Understanding Alloys

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Malaysia SPM Form 4 Chemistry, Chapter 9: Manufactured Substances in Industries

[edit] Introduction

Characteristic of metal

Many metal are also soft. Metals like iron and copper also form oxides easily.
As a result, the uses of pure metals are limited, and alloys are made to improve the malleability, ductileness and hardness of a metal.
A pure metal is composed of layers of atoms which are arranged in an even, orderly and close manner at fixed positions (see Figure 9.8). Each atom is surrounded by 8-12 atoms.

This arrangement of atoms causes the metal to be very dense with high melting and boiling points. The strong forces of attraction between atoms require a great amount of heat to overcome.
However, in spite of strong forces of attraction between atoms, the metal is not hard. If a force is applied on the metal, the layers of atoms can glide and slide on top of each other, causing them to move to new positions. This allows the metal to be drawn into wires (ductile). (See Figure 9.9.)
The spaces left naturally between layers of metal atoms also make it easy to be beaten into sheets (malleable).
The formation of alloys occurs when these empty spaces between metal atoms are filled with atoms of another metal, which may be higher or smaller than the original metal atoms. (Figure 9.10)
The foreign atoms are usually another metal but sometimes a non-metal, like a carbon or silicon is used.
The foreign atoms filling up the spaces between the atoms of the pure metal help to prevent the slipping and sliding of atom layers, thus making the metal harder, and less malleable and ductile.

Alloys improve the strength of metal.
Carbon is added to iron to obtain steel to make it stronger and harder than pure iron. Other metals like manganese, chromium and tungsten are also added to add to the hardness.
Magnalium is made from aluminium and magnesium to improve the hardness of the pure metals but at the same time, maintaining their lightness.

Tin and iron are used vastly in building but they rust easily, thereby causing economical loss. Adding other metals or non-metals to them can prevent rusting.
Stainless steel is made by adding carbon, chromium and nickel to iron.
Adding phosphorus to bronze also improves the lustre and prevents corrosion of bronze.

Making alloys also improve the beauty and lustre of metals. They are thus used as decorative items as they do not tarnish easily.
Stainless steel is used to make forks and spoons.
Copper and antimony added to tin produces pewter, used to make decorative items.

Composition, Characteristic, and Uses of Alloy
Alloy	Composition	Properties	Uses
Cupronickel (Coins)	Cu 75% Ni 25%	Hard, strong, resists corrosion	Coins
Duralumin	Al 95% Cu 4% Mg 1%	Light, strong	Aeroplane parts, electric cables, racing bicycles
Steel	Fe 99% C 1%	Hard, strong, cheap	Vehicles, ships, bridges, buildings
Stainless steel	Fe73% Cr 18% Ni 8% C 1%	Hard, rust resistant	Kitchen appliances, watches, machine parts, knives, forks, spoons
Bronze	Cu 90% Sn 10%	Hard, strong, shining	Decorative items, medals, artwork, pots and pans
Brass	Cu 70% Zn 30%	Harder and cheaper than Cu	Decorative items, electrical appliances, musical instruments, bell, nails, screw, pots
Snider	Pb 50% Sn 50%	Low melting point, strong	Welding and soldering work
Pewter	Sn 91% Sb 7% Cu 2%	Malleable, ductile, rust resistant	Decorative items, souvenirs
Magnalium	Al 70% Mg 30%	Light, strong	Tyre rim of racing cars, skeletal body of aeroplanes