Aluminum, atomic properties, chemical and physical properties

[edit] Biological role

Aluminum is part of the tissues of animals and plants; in the organs of mammals, from 10 −3 to 10 −5% aluminum (per raw material) was found. Aluminum accumulates in the liver, pancreas and thyroid glands. In plant products, the aluminum content ranges from 4 mg per 1 kg of dry matter (potatoes) to 46 mg (yellow turnips), in products of animal origin - from 4 mg (honey) to 72 mg per 1 kg of dry matter (beef). In the daily human diet, the aluminum content reaches 35-40 mg. There are known organisms that are aluminum concentrators, for example mosses (Lycopodiaceae), which contain up to 5.3% aluminum in their ash, and mollusks (Helix and Lithorina), which contain 0.2-0.8% aluminum in their ash.

By forming insoluble compounds with phosphates, aluminum disrupts the nutrition of plants (absorption of phosphates by roots) and animals (absorption of phosphates in the intestines).

Melting point of aluminum

The production of aluminum melt, like many other materials, occurs after thermal energy has been supplied to the original metal. It can be supplied either directly into it or from outside.

The melting point of aluminum directly depends on the level of its purity:

1. Ultra-pure aluminum melts at a temperature of 660.3°C.
2. With an aluminum content of 99.5%, the melting point is 657°C.
3. With a content of this metal of 99%, the melt can be obtained at 643°C.

Aluminum melt

The process of producing aluminum
An aluminum alloy can contain various substances, including alloying ones. Their presence leads to a decrease in the melting point. For example, if there is a large amount of silicon, the temperature can drop to 500°C. In fact, the concept of melting point applies to pure metals. Alloys do not have any constant melting point. This process occurs within a certain heating range.

In materials science there is a concept - solidus and liquidus temperatures.

The first temperature indicates the point at which the melting of aluminum begins, and the second shows at what temperature the alloy will finally melt. In the interval between them, the alloy will be in a mushy state.

Properties and characteristics

Aluminum is a metal with a silvery-white surface. As already noted, its density is 2.7 kg/m3. The temperature is 660°C.

Its electrical conductivity is equal to 65% of copper and its alloys. Aluminum and most of its alloys are resistant to corrosion. This is due to the fact that an oxide film forms on its surface, which protects the base material from exposure to atmospheric air.

In the untreated state, its strength is 60 MPa, but after adding certain additives it increases to 700 MPa. The hardness in this state reaches 250 HB.

Aluminum can be easily processed under pressure. To remove work hardening and restore ductility after processing, aluminum parts are annealed, and the temperature should be within 350°C.

[edit] Receipt

Production of aluminum Aluminum is produced by electrolysis of a solution of alumina (tech. Al2O3) in molten cryolite Na3[AlF6] at 950-960 °C. Electrolyte composition 75-90% by weight Na3[AlF6], 5-12% AlF3, 2-10% CaF2, 1-10% Al2O3, molar ratio NaF / AlF3 = 2.20-2 85.

The industrial complex for the production of aluminum includes the production of alumina from aluminum ores, cryolite and other fluorides, carbon anode and lining materials, and the electrolytic production of aluminum itself.

Electrolysis is carried out in devices in which the cathode is the bottom of the bath, and the anode is pre-burnt carbon blocks or electrodes placed in a molten electrolyte.

Molten aluminum at electrolysis temperature is heavier than the electrolyte and therefore accumulates at the bottom of the bath. O2 is released at the anode, which reacts with the carbon of the anode, which burns out to form CO and CO2.

Current density at the anode is 0.7-0.9 A/cm, at the cathode - 0.4-0.5 A/cm, for various types of electrolyzers the current is 100-250 kA, operating voltage 4.2-4.5 IN.

To obtain 1 ton of rough aluminum, 14500-17500 kWh of electricity, 1925-1930 kg of alumina, 500-600 kg of anode material, 50-70 kg of fluoride salts are consumed. The daily productivity of one medium-power bath is from 550 to 1200 kg of aluminum. Aluminum is taken from the electrolyzer once every 1-2 days.

High-purity aluminum (no more than 0.05% impurities) is obtained by electrolytic refining of crude aluminum containing up to 1% impurities. The electrolyte most often used is a melt of Na3[AlF6], BaCl2 (up to 60%) NaCl (up to 4%). To obtain aluminum of special purity (no more than 0.001% impurities), zone melting is used.

Aluminum is poured into ingots, which are then processed into sheets, foil, profiles, and wire. It is well welded, can be forged, stamped, rolled, drawn and pressed, and can also be processed using powder metallurgy methods.

General information:

Atomic structure and crystal lattice

In the Periodic System D.I. The Mendeleev atomic number of aluminum is 13, its atomic mass is 26.9815 (for carbon 12C) and 26.98974 (for oxygen 16O).

The main isotope is 27Al, which is stable and consists of 14 neutrons and 13 protons. In addition to one isotope 26Al, whose half-life is 106 years, the existence of six more isotopes has been established with mass numbers 23, 24, 25, 26, 28 and 29 and with short half-lives (from 0.13 to 396 s), as well as negligible abundance in nature (from 2×10-5 to 1.5×10-4%).

Aluminum is trivalent, and its 13 electrons are distributed in electron shells l s 2

, 2s
2
,
2р6,
3
s 2
, 3
р1.
The outer electron layer
M
contains three valence electrons: two in the 3
s
orbit with ionization potentials of 1800 and 2300 kJ/mol and one in the 3
p
orbit with a potential of 574.5 kJ/mol, and therefore in chemical compounds aluminum is usually trivalent ( Al3+).
Since an electron in the p
-orbit with the nucleus of an atom is bonded weaker than two paired electrons in the s-orbit, then under certain conditions, losing a p-electron, an aluminum atom becomes a monovalent ion (Al+), forming compounds of lower valence (subconnections), and even less often - Al2+.

The crystal lattice of aluminum is a face-centered cube, which is stable at temperatures from 4°K to the melting point. There are no allotropic transformations in aluminum, i.e. its structure is permanent. The unit cell consists of four atoms with a size of 4.049596×10-10 m; at 25 °C, the atomic diameter (the shortest distance between atoms in the lattice) is 2.86 × 10-10 m, and the atomic volume is 9.999 × 10-6 m3/g-atom. Impurities in aluminum have little effect on the lattice parameter.

Concept of crystal lattice + classification

Before delving into the complex topics of chemistry and physics in the school curriculum, I would like to give you comprehensive information regarding the terminology and classification of metallic elements through the lens of industry.

1) Industrial division of metals + their atomic-crystalline structure

The beginning of the metal era began in the 20th century. Copper, iron, silver and other elements have become an integral part of the life and industry of the population of most developed countries. The basic characteristics of metals, such as elasticity, ductility and strength, are determined by their atomic + crystalline structure.

2 units of measurement, what is the boiling point of iron

Knowledge of these properties will allow you to skillfully manipulate the properties and use them to obtain standard combinations of elements. In industrial terms, metals are divided into 5 large cooperations. I will tell you in more detail about each of them in a separate table.

Alkali metals are also distinguished, but usually they are preferred to be classified in the same group as rare earth metals, because their basic characteristics are very similar to each other. Sodium, lithium and other elements of the group form alkalis during chemical reactions with water - hence the name of the group. Used in the production of all kinds of detergents.

Please note: the atomic crystalline structure of metals directly affects their physical and chemical properties. The electrical conductivity parameter plays a particularly important role in industry.

The crystalline structure is characteristic of metal elements that are in the solid phase of the state. Atoms independently arrange themselves in a clear (sometimes vague) geometric shape of a three-dimensional type. The resulting compounds and atomic locations are commonly called a crystal lattice. From a scientific point of view, the term is presented in almost the same way.

Crystal lattice (CL) is a mesh geometric image for studying the structure of crystals. Consists of nodes in which molecules/ions/atoms can be located, and compounds of these elements.

What parameters are used in the study:

• ECR;
• KR constant;
• packing density;
• the meaning of coordination.

A metal crystal lattice is a set of elementary cells that determines the symmetrical properties of the entire structure as a whole. The characteristics of the structural parts of the crystal lattice are described using 3 Brevet rules.

2) Classification of crystal lattices

The distribution by type of crystal lattices is made based on the natural origin of the particles + types of chemical bonds between the basic elements of the structure. Taking into account the above, we can distinguish 4 types of CR. I will provide more detailed information on 3 of them in a separate table, and we will discuss what a metal crystal lattice is in a separate paragraph of the article just below.

The crystalline structure is characteristic not only of pure substances, but also of various inorganic compounds. This is especially true for metal compounds such as alloys. Considering the proliferation of metals in industry and the domestic sphere, special attention needs to be paid to the analysis of the concept of a metal crystal lattice. What will I do next?

PROPERTIES

Native aluminum. Field of view 5 x 4 mm. Azerbaijan, Gobustan region, Caspian Sea, Here-Zira or Bulla Island

Aluminum is a soft, lightweight, silver-white metal with high thermal and electrical conductivity, and is paramagnetic. Melting point 660°C. The advantages of aluminum and its alloys include its low density (2.7 g/cm3), relatively high strength characteristics, good thermal and electrical conductivity, manufacturability, and high corrosion resistance. The combination of these properties allows us to classify aluminum as one of the most important technical materials. It is easily drawn into wire and rolled into thin sheets. Aluminum is chemically active (in air it becomes covered with a protective oxide film - aluminum oxide) and reliably protects the metal from further oxidation. But if aluminum powder or aluminum foil is heated strongly, the metal burns with a blinding flame, turning into aluminum oxide. Aluminum dissolves even in dilute hydrochloric and sulfuric acids, especially when heated. But aluminum does not dissolve in highly diluted and concentrated cold nitric acid. When aqueous solutions of alkalis act on aluminum, the oxide layer dissolves, and aluminates are formed - salts containing aluminum as part of the anion.

Physical properties of aluminum:

ORIGIN

Aluminum aggregated with a bayerite crust on the surface. Uzbekistan, Navoi region, Uchkuduk

Due to its high chemical activity, it is not found in pure form, but only as part of various compounds. For example, there are many known ores, minerals, and rocks that contain aluminum. However, it is extracted only from bauxite, the content of which in nature is not very high. The most common substances containing the metal in question are: feldspars; bauxite; granites; silica; aluminosilicates; basalts and others. In small quantities, aluminum is necessarily found in the cells of living organisms. Some species of club mosses and marine inhabitants are capable of accumulating this element inside their bodies throughout their lives.

Selecting a mold for casting

When choosing a mold for casting aluminum, a home craftsman must understand for what purpose he is processing aluminum. If the future casting is intended for use as solder, then there is no need to use any special forms. To do this, you can use a metal sheet on which to cool the molten metal.

But if there is a need to obtain even a simple part, then the master must decide on the type of mold for casting.

The mold can be made from plaster. To do this, gypsum in a liquid state is poured into an oil-treated mold. After it begins to harden, a casting model is installed into it. In order for molten metal to be poured into the mold, a sprue must be formed. To do this, a cylindrical part is placed in the mold. Forms can be detachable or not. The process of making a split mold is complicated by the fact that the model will be in two halves. After hardening, they are separated, the model is removed and connected again. The form is ready to use.

Aluminum casting die

To obtain high-quality castings, it is advisable to use metal molds (moulds), but it is advisable to produce them only in factory conditions.