Alloys and rusting

In a nutshell

Alloys are compounds which are made up of two or more elements, one of these being a metal. Rusting is the process of the oxidation of a metal, there are a variety of ways to protect alloys and metals from rusting including galvanisation and sacrificial protection to name a few.

Alloys

Definition

Alloys are a mixture of two or more elements where at least one of the elements is a metal. Alloys are useful because pure compounds such as copper, iron and aluminium are too soft on their own and require mixing with other compounds to meet the standards of everyday use.

Alloy	Element one	Element two
Steel	Iron	Carbon
Bronze	Copper	Tin
Brass	Copper	Zinc

Example

Iron on its own is too soft and easily deformed under stress. However, with the addition of carbon it becomes a perfect construction material by increasing is strength and ability to resist deformation under stress.

Rusting

Rusting is an oxidation reaction, electrons are lost in this reaction. Both air and water are required for rusting to occur. Rusting occurs to both iron and steel as well as other metals.

$iron\ +\ oxygen\ +\ water\ \rightarrow\ hydrated\ iron\ (III)\ oxide\\ \ \\iron\ \rightarrow\ iron\ ion\ +\ 3 \space electrons\\ \ \\Fe(s)\ \rightarrow\ Fe^{3+}(aq)\ +\ 3e^-$

Aluminium is protected from rusting due to a protective layer of aluminium oxide, preventing further rusting. Iron and steel rusting tends to flake off which further exposes the iron and steel.

Chemistry; Separate chemistry 1; KS4 Year 10; Alloys and rusting

	CONDITIONS	APPEARANCE
1.	Air and water	Rust develops
2.	Air without water	No rust develops
3.	Water without air	No rust develops

How to prevent rusting

There are several ways to prevent rusting, these methods include but are not limited to: oiling, galvanisation, painting and sacrificial protection.

Sacrificial protection

Sacrificial protection is when a more reactive metal is used to protect a less reactive metal and become oxidised. This then forms a layer around the less reactive metal protecting it from air and water.

Galvanisation

Galvanisation involves adding a layer of zinc over iron, therefore protecting it. Since zinc is more reactive than iron it gets oxidised and forms a layer preventing iron from being oxidised. This is a form of sacrificial protection.