1. Materials and their uses
Structure of Materials

2. 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

3. Using Materials

4. 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)

5. 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

6. 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

7. 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

8. 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

9. 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.

10. 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

11. The Atom

12. Bohr’s Atom

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

14. Each atom loses control of its outer shell electron resulting in a lattice of positive ions surrounded by a ‘sea’ of electrons

15. 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

16. 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

17. 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

18. 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

19. 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

20. 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

21. Flame tests Lithium Red Sodium Yellow Potassium Lilac Calcium
Brick red
Barium
Green

23. Flame tests
Aurora Borealis

24. 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

25. 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

26. Salt There must be charged particles which are free to move
Salt conducts electricity when it is dissolved in water
There must be charged particles which are free to move
Chlorine
35Cl 17

27. Ions Chlorine atom Sodium atom 17 protons + 17 electrons
= 0
Sodium atom
11 protons + 11 electrons
= 0
Chlorine ion
17 protons + 18 electrons
= -1
Sodium ion
11 protons + 10 electrons
= +1

28. Sodium chloride crystal

29. 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

31. 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

32. 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

33. 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

34. 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

35. Fullerenes Discovered in 1985
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

36. 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

37. Electronegativity increases going across a period
and going up a group
gainers
losers

38. Bond Type IONIC Metal  non-metal COVALENT Non – metal  non –metal
Metal  metal
METALLIC
Low electronegativity
High electronegativity

40. 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

41. 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

42. Thermosoftening
heat: softens
hard, solid soft, pliable
cool: harden

43. These can be heated enough to be reshaped
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

44. 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)

46. Thermosetting
Cool: harden
during permanently
manufacture hard
warm, pliable

47. 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

48. 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

49. 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

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

51. Cold drawing is used to increase a polymers’ strength.

52. 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

53. 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

54. 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

55. 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

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

57. 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

58. Silicon bonding
Silicon giant covalent lattice

59. 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

60. Conduction in semiconductors
Delocalised electrons
Electrons in filled shells

62. 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

63. 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

64. 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

65. 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.

66. 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.

67. 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

68. 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

69. 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.

70. 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

71. 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

72. 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.

73. 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.

74. 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, 700­900°C. The result is hard, somewhat porous glass. It is not transparent or does not otherwise look similar to molten glass. 

75. 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

76. Uses of composites

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

78. 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

79. 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.

80. 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