C15: Using Our Resources

The corrosion of iron to form Fe2O3 Iron + oxygen + water > hydrated iron (III) oxide

Mixture of metals

• Bronze is usually made by mixing copper with tin. It is used to make taps and ship’s propellers, because of its toughness and resistance to corrosion. • Brass is made by alloying copper with zinc. Brass is much harder than copper but it is still workable.

• There are over 300 alloys of aluminium available. • These alloys have very different properties. However, most tend to be low density due to aluminium having a low density • Lightweight but strong aluminium alloys are used to build aircraft whilst others can be used as armour-plating on tanks and other military vehicles.

As with copper and aluminium, gold can be made harder by adding other elements. Gold is usually alloyed with silver, copper, and zinc when it is used to make jewellery. Pure gold wears away more easily than its alloys. By varying the proportions of the metals, it is also possible to get different shades of ‘gold’ objects.

Alloys of iron with carbon and/or other elements

• The simplest steels are the low carbon steels. These are made by removing most of the carbon from the iron obtained from a blast furnace. • In steel-making, the carbon content decreases from about 4% to as little as 0.03%. • These are the cheapest steels to make. They are used in many products, such as the bodies of cars, machinery, ships, containers, and structural steel.

High carbon steel, with a relatively high carbon content, is very strong but brittle. On the other hand, low carbon steel is soft and easily shaped. It is not as strong but is much less likely to shatter on impact with a hard object.

Nickel-steel alloys are used to make long-span bridges, bicycle chains, and military armour-plating. That is because they are very resistant to stretching forces.

Tungsten steel operates well under very hot conditions, so it is used to make high-speed tools such as drill bits.

• The chromium-nickel steels are known as stainless steels. • They combine hardness and strength with great resistance to corrosion; they do not rust • Used in cooking utensils and cutlery. • Also used to make reaction vessels, however often makes set up costs expensive. Used to withstand high temperatures, pressures, and corrosive chemicals

Using very high pressures and a trace of oxygen, ethene forms LD poly(ethene). The polymer chains are randomly branched and cannot pack closely together. Hence its lower density.

• Using a catalyst at 50 °C and a slightly raised pressure • This is made up of straighter poly(ethene) chains. They can pack more closely together than branched chains- hence higher density • It also has a higher ‘softening temperature’ and is stronger than LD poly(ethene).

Monomers used to make it Conditions used to carry out polymerisation reaction

Sand (SiO2), limestone (CaCO3) and sodium carbonate (Na2CO3) These are heated to 1500°C, melt and react to form molten glass

There are many different types of glass. These can be made by varying the glass-making mixture or by incorporating other material into the glass

• Clay ceramics are made by moulding wet clay into the desired shapes, and then heating them in a furnace to around 1000°C. • The clay contains ions and atoms that are arranged in giant structures that form layers. • When wet, the water molecules get between the layers of clay • However, when they are fired in a furnace, the water is driven out and strong bonds form between the layers in the giant structure.

Ceramics are brittle because a sharp blow can distort layers in their structure so that ions with like charges are adjacent, repelling each other away. This causes the ceramic object to crack.

Most composites are made of two materials, making a product with improved properties for a particular use. They are often a matrix (or binder) of one material, surrounding and binding together fibres or fragments of the other material — a process called reinforcement.

Composite glass-ceramic Composite of glass with polymers (eg fibreglass) Wood composites (eg plywood) Concrete

However, heating the two together forms a composite glass-ceramic, which is hard but also very tough. This is because the glass melts then sets between the crystals in the ceramic, so any cracks cannot spread through the whole structure.

• These composites are tough and flexible. They are made of fine threads of glass embedded in a polymer resin that hardens once moulded into shape. They form a tough, flexible, waterproof material with a low density • Advanced composites can use carbon fibres or carbon nanotubes instead of glass fibres. These composites are tough, lightweight materials that can also be made to conduct electricity.

• Plywood is thin sheets of wood glued together, with the grain in each layer at right angles to each other so it resists splitting along the grain. • Medium-density fibreboard (MDF) is another wood composite, made from woodchips, shavings, or sawdust compressed together and bound using a polymer resin- doesn’t splinter

Made from cement, sand, and gravel (small stones) mixed with water and left to set. It is very hard and very strong in compression. ‘Reinforced concrete’ is made more resistant to bending forces by setting it around a set of steel rods.