Indium In

Discovery

In 1863 Ferdinand Reich and Hieronymus Theodor Richter at the Freiberg Mining Academy in Saxony were examining zinc ores with a spectroscope, looking for thallium.

Instead of the expected lines, a brilliant indigo line appeared that belonged to no known element. Reich is said to have been colour-blind, so Richter did much of the spectroscopic observation. On the strength of that line they announced a new element, and they later isolated small amounts of the metal.

For a long time indium was a rare curiosity with few uses. Demand soared in the late twentieth century, when liquid crystal displays spread and ITO became the standard transparent conductor.

Origin of the name

The name comes from the indigo line in its spectrum. Indigo derives from the Latin indicum, "of India". The symbol is In.

Main uses

• Transparent electrodes: indium tin oxide conducts electricity while remaining transparent, making it essential for LCD and OLED displays, touchscreens and some solar cells. This is the largest use of indium.
• Semiconductors: indium phosphide and indium gallium arsenide are used in lasers and detectors for fibre-optic communications, and indium gallium nitride produces blue and green LEDs.
• Solders and alloys: indium alloys melt at low temperatures and wet glass and ceramics, so they are used in low-temperature solders, vacuum seals and thermal interface materials.
• Reactors: silver–indium–cadmium alloy is used in control rods.

Isotopes

Natural indium consists of stable indium-113 (about 4.3%) and radioactive indium-115 (about 95.7%). Indium-115 has a half-life of roughly 4.4 × 10¹⁴ years, so indium is one of the rare elements whose most abundant isotope is radioactive. The artificial isotope indium-111, with a half-life of about 2.8 days, is attached to white blood cells or targeting molecules to locate infections and neuroendocrine tumours in nuclear medicine.

In everyday life

Indium has almost no mines of its own and is recovered as a by-product of zinc smelting. China is the largest producer, and South Korea, home to large zinc refineries, is also a major producer of refined indium.

A thin film of it lies inside nearly every smartphone and television screen. Metallic indium poses little risk in ordinary contact, but lung disease has been reported among workers who inhaled indium compound dust over long periods in ITO processing plants, so dust control is important.