Tin

Tin is a chemical element with the symbol Sn (from the Latin name stannum) and atomic number 50. It is a soft metal, silvery-white in colour, easily bent and melted. Its melting point is lower than that of most common metals, making it suitable for soldering.

Tin is among the earliest metals used by humans. When tin is added to copper, bronze results, which is harder than copper alone; this formed the basis of the period known as the Bronze Age.

Physical and Chemical Properties

Tin exists in two major forms with different structures: white tin (beta), the ordinary metal seen in use, and grey tin (alfa), which forms when temperature drops significantly. The transformation of white tin to grey tin causes the metal to crumble and become powdery—known as 'tin pest'. Chemically, tin most commonly forms compounds with oxidation states of +2 and +4. It forms an oxide layer in air that protects against corrosion; for this reason steel is coated with tin to make food containers.

Extraction and Production

The primary ore of tin is cassiterite, a tin dioxide mineral. Tin is produced by smelting the ore in a furnace with carbon, which removes the oxygen. Production involves both underground hard-rock mining (lode) and recovery from rivers and alluvial deposits (placer). Major tin-producing countries are found in Southeast Asia and South America.

Uses

The largest modern use of tin is in soldering electronic devices: printed circuit boards are joined using various tin-containing alloys. It is also used in coating food containers and in producing alloys such as bronze and pewter. Tin-niobium alloys are used in superconducting magnets that operate at very low temperatures.