A chemical composition of aluminum is a substance that consists of two or more chemical elements, one of which is aluminum. These elements are chemically related, that is, they are formed by covalent, ionic or metallic bonds. Chemical composition has a fixed chemical composition and a fixed chemical formula.
Aluminum alloys are usually not chemical compounds. They are a combination of homogeneous or inhomogeneous chemical elements or their compounds. Therefore, they do not have a fixed chemical composition and do not have a chemical formula.
Aluminum is the most common (more than 8% by weight) element of natural metal, and is also the third most common element among all chemical elements (after oxygen and silicon). However, due to the high chemical activity of aluminum, it is almost always found in combinations with other elements and is very rare in nature as a pure metal.
Pure aluminum is a white, flexible silver metal with a density of atomic number 13 and a relative atomic weight of 26.98. With a few exceptions, it is found in chemical compounds in the form of Al + 3.
This metal has amphoteric properties. Reacts with strong mineral acids and alkalis. Although aluminum is a chemically active metal, it has a very high resistance to corrosion. When a fresh surface of aluminum is in contact with oxygen, water or other oxidants, a dense oxide film (Al 2 O 3) immediately grows on it, creating a high corrosion resistance of the metal.
This oxide film is resistant to certain acids (eg, nitric acid) and prevents further chemical attack on the metal. However, it dissolves in some acids (for example, in hydrochloric acid or hot sulfuric acid) as well as in alkaline solutions, which causes more chemical reactions on the surface of the aluminum.
At high temperatures, aluminum reacts:
The second reaction is used in the production of some metals (aluminotherm), for example, manganese, and some alloys, such as ferro-titanium.
Natural minerals are chemical compounds. Aluminum is found in many minerals – more than 270 species – in combination with oxygen, silicon, alkali and alkaline earth metals and fluorine, as well as in the form of hydroxides, sulfates and phosphates. For example, feldspars – the most abundant minerals in the Earth’s crust (about 50%) – are aluminosilicates.
Metal aluminum in nature
Natural metal aluminum is sometimes found in the absence of oxygen as a minor step, for example, inside certain volcanoes. It is also found in minerals such as braille, cryolite, garnet, spinel and turquoise.
Impurities in Al 2 O 3 oxide crystals, such as chromium or cobalt, form precious stones such as rubies and sapphires, respectively. Pure Al 2 O 3 oxide is known as corundum – one of the hardest materials.
Although aluminum is a very common natural element, most aluminum ores cannot be an economical source of the metal. Almost all primary aluminum metal is produced from bauxite ores called (or bauxite), with the general chemical formula (ALO X (OH) 3-2x) .
Bauxite occurs in nature as a substrate weathering product with small amounts of iron and silicon in tropical climates. Natural bauxites contain different forms of hydrated aluminum oxide that have different crystal systems and also differ in the amount of hydration (number of water molecules per molecule of Al 2 O 3).
About 90% of aluminum ore – bauxite – goes to primary aluminum production, the remaining 10% – to other industrial applications.
Industrial production of primary aluminum has two main stages:
Bauxite is not a mineral or chemical compound. This name – bauxite (or more often, bauxite) – is used to identify the types of aluminum ores that contain aluminum compounds, mainly the types of hydroxides.
Industrial bauxite consists of three main types of hydroxide minerals:
These types of hydroxides in terms of physical properties such as:
Natural bauxite ores are usually composed of one of these types of hydroxides, although in some cases the same aluminum ore may contain mixed hydroxides.
Bauxite varies in color from cream to dark brown with high levels of iron.
The typical bauxite composition for the production of industrial aluminum includes the following compounds:
Almost all alumina is obtained from bauxite, which contains about 50% of Al 2 O 3 oxide as a hydroxide. The aluminum ore is treated in a caustic soda solution under pressure to dissolve alumina as aluminate, separating it from the red precipitate containing iron oxides and other basic impurities. Then, aluminum hydroxide crystals are precipitated from this aluminate solution.
At temperatures below 700 ° C, the technology mass contains the following various types of aluminum compounds – its hydroxides:
The final efficiency of alumina production technology is roasting the mixture of hydroxides obtained in the previous steps. The calculation (calculation) is performed at a temperature of 1200 ° C with the production of pure alumina with an amount of Al 2 O 3 oxide of more than 99%.
Industrial production of 1 ton of aluminum requires about 2 tons of alumina.
Aluminum compounds that are the most important for non-metallurgical industries are:
Aluminum oxide is one of its oxygen compounds. Pure oxide is a white powder in the form of particles of various shapes and sizes. Due to its amphoteric properties, this oxide is soluble in mineral acids and strong alkalis. There may be different changes. The most stable is the alpha corundum (alpha-Al 2 O 3).
Types of oxides
During dehydration of hydroxides, a set of Al 2 O 3 oxide forms is formed which still contains a small fraction of hydroxyl groups and retains some chemical activity. All oxides obtained at low temperatures are called transition corrections. At 1400 ° C, all transitional changes become an alpha change.
Anodic oxide is produced by electrochemical oxidation of aluminum. This compound is a nanostructured material with a unique structure. Anodic aluminum oxide is composed of cylindrical pores that offer a wide range of applications in engineering. Stable thermally and mechanically, it is light transparent and has high electrical insulation properties. The pore size and thickness of the anode oxide layer are easily adjusted by the parameters of this technology, which makes it possible to use it not only as a decorative protective coating for aluminum products but also as a basis for nanotechnology.
Different forms of aluminum hydroxides are known. The studied forms are Al (OH) 3 hydroxide and AlO (OH) hydroxide. In addition to these crystalline forms, several other types are known.
Al (OH) 3 hydroxide is used in large quantities for wastewater treatment as well as for the production of other aluminum compounds, including its salts.
Aluminum sulfate can be present in different proportions of water. The usual form of this compound is Al 2 (SO 4) 3 · 18H 2 O. It is almost insoluble in low water alcohol, but it dissolves well in water. Decomposes to aluminum oxide at temperatures above 770 ° C.
This substance is used in the following industries and fields of life:
Aluminum sulfate combines with one-sided metal sulfates to form double salts, called alum. The most important of these salts is potassium aluminum sulfate. This chemical compound is also known as potassium alum. These alums have been used extensively in leather, medicine, fabrics and dyes since time immemorial.
The bricks are mainly composed of aluminosilicate.
When chlorine gas interacts with molten aluminum, aluminum chloride is formed. This compound is often used as a catalyst in the synthesis reactions of various organic compounds. Hydrated Chloride AlCl 3 ∙ H 2 O, used as an antiperspirant or deodorant. This compound is one of several aluminum salts used in the cosmetics industry.
Aluminum chloride hexahydrate form is used:
Aluminum Forms AlH 3 hydride aluminum with hydrogen, which is widely used in organic chemistry including in the form of lithium aluminum hydride (LiAlH 4). This compound is obtained by the interaction of aluminum chloride and lithium chloride.
An intermetallic compound (intermetallic compound) is a chemical compound of two or more metals. Intermetallic compounds, as they should be for chemical compounds, have a fixed ratio between their components. In intermetallic compounds, the bond between atoms is usually metallic.
Intermetallic compounds are of great importance for the microstructure and properties of aluminum alloys. For example, iron and silicon are impurities that are always present in aluminum. Because the solubility of iron in solid aluminum is very low, Al-Fe or Al-Fe-Si phases can be found in the structure of even ultrasonic aluminum. These phases can be metal compounds FeAl 3, Fe 3 SiAl 12, Al 2 Si 2 Al 9 or FeAl 6.
Aluminum alloys have several tens of phases that are intermetallic compounds. In complex alloys of 2014 type (Al – Cu – Mg – Mn – Fe – Si system), these compounds have 3 SiAl 12 in the form (Mn, Fe).