MATERIALS and their USES - general index AND a comparison survey - examples of uses of materials, relating their properties to a particular application

Doc Brown's Chemistry GCSE/IGCSE/O level Revision Notes

Materials science is the study of the properties of solid materials and how those properties are determined by a material’s composition and structure and how we use these materials in various applications from building constriction, and engineering to a huge variety of objects in the home.

This page surveys how we use different materials, their properties and how to choose a material for a particular use or application.

Sub-index for this page

1. Examples of how we use materials - the end products of materials science!

2. Natural and synthetic materials

3. Typical important physical properties of materials

4. A summary of four widely used types of materials, their properties and uses

5. Case study 1. Properties - choosing materials for car construction

6a. Case study 2. Properties - choosing materials for particular 'domestic' uses

6b. Case study 3. Choosing a material for particular engineering applications

7. Useful extra reading links on materials, their properties and uses

8. Nanochemistry and smart materials index links

9. A comparison of the structure and bonding of different substances - with reference to their use as solid structural materials

1. Examples of how we use materials - the end products of materials science!

CERAMICS

Ceramics are usually:

(i) poor conductors of heat and electricity, hence used thermal and electrical insulators,

(ii) strong and hard wearing, but brittle,

(iii) high melting points - so thermally very stable,

(iv) they don't corrode or degrade when exposed to the weather like metals do.

Most of the glass we use is relatively cheap soda-lime glass, made by heating a mixture of sand, sodium carbonate and limestone

Many ceramic materials are made from clay, a softish material dug out of the ground.

Clay, composed of fine particles of weathered rock, is quite soft with a little moisture and easily moulded into any shape. When heated to a high temperature in an oven it is transformed into a hard, if brittle, material. It is thermally stable and insulating. Its an ideal material for making pottery and bricks - the latter is very strong in compression, so can be used in load bearing walls in the building industry.

Glass is also classed as a ceramic. It can be moulded when hot and is usually transparent.

Soda-lime glass is made by heating limestone (mainly calcium carbonate, CaCO₃), sand (mainly silica, SiO₂) and sodium carbonate. When the molten mixture is cooled, glass is formed. It is brittle and relatively low melting.

Borosilicate glass is made in a similar same way, by melting together mainly silica (silicon dioxide, SiO₂) with a smaller amount of boron oxide (B₂O₃). It has a higher melting point than soda-lime glass and is better at withstanding sudden changes in temperature. Borosilicate glass has many uses e.g. laboratory glassware (Pyrex is a trademark name), scientific lenses and hot mirrors, bakeware and cookware, thermal insulation, high-intensity lighting products and aquarium heaters.

The biggest uses of glass are windows and apparatus in laboratories or chemical plants.

Glass is very hard wearing, doesn't corrode, although brittle, it lasts longer than plastic.

(see also limestone chemistry, glass and ceramics).
 

POLYMERS - many types with varied properties

The properties of polymers depend on what monomers they are made from and the conditions under which they are made.

Most polymers are:

(i) poor conductors of heat and electricity - so used as thermal or electrical insulators.

(ii) thermosoftening polymers are readily moulded into any shape,

(iii) often cheaper for mass production than most other materials,

(iv) less dense than most other materials, more 'lightweight' materials than metals or ceramics,

(v) they can degrade over many years, particularly if exposed to sunlight.

(i) Thermosoftening polymers consisting of individual, tangled polymer chains and melt relatively easily when they are heated. 

For example, low density (LD) and high density (HD) poly(ethene) are produced from ethene using different catalysts and reaction conditions (see thermosoftening addition polymer notes).

Strong rigid high density poly(ethene) is used for water pipes. Poly(propene) and PVC are also strong and also used for piping and guttering and PVC used for weatherproof window frames.

Lighter and more flexible low density poly(ethene) is use for plastic bags and 'squeezy' wash bottles in the laboratory.

Polystyrene foam is used in packaging and thermal insulation, light but flammable and not easy to recycle!

Some thermosoftening polymers, like nylon, can also be drawn out into strong fibres.

These thermosoftening polymers contrast with (ii) thermosetting polymers which consist of polymer chains with cross-links between them and so they do not melt when they are heated (see thermosetting polymer notes).

Polymers like melamine are much stronger and heat resistant and can be used as worktops or appliance casings.

 

COMPOSITES - varied compositions

Most composites are made of two materials, (i) a matrix or binder surrounding and binding together (ii) fibres or fragments of the other material, which is called the reinforcement. Examples of composites include

Wood is a natural composite of cellulose fibres strongly held together by a polymer matrix chemically derived from cross-linked cellulose molecules (similar in this respect to man-made thermosetting resin).

See also natural polymers, structure, function and uses

Concrete is a mixture (aggregate of sand, gravel and cement) - the sand and gravel act as reinforcement, used for basement flooring and road surfaces, but the concrete can also be set with reinforced with steel rods embedded in it, widely used as a building construction material. Concrete is very strong in compression.

Resin-fibreglass - the polymer monomer mixture polymerises via a catalyst and sets hard to form a hard strongly bonded material (thermosetting polymer) and the set resin reinforced by the glass fibres embedded in it, this is a very strong, but low density composite material, used for car body work, boat hulls, sports equipment e.g. surfboards, skis,

Some more technologically advanced composites are made from carbon fibres or carbon nanotubes instead of glass fibres.

Carbon fibre composites are based on a polymer matrix which are reinforced by very strong carbon fibres or carbon nanotubes.

These composites are very strong and of low density ('light'), they are quite costly to produce but are widely used in the aerospace industry, sports car bodies.

Composites based on the very strong polymer Kevlar ®, a reinforcing material embedded in another material. Kevlar adds strength with little extra weight. Kevlar has a high tensile strength, tough and hard wearing and good thermal stability. Kevlar was developed for demanding industrial and advanced-technology applications. Kevlar is as strong as the best carbon fibre and stronger than steel wire for the same thickness!!! Kevlar has many applications, including bicycle tyres and racing yacht sails and body armour e.g. bulletproof vests - all physically demanding situations that benefit from the high tensile strength-to-weight ratio of Kevlar composites.

All sorts of composites are being designed all the time, many replacing metals.

 

METALS - usually alloys

Metals have a wide range of uses e.g. in the car industry, building industry, household appliances, electrical circuits.

Metals are usually:

(i) quite or very  dense,

(ii) have high melting points - most thermally quite stable for most uses,

(iii) malleable - easily moulded into shape, less brittle than composites, can deform under stress without breaking,

(iv) ductile - can be drawn out into wire - including twisting strands of steel together to form strong cables,

(v) varying strength and hardness, particularly when alloyed (mixed) with other elements,

(vi) good conductors of heat and electricity - many applications as thermal or electrical conductors,

(vii)

For lots of other details see Transition and other metals, including alloys

 

It is important to be able to compare the physical properties of glass and clay ceramics, polymers, composites and metals and explain how the properties of materials are related to their uses and select an appropriate material for a particular use.

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2. Natural and synthetic materials

Reminders: All materials are atoms of various elements and they may be pure elements, pure compounds or mixtures of elements and compounds.

For definitions and explanations with examples see Some important ideas and definitions in Chemistry.

This section is more about ideas and decision making than learning lots of facts.

Be able to explain why a material is best suited for a particular purpose based on its characteristic properties.

Naturally occurring materials which have proved useful

Materials from plants e.g.

The timber from trees is used as a construction material and pulped to make paper.

The cotton to make clothing fabrics is grown in fields of the cotton plant.

Latex rubber is collected as a sticky fluid from rubber trees

Materials from animals e.g

Wool for clothing comes from shearing sheep.

Leather goods are made from the skin of cows.

Silk, a fine weaving material is obtained from silkworm larva.

To compliment, and in many cases supersede these naturally occurring materials, we humans have developed an enormous range of ...

Synthetic materials e.g.

The main advantage of man-made synthetic materials compared to natural materials is that you can design their properties to suit a particular use and develop a better product by chemically changing the structure of the material and how it is processed.

The extraction of metals from raw materials from the Earth's crust - ores are mined and processed to produce iron, copper, titanium, aluminium, which are converted into lots of different things and variety of properties enhanced by making alloys to suit specific technical needs.

Plastics - polymers with a huge range of properties and uses have been developed from the products of crude oil in the petrochemical industry e.g.

Synthetic fibres like nylon and polyester can replace silk, cotton, wool and they can be made strong but flexible/stretchy, waterproof ...

plastics don't rot like wood so can replace wooden window frames, they don't corrode like metals to can replace iron/lead piping and guttering,

synthetic rubber polymers replaces natural rubber from the sap of the rubber tree - though car tyres are still made of natural rubber and other materials, polymers have now been developed that can replace rubber - another organic molecule product from oil,

insulating thinsulate can replace natural wool and cotton for protective clothing,

synthetic pigments mixed with solvents and binding agents make hard wearing long lasting coatings, and have mainly replaced traditional paints made from mineral powders + egg yoke + linseed oil.

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3. Typical important physical properties of materials

Mainly physical characteristics here, but chemical character is very important too and it is the properties of a material that decide what it can be used for. So, knowledge of the properties of materials helps you to decide on the suitability of a material for a particular purpose i.e. what is best for the job! The effectiveness of a material is how good it is for the function its supposed comply with.

For properties like strength, stiffness and hardness, you would need to do a 'fair  test' of pieces of the same size material to get an accurate comparison e.g. a similar rectangular block.

Strength of a solid

The strength of a material is measure of how much it can resist a force applied to it.

You might measure the force to break a bar of the material, or what force is needed to permanently deform it, that is changing its shape without snapping it.

There are two types of strength values of importance, depending on how you apply the force to a material.

Tensile strength

This is how much a material can resist being pulled (stretched) in tension until it breaks or deforms.

This depends on how strong the particles are held together in the solid's bond network.

Pure metals are weak because layers of atoms can side over each other, stretching and bending the metal, but alloying the metal with other elements can inhibit this.

See Metal alloys - improved design and strength

Ropes or chains on pulley systems for lifting objects or steel cables supporting the road of a suspension bridge, all need to have a high tensile strength or they would snap under the weight of the load!

Ionic compounds are strong in tensile and compressive strength because the ions are strongly held in the giant ionic lattice, but they are usually brittle and of new use for making useful objects.

Compressive strength

This is how much a material can be compressed ('pushed' or 'squashed') before it gives way or permanently deformed.

Building construction materials like stone, bricks or concrete all have a high 'compression' strength which is needed to support the weight of the rest of the building they support.

Combination of tensile plus compression strength

Sometimes materials must be strong in both tension and compression e.g. concrete is strong in compression but weak in tension. For these reason its tensile strength is increases by adding steel rods to reinforce the concrete.

Stiffness of a solid

The stiffness of a material is a measure of how easily it bends when a force is applied to it, but without permanently deforming it i.e. the material springs back to its original shape. A very stiff material hardly bends when a force is supplied.

Materials like stone, brick and concrete are very inflexible - fortunately!, but blocks of most plastics and wood are flexible and will all bend to some extent without breaking. Rubber is one of the most flexible of materials and can be bent and stretched by quite some margin and still spring back to its original shape. Often, flexibility is desirable in a plastic or rubber object e.g. insulated cable of electrical appliances or blowing up a balloon.

Note that the thickness of the material is important when considering 'stiffness'. Thin sheets of almost any solid can be bent so far without breaking e.g. strands of glass fibre, steel spring.

Hardness of a solid

The hardness of a material is a measure of difficult it is to cut into, so materials like diamond and granite are very hard and butter and sodium metals are soft materials and easily cut into.

Diamond is one of the hardest substance is know and is used to put a strong cutting edge on cutting tools and some industrial drills have diamond tipped tips. Diamonds are so hard that they can only be cut by other diamonds!

 

Brittleness of a solid

Brittle materials break and shatter quite easily if hit by a rapidly applied force.

The particles in brittle solids are held together very strongly and cannot move without permanently breaking bonds.

Most ceramic materials like glass or pottery easily shatter when struck hard with another hard solid object.

Even diamond can be cut by a skilled cutter by breaking down a line of apparently strong C-C covalent bonds!

Similarly, planes of ions, held by strong electrostatic bonds, can be cleaved apart or slid over each other, making most ionic compounds brittle when struck with a hard object - or stressed in a salt cellar where steel metal blades are rotated to cut up large salt crystals into smaller crystals for sprinkling on food.

Most metals (pure or alloyed) are not brittle because the layers of atoms can slide over each other without permanently breaking the bonds between the metal ions in the giant lattice and the delocalised electrons.

How easily can the solid material be reshaped (deformed)

Materials that can be deformed without breaking are useful for shaping particular object.

The particles in such materials, can move without the bonds being permanently broken.

Metals, particularly if pure, are quite malleable and easily bent-moulded into a specific shape because the layers of atoms can slide over each other without permanently breaking the bonds.

Thermosoftening polymers, without cross-link bonds, are quite easily shaped, usually after heating sufficiently to soften or even melt the plastic prior to moulding.

Note that you can't warm and reshape thermoset polymers, the extra cross linking bonds won't allow this - not surprisingly, they are harder and more brittle than thermosoftening polymers..

Electrical and thermal conductivity of a solid

These two properties often go together e.g.

Metals are good conductors of heat and electricity because the thermal kinetic energy and electrical energy is transferred by the delocalised electrons moving through the giant metal lattice.

Non-metallic structures like carbon in the forms of graphite, graphene and some nanotubes, are also moderate or very good conductors of heat and electricity because electrons can move through the structure.

Most non-metallic solid materials without free particles that can carry either electrical energy or thermal kinetic energy, tend to heat or electrical insulators - which makes them equally useful materials.

Ceramic materials are used as electrical insulators where high voltages are involved e.g. look up at pylons and local cable poles of the National Grid electricity supply - you can see the insulating ceramic rings on the cables.

Density of a solid

The density of an object is a measure of the mass of an object in a particular volume.

Density = mass / volume and is usually measured in g/cm³  or x this by 1000 =  kg / m³

The density of water is 1.00 g/cm³, the plastics poly(ethene) and poly(propene) are 0.92 to 0.98 g/cm³ (hence they float on water polluting the surfaces of rivers, lakes and seas), nylon is 1.11 to 1.18 g/cm³.

Metals have a wide range of density e.g. sodium floats on water, but most metals sink in water (unless you shape them like a boat!).

For many contexts of construction like aircraft wings and fuselage you would like a like a low density ('lightweight') material hence the use of aluminium and titanium alloys rather than steel.

Densities of some metals in g/cm³: sodium 0.97, aluminium 2.70, titanium 4.54, iron (~steel) 7.87, gold 19.30

States of matter density: solid > liquid >>> gas.

Solids and liquids have the highest densities because the particles are close together - more mass per unit volume.

Gases have very low densities because the molecules are so far apart as they fly around through mainly empty space!

Durability of a solid material

Durability isn't something that is easily quantified, but you should expect any product to have a reasonable 'working life'. Phrases like 'hard wearing', 'weather resistant' are a bit vague, but they mean a lot to the consumer!

So, how long will the material of a product last? or should last?

You don't want clothing fabrics wearing away after a few months of wear, you expect the soles of you shoes to last a reasonable length of time.

You don't want a carrier bag to fall apart before your reach the car after leaving the supermarket!

You don't want the car tyres wearing away after just a few thousand miles!

Melting point of a solid

Very pure materials have quite sharp melting points where the solid becomes a liquid e.g. water 0^oC, sodium chloride 801^oC.

However, many materials are a mixture of different materials e.g. metal alloys or a range of different sized molecules e.g. thermoplastics like poly(ethene), and in these cases the material tends to melt over a wider temperature range.

In the case of polymers, they have a softening point and very gradually become a liquid over the next few tens of degrees rise in temperature.

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4. A summary of four widely used types of materials, their properties and uses

Which you should be able to relate to their uses, and of course, where they are not used!

What a material can be used for is very dependant on its properties, though cost can be a significant factor too.

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5. Case study 1. Properties and choosing materials for car construction

• Each component in a car must be made of the most suitable material, but production costs must be taken into consideration too.

  • Rubber needs to be strong, soft and flexible to be used for car tyres. Vulcanisation with sulfur makes it tougher and hardwearing, so it lasts longer - an example of modifying the properties of a material by extra processing.

  • The bodywork is made out of steel which has high tensile strength but relatively thin sheets can be hammered or pressed into shape and sections welded or bolted together. Steel is readily protected from rusting by galvanising and layers of paint.

    • Aluminium is much less susceptible to corrosion and lighter (lower density), giving better fuel economy, but it is a more costly metal.

  • However aluminium alloys are strong and is still used for parts of the engine to reduce the overall weight of the car.

  • Windscreens and windows must be made of a transparent material and strong glass sheets are used.

  • Plastics are cheap to make of varied composition for a wide variety of uses even just in the context of building a modern car plastics are light, durable and can be dyed any colour, they can be flexible or rigid and so can be used for e.g. used for

    • for internal fittings e.g. dashboard cover - rigid,

    • flexible floor covers (can be rubber too),

    • rigid door coverings

    • rigid and transparent and coloured covers over headlights and brake lights

    • flexible insulating sheathing for all the electrical wiring.

  • Natural and synthetic fibres are used to make coloured flexible hard wearing fabrics for seat covers.

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6a. Case study 2. Properties and choosing a material for particular 'domestic' uses

Actually, lots on 'mini-cases' of 'suitability' to get you thinking as broadly as possible!

• Electrical wiring - most circuits in the mains supply or in appliances are made of copper - quite strong but flexible, ductile (can be drawn out into a wires) and an excellent electrical conductor. The pins on plugs are usually made of brass alloy (Cu + Zn).

  • BUT, all wiring needs insulating, so the copper wire is sheathed in tough, but flexible polymers like PVC, which are a good electrical insulator. Plugs and sockets are made of tough hard plastic which can be also PVC or poly(propene),

• Cooking utensils for the kitchen need to be made of a strong, high melting, good heat conducting, not toxic (aluminum is not used now!) material like stainless steel or iron.

  • Oven dishes are made of heat resistant (high melting) ceramic materials.

• Children's toys must be made of a tough durable material (stiff & strong), that is non-toxic, hard-wearing (''play resistant'!) and of low density.

  • Not surprisingly, thermosoftening plastics like poly(ethene) and poly(propene) are mass produced to fulfil our children's needs, and such plastics are easily moulded into an infinitely range of objects, which are readily brightly coloured with an array of pigments!

• Clothing fabric needs to be made of hard wearing fibres like Nylon or Terylene with a high tensile strength, but it mustn't be stiff (must be very flexible) and in the case of children's clothing or nightwear it must be fire resistant - so the material must incorporate a flame retardant substance.

• Many 'older' materials have been replaced by more 'modern' synthetic materials e.g.

  • Strong plastics like poly(propene) have replaced iron for drain-pipes and guttering. The plastic doesn't break easily like brittle iron AND they don't rust and corrode away in bad weather!

  • Some compact discs (CDs) were originally made using a layer of aluminium to digitally record the sound, but this was prone to slow corrosion, so after some time the sound quality of reproduction deteriorated. CDs are now made from a very tough, hard wearing and slightly flexible polycarbonate plastic that will NOT corrode! (being plastic!) ...

  • ... and while we are in the music business, very old records were made of a very brittle material that easily shattered and so few have survived, but modern 'vinyl records' are made from strong and slightly flexible PVC plastic [poly(chloroethene), old name polyvinyl chloride] which is far less likely to break, even if dropped!

• Plastics - polymers have a wide variety of physical characteristics, they can be hard, strong, stiff (rigid), flexible, low or high density, soften easily on heating or quite heat resistant.

  • Some are easily moulded when softened on heating (thermosoftening used to make cheap toys).

  • Others set really hard and are strong and don't melt (thermosets used for kitchen worktops and plastic kettles),

  • Strong fibres like nylon are used for outdoor clothing and ropes.

  • Tough wearing and rigid PVC or poly(propene) are used for piping, guttering and window frames - they do not corrode like metal and don't require painting - you can dye the plastic whatever colour you like when fabricating the final product.

  • I've described lots of examples on other pages ....

  • Polymerisation, plastics, poly(ethene), poly(propene), uses, problems, recycling

  • Condensation polymers, Nylon & Terylene, comparing thermoplastics, fibres and thermosets

6b. Case study 3. Choosing a material for particular engineering applications

See also 5. Case study 1. Properties - choosing materials for car construction

(1) Aircraft fuselage and wings

You need a strong 'light' material. Titanium and aluminium alloys are used.

 

(2) Disposable coffee cup for a cafe chain (sit-in or takeaway AND preferably recyclable)

The cup needs to be: not brittle, not melt/deform when hot drank poured into it, thermally insulating so you don't get burnt picking up the cup, cheap to produce in mass production.

Metals are good thermal conductors, not very insulating! and not cheap to produce.

Ceramics are good insulators, but heavy and brittle, can be re-washed but not really recyclable if broken, too costly and not suitable as a takeaway object.

Composites are light, strong and thermally insulating, but not recyclable and relatively expensive to make.

Plastic is the best material, good thermal insulators, cheap to produce in large quantities, maybe recyclable, but you need a more thermally stable plastic than poly(ethene) e.g. poly(propene).

However, there are big environmental questions about the use of plastics as the levels of plastic pollution are rising all the time, so, ....

a growing alternative is paper-cardboard, this is thermally insulating, cheap to produce and recyclable.

 

(3) The hull of a boat or ship

The material must be strong and forged/bent into shape - steel good, will corrode, but can be economically protected e.g. with paint.

For larger boats and navy vessels, much of the superstructure can be made of aluminium - less dense and good anti-corrosion properties.

Small boats and yachts can be fabricated from resin-fibreglass composites - waterproof and quite strong and light. Carbon fibre composites are used too.

The material mustn't be porous or brittle - ceramic no good

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7. Useful extra reading on materials, their properties and uses

This page can't cover all the materials or contexts you may come across on your course or in the exam,

so, for more on the uses of materials where their use is related to their properties see ...

• Polymerisation, plastics, poly(ethene), poly(propene), uses, problems, recycling

• Condensation polymers, Nylon & Terylene, comparing thermoplastics, fibres, thermosets

  • Both the two pages above include the same decision making exercise on choosing a plastic for a particular job.

• Transition Metals - properties and uses

• Giant covalent structures and uses

• Structure and properties of metals

• Uses of carbon nanotubes

• and checkout the 'smart/nano-materials' indexes on this page below.

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8. Nanochemistry and Smart Materials Indexes

NANOCHEMISTRY

Part 1. General introduction to nanoscience, nanoparticles and commonly used terms explained

Part 2. NANOCHEMISTRY - an introduction and potential applications

Part 3. Uses of Nanoparticles of titanium(IV) oxide, fat and silver

Part 4. From fullerenes & bucky balls to carbon nanotubes

Part 5. Graphene and Fluorographene

Part 6. Cubic and hexagonal boron nitride BN

Part 7. Problems, issues and implications associated with using nanomaterials

Word-fill quiz "Aspects of nanochemistry"

SMART MATERIALS

Part 1 Chromogenic materials - Thermochromic, Photochromic & Electrochromic Materials

Part 2 Shape memory alloys e.g. Nitinol & Magnetic Shape Memory Alloys

Part 3 Shape memory polymers, pH and temperature sensitive-responsive polymers, self-healing materials

Part 4 Lycra-Spandex

Part 5 High performance polymers like kevlar

Part 6 Gore-Tex, Thinsulate and Teflon-PTFE

Part 7 Piezoelectric effect/materials & Photomechanical materials

Part 8 Carbon fibres

Word-fill quiz "Designer Smart Materials"

 Doc Brown's Chemistry 

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