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Materials and their uses

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					Materials and their uses

   Structure of Materials
          Using Materials
• The first record of the use of salt
  dates back to around 4000 BC.
• In ancient Rome salt was used as a
  method of payment
 (the origin of the word salary)
and people can still be referred to
‘as worth their salt’
• Gold has been highly valued since
  prehistoric times

                 Egyptian
                 hieroglyphs from
                 as early as 2600     Around 2000 BC
                 BC describe gold
                 as ‘more plentiful
Around 1300 BC
                 than dirt’
• The word diamond derives from the
  Greek word ‘Adamas’ meaning
  unconquerable and indestructible




• Diamonds are thought to have been
  mined in India around 296 BC
      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*
 Diamonds are crystalline, they have a high melting
 point, they are insoluble and they do not conduct
 electricity*
 Salt is crystalline, it is soluble in water, it has a
 high melting point and it conducts electricity in
 solution*
                *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
     Conducting electricity
Two types of materials that we know
 conduct electricity are
Metals
Salt
The search to find their ‘charged
particles’ eventually led to an
understanding of the structure and
properties of materials
                   The Atom
    •The electron was discovered around 1987
    •Between 1911 and 1932 protons, neutrons and the
    idea of a central nucleus were discovered
•N. Bohr (1940) provided the
modern concept of the atomic
model. According to Bohr, the
atom is made of a central
nucleus containing protons
(positively-charged) and
neutrons (with no charge). The
electrons (negatively-charged)
revolve around the nucleus in
different imaginary paths
called orbits or shells.
                Metals
Metals conduct
 electricity
They have charged
 particles which are
 free to move
        Properties of metals
       Properties of metals
                Slip

•Hard  but malleable and ductile – metals
can be hammered into sheets or drawn into
wires because the metal atoms can slip over
one another.



the block slip theory – when stress is applied to the structure,
blocks of atoms become displaced as they slip past one another
•Conduct electricity because the delocalised
electrons are free to move towards the positive
terminal
•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 as light
                  Flame tests




Aurora Borealis
              Flame tests


Lithium   Sodium   Potassium   Calcium     Barium
 Red      Yellow     Lilac     Brick red   Green
• Metals objects are formed by casting
• The process is controlled by
  temperature and other factors
• As the metal cools small crystals
  (grains) appear
• The crystals grow until they form a
  solid mass of small crystals
    Grains/ crystals in metals
• In a crystal the molecules of the
  material lock together in a regular and
  repeating pattern. If a crystal is
  allowed to grow undisturbed, it will form
  regular shapes such as cubes, or
  hexagon columns. The type of substance
  and how its molecules
  interlock determine
  the shape of the crystal
                             Crystal lattice

If a material cools
quickly, small crystals
are formed
If a material cools
slowly, large crystals are
formed
                 Brittleness
Metals can be ‘cold –worked’ – forced into new
shapes at a low temperature
Grains are changed in shape and the metal
becomes stronger but less ductile
Dislocations occur in the lattice as it is worked.
If a material cools slowly , large crystals are
formed
                  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 can form to replace the deformed ones
                     Salt
Salt conducts electricity
  when it is dissolved in
  water
There must be               Chlorine

charged particles           35Cl



which are free to
                            17



move
                            Ions




Sodium atom                    Chlorine atom

11 protons + 11 electrons      17 protons + 17 electrons

+11 -11 = 0                    +17 -17 = 0
 Sodium ion                    Chlorine ion

11 protons + 10 electrons      17 protons + 18 electrons

+11 - 10 = +1                  +17 -18 = -1
                       Electrolysis
 Positive ions move to the negative
 electrode - Negative ions move to the
Electrolysis is used to separate         a metal from its compund.
 positive electrode

                                           When we electrolysed
                                         copper chloride the _____
                                         chloride ions moved to the
                                         ______ electrode and the
                                         ______ copper ions moved
                                         to the ______ electrode –
                                          OPPOSITES ATTRACT!!!


                                               = chloride ion

                                               = copper ion
                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 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
Repeating
crystal lattice
High melting
point due to
strength of
covalent bonds
Cannot conduct
electricity as
it has no free
charged
particles
What decides the type of bond?
 Elements on the left of the periodic table
 (groups 1 & 2) tend to lose electrons    Sodium 2.8.1
                                            Magnesium 2.8.2
 Elements on the right (groups 7 & 8) tend
 to lose electrons                     Fluorine 2.7
                                          Oxygen 2.6

 Electronegativity is a measure of the
 tendency of an atom to attract electrons in a
 bond – the greater the electronegativity, the
 greater the ability to attract the electrons
Electronegativity increases going across a period and goin
                        up a group




   losers                           gainers
            Bond Type

Metal  non-metal     IONIC

Non – metal  non –metal COVALENT

Metal to metal       METALLIC
                         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
                  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

                                               Weak bonds
                                               between chains
• Thermosoftening
             heat: softens

    hard, solid              soft, pliable

              cool: harden
           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
                                      thermoplastics which can be
                                      melted and re-moulded.


                                        A thermosetting plastic


                                           Covalent bonds
                                           between chains)
• Thermosetting
             Cool: harden



        during              permanently
    manufacture                 hard
    warm, pliable
• Both thermoplastics and thermoset plastics
  can be strong, tough, rigid and stable towards
  chemical attack
Bonds between atoms are strong covalent
bonds
•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
Cross linking
              Uses of thermosets
NAME                PROPERTIES             USES
Epoxy resin         Good electrical        adhesives, bonding of
                    insulator, hard,       other materials
                    brittle unless
                    reinforced, resists
                    chemicals well
Melamine            Stiff, hard, strong,   Laminates for work
formaldehyde        resists some           surfaces, electrical
                    chemicals and stains   insulation, tableware
Polyester resin     Stiff, hard, brittle   bonding of other
                    unless laminated,      materials
                    good electrical
                    insulator, resists
                    chemicals well
Urea formaldehyde   Stiff, hard, strong,   Electrical fittings,
                    brittle, good          handles and control
                    electrical insulator   knobs, adhesives
               Uses of thermoplastics
NAME                PROPERTIES                           USES
Polycarbonate       high impact resistance,              lighting lenses,sunglass/
                    temperature resistance and optical   eyeglass lenses, safety
                    properties                           glasses, compact discs,DVDs
                                                         automotive headlamp lenses,
                                                         lab equipment and drinks
                                                         bottles
Polyamide (Nylon)   Creamy colour, tough, fairly         Bearings, gear wheels,
                    hard, resists wear, self-            hinges for small cupboards,
                    lubricating, good resistance to      curtain rail fittings and
                    chemicals and machines well          clothing
Polymethyl          Stiff, hard but scratches easily,    Signs, covers of storage
methacrylate        durable, brittle in small            boxes, aircraft canopies and
(Acrylic)           sections, good electrical            windows, covers for car
                    insulator, machines and polishes     lights, wash basins and
                    well                                 baths
Polystyrene:        Light, hard, stiff, transparent,     Toys, especially model kits,
- conventional      brittle, with good water             packaging, castes for
                    resistance                           televisions, 'plastic' boxes
                                                         and containers
            Cold drawing
• Cold drawing is the process of
  stretching out a polymer fibre to line up
  the chains
• When a polymer is stretched a ‘neck’ forms.
• The chains in the ‘neck’ straighten out
  (become aligned)
• Cold drawing is used to increase a polymers’
  strength.
• 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
              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         Surgeons
                                       gloves made of
  strength and yet are very flexible. fabric woven
                                       with oriented
                                       plastic
                    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
       Bonding in ceramics
• Bonding are usually ionic as in magnesium
  oxide or aluminium oxide in which the
  ions are arranged in a regular repeating
  pattern - a giant lattice
  2     Combine with 3   To give
• Bonding can also be covalent e.g. in
  silicon carbide or silicon nitride
• The structure is a giant covalent lattice
                 Semi Conductors
                                 A chip




                                          An LED


  A transistor

Semiconductors have had a monumental impact on our
society. You find semiconductors at the heart of
microprocessor chips as well as transistors. Anything
that's computerized or uses radio waves depends on
semiconductors. Silicon is a semi conductor
Silicon bonding




   Silicon giant
   covalent lattice
•Generally in a giant covalent lattice all the
electrons are tied into the bonds and are
not free to conduct electricity

•In a semiconductor (like silicon) if electrons
get enough energy they escape from the
atom. Heat provides this energy

•Given enough energy electrons can escape
to the conduction band (like the delocalised
electrons in metals) and are free to move
and conduct electricity
Conduction in semiconductors

                      Delocalised
                      electrons




Electrons
in filled
shells
      Doping silicon: diodes and
             transistors
You can change the behaviour of silicon and turn
it into a conductor by doping it. In doping, you
mix a small amount of an impurity into the silicon
crystal.


There are two types of impurities
1. phosphorus or arsenic – called N-type
2. boron or gallium – called P-type
         N type semiconductor
                                      Si


                               P
Contaminated                               One phosphorus
by phosphorus                              electron has
                                           nothing to bond
which has 5
                                           with and is free to
outer electrons
                                           move around. It
4 of these are                             needs little energy
involved in the                            to jump to the
covalent bonds                             conduction band

   It takes very little impurity to create enough free
   electrons to allow an electric current to flow
             P type semiconductor

                                           Si

Contaminated by
boron
                                   B
which has 3 outer
shell electrons
A fourth electron is
taken from a silicon
atom creating a
positive hole
This silicon takes an
electron from another
                        The ‘positive hole’ is moving
silicon and so on       through the semi conductor
….............
     Uses of semi conductors

 A diode is the simplest possible semiconductor
   device. A diode allows current to flow in one
 direction but not the other. You may have seen
 turnstiles at a stadium or a subway station that
  let people go through in only one direction. A
    diode is a one-way turnstile for electrons.
When you put N-type and P-type silicon together
you get a very interesting phenomenon that gives
           a diode its unique properties.
Even though N-type silicon by itself is a conductor, and P-type silicon by
itself is also a conductor, the combination shown in the diagram does not
conduct any electricity. The negative electrons in the N-type silicon get
attracted to the positive terminal of the battery. The positive holes in the P-
type silicon get attracted to the negative terminal of the battery. No current
flows across the junction because the holes and the electrons are each
moving in the wrong direction.
    Amorphous Materials




An amorphous solid is a solid in which there is
no long-range order of the positions of the
atoms. For instance, common window glass is an
amorphous ceramic, many polymers (such as
polystyrene are amorphous, and even foods such
as candy floss are amorphous solids.
•   When glass is broken the
•   edges of the piece have a
•   range of shapes and sizes
•   If a crystal is broken it cleaves along the grain
    of the crystal
 • This difference in behaviour is due to the
   fact that glass is an amorphous solid - its
   particles are jumbled up
•Amorphous solids behave more like liquids than
solids in terms of their structure and are
sometimes referred to as ‘supercooled liquids’ –
liquids cooled below their melting point
 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
                           Glass
• Glass is an amorphous material usually
  produced when the viscous molten
  material cools very rapidly to below its
  without sufficient time for a regular
  crystal lattice to form
  Amorphous materials are often prepared by rapidly cooling
  molten material, such as glass. The cooling reduces the
  mobility of the material's molecules before they can pack
  into a more crystalline state. Amorphous materials can also
  be produced by additives which interfere with the ability to
  crystallize. For example addition of soda to silicon dioxide
  results in window glass.
               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 portioned
  out into a metal die and pressed. The pressed
  article is removed from the die and fired in a
  kiln to the sintering temperature, 700-900°C.
  The result is hard, somewhat porous glass. It
  is not transparent or does not otherwise look
  similar to molten glass.
                 Composites
•   Composites are combinations
•    of materials with different
•   properties                     Reinforced concrete

•   The parts of the composite
•    retain their identity and
•   do not dissolve or
•   completely merge together
•   They act together              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.
                      The Future
 Nanotechnology is the art and science of manipulating
    Nanotechnology
•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
• One of the first applications that uses ‘smart’ fabric is an
  ergonomic seat first seen at the Paris Motor Show 2000. The
  sensitive fabric monitors the movement of the occupants of
  the vehicle at their backs and legs and communicates with
  the seat's motors to adjust the seat for optimum comfort.
• we already have ‘smart’ clothes
                     The Future
 • Nanotechnology involves using nanoparticles of different
    elements or compounds to alter the properties of materials
 • e.g.
 - developing cheap, disposable solar panels by developing
 specialist inks containing silicon nanoparticles
- 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
  - nanocatalytic fuel cells capable of powering a laptop
  with the equivalent amount of alcohol as 2 or 3 drinks
 - implants made of materials that will bond with natural
 tissues and not be rejected by the body especially
 neural and retinal tissue

				
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