Download Types of Materials

Metals
Aluminium
Aluminium is a metallic element. It is a soft metal with a silvery appearance.
Aluminium exists in a metal lattice structure as Al3+ ions in a 'sea' of electrons where
the bonding between the ions and the free electrons is very strong. This gives the
aluminium a tightly bound metallic lattice making the melting point of aluminium very
high. Aluminium has a low density, high electrical and thermal conductivity and
excellent corrosion resistance. It has a high strength-to-weight ratio. Although it is a
good conductor of heat it will reflect up to 90% of radiant heat. It is used for engine
parts, aircraft structures, cooking utensils, drink cans, aluminium foil for heat
reflection, window and door frames.
Chromium
Chromium is a transition element. It is a hard silvery metal and pure chromium exists
as a typical metal lattice. That is, the metal consists of chromium ions in a sea of
electrons. Chromium can have more than one valency. The main oxidation states of
chromium in its compounds are +3 and +6. Chromium is a shiny metal that does not
oxidise or corrode easily; it is brittle with a high melting point. It is used in alloys such
as stainless steel and high strength and heat resistant alloys. It is used in cooking
utensils, and as plating on bicycle handle bars and car parts.
Copper
Copper is a red-brown transition element. The metal is composed of copper ions in a
sea of electrons, forming the metal lattice. Compounds of copper contain the metal in
the +1 or +2 valency state. The +2 oxidation state is the more stable of the two. The
metal is resistant to corrosion and has low electrical resistance and good thermal
conductivity. It is easily worked and can be joined by soldering, brazing and welding.
It is used in water pipes, electrical wires and in alloys.
Gold
Gold is a transition metal. It exists, like other metals, in a metallic lattice structure as
close packed ions in a sea of electrons. Gold is a very unreactive metal but can form
compounds. The compounds of gold are strong oxidising agents. In these
compounds gold can exist in the +1 or +3 valency states. Gold is very ductile and
worked easily. It has good electrical and thermal conductivity. Gold is used as
currency and used in electronic micro circuits. Gold resists infrared radiation, so if a
little is added to glass or plastic an effective heat shield can be formed. Being
unreactive it is used in dental work and in plating corrosive containers as well as in
jewellery.
Iron
Iron is a silvery transition element. Pure iron exists in a metallic crystal structure. In
the metallic lattice the iron atoms are ionised forming ions and are closely packed
together. Electrons form a sea around these ions. Iron can have a valency of +2 or
+3. Iron is used in alloys such as carbon steels, cast irons, alloy steels and stainless
steels. Mild steels are used for joists in buildings, bodywork for cars and ships,
screws, nails and wire. Medium-carbon steels are used for shafts and parts in car
transmissions, suspensions and steering. High-carbon steels are used for machine
tools, saws, axes, cold chisels, punches and drills. Stainless steels are high alloy
steels with more than 12% chromium. They are used where high corrosion is
required in chemical and food-processing equipment. Cast iron is hard and brittle.
They are used for machine castings, manhole covers, heavy-duty piping and
machine tool beds.
Lead
Lead is a soft metal. It is a silvery metal but usually appears dull grey due to its
reaction with air. The lead atoms exist in a metallic crystal lattice in which the lead
exists as ions in a sea of electrons. It has a valency of +2 when forming its
compounds.
Lead is highly resistant to corrosion, has a low melting point and is electrically
conductive. It is very dense and malleable. Lead is used in lead acid batteries, water
pipes, as an electrical insulator, in roofing noise insulation and in paint pigments.
Nickel
Nickel exists, like other metals, in a metallic lattice structure as close packed ions in a
sea of electrons. Nickel is used for a number of alloys with excellent corrosion
resistance and strength at high temperatures. The alloys are basically nickel-copper
and nickel-chromium-iron. They are used for pipes and containers in the chemical
industry where high resistance to corrosive atmospheres is required, food-processing
equipment, and applications, such as gas turbine blades and parts, where strength at
high temperatures is required.
Silver
Silver is a soft metallic transition element. It exists, when pure, in a metallic lattice
structure. In the metal lattice, the silver ionises and the silver ions pack closely
together in a sea of electrons. Silver is not very reactive. In its compounds it has a
valency of +1, forming the ion Ag+.
Silver has a high thermal and electrical conductivity, and is very soft and ductile. It
has high reflectivity.
Silver is used in jewellery and the photographic industry as certain silver compounds
darken when exposed to light. Silver is the best conductor known to man so the
electronics industry uses it in nearly all its products. Silver batteries are smaller and
more powerful than conventional batteries so are ideal for hearing aids, cameras and
even space satellites. In powdered form it is an excellent catalyst used in industrial
alcohols, solvents and with ammonia compounds to produce fertilizers.
Silver is useful in medicine as it absorbs the oxygen that germs need to live and
therefore kills them. Surgeon's instruments are often made from silver to reduce the
chance of infection, and silver wire and plates can be used to repair broken limbs.
Tooth fillings are made out of a silver, tin and mercury compound.
Tin
Tin is a silvery-white element. It exists in a crystal lattice structure as tin ions in a sea
of negative electrons. In its compounds, tin can appear in the +2 or +4 valency
states.
Tin has a low tensile strength, is fairly soft and can be very easily cut. Tin plate is
steel plate coated with tin, the tin conferring good corrosion resistance. Solders are
essentially tin alloyed with lead and sometimes antimony. Tin alloyed with copper
and antimony gives a material widely used for bearing surfaces.
Zinc
Zinc is a blue white transition metal. Pure zinc is found as a metallic crystal structure
with ions of zinc packed together in a sea of electrons. When forming compounds
zinc forms the Zn2+ ion. Zinc has very good corrosion resistance and hence finds a
use as a coating for steel, the product being called galvanised steel. It has a low
melting point and hence zinc alloys are used for products such as small toys, cogs,
shafts, door handles. It is also used in battery electrodes, coinage and in paint.
Polymers
Acetate
Acetate, which is really called cellulose acetate, can be produced as long, strong
fibres (known as rayon, dicel or tricel) similar in feel to natural fibres, and is widely
used in clothing. Cellulose fibres are used to produce filter tips for cigarettes. A
sheet form of cellulose acetate is called Clarifoil. This is a transparent film used to
give a shiny finish to cosmetics packs and high quality print brochures and
magazines. It is also used in adhesive tapes, labels and as photographic and
cinema film. A further form of cellulose is Dexel, which can be produced in a variety
of colours and moulded into many different shapes. It is used to manufacture plastic
products such as tool handles, combs, toothbrush handles, goggles, masks and
spectacle frames.
Bakelite
Bakelite is a thermoset and is hard, rigid and is a good electrical insulator. It is low
cost and has good heat resistance and water resistance. It is used for electrical plugs
and sockets, switches, door knobs and handles.
Epoxy
Epoxy resins are thermosets which are used with glass fibres to form composites or
laminates with high strength and stiffness.
Ethylene
Ethylene vinyl acetate is an elastomer that has good flexibility, impact strength and
electrical insulation properties. It is used for cable insulation, flexible tubing and
gaskets.
Melamine
Melamine formaldehyde is a thermoset resin. When impregnated in paper it is used
as a laminate for table and kitchen unit surfaces. It is also used with fillers for
moulding knobs, handles, cups, saucers, toys and light fittings.
Nylon
Nylon is a thermoplastic used as a synthetic fibre. It has structural similarity to real
fibres and is a strong, hard-wearing material making it ideal for use in clothes such as
ladies tights and stockings and in raincoats. In addition to its strength and toughness,
nylon has a relatively high softening temperature and this makes it ideal for use in
various engineering materials like machine gear wheels and bearings as it has a low
coefficient of friction.
Perspex
Perspex is a clear glass-like plastic.
It has strong resistance to outdoor
environments, heat and ultraviolet radiation and will transmit 90% of daylight.
Perspex is also much lighter, tougher and cheaper than glass. Perspex is used as a
substitute for glass in aircraft glazing, roof lighting, advertising displays, windows and
windscreens, vehicle tail lights, double glazing and protective shields as well as in the
lenses of glasses.
Plastics
Plastics is a common name for a wide range of materials. Thermosetting plastics
tend to be hard, rigid plastics which can withstand high temperatures. They are used
for making objects which require durability. These include ship's hulls, heavy duty
flooring and road surfacing, car tyres, heating pipes, adhesives and car and electrical
parts.
Thermosoftening plastics tend to be a lot more flexible and mouldable. They include
synthetic polymers such as nylon and polyester which can be easily woven.
Thermoplastics are also used in packaging, plastic bags, footwear, guttering and
piping, to name a few.
Polyester
Polyester can be produced in two forms; thermoplastics and thermosets.
Thermoplastic polyesters have long unlinked polymer chains. They have excellent
electrical resistivity, are tough and discolour when subject to ultraviolet radiation.
These polymers are used to produce synthetic fibres which are long, strong and can
easily be woven into clothes. Thermosetting polyesters have interlinked polymer
chains. These polyesters, with glass fibre as a reinforcement, can be created with
great tensile strength, similar to that of metals. Reinforced polyesters are used in
hulls of boats, car bodies, wheelbarrows, helmets, swimming pools, fishing rods and
archery bows because of their strength and toughness.
Polythene
Polythene is a thermoplastic material. There are two main types: low density (LDPE),
which has a branched polymer chain structure and a fairly low tensile strength and
high density (HDPE), with linear chains being stronger and stiffer. Both forms have
good impermeability to gases and very low absorption rates for water. LDPE is used
for bags, squeeze bottles, ballpoint pen tubing, and wire and cable insulation. HDPE
is used for piping, toys and household ware.
Rubber
Rubber is a natural material which is an elastomer that is elastic and resilient. A main
property of rubber is that heat builds up slowly within the material. Rubber is
essential for tyres as a build up of heat in car or plane tyres could lead to bursting.
Because of the resilience of rubber it is used in engine mounts. The good cold
weather resistance of rubber makes it a good material to use for bridge bearings.
Rubber is used in gloves as it is tough, flexible and water resistant. Rubber is used in
bands and as foam due to its elasticity.
Ceramics
Alumina
Alumina is a ceramic that has excellent electrical insulation properties and resistance
to hostile environments. Combined with silica, it is used as refractory bricks.
Cement
Cement, when mixed with water, causes a reaction which results in a silicate
structure being formed. Portland cement is used in the manufacture of concrete, a
composite material involving cement, gravel and sand. As the tensile strength of
concrete is very low, concrete structures are built to exploit the materials impressive
compressive strength. Where additional tensile strength is required concrete is
usually reinforced by steel. Common uses for concrete include all kinds of building
work, railway lines and road building.
Clay
Clay is used in many ceramic materials with other materials such as silica and
feldspar being added. The materials are mixed with water and the product formed. It
is then dried and fired to produce the ceramic bonds. Earthenware, such as drain
pipes, are fired at a low temperature and have a relatively porous structure.
Glass
Glass is a non-crystalline solid in which there is no orderly pattern or arrangement of
atoms. Glass tends to have low ductility, low thermal expansivity and conductivity but
good resistance to chemicals and good electrical insulation properties. Common
glass, used in windows, is a form of calcium and sodium silicates. Pyrex glass, a
more heat resistant glass has some boron atoms replacing the silicon atoms in the
calcium silicate. Optical glass, have different elements incorporated, such as barium
or lead.
Composites
Ceramic
Ceramic composites such as alumina with silicon carbide fibres and Pyrex glass with
aluminium oxide fibres. Toughness is increased in the composite. Industrial cutting
tools are made with alumina reinforced with silicon carbide fibres.
Laminates
Laminates are made by gluing together sheets of materials together. An example of
such a material is plywood with thin layers of wood. Three-ply wood consists of a first
layer with fibres in one direction, a second layer with fibres at right angles, and then a
final layer with fibres in the same direction as the initial layer; this gives added
strength.
Metal
Metal composites such as alumina and silicon carbide have been used as
reinforcement for metals. The composite is stiffer and stronger than the metal alone,
but less ductile.
Natural
Natural composites, such as wood, consist of longitudinal cellulose cells bound
together with lignin. The properties along the fibre direction are different from those at
right angles to it. Bone is another example of a natural composite. Wood is used
extensively in the building trade for beam supports for floors and ceilings. It can also
be used to panel walls, for staircases and is used for doors. Often the whole frame of
a house is made of wood.
Polymer
Polymer composites such as epoxy resin with glass fibre and polyester with glass
fibre are much stiffer and stronger than the polymer alone and have stiffnesses and
strengths as good as some metal alloys.