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

Copper - metallic

Salt -ionic

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 MaterialsWe have known many of the properties

of materials for thousands of years

Diamonds are covalent. They are crystalline, they have a high melting point, they are insoluble and they do not conduct electricity*

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*

*All later discoveries

Why?

• We know how materials behave – their properties

i.e. The understanding that electricity is a flow of charged particles

•An important development in our scientific knowledge pointed to the answer

•The next question is why?

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 metalsMetals have a crystalline structure which is not usually visible

When the metal firstsolidified from the molten state, millions of tiny crystals growThe 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 testsFlame tests

LithiumRed

SodiumYellow

Potassium

Lilac

CalciumBrick red

BariumGreen

Flame tests

Aurora Borealis

Cold Working

This creates more dislocations in the crystals

The metal becomes stronger but less ductile – more brittle

Metals can be ‘cold –worked’ – forced into new shapes at a low temperature

The more dislocations a metal has, the more they get in the way of each other

Annealing

• Annealing is a treatment used to restore softness and ductility to metals

•It is then allowed to cool slowly so that new crystals form and there are fewer dislocations

•The metal is put in a furnace to soften the metal

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

SaltSalt conducts electricity

when it is dissolved in water

There must be charged particles which are free to move

Chlorine

35Cl

17

The understanding that electricity is a flow of charged particles

An atom has no charge:number of positive protons = number of negative electronsWhen 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

An uncut diamond

It has no free charged particles

Diamond consists of atoms of carbonbonded together to form a material witha very high melting

point

Bonding in diamond

• Covalent bonds form when outer shell electrons are attracted to the nuclei of more than one atom

Carbon atoms are bonded by sharing electrons in a covalent bond

•Both nuclei attract the electrons equally so keeping them held tightly together

Giant Covalent BondingRepeating crystal lattice

Cannot conduct electricity as it has no free charged particles

High melting point due to strength of covalent bonds (3550oC)

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 BuckyballCarbon nanotube

Discovered in 1985

Fullerenes are a type of carbon made up of ‘cages’ or tubes of at least 60 atoms of carbon

‘Buckyball’

• 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 bondingThe bonding between chains can create either thermsoftening plastics or thermosetting plastics

polyester

polytetrafluorethylene

polyvinylchloride

Polymer 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.

A thermosoftening plastic (thermoplastic)Weak bonds between chains

Can be recycled

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

Fibresnylon

Hydrogen BondingHydrogen 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

A thermosetting plastic

Covalent bonds between chains)

They do not lend themselves to recycling like thermosoftening plastics which can be melted and re-moulded.

Thermosets

Bakelite, melamine resin, epoxy, urea formaldehyde

• Both thermoplastics and thermoset plastics can be strong, tough, rigid and stable towards chemical attack

• When plastics melt or dissolve it is the intermolecular forces that are broken so the different parts can slide past one another

• Bonds between chains are weak intermolecular bonds

• Bonds between atoms are strong covalent bonds so they do not conduct electricity

Uses of thermosetsNAME 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

Uses of thermoplasticsNAME 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

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

•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

•but not in conditions of tensile stress because they are brittle (low tensile strength)

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•  

Dust mite and gears produced by nanotechnology

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.

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.

• 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.

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 protectionToothpaste

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 panelscheap, 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 othermaterials, making the clothing stain-resistant.

- implants made of materials that will bond with natural tissues and not be rejected by the body especially neural and retinal tissue

- 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.

In medicine:

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

nanocatalytic fuel cells capable of powering a laptop with the equivalent amount of alcohol as 2 or 3 drinks