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© Boardworks Ltd 20051 of 17
Resistant MaterialsMetals
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© Boardworks Ltd 20051 of 17
© Boardworks Ltd 20052 of 17
Learning objectives
© Boardworks Ltd 20052 of 17
Lea
rnin
g o
bje
ctiv
es To know where metals come from and how they are obtained.
To understand the differences between, and properties of, ferrous and non-ferrous metals and alloys.
To understand how the properties of different metals make them suitable for different uses.
To know how the properties of metals can be altered by heating.
© Boardworks Ltd 20053 of 17
Metals are part of the earth’s crust. Economic, chemical and technological problems have to be solved to obtain them.
How desirable a metal is often depends on how scarce it is.
Gold diggers dig up tonnes to obtain a few grams, whereas there is so much iron that materials technologists are only interested if they can obtain hundreds of kilograms from each tonne of ore.
Where do metals come from?
© Boardworks Ltd 20054 of 17
Copper ore is mined, then washed to remove other minerals and unwanted materials.
It is heated in a furnace and the molten copper is run off.
This process is known as smelting.
Where do metals come from?
Pure metals like copper form part of the earth’s crust as metal ore.
© Boardworks Ltd 20056 of 17
Aluminium is the most plentiful metal found in the earth’s crust, and is in high demand because it is both light and strong.
Aluminium is extracted from aluminium oxide (bauxite) by electrolysis. Electricity passes between the electrodes and pure aluminium forms at the cathode.
Extracting metals – electrolysis
molten aluminium metal
cathode lining
carbon anode
© Boardworks Ltd 20057 of 17
Ferrous metals are metals which contain iron. They will corrode if unprotected. Ferrous metals will be attracted by a magnet.
Non-ferrous are metals which do not contain iron. Pure metals such as aluminium, copper, tin and lead are non-ferrous, and do not rust.
Ferrous and non-ferrous metals
Metals can be classified into three groups: ferrous metals, non-ferrous metals and alloys.
Alloys are metals which are a mixture of two or more metals, benefiting from the properties of both. For example, brass is an alloy of copper and zinc.
© Boardworks Ltd 200516 of 17
Metals are commercially available in a range of stock shapes and sizes.
Market forms of metals
channel
angle
square tube
round tube
flat strip
sheet
round rod
square rod
hexagonal rod
octagonal rod
© Boardworks Ltd 200517 of 17
Key points
© Boardworks Ltd 200517 of 17
Key
po
ints
Metals are extracted from the earth’s crust. Iron ore is smelted to obtain iron, while aluminium is obtained by electrolysis.
Ferrous metals come from iron ore and include cast iron and steel. Non-ferrous metals include aluminium, copper and tin.
Alloys such as brass and stainless steel are formed from two or more metals and other elements.
Heating metals alters their properties. Annealing involves heating a metal and then allowing it to cool, which makes the metal more workable. Tempering steel makes it less brittle.