What determines what a material is useful for?
Its properties
Working properties of a material
Strength
Hardness
Toughness
Elasticity
Malleability
Ductility
Strength
Ability to withstand forces without breaking
Rope in tug-of-war is resists pulling forces
Hardness
Ability to withstand scratching, abrasion or denting
A very hard metal is likely to crack upon impact or force
Toughness
When a material is hard to break (it may change shape)
The ability to absorb the force of an impact
A tough material may scratch easily on the surface but can withstand large impacts
Elasticity
Materials that can stretch and bend and then return to their original shape
Malleability
Materials that can be bent and shaped
Metals can be hammered into thin sheet without breaking
Can be rolled or pressed into sheets easily but will deform if compressed
Ductility
Can be drawn out into a wire
Physical properties of materials
Electrical conductivity
Thermal conductivity
Fusibility
Density
Absorbency
Electrical conductors
Let electricity travel through them easily
Thermal conductors
Let heat travel through them easily
Examples of electrical insulators and conductors and thermal conductors
Fusibility
The ability of a material to be heated and joined to another material when cooled
What do materials with a high fusibility have?
Low melting points
Only a small amount of heating is required to convert these materials to liquids
Density
A measure of its mass per unit volume
kg/m^3
Absorbency
The more absorbent fibres and fabrics are, the better they are at soaking up moisture
Properties of absorbent materials
Good at soaking up moisture
Can be dyed easily
Dry slower
Vulnerable to stains
Examples of absorbent and non-absorbent materials
Absorbant:
Natural fibres (wool, cotton, cellulose fibres)
Not absorbant:
Synthetic fibres (polyester and lycra)
Metals vs Non-metals physical properties
Alloy
A mixture of 2 or more elements one of which must be a metal
Stronger than elements in their pure form
Timber
Sawn chunks of solid wood that are used as building material
Types of wood
Expensive hardwoods
Cheaper softwoods
Softwood vs hardwood
Pine (softwood)
Yellow with brown streaks
Lightweight
Strong and cheap
Knotty (hard to work with)
Used for telegraph poles, fences and cheap furniture
Larch (softwood)
Attractive yellow to reddish-brown colour
Harder, tougher and more durable than most softwoods
Resistant to rot
Used for decking, cladding the outsides of buildings, fence posts
Spruce (softwood)
Reddish brown colour
Hard and good strength to weight ratio
Knotty and not durable
Used for structural purposes- aircraft, crates, ship masts
Oak (hardwood)
Light brown and attractive grain markings
Tough, durable, very strong
Finishes well
Corrodes steel screws and fittings
Used for interior panelling, flooring, furniture
Mahogany (hardwood)
Reddish brown colour→ beauty and warmth
Durable and easy to work with
Expensive
Used for good quality furniture, musical instruments, boats and interior panelling
But increased desire for mahogany has increased the destructive and illegal logging trade
Beech (hardwood)
Pinkish-brown
Hard enough to resist being dented, but can be bent with steam
Used for chairs and toys
Balsa (hardwood)
White or tan colour
Very low density and lightweight
Very soft → Easy to cut and shape
High strength to weight ratio
3+4 → good for modelling
Balsa trees are very fast growing
Gives the wood a coarse, open grain
The living tree has large cells that fill with water
Gives the wood its spongy texture
Used for lightweight, rigid structures:
Prototypes, model bridges and model aircraft
Ash (hardwood)
Pale cream colour and attractive
Tough
Used for tool handles, wooden sports equipment and furniture
Ferrous metals
Metals or alloys made up of iron (ferrite)
So they are magnetic
Can corrode/rust
Properties and uses of ferrous metals
What is applied to prevent ferrous metals from rusting
Protective coatings like paint and enamel
Except steel (resistant to rust so doesn’t need to be coated)
Non-ferrous metals
Metals and alloys that don’t contain iron
They don’t rust
Useful if they are exposed to moisture
Properties and uses of non-ferrous metals
Properties and uses of alloys
Polymers
Made from synthetic materials
Derived from crude oil or other finite resources, such in as coal or natural gas
What are plastics made up of
Polymers
Renewable and sustainable materials used to make bio-plastics
Vegetable starches
2 types of plastic
Thermoforming
Thermosetting
Thermoforming plastics (thermoplastics)
Doesn’t resist heat well
When heated becomes soft and flexible
Easily formed into different shapes (bendy)
By heating, melting and remoulding
Easy to recycle
Ground down, melted, re-used and remoulded
Plastic memory
Each time the plastic is reheated it will try to return to its original shape
Properties and uses of thermoforming plastics
Thermosetting plastics (thermosets)
Resist heat and fire
Have strong chemical bonds between the molecules, which do not separate on heating
Used for electrical fittings and pan handles
Undergo a chemical change when heated and moulded to make a product
They are permanently hard and rigid
Non-recyclable
Can’t be melted and reshaped again
Plastic cannot be reformed once set in to shape
Properties and uses of thermosetting plastics
Molecular structure of thermosets vs thermoplastics
Pros and cons of thermoplastics
Pros and cons of thermosets
Modern materials
Materials that have been recently developed with a specific application in mind
Can be developed by inventing new or improved manufacturing processes
Or by altering an existing material to perform a particular function
Graphene
Single, thin layer of graphite
Light, strong, great conductor of heat and electricity
Since 2004, manufacturing processes have been invented and improved to make production cheaper
Used in tennis rackets
Future applications: aerospace, vehicles, water purification, flexible electronics
Metal Foams
A metal that contains many gas-filled spaces
This makes them lightweight
The foam keeps some of the metals properties: stiff, tough, strong under compression
Developed in the 1940s
Used for lightweight car parts and bone implants
Titanium
Corrosion-resistant metal and high strength-to-weight ratio
Used in aerospace industry
Difficult and expensive to machine (drill, cut, polish)
Recent developments in CAD/CAM reduce machine costs and make it a more usable material
Bone replacements, dental implants, bikes, ships, armour
Liquid Crystal Displays LCDs
Used in flat-screen displays that are thin, lightweight and energy efficient
LC in the display are made of a mixture of chemicals
When an electric current is applied, the crystals shape is modified
This changes the image seen on the screen
Originally used in calculators and other small displays were black and grey
Developed to become high-definition, full-colour displays used in TV and computer screens
Coated metals
Coating metals with a different material alters their properties
Iron and steel can be galvanised/electroplated (coated with zinc to prevent rusting)
Nickel-plated steel is a cheaper, corrosion-resistant alternative to stainless steel in car parts
Anodised aluminium has a coating of aluminium oxide to make the surface harder and more corrosion-resistant
Metals can be coated with PVC used for roofing. It becomes corrosion-resistant and can be coloured
Nanomaterials
Made of tiny particles
Carbon nanotubes are tiny carbon cylinders used in electronics and tennis racquets
High strength to weight ratio and are good conductors of heat and electricity
Can be added to a material to strengthen it without adding much weight
Self-cleaning fabrics have a nanoparticle coating
Removes odour and stains upon exposure to light
Antibacterial fabrics use nanoparticles of silver to kill bacteria
Medical uses in face masks and dressings
Used in anti-bacterial toys and odour free socks
Smart materials
Change their properties as they respond to an external stimulus
They usually return to their original state when the stimuli is taken away- change is reversible
Examples of external stimuli
Temperature
Light
Moisture
pH
Stress
Shape memory alloys SMA
Alloys that ‘remember‘ their original shape
Can be easily shaped when cool, but return to their original shape when heated above a certain temperature
E.g nitinol- if you bend (stress) glasses made of nitinol, you can put them in a bowl of hot water and they will return to their original shape
Photochromic pigments
Change colour reversibly in response to light
Can be put into spectacle lenses to make glasses turn into sunglasses when its sunny
Photochromic inks can be used to print t-shirts with designs that only show up in sunlight
Thermochromic pigments and inks
Used in colour changing products- they react to temperature
When the temperature changes, the product changes colour. The colour changes back when the object returns to its original temperature
Used in babies’ feeding spoons to check if the food is too hot, and in novelty mugs and t-shirts
How can biodegradable polymers (Biopol®) reduce damage to the environment
It is a thermoplastic produced by the action of microbes on plant matter
It biodegrades within months
Used as packaging as it is non-toxic with a high MP
Suitable for take-away food and drinks
It sinks in water which aids biodegradation and reduces risk of harm to sea life
HIPS
Shatterproof and a good insulator
Flexible and lightweight
Ideal for vacuum forming
Impact resistant, it is suitable for food containers
Easily mouldable and has a good gloss finish
Acrylic (Polymethyl-Methacrylate)
Versatile and tough
Comes in a variety of thicknesses and colours
Scratches easily and becomes brittle if thin
Acrylic fibres can be spun into threads for weaving and knitting
Resin identification codes
Thermoplastics must be recycled separately to enable effective processing
Polyester resin
Viscous, clear polyester solution
The addition of a catalyst hardens the resin
The hardened resin is tough with high abrasion resistance which makes a high-performance coating for areas of high wear
Clear polyester resin is suitable for embedding objects, casting clear sculpture and jewellery making
Resin replicas such as anatomical models can also be cast and painted
Urea formaldehyde UF
Good electrical insulator
With good heat resistance it is used for manufacturing electrical fittings
Textiles industry- treats fabrics with UF resins to for easy care properties such as anti-wrinkling
Paper industry- uses UF to improve tear strength
Timber industry- uses UF resin to bind particles in the making of manufactured boards such as MDF
Properties of plastic
Versatile material
Plastic is self-finishing
Easy to colour and clean
Provides a cheap alternative to traditional materials
Electrical insulator
Thermal insulator
Tough
Where are metals found?
Metallic minerals are found naturally in rock or ore in the Earths crust
How are ores and the metals within obtained?
Ore- mining
Metals within- extraction
The method used for extraction depends on the metal’s reactivity with air, water or acids
What is the link between the reactivity of a metal and the cost to extract it?
The more reactive the metal, the more expensive it is \n to extract
Examples of extraction processes
Most metals are smelted in a blast furnace
Electrolysis is used to extract metals such as aluminium
Smelting
The process of extracting metals from their ores in a blast furnace
Metals are drawn off in a liquid state (‘hot metal’)
The blast furnace reaches about 1,700°C to extract iron from iron ore
The impurities are removed
Used for industrial metals like iron and copper
Physical structure of a metal
Crystalline structure of metals can be modified by heat treatments
The larger the grains; the tougher and more ductile the material
Molecular structure of a metal
Strong bonds between the ions and electrons give metals strength and high MP
Positive ions in a sea of delocalised electrons make metals good electrical conductors
Rust
Compound called iron oxide
Formed when iron and oxygen react in the presence of moisture
Cause of oxidisation
By corrosion or weather exposure over a period of time
Patina
The thin layer of tarnish that appears on the surface of the metal
Do non-ferrous metals rust or oxidise?
Oxidise
Examples are copper and bronze
Verdigris
The green-turquoise patina occurring on copper
Conductivity of metals
Why are non-ferrous metals more expensive than ferrous metals?
Due to their desirable properties:
Lightweight
Good conductivity
Ductile and malleable
Resistant to corrosion
Brass properties and uses
Copper and zinc alloys with differing properties:
Decorative properties: it is hard, ductile, resistant to wear and is antimicrobial
Used for low-friction applications such as padlocks, gears, valves, bearings and musical instruments
How can the hardness, machinability and corrosion resistance be adjusted for brass?
Hardness- Ratio of copper to zinc
Machinability- Lead
Corrosion resistance- Aluminium
Aluminium
Very versatile material used in many shapes and forms
A light grey metal, efficient thermal insulator and doesn’t degrade when recycled
Where is aluminium ore found?
Bauxite is in the Earth’s crust
Why is wood a useful and versatile material
Aesthetically pleasing
Good insulator
Durable and tough
Good strength to weight ratio
Felling
A tree is ‘felled’ when it is cut down
Agricultural logging uses machinery with large chainsaw attachments.
These can fell, de-branch and log a tree in one swift action
What equipment is used in felling
Traditional- Saws and axes
Modern- Chainsaws
Seasoning
Involves reducing the moisture content of the timber to between 10-20%
Processing and seasoning
Once felled, natural timber is processed into standard sizes and seasoned
Timber is left to dry naturally or dried artificially in kilns
How can you identify manufactured and natural timbers?
Manufactured timbers- sheets, fibres or chips from which they are made are visible
Natural timbers- only the grain on natural timbers will connect seamlessly to the end grain
Coniferous trees
Evergreen and have needle-like leaves
Softwood
Most softwood trees (evergreen) grow faster than hardwood trees
So it is relatively cheap and readily available
The grain is wider making it more absorbent
Deciduous trees
Drop their leaves in the autumn and new leaves grow in spring
Hardwood
Sourced from deciduous trees
Hardwood is usually slower growing and so is more expensive
Comes in variety of colours and grains
It has good aesthetical and physical properties
Most have a closer grain, making them more dense and hardwearing
Which hardwoods are tough or hard?
Beech- tough, very durable with a fine finish
Oak- tough, hard and durable with a variable grain
Mahogany- durable and fairly hard with a distinctive grain
Cedar- very tough, but also flexible and shock resistant
Cedar (softwood)
Contains natural oils which offer natural water resistance
Tonewood
Woods that possess tonal properties that make them ideal for use in instruments:
Spruce- violins, piano and guitars
High stiffness to weight ratio → ideal for the soundboard
Cedar- a richer tone for classical guitars
Less dense than spruce
Mahogany- necks and sides of acoustic guitars, the body of electric guitars
Manufactured boards
Made from sawmill scraps, recycled wood, low grade timbers and sawdust
Wood pieces are bound together with adhesives to make man-made / manufactured board
Susceptible to moisture
Boards are rigid, stable and supplied in large sheets
Manufactured board structure
Plywood- made up of an odd number of thin layers (or ply) arranged with the grain running in alternating directions at 90º
MDF- made from compressed sawdust and adhesive