Properties of Aluminium. Physical Properties. Chemical Properties, страница 2


Aluminium does not react at ordinary temperature with con­centrated nitric acid, although it does react with the dilute acid. For this reason concentrated nitric acid is stored in aluminium vessels  and transported  in  aluminium  tanks.

Aluminium reacts with the oxides of most metals, including ferric oxide. The reaction produces iron and aluminium oxide:


Fold some asbestos -sheet to form a bottomless glass, tying some wire around it to make it keep shape. Place the asbestos glass on a sheet of iron, and the iron on a trivet, with a bowl of sand under it. Now pour a mixture of powdered aluminium and 138

powdered iron scale into the asbestos glass, insert some magnesi­um ribbon into the mixture, light the ribbon, and step aside. The burning magnesium will set fire to the mixture, scattering sparks, which are red-hot drops of reduced iron. The reaction produces so high a temperature (up to 3,000°) that both products (that is, not only the iron, but also the aluminium oxide) melt. When the burn­ing of the mixture reaches the iron sheet, this too melts at once; the molten mass pours down into the sand. After it has hardened, the ingot of iron can be hammered free. The reactions of the reduct­ion of metals from their oxides by aluminium were discovered by N. Beketov, a Russian chemist, and are of great practial import­ance.

Aluminium is thus one of the chemically active metals, occupy­ing a position immediately following the alkali and the alkaline earth metals.

Uses of Aluminium. The principal uses of aluminium are con­nected with the lightness and strength of its alloys, as well as their resistance to the action of air and water (Fig. 49). Such a combination of properties is especially important in transport facilities, and the aircraft and automobile industries are, accord­ingly, the chief consumers of aluminium alloys. The substitution of aluminium alloys for steel in motor cars and aircraft makes for greater manoeuvrability, easier control, and lower petrol con­sumption.

The same three properties of aluminium alloys are valuable in the building industry. Here aluminium alloys often successfully replace steel, wood, and reinforced concrete, especially in areas where building materials are lacking and their delivery from distant regions presents formidable problems. For example, in the new grainfields in the eastern part of the Soviet Union granaries for many hundreds of thousands of tons of grain are built out of corrugated aluminium  sheet.

Another aluminium product widely used in civil engineering and architecture is aluminium paint, which is a mixture of pow­dered aluminium with mineral oil. It not only imparts an attractive finish to various structures, but protects them from the corroding effect of chemicals and from radiant heat. Oil products are thus kept in storage tanks coated with aluminium paint to protect them from  overheating by  sunlight.

The high conductivity of pure aluminium is used in electrical engineering. Aluminium serves as material for wire that transmits electricity over long distances with minimal losses. Aluminium wire weighs only half as much as copper wire of the same resist­ance, a factor facilitating the construction of the pylons supporting the  transmission  lines.

In everyday life aluminium is encountered chiefly in the form of various household utensils. This use of aluminium is based not only on its lightness and strength, but on other valuable properties as well: its high heat conductivity, its resistance to the action of not only cold, but boiling water, and the non-poisonous nature of its compounds, small quantities of which may be formed by the action of the weak organic acids contained in food upon the metal.