Classification of materials

Metals

• FERROUS: Contains mostly iron and carbon. They are magnetic and will rust. Eg Low carbon steel, medium carbon steel, cast iron.
• NON-FERROUS: Doesn't contain iron. They aren't magnetic and don't rust. Eg Aluminium, copper, zinc, silver, gold, titanium, tin.
• ALLOY: Made of two or more metals, or combining two or more elements, one of which must be a metal. They can also be sub classified as ferrous alloys or non-ferrous alloys. Eg Ferrous alloys: Stainless steel, die steel (tool steel) . Non-ferrous alloys: Bronze, brass, duralumin, pewter.
• Eg Aluminium:
• It is suitable for a drinks can for a number of reasons:
• Malluable: can be deep drawn into shape.
• Lightweight: easier to lift and transport.
• Food safe: user won't be poisoned.
• Non-ferrous: won't rust on contact with liquid inside.
• Very easy to recycle and use again: it has a low melting point (660) so saving finite resources.
• Aesthetically pleasing: natural silver colour so offers a contemporary and clean look

Woods

• HARDWOOD: From broad-leafed (deciduous) trees. Generally slow growing and lose their leaves in autumn. Eg Oak, ash, mahogany, teak, birch, beech.
• Softwood: From a coniferous (cone bearing) tree. Generally fast growing and tend to be evergreen. Eg Pine, spruce, Douglas fir, redwood, cedar, larch.
• Manufactured board: Man-made wood-based composite material. They're available in much larger sizes than solid wood. Eg Plywood, marine plywood, aeroply, flexible plywood, chipboard, MDF.
• Eg Teak:
• Teak is suitable for an outdoor garden bench because:
• Contains natural oils resistant to moisture: weather resistant and unlikely to quickly degrade because of weather.
• Contains natural oils which resist acids and alkalis: unlikely to degrade due to bird droppings or cleaning detergents.
• Aesthetically pleasing: natural dark brown/red colourand a straight grain.
• Hard: it'll withstand scratches.

Polymers

• THERMOPLASTICS: Material which can be repeatedly reheated and reshaped so can be recycled after initial use. They have long linear chain molecules held by van der Walls forces. Eg LDPE, HDPE, PP, HIPS, ABS, PMMA, PET, PVC.
• THERMOSETTING POLYMER: Material which when heated undergoes a chemical change whereby the molecules form rigid cross links. They cannot be reheated and reshaped, even at very high temperatures.
• ELASTOMER: Material which at room temperature can be deformed under pressure and then upon release of the pressure will return to it's origional shape. They have weak bonds which allow them to stretch easily. Can be stretched repeatedly and upon immediate release of the stretch will return with force to the origional length.
• Eg Polyethylene terephthalate (PET)
• PET is suitable for a drinks bottle because:
• It's a thermoplastic: can be recycled so won't contribute to landfill

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