10. metals and alloys

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How many different uses of metal can you spot?

What are metals used for?


Why are metals important?

Metals are a highly valuable group of materials, used for hundreds of products and produced in huge quantities.

35,500,000 tons of aluminium were produced in 2005.

The production of copper increased by more than 20 times in the 20th century.

Gold is worth more than £10,000 per kilogram.

Metals have played a vital role in human development. Periods of civilization are even classified by the metals that were used during those times, such as the Iron Age.


Using metals


Uses of metals – activity


What else can metals be used for?

It is easy to find products made from metals, but there are other uses of metals that are less obvious.

Compounds containing metals have many uses. For example, metal compounds are used to colour materials including stained glass and even make-up!

Metals are used as catalysts to speed up reactions. Nickel is used as a catalyst to make margarine. Platinum is used in catalytic converters in car exhausts to clean up fumes and reduce pollution.

Can you find any other uses of metals?


What decides what metals are used for?

It is not only the properties of a metal that determines its use.

What other factors might determine how metals are used?

For example, aluminium only became a commonly used metal in the late 19th century as better extraction methods made it cheaper.

For example, silver is a better conductor than copper but it is too expensive to be used for electric wires.

Cost. A metal may have the best properties for a job but it might be too expensive.

Extraction method. This can greatly affect the price and availability of a metal.


What are the properties of different metals?

Do all metals behave in the same way?


What are the general properties of most metals?

solid at room temperature

Why do metals have these particular properties?

Typical properties of metals

high melting point

good conductors of electricity and heat

malleable: they can be shaped

ductile: they can be drawn into wires

strong

dense


What is the structure of metals?

sea of electrons

metal ions

The atoms in a pure metal are in tightly-packed layers, which form a regular lattice structure.

The outer electrons of the metal atoms separate from the atoms and create a ‘sea of electrons’.

These electrons are delocalized and so are free to move through the whole structure.

The metal atoms become positively charged ions and are attracted to the sea of electrons. This attraction is called metallic bonding.


Electrons and metallic bonding

How does the sea of electrons affect the properties of metals?


Why do metals have high melting points?

Metals often have high melting points and boiling points. Gold, for example, has a melting point of 1064 °C and a boiling point of 2807 °C.

The properties of metals are related to their structure.

In metal extraction and other industrial processes, furnaces often run continuously to maintain the high temperatures needed to work with molten metals.

This property is due to the strong attraction between the positively-charged metal ions and the sea of electrons.


How do metals conduct heat and electricity?

Delocalized electrons in metallic bonding allow metals to conduct heat and electricity.

This makes heat transfer in metals very efficient.

Delocalized electrons also conduct electricity through metals in a similar way.

For example, when a metal is heated, the delocalized electrons gain kinetic energy.

These electrons then move faster and so transfer the gained energy throughout the metal.

heat


Metals are usually strong, not brittle. When a metal is hit, the layers of metal ions are able to slide over each other, and so the structure does not shatter.

Why are metals strong?

The metallic bonds do not break because the delocalized electrons are free to move throughout the structure.

metal after it is hit

forceforce

This also explains why metals are malleable (easy to shape) and ductile (can be drawn into wires).

metal before it is hit


Metallic bonding


Corrosion is the gradual destruction of a metal due to reactions with other chemicals in its environment.

Over time, corrosion changes the appearance of the metal as it breaks down and it becomes weaker.

What is corrosion?

Coating the surface of a metal with paint and certain chemicals can protect it from corrosion.

What happens if the protective coating becomes damaged?

Corrosion can seriously damage metallic objects and structures.


Metals behave differently when exposed to the environment.

Items made from gold can survive for thousands of years and have even been found in good condition underwater.

Do all metals corrode?

In many cultures, gold is considered a precious metal and is used to make sacred and decorative objects.

Gold is an unreactive metal and does not corrode easily.

In general, objects made from metals that corrode easily do not survive for as long.


coating of oxygen atoms

The outer aluminium atoms react with oxygen in the atmosphere. This forms a thin layer of aluminium oxide on the metal’s surface, which protects the metal from corrosion.

Aluminium is a very reactive metal. However, it does not corrode in the presence of oxygen. Why is this?

oxygen in the atmosphere

aluminium atoms

Why doesn’t aluminium corrode?


Salt can increase the rate of rusting. This iron bolt is on a seaside structure and is nearly completely corroded.

Rusting is the specific name given to the corrosion of iron. It is a chemical reaction between iron, oxygen and water.

What is the word equation for the formation of rust?

What is rusting?

The chemical name for rust is hydrated iron oxide. Rust can form on cars and buildings, making them unsafe. It is an expensive problem.

hydrated iron oxidewater+ +iron oxygen


Rate of corrosion experiment


Are some metals easier to find than others?

Finding metals


Most metals are actually found combined with other elements, as compounds in ores. These metals must be extracted from their ores before they can be made useful.

Metals can be found in the Earth’s crust combined with other elements or uncombined as pure substances.

Where do metals come from?

Metals that are found in a pure form are said to occur ‘native’.

Highly reactive metals, such as titanium, require complicatedextraction. This can increase the cost of the pure metal.

Some unreactive metals, like gold, silver and copper, can be found uncombined as elements.


potassiumsodiumcalcium

magnesiumaluminium

zinciron

copper

gold

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Metals above carbon in the reactivity series must be extracted using electrolysis. Electrolysis can also be used to purify copper.

Metals below carbon can be extracted from their ores by reduction using carbon, coke or charcoal.

Platinum, gold, silver and copper can occur native and

do not need to be extracted.

lead

silver

How does reactivity affect extraction?

The reactivity of a metal determines how it is extracted.

(carbon)

(hydrogen)

platinum


Metals that are less reactive than carbon can be extracted from their ores by burning with carbon.

Iron is extracted by this method in a blast furnace. The iron ore is heated with carbon-rich coke at very high temperatures.

The iron collected from a blast furnace is only 96% pure.

How is carbon used to extract metals?

molten iron

hot air

molten slag

raw materials

Usually, this product will be treated further because the impurities make iron brittle.


Metals that are more reactive than carbon are extracted using electrolysis.

This process uses an electrical current to extract the metal.

Electrolysis is more expensive than using a blast furnace, and this increases the price of the metal.

What is electrolysis?

Electrolysis is also used to further purify metals, such as copper, after extraction with carbon.

Aluminium is extracted from its ore, bauxite, using this method.


Extraction quiz


Metals are easy to recycle and do not change their properties. What are the benefits of recycling metals?

Saves energyRecycling aluminium uses 95% less energy than extracting it from its ores.

Uses fewer resources

Reduces waste

Less damage to environment

Profitable

Recycling reduces the need to mine sensitive areas for new ores.

Recycling one car saves over 1,000 kg of iron ore and over 600 kg of coal.

14 million fewer dustbins would be filled per year by recycling aluminium in the UK.

Recycled copper can be resold for up to 90% of what it was worth when new.

Can metals be recycled?


What are the drawbacks of recycling?

Recycled copper is too impure for electric wires. However, scrap copper can be used in products that do not need pure metal, such as coins and ornaments.

Metallic materials are often mixtures of different metals. Pure metals can be obtained by purifying recycled materials but this can be expensive and may use more electricity than extracting metals from ores.

Sorting mixed metals for recycling can be difficult. Iron and steel (a mixture of iron and other elements) are exceptions. These materials can be separated from wasteusing a magnet.


Recycling or extraction?


Guess the metal


An alloy is a mixture of a metal with at least one other element.

The final alloy may have very different properties to the original metal.

By changing the amount of each element in an alloy, material scientists can custom-make alloys to fit a given job.

What is an alloy?

Steel is a common example of an alloy. It contains iron mixed with carbon and other elements. Adding other elements to a metal changes its structure and so changes its properties.


What types of alloys are there?

Alloys have been used for thousands of years. Bronze, an alloy of copper and tin, was commonly used by civilizations before iron extraction methods were developed.

brass: an alloy of copper and zinc. It does not tarnish and is used for door knobs, buttons and musical instruments.

solder: an alloy of zinc and lead. It is used in electronics to attach components to circuit boards.

amalgam: an alloy of mercury and silver or tin. It is used for dental fillings because it can be shaped when warmand resists corrosion.

Other well-known alloys include:


Although pure gold is sometimes used in electronics, gold jewellery is always a mixture of gold and other metals.

Pure gold is actually quite soft. Adding small amounts of other metals makes the gold hard enough to use in jewellery.Alloying gold with different metals also affects its colour.

The familiar yellow gold is an alloy of gold with copper and silver. Adding more copper than silver gives redder shades.

White gold is an alloy of gold with nickel, platinum or palladium. Around 12% of people may be allergic to the nickel in white gold.

Is gold an alloy?


When is a copper coin not a copper coin?

When it is a copper-coated alloy!

Since 1992, UK copper coins have been made from copper-plated steel and are magnetic. A magnet can be used to separate copper coins by age.

Copper coins used to be made from pure copper but most ‘copper’ coins used around the world are now made from copper alloys.

Previously, as the value of copper increased, the metal used to make the coin became worth more than the actual coins. A melted-down, pure copper coin could have been sold for more than the face value of the coin!


Steel is an alloy of iron and other elements, including carbon, nickel and chromium.

Steel is stronger than pure iron and can be used for everything from sauce pans… …to suspension bridges!

What is steel?


The atoms of other elements are different sizes. When other elements are added to iron, their atoms distort the regular structure of the iron atoms.

The atoms in pure iron are arranged in densely-packed layers. These layers can slide over each other. This makes pure iron a very soft material.

Why is steel stronger than iron?

It is more difficult for the layers of iron atoms in steel to slide over each other and so this alloy is stronger than pure iron.


Steel can contain up to 2% carbon.

low carbon steel contains less than 0.25% carbon high carbon steel contains more than 0.5% carbon.

Two other important types of steel are:

What types of steel are there?

stainless steel – an alloy of iron that contains at least 11% chromium and smaller amounts of nickel and carbon titanium steel – an alloy of iron and titanium.

Varying the amount of carbon gives steel different properties. For example, a higher carbon content makes a hard steel.

Different types of steel are classified by how much carbon they contain.


Using different types of steel


What’s so clever about smart alloys?

Shape memory alloy is a type of smart material made from metals that returns to its original shape after being deformed.

A smart material can change one or more of its physical characteristics under the influence of an external stimulus.

Nitinol is a type of shape memory alloy made from nickel and titanium.

Nitinol has also been used to hold badly broken bonesin place while they heal.

This material can be used to make a pair of glasses that ‘remembers’ its shape and does not break when crushed.


Glossary (1/2)

alloy – A mixture of a metal and at least one other element.

amalgam – An alloy of mercury that is used for dental fillings.

blast furnace – A tall oven used to extract iron from iron ore by burning it with carbon at high temperatures.

brass – An alloy of copper and zinc that is used for ornaments.

corrosion – The destruction of a metal caused by reactions with chemicals in the environment.

ductile – The ability of metals to be drawn into wires.

electrolysis – A process that uses electricity to extract or purify metals.


Glossary (2/2)

malleable – The ability of metals to be bent or hammered into different shapes.

native – The natural occurrence of a metal as an element in the environment.

ore – A rock that contains a metal combined with other elements in concentrations that make it profitable to mine.

rusting – The specific name for the corrosion of iron and iron-containing alloys, such as steel.

shape memory alloy – A type of alloy that can return to its original shape after being deformed.

solder – An alloy of lead and tin that is used in electronics.

steel – An alloy containing iron and other elements.


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Multiple-choice quiz

10. metals and alloys

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