What is Aluminium and its Features

What is Aluminium

Light, durable and functional: these are the qualities that make aluminium one of the key engineering materials of our time. We can find aluminium in the homes we live in, in the automobiles we drive, in the trains and aeroplanes that take us across long distances, in themobile phones and computers we use on a daily basis, in the shelves inside our fridges and in modern interior designs, but a mere 200 years ago very little was known about this metal.

Aluminium is a silvery-white metal, the 13 element in the periodic table. One surprising fact about aluminium is that it's the most widespread metal on Earth, making up more than 8% of the Earth's core mass. It's also the third most common chemical element on our planet after oxygen and silicon.

At the same time, because it easily binds with other elements, pure aluminium does not occur in nature. This is the reason that people learned about it relatively recently. Formally aluminium was produced for the first time in 1824 and it took people another fifty years to learn to produce it on an industrial scale.

The most common form of aluminium found in nature is aluminium sulphates. These are minerals that combine two sulphuric acids: one based on an alkaline metal (lithium, sodium, potassium rubidium or caesium) and one based on a metal from the third group of the periodic table, primarily aluminium.

Aluminium sulphates are used to this day to clean water, for cooking, in medicine, in cosmetology, in the chemical industry and in other sectors. By the way, aluminium got its name from aluminium sulphates which in Latin were called alumen.

Today we know about almost 300 various aluminium compounds and minerals containing aluminium, from feldspar, a key source mineral on Earth, to ruby, sapphire and emerald, which are far less common.

But regardless of how common aluminium may be, it may have remained hidden forever if it hadn't been for electricity. The discovery of aluminium was made possible when scientists were able to use electricity to break down chemical compounds into their elements. In the 19 century the Danish physicist Christian Oersted used electrolysis to obtain aluminium. Electrolysis or electrolytic reduction is the process that is used to produce aluminium today as well.

Another rather common mineral, bauxite, is used today as the primary raw material in aluminium production. Bauxite is a clay mineral comprising various modifications of aluminium hydroxide mixed with iron, silicon, titanium, sulphur, gallium, chromium, vanadium oxides, as well as sulphuric calcium, iron and magnesium carbonates. In other words, your typical bauxite contains almost half the periodic table. By the way, because of the texture of bauxite about a hundred years ago aluminium was often referred to rather poetically as silver obtained from clay. On the average 4-5 tonnes of bauxite are needed to produce 1 tonne of aluminium.

Properties of aluminium

Aluminium offers a rare combination of valuable properties. It is one of the lightest metals in the world: it's almost three times lighter than iron but it's also very strong, extremely flexible and corrosion resistant because its surface is always covered in an extremely thin and yet very strong layer of oxide film. It doesn't magnetise, it's a great electricity conductor and forms alloys with practically all other metals.

Aluminium can be easily processed using pressure both when it's hot and when it's cold. It can be rolled, pulled and stamped. Aluminium doesn't catch fire, it doesn't need special paint and unlike plastics it's not toxic. It's also very pliable so sheets just 4 microns thick can be made from it, as well as extra thin wire. The extra-thin foil that can be made from aluminium is three times thinner than a human hair. In addition, aluminium is more cost effective than other metals and materials.

Since aluminium easily forms compounds with other chemical elements, a huge variety of aluminium alloys have been developed. Even a very small amount of admixtures can drastically change the properties of the metal, making it possible to use it in new areas. For example, in ordinary life you can find aluminium mixed with silicon and magnesium literally on the road, i.e. in the aluminium alloy wheels, in the engines, chassis and other parts of modern automobiles. As for aluminium zinc alloy, chances are you might be holding it in your hands right now as it's this alloy that's widely used in the production of mobile phones and tablet PCs. In the meantime, scientists keep developing new aluminium alloys.

Physical Properties of Aluminium

- Aluminium has a lower density than any other commercial metal except magnesium. Given the right type of surface, aluminium makes an excellent reflector, especially for ultraviolet light.

- Aluminium is an odourless, tasteless, silvery white metal. With increasing silicon and ductile and quite soft. The aluminium crystal has a face centred cubic structure.

- The concentration of the lattice in the less pure metal results from the formation of impurity segregations. Purity also affects most other physical properties.

- Aluminium has a lower density than any other commercial metals except magnesium.

- Aluminium may also be used as a selective cold or hot wall or as a body approximating to the effect of a black body. In the infrared region the reflectivity of aluminium is exceeded only slightly by that of gold and silver.

Chemical Properties of Aluminium

1. Reaction of Aluminium with Air

Generally, Aluminium metal does not react with air as its surface is covered with a thin layer of oxide that helps protect the metal from attack by air. However, in case the oxide layer gets damaged and the Aluminium metal gets exposed, it reacts again with oxygen forming amphoteric oxide (Aluminium (lll) Oxide), Al2O3.

4Al (s) + 3O2 (l) → 2Al2O3 (s)

2. Reaction of Aluminium with Acids:

Aluminium reacts readily with mineral acids to form solutions containing aquated Al (lll) ion along with the liberation of hydrogen gas, H2. For example, it dissolves in hydrochloric acid (HCl) liberating dihydrogen gas.

2Al(s) + 6HCl (aq) → 2Al3+ (aq) + 6Cl– (aq) + 3H2 (g)

In case of reaction with Nitric acid, it reacts passively by forming a protective oxide layer on its surface of Aluminium Oxide.

Al2O3 +6 HNO3 → 2Al(NO3)3 + 3H2O

3. Reaction of Aluminium with Alkalis

Aluminium reacts with alkalis to form aluminates along with the liberation of hydrogen gas, H2. Comparable electronegativity of Oxygen and Aluminium makes it possible for Aluminium to form covalent bonds with oxygen. This can be seen as a prominent reason for the formation of aluminates. For example, Aluminum reacts with hot, concentrated sodium hydroxide solution to produce a colourless solution of sodium tetrahydroxoaluminate along with the evolution of dihydrogen gas.

2Al (s) + 2NaOH (aq) + 6H2O → 2Na+ (aq) + 2[Al(OH)4]– + 3H2 (g)