Alloys to improve properties and problems using metals e.g.
Brown's Chemistry: Chemical Bonding and structure GCSE level, IGCSE, O, IB, AS, A
level US grade
9-12 level Revision Notes
Potential problems with metal
and may lead to
a very dangerous situation of mechanical failure of the structure.
So it is important develop alloys which are well designed, well tested and
will last the expected lifetime of the structure whether it be part of an
aircraft (eg titanium aircraft frame) or a part of a bridge (eg steel
metals are easily oxidised and corrode easily when exposed to air (oxygen)
and rain (water).
For the rest of the corrosion story see notes on
Metals and Rust Prevention
on Alloy Structure and uses via a very simplified 2D diagram
An alloy is a mixture of a metal with other
elements (metals or non-metals).
Metals can be mixed together to make alloys to improve the metal's properties
to better suit a particular
An alloy mixture often has superior desired properties compared to
the pure metal or metals,
i.e. the alloy has its own unique properties
and a more useful metal.
Aluminium, copper, gold and iron not
strong enough for many of their uses.
We need alloys of a specialised composition for
An alloy is where a metal is mixed with
other metals or non-metals, usually to make a stronger metal.
From several thousand years ago we had learned how to
make bronze my mixing tin with copper.
A few % of tin in copper makes a harder
metal, better than copper for making axes, knives and swords.
An archaeological period is called the bronze age bronze age (in
Britain this was from 3500 to 2500 years ago),.
This was followed by the 'iron age' and later the
'Industrial Revolution' built in steel and powered by coal.
Brass is made by mixing copper with zinc to
make a much tougher hard wearing alloy.
Zinc is too brittle and copper is too
soft, but the mixture is much stronger, not too soft and not too brittle.
The are multiples alloys of steel make by
adding carbon to iron.
You then add other metals like nickel,
tungsten or chromium to make specialised steels.
This produces steel alloys with great strength and
impressive anti-corrosion properties.
Sometimes need to lower the melting point of a metal
for some specific task.
melts at 328oC and tin at 232oC. The alloy solder
is a mixture of the two and melts ~180oC.
Solder is a good electrical conductor and ideal for
'soldering' together electrical wires.
BUT, you don't want to operate the soldering iron at too
high temperature or you might damage the circuit board.
Aluminium has good anti-corrosion properties due to a
protective oxide layer always present on its surface.
However, aluminium is too soft for many
purposes and so is alloyed
with copper, magnesium, manganese or tin.
An aluminium plus copper alloy is called Duralumin and is
much stronger than pure aluminium.
The right-hand side of the diagram below could represent such an alloy.
A particle model of a pure metal and an alloy
- Shows the regular arrangement of the
atoms in a pure metal crystal and the white spaces show where the free
electrons are (yellow circles actually positive metal ions).
- Shows what happens when the metal is
stressed by a strong force.
- The layers of atoms can slide over each
other and the bonding is maintained as the mobile electrons keep in
contact with ions of the giant lattice, so the metal object remains intact BUT the metal is
physically a different
- This is why most metals are so malleable
(easily bent or hammered into shape) and ductile (can be drawn out
into a thin wire without breaking).
For the same reason, most metals
(pure or alloyed), are not brittle because as the layers of
atoms slide over each other, no bonds between the metal ions in the
giant lattice and the delocalised electrons are permanently broken.
- Shows an alloy mixture.
are not usually considered as compounds (despite the fact that all
the atoms are chemically bonded together), but described as a physical mixing of a metal plus at least one other
material (shown by red circle).
- The other material can be another metal e.g.
nickel or manganese added to iron in steel, or a non–metal e.g.
carbon, and it can be bigger or smaller than the original metal atoms.
- Many alloys are produced like
this to give
a stronger metal.
- The presence of the other atoms (smaller or
bigger) disrupts the symmetry of the layers and this distortion reduces the 'slip
ability' of one layer to slide next to another layer of metal atoms.
- Iron has an atomic metallic radius of 0.126
- Carbon is a smaller atom, C radius 0.077 nm,
silicon Si radius 0.117 nm, both found in steel.
- Both have a smaller radius than iron, both
increase the hardness of steel.
- Other metals in steels have a similar
metallic radii/nm compared to iron
- e.g. chromium Cr 0.125, nickel Ni 0.124 and
manganese Mn 0.129.
- BUT, they can have other positive effects
like Cr increasing the steels anti-corrosion properties.
- Tungsten W, has an metallic atomic radius of
0.137 nm, larger than iron atoms, and also increases the hardness
and strength of steel.
- Sometimes the added element or compound
chemically bonds strongly to the surrounding metal atoms of the
original metal atoms.
- You don't need to know this, but the compound
'cementite', Fe3C, is found in steel.
- The result is a stronger
harder less malleable metal, but one better suited to most
uses of steels.
- The main point about using
alloys is that you can make up, and try out, all sorts of different
compositions until you find the one that best suits the required
purpose in terms of tensile/compression strength, malleability,
electrical conductivity or corrosion resistance etc.
- Most metals in everyday use in the
home or industry are alloys.
- This is because pure metals such as
copper, gold, iron and aluminium are too soft for most uses and
so are mixed with other metals to make a far more useful harder
- The are hundreds of alloys of
steel made by alloying iron with other metals to increase the
strength or anti-corrosion properties of the metal.
- Steel is used in building and
bridge construction, car bodies, railway lines and countless
other objects that need to have a high tensile strength.
- Pure metals can be either too
soft (e.g. like copper or tin) or too brittle (e.g. like zinc)
to be used directly and are therefore often alloyed to make
superior metals like brass or bronze.
- The properties of metals are
readily matched to a particular use e.g.
- Aluminium alloys are strong and
light (relatively low density for a metal), they do not corrode
easily and so are used in aircraft construction, greenhouse
frames and not as expensive as titanium alloys.
- Cooking pans made of stainless
steel are good conductors of heat, strong with good
anti-corrosion properties and steel has a high melting point.
- Copper is malleable and ductile,
easily drawn out into wire, an excellent conductor of
electricity, and so is widely used in electrical circuitry.
Steel alloys of varying strength and
anti-corrosion properties are used in thousands of products and
constructions e.g. reinforcing rods in concrete buildings, bridge
girders, car engines, domestic appliances from washing machines to
electric kettles, saucepans, tools like chisels, ship hulls and
superstructure, very hard drill bits,
- For more on specific metals and
alloys see my detailed notes on
Contrasting metals and non-metals
Sub-index: Part 5
Metallic Bonding – structure and properties of metals
bonding and structure notes
Perhaps of interest?
Metals and Rust Prevention
The Reactivity Series of
metals be made more useful? (useful links)
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