Materials and their uses
Structure of Materials
The specification states;
Materials behave as they do because of
their structure; the way their atoms
and molecules fit together
You need to know;
- how the internal structure of a material
influences the way it behaves
- ways in which properties materials can
be modified by altering the structure of
the material
Using Materials
Materials
Salt -ionic
Copper - metallic
Diamond - covalent
• Why choose the three materials?
 salt
 copper
 diamond
Materials behave as they do because
of their structure; the way their
atoms and molecules fit together
Properties of Materials
We have known many of the properties of
materials for thousands of years
Metals are shiny, they have a high melting
point, they are malleable, ductile, they are
insoluble and they conduct electricity*
Salt is an ionic compound. It is crystalline, it is
soluble in water, has a high melting point and it
conducts electricity in solution*
Diamonds are covalent. They are crystalline, they
have a high melting point, they are insoluble and
they do not conduct electricity*
*All later discoveries
Why?
• We know how materials behave – their
properties
•The next question is why?
•An important development in our
scientific knowledge pointed to the
answer
i.e. The understanding that electricity is
a flow of charged particles
The flow of charge is called the current and it is the rate at which
electric charges pass though a conductor. The charged particle can
be either positive or negative.
Conducting electricity
Two types of materials that we know
conduct electricity are
Metals
Salt (in solution or molten)
The search to find their ‘charged
particles’ eventually led to an
understanding of the structure and
properties of materials
Structure of the Atom
The bigger the orbit – the higher the energy
Electrons can move between energy levels. To move up they
must take in energy (incoming radiation) / when moving down
they give out energy as electromagnetic radiation
Metals
Metals conduct
electricity
They have charged
particles which are
free to move
The understanding that
electricity is a flow of
charged particles
Metallic Bonding
Each atom loses control of its outer shell
electron resulting in a lattice of positive
ions surrounded by a ‘sea’ of electrons
Metallic bonding is the result of strong
electrostatic attraction between the
positive core and the negative ‘sea’ of
electrons
The strength of the bond gives metals
their high melting point
The melting point of gold is 1064oC
Crystals in metals
Metals have a crystalline structure which is not
usually visible
When the metal first
solidified from the
molten state, millions of tiny crystals grow
The longer the metals takes to cool, the larger
the crystals
Grains
• When the molten metal
solidifies, different
regions crystallise at the
same time
• The crystalline areas are
known as ‘grains’
• Eventually growing grains
meet at grain boundaries
• At these boundaries
there are can be atoms
which do not fit into the
crystal structure
dislocation
• Metals objects are formed by casting
• Molten metal is pored into a mould and
allowed to cool
• As the metal cools small crystals
(grains) appear
• The crystals grow until they form a solid mass
of small crystals
• The objects formed from the casting process
have dislocations
Properties of metals
•Hard but malleable and ductile – metals can
be hammered into sheets or drawn into
wires because blocks of atoms or grains can
slip or roll over one another.
•This movement is helped by the
presence of dislocations
• If a small stress is put onto the metal, the layers of atoms will
start to roll over each other. If the stress is released again,
they will fall back to their original positions. Under these
circumstances, the metal is said to be elastic.
• If a larger stress is put on, the atoms roll over each other into a
new position, and the metal is permanently changed.
•Conduct electricity because the delocalised
electrons are free to move to move around the
structure
•Are shiny because as light shines on the metal the
electrons absorb energy and jump temporarily to a
higher energy. When the electron falls back to its
lower level the extra energy is emitted
• The energy is emitted as light and as different metal
elements have different separations in the electron
orbits they emit different quantities of energy
Flame tests
Lithium
Red
Sodium
Yellow
Potassium
Lilac
Calcium
Brick red
Barium
Green
Flame tests
Aurora Borealis
Cold Working
Metals can be ‘cold –worked’ – forced into new
shapes at a low temperature
This creates more dislocations in the crystals
The more dislocations
a metal has, the more
they get in the way of
each other
The metal becomes
stronger but less
ductile – more brittle
Annealing
• Annealing is a treatment used to
restore softness and ductility to metals
•The metal is put in a furnace to soften the
metal
•It is then allowed to cool slowly so that new
crystals form and there are fewer dislocations
Alloying – mixing elements one
of which is a metals
• a. Prevent rust(corrosion)
Chromium and nickel are added to iron to form
stainless steel. The chromium can form an oxide layer
that can prevent iron from oxidising (rust). Suitable
for make cutlery, sinks etc.
b. To make it harder
Carbon is added to Iron to form steel. Steel is very
hard, however brittle also. Suitable for making
bridges, car bodies, pipes etc.
•
Aluminium is very light but very malleable. When it is
added to copper and magnesium, it forms duralumin
which is very hard, withstands corrosion and
lightweight. It is strong but light enough to
make an airplane body.
c. To improve the appearance
A normal metal usually gets dull when it exposed to
air, water and uv light over a long time. To create an
attractive surface and look, metals such as nickel and
chromium are added. Nickel is added to copper to
form an alloy used to make coins attractive and shiny
Salt
Salt conducts electricity
when it is dissolved in
water
The understanding that
electricity is a flow of
charged particles
There must be
charged particles
which are free to
move
Chlorine
35Cl
17
An atom has no charge:
number of positive protons = number of negative
electrons
When sodium loses an electron it becomes a charged particle/ a
positive ion
When chlorine gains an electron it becomes a charged particle/ a
negative ion
Sodium chloride crystal
Ionic Bonding
As with metals the strong electrostatic
attraction between the positive and negative
ions results in ionic compounds having a high
melting point (salt melts at 808oC)
Ionic compounds conduct because when they
are dissolved in water they separate into
positive and negative ions (the charged
particles) which move to the positive and
negative terminals
Carbon
•
•
•
•
Carbon is all around us
It’s in proteins, fats, carbohydrates
It makes up 20% of the human body
We use it to symbolise love and
commitment and to write on paper
• It is the main component in fossil fuels
• It is a key ingredient in the emerging field
of nanotechnology
Diamond
• Diamond does not conduct electricity
Diamond consists of
atoms of carbon
bonded together to
form a material with
a very high melting
point
It has no free
charged particles
An uncut diamond
Bonding in diamond
Carbon atoms are bonded by sharing
electrons in a covalent bond
•
Covalent bonds form
when outer shell
electrons are attracted
to the nuclei of more
than one atom
•Both nuclei attract the electrons
equally so keeping them held
tightly together
Giant Covalent Bonding
Repeating crystal
lattice
High melting point
due to strength
of covalent bonds
(3550oC)
Cannot conduct
electricity as it
has no free
charged particles
Graphite
Like diamond graphite has strong covalent carbon to
carbon bonds and a high melting point (3720OC)
Graphite conducts
electricity
The bonds between the
covalently bonded
sheets of carbon are
weak bonds and the
electrons are easily
attracted to a positive
terminal
Fullerenes
C60 Buckyball
‘Buckyball’
Carbon nanotube
Discovered in 1985
Fullerenes are a type of carbon made up of ‘cages’ or
tubes of at least 60 atoms of carbon
•
Fullerenes are highly stable chemically and have a
variety of unusual properties.
• Chemists have been able to add branches of other
molecules to them, place atoms inside of them, and
stretch them into rods and tubes. Fullerenes can be
made to be magnetic, act as superconductors, serve as
a lubricant, or absorb light.
Current work on the fullerene is largely theoretical and
experimental.
Recent research has suggested many uses for
fullerenes, including medical applications,
superconductors, and fibre-optics.
Polymers
The largest group of covalent compounds
are polymers
Polymers are long carbon chains sometimes
with different functional groups added and
all held together by covalent bonds
The bonding in a polymer chain is
strong covalent bonding
The bonding between chains can
create either thermsoftening
plastics or thermosetting plastics
Polymer
polyester
polytetrafluorethylene
polyvinylchloride
Monomer
Thermoplastics
• In thermosoftening plastics like poly(ethene) the
bonding is like ethane except there are lots of carbon
atoms linked together to form long chains. They are
moderately strong materials but tend to soften on
heating and are not usually very soluble in solvents.
Can be recycled
A thermosoftening
plastic (thermoplastic)
Weak bonds
between chains
Thermoplastics
Polyethene, polypropene,polyvinylchloride, polytetrafluoroethylene
• These can be heated enough to be reshaped. This
stretches the cross links. When cooled in the
stretched state they stay stretched and retain the
new shape
• If reheated the
chains are free
to slide back to their
original shape
Fibres
nylon
Hydrogen Bonding
Hydrogen bonding is a result of the electrostatic
attraction between hydrogen and oxygen due their different
electronegativities
Thermoset plastics
• Thermosetting plastic structures like melamine have
strong 3D covalent bond network they do not dissolve in any
solvents and do not soften on heating and are much stronger
than thermoplastics
They do not lend themselves
to recycling like
thermosoftening plastics
which can be melted and remoulded.
A thermosetting plastic
Covalent bonds
between chains)
Thermosets
Bakelite, melamine resin, epoxy, urea formaldehyde
• Both thermoplastics and thermoset plastics
can be strong, tough, rigid and stable towards
chemical attack
• Bonds between atoms are strong covalent
bonds so they do not conduct electricity
• Bonds between chains are weak
intermolecular bonds
• When plastics melt or dissolve it is the
intermolecular forces that are broken so
the different parts can slide past one
another
NAME
Uses of thermosets
PROPERTIES
USES
Epoxy resin
Good electrical
insulator, hard,
brittle unless
reinforced, resists
chemicals well
adhesives, bonding of
other materials
Melamine
formaldehyde
Stiff, hard, strong,
resists some
chemicals and stains
Laminates for work
surfaces, electrical
insulation, tableware
Polyester resin
Stiff, hard, brittle
unless laminated,
good electrical
insulator, resists
chemicals well
bonding of other
materials
Urea formaldehyde
Stiff, hard, strong,
brittle, good
electrical insulator
Electrical fittings,
handles and control
knobs, adhesives
NAME
Uses of thermoplastics
PROPERTIES
USES
Polycarbonate
high impact resistance,
temperature resistance and optical
properties
lighting lenses,sunglass/
eyeglass lenses, safety
glasses, compact discs,DVDs
automotive headlamp lenses,
lab equipment and drinks
bottles
Polyamide (Nylon)
Creamy colour, tough, fairly
hard, resists wear, selflubricating, good resistance to
chemicals and machines well
Bearings, gear wheels,
hinges for small cupboards,
curtain rail fittings and
clothing
Polymethyl
methacrylate
(Acrylic)
Stiff, hard but scratches easily,
durable, brittle in small
sections, good electrical
insulator, machines and polishes
well
Signs, covers of storage
boxes, aircraft canopies and
windows, covers for car
lights, wash basins and
baths
Polystyrene:
- conventional
Light, hard, stiff, transparent,
brittle, with good water
resistance
Toys, especially model kits,
packaging, castes for
televisions, 'plastic' boxes
and containers
Cold drawing
• Cold drawing is the process of
stretching out a polymer fibre to line up
the chains
Cold drawing improves the strength and appearance of the fibre
Crystalline Plastics
• A very strong material can be produced
• by arranging the molecules of a plastic to
produce a highly ordered material.
• This material is sometimes called oriented plastic
describing the way the molecules line up
• A recent example of such polymer
engineering is a substance called
‘spectra’ produced by an American
chemical company.
• Spectra fibres have enormous
strength and yet are very flexible.
Ceramics
• Ceramics are materials that include
glass, enamel, concrete, cement,
pottery, brick, porcelain, and chinaware.
Ceramics can be defined as inorganic, non metallic
materials. They are typically crystalline in nature and
are compounds formed between metallic and non
metallic elements such as aluminium and oxygen
calcium and oxygen , and silicon and nitrogen
• Ceramics are hard and strong so are used as
structural material such as bricks in houses,
stone blocks in the pyramids
•but not in conditions of tensile stress because
they are brittle (low tensile strength)
•Most ceramics do not conduct electricity
but this depends on the type - chromium
dioxide does, silicon dioxide is a semi–
conductor, aluminium dioxide does not
conduct
Glass
• Glass is an amorphous solid - its particles are
jumbled up
• This type of solid has no definite melting
point but softens as it is heated (like glass or
some plastics) and can be shaped by heating
•
Amorphous materials, like glass, are usually produced when
the viscous molten material cools very rapidly to below its
melting point without sufficient time for a regular crystal
lattice to form
What is glass?
The term glass refers to amorphous oxides, and
especially silicates (compounds based on silicon and
oxygen). Ordinary soda-lime glass, used in windows and
drinking containers, is created by the addition of soda
and lime (calcium oxide) to silicon dioxide. Without
these additives silicon dioxide will (with slow cooling)
form quartz crystals, not glass
Properties of
glass
- Solid and hard material
- Disordered and amorphous structure
- Fragile and easily breakable into sharp
pieces
- Transparent to visible light
- Inert and biologically inactive material.
- Glass is 100% recyclable and one of the
safest packaging materials due to its
composition and properties
Tempered/ heat toughened
glass
Tempering: Tempered safety glass is a
single piece of glass that gets
tempered using a process that heats,
then quickly cools the glass to harden
it. The glass is heated in a furnace and
cooled quickly. The outside hardens
but the inside remains fluid and flows
out to the edges compressing the
molecules together. The tempering
process increases the strength of the
glass from five to 10 times that of
untempered glass.
Advantages of toughened glass
• Toughened glass or tempered
glass is a type of safety glass
that has increased strength
and will usually shatter in small,
square pieces when broken. It
is used when strength, thermal
resistance and safety are
important considerations.
Sintering
• In the sintering and pressing process,
• first the glass is ground to a fine powder and
mixed with a binder. The mixture is pressed.
and then fired in a kiln to the sintering
temperature, 850°C. The atoms fuse together
and the result is hard, somewhat
porous glass. It is not transparent
or does not look similar to molten
glass.
Composites
• Composites are combinations
of materials with different
properties
• The parts of the composite
retain their identity and
do not dissolve or completely
merge together
• They act together
Reinforced concrete
fibreglass
Uses of composites
Glass- ceramic composite
• Glass-ceramic is a
mechanically very strong
material and can sustain
repeated and quick
temperature changes up to
800 – 1000oC.
• They show the properties of
glass and ceramic such as
ability to withstand high
temperatures, high strength
and durability
The Future
•Nanotechnology is the art and science of manipulating
matter at the nanoscale (down to 1/100,000 the width
of a human hair) to create new and unique materials
and products. The opportunities to do things
differently with nanotechnology have enormous
potential to change society.
Dust mite and gears
produced by
nanotechnology
• Nanotechnology involves using nanoparticles of
different elements or compounds to alter the
properties of materials
•
Sunscreen Aluminum oxide, the active
ingredient in sunblock that absorbs UV rays,
degrades when mixed with other molecules like
the sweat on your skin. Put these active
ingredients into a nano-emulsion, however, and
they remain distinct from their surroundings
and maintain their UV-absorbing powers.
Antimicrobial bandages - Scientist Robert Burrell
created a process to manufacture antibacterial
bandages using nanoparticles of silver. Silver ions
block microbes' cellular respiration . In other words
silver smothers harmful cells, killing them.
iPhone
Smartphones use nanotech in a variety of ways, and one of the most
ingenious is a nano-engineered accelerometer that tracks the phone's
motion for games and safety. Your iPhone knows when you drop it and
shuts down parts of its system for protection
Toothpaste
Brush certain types of toothpaste across your teeth, and nanoparticles
of hydroxyl apatitea calcium-based mineral found in bones will fill in
microscopic cracks in your enamel and keep them cavity-free.
Tennis balls
Tennis balls lose their bounce because their rubber core is gas
permeable and loses air over time (which is also why balloons deflate).
To combat this, the cores are coated in a nano-clay composite that
makes them more airtight and allows them to last longer on the courts.
Car paint
Mercedes owners need no longer fear about scratches on their car,
since nanoparticles of paint act like a layer of microscopic marbles,
filling in any gouges to its surface.
Solar panels
cheap, disposable solar panels by developing specialist inks
containing silicon nanoparticles
Clothing - Scientists are using nanoparticles to enhance your
clothing. By coating fabrics with a thin layer of zinc oxide
nanoparticles, manufacturers can create clothes that give
better protection from UV radiation. Some clothes have
nanoparticles in the form of little hairs or whiskers that hellp
repel water and other
materials, making the clothing stain-resistant.
In medicine:
- nanodevices capable of detecting cancer and other diseases at
the earliest stages, pinpointing the location of the disease,
delivering effective drugs only to the site of the disease and
monitoring the progress of the treatment.
Buckyballs can be filled with the drug and then attached to an antibody. The
antibody will then seek out the antigen produced by the disease and deliver
the drug. The medicine goes only to the diseased cells leaving healthy cells
alone
- implants made of materials that will bond with natural tissues and
not be rejected by the body especially neural and retinal tissue
nanocatalytic fuel cells capable of powering a laptop with the
equivalent amount of alcohol as 2 or 3 drinks