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Why Are Metals Malleable?

When the universe burst into existence around 14 billion years ago, it took 380,000 years before things were cool enough for the first atoms to form. Iron didn’t arrive on the scene until 150 million years later, formed in the hearts of stars before being catapulted across the universe in dramatic stellar explosions, some of which smashed into earth.

Every element in our universe is defined by its atoms. These determine every one of its characteristics, including its shape, colour, conductivity, melting point, strength, and malleability.

Metals are one of the most malleable materials in the universe. But why are metals malleable, exactly? What is it about their atomic structure that makes them so easy to manipulate?

The answer is in their electrons—those little electronically-charged particles that whizz around their atom. Many metals have an atomic structure with shared valence electrons, which are electrons that sit around the outer shell of an atom, and can easily form chemical bonds. When a metal has these kinds of electrons—for example iron, aluminium, and copper—they’re highly malleable when heated, because the atoms are able to easily slide over each other2, allowing us to hammer them into useful shapes.

Since the dawn of the Bronze Age, our species has used metals to create weapons, jewellery, coins, cars, trains, ships, boats, skyscrapers, televisions, balustrades, wrought iron gates, and a whole lot more, purely because of the atomic structures of certain metals.

Which metals are malleable?

There are 95 known metals in the universe, making up 78% of the elements in the periodic table, and not all of them are malleable.

The most commonly used malleable metals include:

Iron

Iron is the universe’s original metal. It forms much of Earth’s outer and inner core, making it the most common element on our planet. It also forms about 0.005% of our bodies, residing in our blood and allowing our hearts to distribute oxygen to our organs.

Three types of malleable iron are recognised in the casting industry: blackheart malleable iron, whiteheart malleable iron, and pearlitic malleable iron, created with different processing methods.

Cast iron isn’t a pure iron, but an iron-carbon alloy with a carbon content of 2% or more. Cast iron is a popular material because of its low melting temperature, fluidity, cast-ability, machinability, and resistance to deformation and wear4.

Aluminium

Aluminium is another common element on earth, making up about 8% of its crust. The material is recognisable due to its silvery-white colour, and its shiny surface. The incredible lightness of aluminium and its ability to resist corrosion has made it the material of choice for a huge range of applications, including airplanes, space shuttles, high-speed trains, building components, power lines, smartphones, laptops, and more5.

Aluminium is an incredibly ductile material, able to be stretched between 50 to 70% of its length before breaking. It’s also highly malleable, and with a lower melting temperature of 660°C, allowing it to be easily manipulated6.

Copper

As with iron and aluminium, copper is an abundant element on earth, with large concentrations found in its crust. The material is a great conductor of heat and electricity, making it popular for choice for electricity wiring. It’s also commonly used in building material, marine hardwares, coins, and more, and is the third most used metal in the world (behind iron and aluminium).

Copper was the first metal to be worked by humans, with its first usage found in a copperhead axe used by five thousand year old Otzi the Iceman, discovered in the Ötztal Alps on the border of Austria and Italy. Toxic levels of arsenic were found in Otzi’s hair, which suggests that he was exposed to the element while smelting the copper for his axe7.

Gold

Gold is the most malleable metal in the universe. If you gain a few kilos in your later years, and your gold wedding ring starts to restrict your finger’s blood flow, the resizing cost is kept low because of the material’s malleability (but not too low because of its rarity). It’s estimated that around 190,000 tonnes of gold have been mined, which when combined together, would make a cube measuring 21.3 meters in width.

The malleability of gold is staggering. It can be stretched into a wire as thin as a single atom, and then stretched even more before breaking. A single gram of gold can be beaten into a one square meter sheet, and gold leaf can be beaten thin enough to become semi-transparent8.

Other common malleable metals include silver, lead, and zinc, which are used extensively throughout industry and commerce.

Ductility vs malleability

Malleability and ductility are two similar properties that are often confused. In metallurgy, a malleable material is one that can be easily formed by hammering, rolling, or pressing it. The material is considered malleable because it can be manipulated under compressive stress. By contrast, ductility is the ability of a material to be manipulated under tensile stress, which is how easily it can be stretched. A material that can be easily stretched into a wire is considered ductile3.

References

  1. Alison Klesman, How did the first chemical element appear in the universe?, Astronomy
  2. Metals – Iron and aluminium – GCSE Chemistry (Single Science) Revision – Other, BBC
  3. Malleability and Ductility | MATSE 81: Materials In Today’s World, PennState College of Earth and Mineral Sciences
  4. Cast iron, Wikipedia
  5. Most Common Uses of Aluminum, Metal Supermarkets
  6. Aluminium, Wikipedia
  7. Anne Marie Helmenstine, Ph.D, 2018, 10 Copper Facts, ThoughtCo
  8. Gold, Wikipedia
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