Alloys as Useful Materials (AQA GCSE Chemistry)

• Alloys are mixtures of metals where the metals are not chemically combined
• They can also be made from metals mixed with non-metals such as carbon or phosphorus
• Alloys often have properties that can be very different from the metals they contain, for example they can have more strength, hardness or resistance to corrosion or extreme temperatures
• Alloys contain atoms of different sizes, which distorts the regular arrangements of atoms
• This makes it more difficult for the layers to slide over each other, so they are usually much harder and stronger than the pure metal

The regular arrangement of a metal lattice structure is distorted in alloys

• Many of the metals that are in everyday use around us are alloys
• Some common examples are discussed below

Copper Alloys

• Bronze is an alloy made of copper and tin. It is harder than copper and is used to make ornaments and medals
• Brass is a common example of an alloy which contains 66% copper and 34% zinc. It is decorative and corrosion resistant and is used for low friction ornamental purposes such as plumbing and carpentry fittings

Brass is used extensively in modern kitchen and bathroom fittings

Aluminium Alloys

• Aluminium is mixed with copper, manganese and silicon for aircraft body production as aluminium alloys tend to be stronger and lighter than pure aluminium
• Aluminium and magnesium (5%) make an interesting alloy called magnalium which is also used extensively in automobile and aircraft construction
• As well as being lighter and stronger, it is also more corrosion resistant than aluminium
• Magnalium with 50% magnesium is used in the production of fireworks as it is more stable than pure magnesium but still burns brightly

Gold Alloys

• Gold alloys are used to make jewellery
• Gold metal is relatively soft and malleable so other metals such as copper, zinc and silver are added to provide strength and toughness
• Carats are used to express the purity of gold jewellery.
• Pure gold with nothing else added is said to be 24 carat
• A 12 carat piece of gold jewellery therefore contains 50% gold
• For example a 12 carat necklace that weighs 50g contains 50% gold, so 25 grams

Steel Alloys

• Iron from a blast furnace is an alloy of 96% iron, with carbon, phosphorus, silicon and sulfur impurities
• It is called cast iron and is too brittle for many uses, so most of it is converted into steel by removing some of the impurities
• Not all of the carbon is removed as steel contains some carbon, the percentage of which depends on the use of the steel
• Alloys of steel are made from adding other metals to steel such as chromium, manganese or nickel
• By carefully controlling the amounts added, the particular type of alloy required can be produced
• Steel alloys are used in construction, transport, manufacturing and other industries