Uses of metals

Most metals in everyday use are alloys. An alloy is a mixture of two or more elements, where at least one element is a metal. Many alloys are mixtures of two or more metals.

Copper alloys

Bronze was the first alloy to be made by humans, around 6000 years ago. Bronze is an alloy of copper and tin. Nowadays, bronze is used to make statues, bells and coins.

Brass is an alloy of copper and zinc, and is used to make musical instruments, door knobs, locks and taps.

Gold

Gold is a very soft and malleable metal. It is also very unreactive, so it resists corrosion and stays shiny. The visors on space helmets are coated with a layer of gold. This is thin enough for the astronaut to see through but thick enough to reflect sunlight.

The gold used for jewellery is gold alloyed with other metals, often silver, copper and zinc. This makes the jewellery much stronger while keeping its ability to stay shiny. The proportion of gold in the alloy is measured in carats, with 24 carat gold being pure gold. The percentage of gold in different gold alloys is summarised in the table below.

Carat of goldPercentage of gold in the alloy
24100%
1875%
1250%
937.5%
Question

A piece of gold jewellery is made from 14 carat gold. Calculate the percentage of gold in this alloy.

(14 ÷ 24) x 100 = 58%

Alloy steels

Steels are alloys of iron that contain specific amounts of carbon (a non-metal) and certain metal elements. Different steels have different properties, depending on their composition. The table shows three common examples.

Alloy steel Elements in addition to ironProperties
High carbon steelCarbonStrong, brittle
Low carbon steelCarbonSofter, more easily shaped
Stainless steelChromium and nickelHard, resistant to rusting

High carbon steels are used for construction because of their strength. Low carbon steels are used for making car body panels because they are malleable. Stainless steel is used for cutlery because it does not rust.

Question

Explain why stainless steel is used to make washing machines and dishwashers.

Washing machines and dishwashers contain water. This would cause other steels to rust, but stainless steel does not rust.

Aluminium and magnalium

Aluminium does not react with water. Its surface is protected by a natural layer of aluminium oxide that allows the metal to resist corrosion. Aluminium foil is used in the home for wrapping and storing food because it does not react to substances in food. It is malleable, so it is easily folded into shape around the food.

Aluminium has a low density, so pieces of aluminium are relatively lightweight. Magnalium is an alloy of aluminium and magnesium. It is stronger than aluminium alone but still has a low density. It is used to make aircraft parts.

Question

Suggest an explanation for why aluminium is used to make overhead electricity cables.

Aluminium is a good electrical conductor. Its low density prevents the wires from sagging too much or breaking under their own weight.