Materials and their uses

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Materials and their uses

• Structure of Materials

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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

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Using Materials
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• The first record of the use of salt dates back to
  around 6050 BC.
• It was used as part of Egyptian religious
  offerings
• In ancient Rome salt was used as a method of
  payment
• (the origin of the word salary)

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• Gold has been highly valued since prehistoric
  times.
• It was associated with beauty, power and wealth.

Egyptian hieroglyphs from as early as 2600 BC
describe gold as more plentiful than dirt
Around 2000 BC
Around 1300 BC
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• The word diamond derives from the Greek word
  Adamas meaning unconquerable and indestructible
• Diamonds are thought to have been mined in India
  around 800 BC

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• Why choose the three materials?
• salt
• gold
• diamond

Materials behave as they do because of their
structure the way their atoms and molecules fit
together
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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 crystalline, it is soluble in water, it
  has a high melting point and it conducts
  electricity in solution

• Diamonds are crystalline, they have a high
  melting point, they are insoluble and they do not
  conduct electricity

All later discoveries
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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.
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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
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The Atom
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Bohrs Atom
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Metals

• Metals conduct electricity
• They have charged particles which are free to
  move

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Each atom loses control of its outer shell
electron resulting in a lattice of positive ions
surrounded by a sea of electrons
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• 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

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• 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

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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 hexagonal
  columns. The type of substance and how its
  molecules
• interlock determine
• the shape of the crystal

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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
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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 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
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• 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

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Flame tests
Lithium Red
Sodium Yellow
Potassium Lilac
Calcium Brick red
Barium Green
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Flame tests
Aurora Borealis
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Cold Working
Metals can be cold worked forced into new
shapes at a low temperature
Dislocations occur at the grain boundaries as it
is worked.
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
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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

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Salt

• Salt conducts electricity when it is dissolved in
  water

There must be charged particles which are free to
move
Chlorine 35Cl 17
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Ions
Chlorine atom 17 protons 17 electrons 17 -17
0
Sodium atom 11 protons 11 electrons 11 -11 0
Chlorine ion 17 protons 18 electrons 17 -18
-1
Sodium ion 11 protons 10 electrons 11 - 10 1
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Sodium chloride crystal
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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 electricity when in
solution as the ions (the charged particles) are
free to move to the positive and negative
terminals
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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
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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

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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
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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
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Fullerenes
C60 Buckyball
Carbon nanotube
Discovered in 1985 Fullerenes are resilient to
impact and deformation. This means, that
squeezing a buckyball and then releasing it would
result in its popping back in shape. Or ,if it
was thrown against an object it would bounce back
Buckyballs are also extremely stable in the
chemical sense Their hollow structure allows
other atoms to be carried within them
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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 gain
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
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Electronegativity increases going across a period
and going up a group
gainers
losers
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Bond Type
IONIC
Metal ? non-metal
COVALENT
Non metal ? non metal
Metal ? metal
METALLIC
Low electronegativity
High electronegativity
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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
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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
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• Thermosoftening
• heat softens
• hard, solid soft, pliable
• cool harden

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• 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

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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
re-moulded.
A thermosetting plastic
Covalent bonds between chains)
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• Thermosetting
• Cool harden
• during permanently
• manufacture hard
• warm, pliable

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• 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

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Uses of thermosets
NAME 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
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Uses of thermoplastics
NAME 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, self-lubricating, 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
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Cold drawing

• Cold drawing is the process of stretching out a
  polymer fibre to line up the chains

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• Cold drawing is used to increase a polymers
  strength.

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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.

Surgeons gloves made of fabric woven with
oriented plastic
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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
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• 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 semiconductor, aluminium
  dioxide does not

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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
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• Bonding can also be covalent e.g. in silicon
  carbide or silicon nitride
• The structure is a giant covalent lattice

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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
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Silicon bonding
Silicon giant covalent lattice
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• 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
  or light 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

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Conduction in semiconductors
Delocalised electrons
Electrons in filled shells
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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
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N type semiconductor
Si
P
Contaminated by phosphorus which has 5 outer
electrons 4 of these are involved in the
covalent bonds
One phosphorus electron has nothing to bond with
and is free to move around. It needs little
energy to jump to the conduction band
It takes very little impurity to create enough
free electrons to allow an electric current to
flow
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P type semiconductor
Si
Contaminated by boron 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 silicon
and so on .............
B
The positive hole is moving through the semi
conductor
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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.
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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.
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• 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

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• 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

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Glass

• Glass is an amorphous material 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

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.
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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
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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
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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.
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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.

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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, 700900C. The result is hard,
  somewhat porous glass. It is not transparent or
  does not otherwise look similar to molten glass. 

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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
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Uses of composites
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Glass- ceramic composite

• Glass-ceramic is a mechanically very strong
  material and can sustain repeated and quick
  temperature changes up to 800 1000oC.

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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
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• Sunscreen - Many sunscreens contain nanoparticles
  of zinc oxide or titanium oxide. Older sunscreen
  formulas use larger particles, which is what
  gives most sunscreens their whitish color.
  Smaller particles are less visible, meaning that
  when you rub the sunscreen into your skin, it
  doesn't give you a whitish tinge.

• 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 help repel water and other
  materials, making the clothing stain-resistant.

• 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.

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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