Aluminum (Al): Metal to the Stars
- Sylvia Rose
- Mar 14
- 4 min read
Aluminum is lightweight, strong and resistant to corrosion. The most abundant metal in the Earth's crust, it's used in spacecraft, vehicles, robots, computers and phones. It creates striking sapphires and rubies.
About Aluminum
Aluminum (Al), with an atomic number of 13, is a silvery-white, lightweight metal belonging to the boron group in the periodic table. It's the most plentiful metallic element in the Earth's crust, at 8% of weight.
Its formed after the fusion of carbon in massive stars destined to become Type II supernovas. The fusion produces 26Mg, which, after capturing free protons and neutrons, transforms into aluminium.
Aluminum, belongs to the group known as post-transition metals. It doesn't exist in its pure, metallic form naturally. I’s bound up in various minerals, primarily bauxite ore. Bauxite is the main source of aluminum.
This mineral is found in tropical and subtropical areas. Bauxite contains 30 - 60% aluminum oxide (Al2O3). The rest is a mix of silica, titanium dioxide, and iron oxides. In extraction aluminum oxide is separated.
Extraction
Crushing and refining: Bauxite is crushed and processed using the Bayer process, which separates aluminum oxide from impurities. A detailed explanation of the Bayer Process is here.
Then comes the Hall-Héroult process, the popular method of modern aluminum production. Alumina (aluminum oxide) extracted from bauxite ore is set in a molten bath of cryolite (sodium aluminum fluoride).
An electric current is then passed through the mixture, separating the aluminum from the oxygen. The molten aluminum is collected at the bottom of the electrolytic cell and can then be cast into ingots.
This process, while efficient, is energy-intensive. Recycling aluminum can greatly conserve resources and reduce environmental effects. In 2023, the global aluminum production is 70 million tonnes, up from 65 million in 2020.
Properties
Lightweight: About a third the weight of steel.
High Strength-to-Weight Ratio: Can be alloyed for impressive strength while maintaining light weight.
Excellent Corrosion Resistance: Forms a thin, protective layer of aluminum oxide on its surface, preventing further oxidation.
Good Electrical Conductivity: Although not as conductive as copper, it's a far lighter conductor for a given electrical resistance.
Non-Magnetic: Makes it suitable electronic equipment and environments where magnetic interference is a concern.
Highly Malleable and Ductile: Can be easily formed into various shapes and drawn into wires.
Recyclable: Can be recycled repeatedly without loss of quality.
Alloys
Pure aluminum forms alloys with other elements like copper, magnesium, silicon, zinc and manganese. These alter its properties, enabling creation of aluminum alloys geared to specific applications.
Aluminum-Copper Alloys: Higher strength and good machinability, often used in aerospace.
Aluminum-Magnesium Alloys: Excellent corrosion resistance, even in marine environments, used for shipbuilding.
Aluminum-Silicon Alloys: Improved casting characteristics, ideal for intricate shapes and automotive components.
Aluminum-Zinc Alloys: Ideal for aerospace applications, combining high strength with a lightweight structure.
Aluminum in the Modern World
Aerospace: Aircraft fuselages, wings, and engine components rely on lightweight, high-strength aluminum alloys.
Robotics: Robot frames and structural elements benefit from aluminum's lightweight nature, enabling faster and more agile movements.
Spacecraft and Satellites: Used extensively in spacecraft construction for its lightweight, strength and ability to withstand extreme temperature variations.
Electronics: Mobile phones, laptops, and other electronic devices use aluminum for their casings, heat sinks, and internal components.
Construction: Aluminum frames, roofing, cladding, and windows are durable, corrosion resistant, and easy to install. Aluminum is widely used in architecture and construction, especially in windows and facades.
Transportation: Cars, trucks, trains, and ships use aluminum to reduce weight and improve fuel efficiency.
Packaging: Aluminum foil, beverage cans, and food containers are lightweight and recyclable. Patented in 1903, aluminum foil is a household basic.
Facts About Aluminum
Rubies and sapphires are made of aluminum oxide. Minerals seeping into the aluminum oxide give dramatic hues. Chromium creates the deep red of rubies, and iron or titanium yield sapphire blues.
Aluminum is a key component in many antacids used to neutralize stomach acid.
The Washington Monument, one of Washington D.C.'s most iconic landmarks, is originally capped with a small pyramid of aluminum.
Recycling aluminum needs only 5% of the energy to produce new aluminum from bauxite ore.
Aluminum is used in some types of fireworks to create bright silver sparks and flashes.
Duralumin: This specific aluminum alloy, introduced in 1909, is popular in contemporary aircraft design and engineering.
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