Aluminium

[edit] Introduction

Aluminium makes up more than 8% of the Earth’s core mass and is the most widespread metal. It is also the third most common chemical element after oxygen and silicon. It is the 13 element on the Periodic Table and has a silvery-white appearance.

Pure aluminium does not occur in nature because it binds very easily with other elements. It is because of this that aluminium was only discovered in the 19th century when scientists were able to break down chemical compounds into their elements.

Because of the high costs of the extraction process, it wasn't until the late 19th century that it was possible to produce aluminium on an industrial scale for use in construction and other industries.

[edit] Extraction process

Aluminium is relatively expensive because of the amount of energy required for its extraction. It is extracted from aluminium oxide, a white powder which is purified from aluminium ore (bauxite).

The aluminium oxide is dissolved in molten cryolite (an aluminium compound that has a lower melting point than aluminium itself). Aluminium is then extracted by a process of electrolysis or electrolytic reduction. Electricity is passed through the liquid, and aluminium forms at the negative electrode. It then sinks to the bottom of the tank, where it can be tapped off.

[edit] Properties of aluminium

One of the main reasons for aluminium’s widespread application is its combination of properties:

• Lightweight: Almost three times lighter than iron.
• Durable: Almost as durable as steel.
• Ductile: Extremely flexible and easily processed using pressure when hot or cold.
• Corrosion-resistant: Its surface is protected by an extremely thin yet very strong layer of aluminium oxide.
• Non-magnetic.
• Excellent conductivity.
• Fire-resistant.
• Non-toxic.
• Bonds with other elements relatively easily, enabling the formation of a wide variety of aluminium alloys.
• Re-usable: Aluminium and its alloys can be melted down and reused without any impact on their mechanical properties. Estimates suggest that around 75% of all aluminium produced is still in use in some form.

[edit] Aluminium in construction

As the extraction process is relatively expensive, aluminium was generally not used in construction until the early-20th century. In the 1920s, it began to be used primarily for decorative detailing and Art Deco structures. In the 1930s, a breakthrough was achieved when the Empire State Building used aluminium for much of its interior structures and its famous spire. Subsequently, it began to be used for roofing, flashing, wall panels, spandrels, and so on.

Today, aluminium is the second most used metal in buildings after steel.

Because of its ductility, aluminium can be formed into many shapes and profiles. Aluminium wall cladding systems are commonly used for building exteriors, with large wall panels requiring fewer joints, resulting in time-efficient installation.

Some of the most common applications for aluminium are:

• Long-span roof systems covering large areas such as halls and auditoriums.
• Structures located in inaccessible places where the economy of transport and ease of installation are important, such as electrical transmission towers.
• Structures in corrosive or humid environments, such as swimming pools, bridges, hydraulic structures, offshore superstructures, and so on.
• Structures with moving sections, such as moving bridges.
• Structures to which access for maintenance is limited, such as masts, lighting towers, antenna towers, and so on.

[edit] Find out more

[edit] Related articles on Designing Buildings Wiki

• Cast iron.
• Difference between cast iron and wrought iron.
• Failure of metals.
• Flashing.
• Galvanised steel.
• Iron.
• Lead in construction.
• Major cast metal components.
• Metal fabrication.
• Metal roofing.
• Stainless steel.
• Structural principles.
• Structural steelwork.
• Types of steel.
• Weathering steel.

[edit] External resources

• Aluminium Leader - What is aluminium?