Chemical aluminum compound

Below is a brief overview of the most important chemical compounds of aluminum, that are found in nature, as well as their industrial applications.

Что такое химическое соединение?

The chemical compound of aluminum - this substance, which is formed of two or more chemical elements, one of which is aluminum. These elements are interconnected chemically, ie by covalent, ionic or metallic bonds. The chemical compound has a fixed and constant chemical composition of the chemical formula.

aluminum alloys usually are not chemical compounds. They are homogeneous or heterogeneous mixtures of their constituent chemical elements or compounds. Therefore they do not have a fixed chemical composition and do not have the chemical formula.

Classification of aluminum compounds

Современная классификация соединений алюминия из Энциклопедии Алюминия [4] представлена ниже.

Классификация соединений алюминия [4]

Aluminum in nature

Алюминий является самым распространенным (более 8 % по массе) природным металлическим элементом, а также третьим природным элементом среди всех химических элементов (после кислорода и кремния). However, because of the high chemical activity aluminum it is almost always in compounds with other elements and is very rare in nature in the form of pure metal.

Table – The proportion of chemical elements in the earth's crust

aluminum metal

Pure aluminum - is a silvery-white, malleable, ductile metal having an atomic number 13 and relative atomic mass 26,98. With few exceptions, it is in the form of chemical compounds in the Al+3.

This metal has amphoteric properties. It reacts with mineral acids and strong alkalis. Although aluminum is one of the most chemically active base metals, it has a very high resistance to corrosion. When contacting the aluminum surface with fresh oxygen, водой или другими окислителями на ней мгновенно вырастает плотная оксидная пленка (Al2O3), metal which provides high resistance to corrosion. Эта оксидная пленка растворяется в щелочных растворах с выделением водорода и образованием растворимых щелочноземельных алюминатов [1].

Эта оксидная пленка является стойкой к некоторым кислотам (например, азотной кислоте) и предотвращает дальнейшее химическое воздействие на металл. Однако она растворяется в некоторых кислотах (например, в соляной кислоте или горячей серной кислоте), as well as in alkaline solution, that it makes it possible to further chemical reactions on the aluminum surface.

При повышенных температурах алюминий реагирует:

  • с водой (выше 180 ºС) с образованием гидроксида Al(OH)3 and hydrogen H2;
  • many metal oxides to form oxide Al2O3 and metal, reduced from its oxide.

Последняя реакция применяется при производстве некоторых металлов (алюмотермия), for example, manganese and some alloys, for example, ferrotitanium.

natural compounds

minerals

Natural minerals are chemical compounds. Aluminum is present in many minerals – more 270 species – in combination with oxygen, silicon, alkali and alkaline earth metals and fluorine, as well as hydroxides, sulfates and phosphates. for instance, полевые шпаты – наиболее распространенные минералы земной коры (около 50 %) – являются алюминосиликатами [1]. Ниже представлены важнейшие минералы алюминия из фундаментальной энциклопедии про алюминий [4]

Важнейшие минералы алюминия [4]

Aluminum metal in nature

Natural aluminum metal are sometimes found as a minor phase in the conditions of oxygen deficiency, for example, inside some volcanoes. It is also found in such minerals, like beryl, cryolite, Garnet, шпинель и бирюза [1].

Gems

Impurities in the Al oxide crystals2O3, such as cobalt or chromium yield gemstones ruby ​​and sapphire, respectively. Pure oxide Al2O3 izvesten Heartland corundum – one of the hardest materials.


Ruby

Boksity

While aluminum is a very common element in nature, Most minerals of aluminum may not be economically viable sources of this metal. Nearly the whole primary aluminum metal produced from ore, которая называется бокситом (или бокситами) с обобщенной химической формулой (AlOx(OH)3-2x) [1].

Bauxite occur in nature as weathering products bedrock with a low content of iron and silicon in tropical climates. Natural bauxite contain various hydrated forms of alumina, which have different crystal system, а также различаются по степени гидратации (количеству молекул воды на одну молекулу Al2O3).

alumina production

Near 90 % aluminum ore - bauxite - is the production of primary aluminum, rest 10 % – for other industrial applications.

industrial production primary aluminum имеет две основных стадии:

  • production from bauxite ore source of pure alumina – глинозема;
  • electrochemical reduction of the oxide to aluminum metal in a bath of molten cryolite.

Boksity

Bauxite is not mineral and chemical compound. Это наименование – боксит (или, more, бокситы) – применяется для обозначения различных типов алюминиевых руд, which contain aluminum compound, basically - different kinds of hydroxides.

Промышленные бокситы содержит три основных типа гидроксидных минералов:

  • гибсит: Al2O3·3H2O
  • bogemit – Al2O3·H2O
  • diasporas – Al2O3·H2O.

These types of hydroxides significantly differ in such physical properties, as:

  • water content,
  • crystal system
  • hardness,
  • density,
  • dehydration temperature
  • solubility in technological solutions.

Usually natural bauxite deposits consist of one of these types of hydroxides,, although in some cases the same bauxite may contain mixed hydroxides.

Bauxite vary in color from cream to dark brown with a high iron content.

typical bauxite

В состав типичного боксита для промышленного производства алюминия входят следующие соединения:

  • alumina - Al2O3: 40-60 %
  • silica - SiO2: 1-6 %
  • ferric oxide - Fe2O3: 2-25 %
  • titanium oxide - TiO2: 1-5 %
  • calcium and magnesium oxides - CaO + MgO: 0,2-0,6 %
  • оксиды других элементов: от 0,01 by 0,4 % (каждого).

Alumina

Almost all alumina produced from bauxite, which contain about 50 % oxide Al2O3 as hydroxides. This aluminum ore was treated under pressure in caustic soda solution, to dissolve the alumina in aluminate form, and separate it from the red sludge, containing oxides of iron and other major impurities. Then this solution was precipitated aluminate crystals of aluminum hydroxide.

At temperatures below 700 ºС в технологической массе содержатся следующие различные типы соединений алюминия – его гидроксидов:

  • giʙʙsit
  • bayerit
  • nordstrandid
  • diasporas
  • bogemit.

The final process step of manufacture of alumina is obtained by calcining at previous stages hydroxides mixture. Обжиг (кальцинация) производится при температуре 1200 ° C to yield pure alumina with a content of Al oxide2O3 more 99 %.

Alumina

For industrial production 1 alumina ODP requires about 2 tons of alumina.

aluminum compounds, which are most important for non-metallurgical industries – являются его:

  • оксид;
  • sulfate,
  • silicates.

Aluminium oxide

Oxygen aluminum compound

Alumina - this is one of its oxygen compounds. pure oxide – It is a white powder in the form of particles of various shapes and sizes. Because of its amphoteric properties of the oxide is soluble in mineral acids and strong alkalis. It can have various modifications. Наиболее стабильным является его альфа-модификация «корунд» (альфа-Al2O3).

types oxides

During dehydration of hydroxides formed Al oxide series type2O3, which still contains a small proportion of hydroxyl groups and retain some reactivity. All oxides, obtained at lower temperatures is called transitional modifications. At a temperature 1400 ºС все переходные модификации превращаются в альфа-модификацию [1].

anodic oxide

The anodic oxide obtained by electrochemical oxidation of aluminum. This compound is a nanostructured material having a unique structure. Anodic aluminum oxide consists of cylindrical pores, that provide him widely used in the art. It is thermally and mechanically resistant, an optically transparent and have high electrical insulation properties. The pore size and thickness of the anodic oxide layer can be easily adjusted parameters Technology, which enables its use not only as protective coatings for decorative aluminum products, but also as the basis for nanotechnology.

 

Structure anodic oxide coating

hydroxides

Various forms of aluminum hydroxide. Наиболее изученными формами являются тригидроксид Al(OH)3 и оксид-гидроксид AlO(OH). Кроме этих кристаллических форм известны еще несколько других типов [1].

Гидроксид Al(OH)3 It is used in large volumes for sewage treatment, as well as the manufacture of other aluminum compounds, including its salts.

aluminum sulfate

The structure and composition

Aluminum sulfate may exist with different proportions of water. A common form of this compound is Al2(SO4)3·18H2O. He is almost insoluble in anhydrous alcohol, but it is highly soluble in water. At temperatures above 770 ° C decomposes to alumina.

application

Находит применение в следующих отраслях промышленности и областях жизни [1, 2]:

  • системы очистки воды и обработки сточных вод;
  • производство бумаги;
  • противопожарная защитная одежда;
  • очистка масел и жиров;
  • гидроизоляция бетона;
  • производство антиперспирантов;
  • выделка кож;
  • производство красок;
  • в сельскохозяйственных пестицидах;
  • производство химикатов;
  • средство для повышения кислотности почв;
  • производство косметики и мыла;
  • medical preparations.

alum

Aluminum sulphate is included in combination with monovalent metal sulfates to form double salts, called alum. The most important of these salts is aluminum potassium sulfate. This chemical compound is also known as potassium alum. These alum are widely used since ancient times in leather production, drugs, fabrics and colors.

clays

Clays are composed mainly of aluminosilicates.

Chloride

In the reaction of chlorine gas with the molten aluminum is formed of aluminum chloride. This compound is commonly used as a catalyst in the synthesis reactions of various organic compounds. Hydrated chloride AlCl3∙H2O, It is used as a deodorant or antiprespirant. This compound is one of several aluminum salts, that apply to the cosmetic industry.

Гексагидратная форма хлорида алюминия применяется:

  • for the protective treatment of wood,
  • как дезинфицирующее средство в животноводстве и при производстве мяса;
  • crude oil refinery
  • papermaking

aluminum hydride

Since aluminum forms a hydride with hydrogen AlH3, which is widely used in organic chemistry, including, в виде литиевого гидрида алюминия (LiAlH4). This compound was prepared by reacting aluminum chloride with lithium chloride.

intermetallic compounds

Интерметаллид (интерметаллическое соединение) — это химическое соединение двух или более металлов. intermetallic compounds, as it should be in chemical compounds, have a fixed relationship between its components. Usually in the intermetallic compounds the bond between atoms - metal.

The intermetallic compound is very important for the microstructure and properties of alloys of aluminum. for instance, iron and silicon are impurities, which are always present in aluminum. Since iron is very low solubility in solid aluminum, the phase Al-Fe or Al-Fe-Si can be found in the microstructure even ultrapure aluminum. These phases may be FeAl intermetallic compound3, Fe3unlucky12, Al2Si2Al9 or FeAl6.

In aluminum alloys, there are several tens of phases, which are intermetallic compounds. In complex alloys of the type 2014 (система Al-Cu-Mg-Mn-Fe-Si) эти соединения имеют вид типа (Mn,Fe)3unlucky12 [3].

Table – Интерметаллические соединения алюминия [2]

Sources:

1. http://www.inchem.org/documents/ehc/ehc/ehc194.htm

2. Handbook of Aluminum: Vol. 1: Physical Metallurgy and Processes / ed. G. E. Totten, D. S. MacKenzie – 2003.

3. Aluminium and Aluminium Alloys /ed. J.R. Davis – ASM International, 1993.

4. Тринадцатый элемент: Энциклопедия /А. Drozdov – RUSAL library, 2007