Introduction
Aluminum is a metallic element with symbol Al and atomic number 13. Its element is a silver-white light metal. malleable. Commodities are often made into rods, flakes, foils, powders, ribbons and filaments. In humid air, an oxide film can be formed to prevent metal corrosion. Aluminum powder can burn violently when heated in the air, and emit a blinding white flame. Soluble in dilute sulfuric acid, nitric acid, hydrochloric acid, sodium hydroxide and potassium hydroxide solution, insoluble in water. The relative density is 2.70. The melting point is 660°C. The boiling point is 2327°C. The content of aluminum in the earth's crust is second only to oxygen and silicon, ranking third, and is the most abundant metal element in the earth's crust. The development of the three important industries of aviation, construction, and automobile requires that the material properties have the unique properties of aluminum and its alloys, which greatly facilitates the production and application of this new metal aluminum. The application is extremely extensive.
Content Distribution
The content of aluminum in the earth's crust is second only to oxygen and silicon, with a content of 8.3%, ranking third. It is the most abundant metal element in the earth's crust, and its reserves rank second among metals. Among metal varieties, it is the second largest category of metals after steel. It mainly exists in aluminosilicate ores, as well as bauxite and cryolite. Alumina is a white amorphous powder with many variants, the most familiar of which are α-Al2O3 and β-Al2O3. The corundum that exists in nature belongs to α-Al2O3. Its hardness is second only to diamond, with high melting point and acid and alkali resistance. It is often used to make some bearings, abrasives and refractory materials. Such as corundum crucible, can withstand high temperature of 1800 ℃. Al2O3 has various colors due to different impurities. For example, those containing a small amount of Cr(III) are red, called rubies; those containing Fe(II), Fe(III) or Ti(IV) are called sapphires.
Physical Properties
The peripheral electron configuration of the aluminum atom is 3s²3p¹, which often exhibits the +3 oxidation state in compounds. The aluminum atom has an empty 3d orbital, and can form a stable complex with a coordination number of 6 or 4 with the electron pair donor. If an aluminum atom loses two 3s electrons and one 3p electron at the same time, it will generate trivalent aluminum ions (Al³⁺); if it loses one 3s electron and one 3p electron, it will generate divalent aluminum ions (Al²⁺); if If one 3p electron is lost, monovalent aluminum ions (Al⁺) are generated, and low-valent aluminum ions are usually unstable at low temperatures.
Aluminum is a silvery white light metal. malleable. Commodities are often made into columns, rods, flakes, foils, powders, ribbons and filaments. The melting point is 660°C. The boiling point is 2327°C. The relative density is 2.70, and the density of aluminum liquid is 2.303 g/cm³. Elastic modulus 70Gpa, Poisson's ratio 0.33. The electrical conductivity of aluminum is about 60% of that of copper. If calculated by unit mass, the electrical conductivity of aluminum exceeds that of copper, and it often replaces copper in long-distance transmission. It is widely used for its light weight, good electrical and thermal conductivity, high reflectivity and oxidation resistance. Aluminum used for daily utensils is usually called "steel fine" or "steel type". The thermal expansion coefficient of Al at (room temperature) 25°C is 0.0000236mm/°C or 23.6ppm·k-1.
Application
Aluminum and aluminum alloys are currently one of the most economically applicable materials that are widely used. Since 1956, the world's aluminum output has surpassed that of copper, and it has always ranked first in non-ferrous metals. The current output and consumption of aluminum (calculated by ton) is second only to steel, and has become the second largest metal used by human beings; moreover, aluminum resources are very abundant. According to preliminary calculations, the mineral reserves of aluminum account for more than 8% of the earth's crust.
Aluminum's light weight and corrosion resistance are two outstanding features of its performance.
1. The density of aluminum is very small, only 2.7g/cm³. Although it is relatively soft, it can be made into various aluminum alloys, such as hard aluminum, super hard aluminum, anti-rust aluminum, cast aluminum, etc. These aluminum alloys are widely used in manufacturing industries such as aircraft, automobiles, trains, and ships. In addition, space rockets, space shuttles, and artificial satellites also use a large amount of aluminum and its aluminum alloys. For example, a supersonic aircraft is approximately 70% aluminum and its alloys. Aluminum is also used in large quantities in shipbuilding, and a large passenger ship often uses thousands of tons of aluminum.
2. The conductivity of aluminum is second only to silver, copper and gold. Although its conductivity is only 2/3 of that of copper, its density is only 1/3 of that of copper. Therefore, the quality of aluminum wire is only copper wire when transporting the same amount of electricity. half of. The oxide film on the surface of aluminum not only has the ability of corrosion resistance, but also has a certain degree of insulation, so aluminum is widely used in the electrical manufacturing industry, wire and cable industry and radio industry.
3. Aluminum is a good conductor of heat, and its thermal conductivity is three times greater than that of iron. In industry, aluminum can be used to manufacture various heat exchangers, heat dissipation materials and cooking utensils.
4. Aluminum has good ductility (its ductility is second only to gold and silver), and it can be made into aluminum foil thinner than 0.01mm at 100°C to 150°C. These aluminum foils are widely used for packaging cigarettes, candies, etc., and can also be made into aluminum wires and bars, and can be rolled into various aluminum products.
