Alloys

Chemistry: IB Diploma Higher Level, topic 2.5.1

Metal Alloys

An alloy is a metal that is mixed with other elements. By adding these other elements, we can change a metal's properties. Most metals that we use in everyday life are alloys.

Bronze

Bronze is an alloy of copper and tin.
Adding tin increases the hardness of the material.
Uses include making coins, electrical hardware and statues.

Brass

Brass is an alloy of copper and zinc.
Adding zinc makes the material more malleable.
Uses include door fittings and water taps.

Gold

Pure gold is soft and so jewelers will often add metals such as silver, copper and zinc to produce a more resilient substance.
Carats provide a measure for the purity of a gold alloy:
24 carats = 100% gold.
Therefore, 18 carats = 75% gold.

Steel

Steels are alloys of iron that contain carbon as well as other metals.
High carbon steels are strong but brittle. Uses include making cutting tools and blades.
Low carbon steels are soft but malleable. Uses include making car bodies.
Stainless steels (steels containing chromium and nickel) are strong and resistant to corrosion. Uses include cooking utensils and cutlery.

Aluminum

A key feature of aluminum alloys is their low density, which makes them suitable for use in manufacturing aircrafts.
Other uses include armor plating for military vehicles.

Forming Alloys

Alloys are formed typically through melting two or more elements and then solidifying them to create the alloy.

Types of alloy

Some alloys contain a mixture of metals while others can have non-metals involved, such as Carbon.
The purpose of an alloy is to create a material with physical properties superior to the individual metals themselves.
Alloys can broadly be classed as either substitutional or interstitial.

Substitutional alloys

A substitutional alloy occurs when one atom of one type of metal replaces another type of metal atom, in other words, it substitutes.
For example, brass is a substitutional alloy in which copper and zinc atoms are mixed throughout the metallic bonds.

Interstitial alloys

An interstitial alloy occurs when an atom of small enough radius fills the spaces between the metallic atoms.
Typically, carbon is used to fill these spaces and helps create a stronger material by effectively filling in the empty spaces that may otherwise cause the alloy to be weak.
For example, steel is an interstitial alloy of carbon and iron.

Test yourself on Alloys

Example metal alloys
What type of alloy is brass?

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