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Indium (In)

QUICK REFERENCE

  • Symbol: In
  • Atomic Number: 49
  • Atomic Weight: 114.818
  • Element Classification: Post-transition Metal
  • Discovered By: Ferdinand Reich and Hieronymus Theodor Richter
  • Discovery Date: 1863
  • Name Origin: From the indigo blue line in its spectrum
  • Density(g/cc): 7.31
  • Melting Point: 156.60°C
  • Boiling Point: 2072°C
  • Appearance: Silvery-white, very soft and malleable metal
  • Atomic Radius(pm): 156

Discovery

Indium was discovered in 1863 by German chemists Ferdinand Reich and Hieronymus Theodor Richter. While analyzing zinc ore samples from the Freiberg, Saxony region, Reich and Richter observed a brilliant indigo blue spectral line, indicating the presence of an unknown element. They named this new element indium, derived from the Latin word ‘indicum’, meaning indigo, in reference to its distinctive spectral color. The metal was isolated the following year by Richter.

Relation to Other Elements

Indium is classified as a post-transition metal, positioned in group 13 of the periodic table, between cadmium and tin. It shares many physical and chemical properties with gallium and thallium, its group neighbors. Indium is known for its softness, low melting point, and the ability to wet glass, making it useful in low-melting alloys and solders. It predominantly forms +3 oxidation state compounds and is considered less reactive than the metals in groups 1 and 2.

Natural Occurrence

Indium is a relatively rare element in the Earth’s crust, with an abundance similar to silver. It is not found in nature in its elemental form but occurs primarily as a trace element in zinc, lead, and copper ores. The primary source of indium is the byproduct of zinc ore processing, but it can also be recovered from iron, lead, and copper ores.

Uses

Indium has several specialized applications in electronics and other industries:

  • LCDs and Touchscreens: Indium tin oxide (ITO) is a transparent conductor used in liquid crystal displays (LCDs), touchscreens, and flat-panel displays. ITO’s transparency and electrical conductivity make it ideal for these applications.
  • Solders: Indium is used in low-temperature solders and fusible alloys. An alloy of indium and gallium is liquid at room temperature, making it useful in thermal interface materials.
  • Semiconductors: Indium compounds, such as indium arsenide (InAs) and indium phosphide (InP), are used in semiconductors for high-speed and high-frequency electronics.
  • Photovoltaics: Copper indium gallium selenide (CIGS) is a material used in thin-film solar cells, offering high efficiency and stability.
  • Sealing and Bonding: Due to its ability to wet glass, indium is used in hermetic seals and in vacuum systems.

The discovery of indium added an important element to the toolkit of materials scientists and engineers, particularly in the fields of electronics and renewable energy. Its unique properties, especially in alloys and semiconductors, continue to facilitate advancements in technology and industrial applications.

Cadmium (Cd)

Tin (Sn)