extracted from the bath, which immediately reacts with carbon to form carbon dioxide CO2. Pure aluminum is isolated in the form of a melt on the cathode plates that line the furnace. This is later cast into clay molds. The production of aluminum is very energy intensive.
Amphoteric characterAl, Al2O3 a Al(OH)3
Amphoteric character means that it reacts with both acid and base.
- reaction with hydroxide anion OH-
Al3+ → Al(OH)3 (S) → [Al(OH)4]-
Al(OH)3 (S) -white turbidity is formed
reaction with a cationH3O+
[Al(OH)4]- → Al(OH)3 (S) → AI3+
Production in Slovakia
In the premises of the aluminum smelter in Žiar nad Hronom, the company Slovalco (majority owner of Hydro) produces aluminum and its alloys for further processing.[1] For example, the company Hydro Extrusion Slovakia produces and sells aluminum sheets, pressed profiles, building systems.[2] Other companies operating in Žiar are manufacturers and suppliers in the automotive, consumer and construction industries: Nemak, Fagor Ederlan Slovakia, Thermosolar.
In Slovakia, scientists led by František Simančík from the SAV Institute of Materials and Machine Mechanics developed technologies for the industrial serial production of various parts from aluminum metal foam. These technologies are protected by world patents.[3]
Properties and use
Aluminum is resistant to corrosion and burns to aluminum oxide Al2O3 when ignited. It is harmless in all environments except acidic, it dissolves in acidic (sauerkraut, tea). Due to its toxic and carcinogenic effects (it replaces metals in metalloproteins), it is forbidden to use aluminum utensils.
It is mainly used in aluminothermy - it is a method of obtaining metals from their oxides, while the reducing ability of aluminum is used.
e.g. Fe2O3 + 2 Al = Al2O3 + 2 Fe
Another use of aluminum - the production of aluminum foil, in the production of polyethylene and alloys.
The production of alloys is used in the metallurgical industry in the production of means of transport and various light constructions.
The best-known aluminum alloy is dural (durable aluminum), which is an alloy of aluminum with copper and magnesium (Al-Cu4-Mg). The main application of duralumin was in the aviation industry. In the past, it found its place in the production of household items such as cutlery and crockery - it was replaced by more expensive antiques. It is often used in electrical engineering because of its good electrical conductivity and lower cost than copper, where aluminum alloys are used to make conductors. It is used in cables for high voltage distribution (power distribution network). It stopped being used in residential divorces at the end of the 80s. The reason is that aluminum "flows" under pressure - screwed electrical connections with aluminum conductors need to be tightened, otherwise the electrical contact will be lost over time. Its very good thermal conductivity is also used for the production of various coolers and heat exchangers. In construction, it is used for cladding panels. Aluminum is not very resistant to weathering, so it must be surface treated - by anodizing (electrochemically, an oxide layer is formed on its surface, which is resistant and can be painted and polished).
In addition, gem varieties of corundum Al2O3 - ruby and sapphire - are used. Al2O3 is also used to make emery paper.
In medicine, it is used e.g. aluminum acetate Al(CH3COO)3 - acetic acid salt; as a poultice against inflammation.
The ceramic industry is also important - production of porcelain and coarse ceramics. The basic component is kaolin (it contains the mineral kaolinite). Porcelain is created by firing a mixture of kaolin and crushed feldspar with quartz (known as Karlovy Vary porcelain). Coarse ceramics are made, e.g. fireproof material, roofing, stoneware, flower pots, pipes, etc.
Al3+ salts are found in drinking water, in medicines (acylpyrine, superpyrine - reduce stomach irritation), in baking powder, for frozen fruits and vegetables (for appearance), whipped cream stiffener, powdered milk, instant coffee, etc.
In industry, the production of metal foam, the so-called foamed aluminum, which has an advantageous stiffness-to-weight ratio (e.g., a plate made of aluminum foam has a significantly higher bending stiffness compared to an aluminum sheet of the same weight). The foam is better at dampening the vibration and noise caused by the vibration of the part than when it is cast from solid aluminum.