There are many metals which you are familiar with - copper pipes and wire, aluminium saucepans and cast iron stoves. Metals may be mixed with other elements especially other metals to produce alloys which will have improved properties. Heat treatment can also be used to change the properties of alloys e.g. hardening and tempering of high carbon steel.

All metals are good conductors of heat and electricity. Copper is a particularly good conductor but is not very strong, it is also fairly dense. Aluminium is a good conductor has a low density and when alloyed has a high tensile strength. Some alloys such as pewter and zinc alloys have a low melting point and can be easily formed by casting or moulding but they have a low tensile strength.

Metals in common use are corrosion resistant except iron and steel which rust quickly. Corrosion resistance is achieved by electroplating to add a layer of corrosion resistant material such as chromium or zinc, painting, plastic coating, and coating with an oil or grease. The alloy stainless steel is very rust resistant.

When choosing a metal for a particular job the properties must be carefully considered. For example aluminium could be used for overhead power lines as its lower density and good tensile strength offset its slightly lower electrical conductivity.

Types of metal available in school - link to GCSE engineering materials page

Polymers are made from long chain molecules which may have cross linking bonds affecting flexibility/stiffness.

There are three groups of polymer:-

Thermoplastics which may be reformed with heat. e.g. PVC, HIPS, nylon, polycarbonate, PET, acrylic.

Thermosetting plastics which once moulded or formed cannot be reformed by heat. e.g. Melamine(MF), epoxy resin, Urea formaldehyde (UF).

Elastomers - rubbers long chain elastic molecules. e.g. neoprene, natural rubber. Used for car tyres and elastic bands.

Applications

Nylon is used for bearings and the cases for power tools also used for fishing line and ropes. Nylon is very strong and wear resistant it is also slippery without the need for lubrication. Originally used as a silk substitute - stockings and climbing ropes.

PVC is used for casings for electical consumer items and is also used in its flexible form as the insulating sheath on electrical cable and flex.

Melamine is used as the protective layer on worksurfaces and laminated flooring.

UF is used to make electrical components when a good insulator is needed such as plug tops and switch buttons.

Acrylic is used for safety shields but is not as tough as polycarbonate. Polycarbonate is used for the lenses in safety eye protection e.g. goggles.

This class of material includes plates and cups, bricks, earthenware pots, engineering ceramics, glasses [glasses are non-crystalline and not normally classed as ceramics], and refractory (furnace) materials. Ceramics are made by heating together materials such as silica, chalk and clays. Other chemicals may be included to act as flux and to change colour etc.

Engineering Ceramics Include

Silicon carbide
Zirconia
Silicon nitride
Diamond
Cubic boron nitride
Tungsten Carbide

Properties
Engineering ceramics are ideally suited for high performance applications where a combination of properties such as wear resistance, hardness, stiffness and corrosion resistance are important. In addition to these properties, engineering ceramics have relatively high mechanical strength at high temperatures. They are good electrical insulators, They often have a close thermal expansion coefficient to metals (they can be bonded to metals - e.g. carbide tipped tools).

Ceramics have been regarded as hard but brittle, however modern ceramics have been developed which are viable alternatives to metals and their alloys in many applications - engineering ceramic parts and components are more durable and have longer life-spans under given operational conditions. Ceramic cutting tools, for instance, require less sharpening or replacement due to wear, and will last at least 60 to 100 times longer than steel blades.

Engineering ceramics are chemically resistant to most acids, alkalis and organic solvents and can withstand high temperatures. Metals weaken rapidly at temperatures above 816 degrees C while engineering ceramics retain a good degree of their mechanical properties at much higher temperatures.

Applications
Mechanical components include wear plates and thermal barriers, bearings for high speed and high stiffness spindles, bushes, gears.

Process components include pump shafts, seats, bearing surfaces, gears and even complete pump bodies, valve guides and seats.

Ceramics are used for cutting tools including razor blades for film and tape cutting to 300mm diameter circular slitters for the paper industry.

Ceramic turbine blades are used in most turbochargers providing lighter units than the steel alternatives allowing improved performance at higher temperatures.

Are mixtures of materials which give improved properties. One of the materials is the matrix or binding chemical and the other is the reinforcer. A good example is GRP - glass reinforced polyester(plastic) resin. where the glass fibres increase the strength of the polyester resin. Carbon fibre reinforced epoxy resin is stronger and lighter than steel.

Concrete is a composite (the cement is the matrix and the gravel and steel rods are the reinforcer) as are bricks made from clay reinforced with straw.

Natural composites include wood, shell and bone.

Applications

Car bodies - especially sports cars, F1 racing cars, boat hulls, lightweight struts and supports in bridge building and the construction industry. Aerospace - use of carbon fibre composites as well as high tech ceramic parts has revolutionised this industry.