Metals - Uses of metals and alloys

Alloys are mixtures of a metal with one or more other elements (usually other metals or carbon). For example, Steel is an alloy of Iron ($Fe$) and Carbon ($C$).

In a pure metal, atoms are of the same size and arranged in regular layers. These layers can slide over each other easily, making pure metals relatively soft and malleable.

In an alloy, the introduction of different-sized atoms (e.g., $C$ atoms in $Fe$) disrupts the regular lattice arrangement. This prevents the layers from sliding over each other easily, making alloys harder and stronger than pure metals.

Aluminum ($Al$) is widely used in the manufacture of aircraft because of its low density and its ability to resist corrosion due to a thin, tough layer of aluminum oxide ($Al_2O_3$) on its surface.

Copper ($Cu$) is used for electrical wiring because it has very high electrical conductivity and is ductile (can be drawn into wires). It is also used in cooking utensils due to its high thermal conductivity.

Stainless steel is an alloy of iron ($Fe$) containing chromium ($Cr$) and nickel ($Ni$). It is used for cutlery and chemical plants because the chromium forms a passive oxide layer that prevents rusting.

Zinc ($Zn$) is used for galvanizing iron ($Fe$). This provides sacrificial protection because $Zn$ is more reactive than $Fe$ and will oxidize preferentially according to the half-equation: $Zn ightarrow Zn^{2+} + 2e^-$.