IndiumEdit

Indium is the chemical element with the symbol In and atomic number 49. It is a soft, silvery‑white post‑transition metal that occurs only in trace amounts in the Earth's crust. It is typically recovered as a byproduct of refining zinc ores such as sphalerite and is notable for its unusually low melting point among metals, around 156.6 degrees Celsius. In its natural state it forms a protective oxide layer that helps resist corrosion, and it can be drawn into wires or rolled into sheets.

In modern technology, indium is best known for its role in indium tin oxide (ITO), a transparent conductor used extensively in touch screens, liquid crystal display (LCD) panels, and certain solar cell coatings. Beyond ITO, indium is used in low‑melting‑point solders and fusible alloys for electronics, as well as in specialized semiconductors and optoelectronic materials, including Indium phosphide and compounds such as InGaAs for high‑speed detectors and fiber‑optic applications. The element’s prominence in electronics ties its importance to the broader industrial priorities of advanced manufacturing and global supply chains, which in turn intersect with considerations of resource security and recycling of electronic waste.

Indium was discovered in 1863 by Ferdinand Reich and Hieronymus Theodor Richter while analyzing zinc ores with a spectroscope. They named the new element for the distinctive indigo blue line observed in its spectrum. The initial discovery and subsequent confirmation of indium’s existence occurred in the context of 19th‑century efforts to catalog the elements by spectral lines, a methodological advance that helped drive later applications in metallurgy and electronics. The metal was later purified and produced on a commercial scale as demand grew for specialty materials in electronics and communications.

History

Discovery and naming: The identification of indium arose from spectroscopic analysis of zinc ores, leading to the recognition of a new blue spectral line and the attribution of the element name derived from that indigo line. The principal investigators behind the discovery were Ferdinand Reich and Hieronymus Theodor Richter.
Early development: Following the initial report, researchers developed methods to isolate and refine indium for practical use, laying the groundwork for its eventual integration into commercial electronics, coatings, and specialty alloys.
Evolution of applications: As electronics matured, indium found its niche in transparent conductors and low‑melting alloys, with research expanding into semiconductor materials such as Indium phosphide and compound semiconductors used in fast photonics and detectors.

Properties

Physical properties

Atomic number: 49; symbol: In.
Appearance: soft, silvery‑white metal with a low hardness.
Melting point: about 156.6 °C; boiling point well above 1000 °C.
Density: roughly 7.31 g/cm³ at room temperature.
Oxide behavior: forms a thin, protective oxide layer that passivates the surface.

Chemical properties

Common oxidation state in compounds is +3, though indium forms multiple compounds with varying stoichiometries.
It is relatively low in reactivity compared with many other metals, contributing to its usefulness in stable alloys and protective coatings.
It is often processed in metallic form or as alloys and compounds designed for electronics and optics.

Special notes

Indium is part of the group 13 elements in the periodic table, and it is classified as a post‑transition metal. Its physics and chemistry underpin its use in both conduction and optical applications, balancing softness and stability in engineered materials.

Occurrence and production

Indium occurs in trace amounts in the Earth's crust, most commonly in association with zinc sulfide minerals such as sphalerite. It is produced commercially largely as a byproduct of zinc refining and other metal ore processing. Because it is not mined as a primary metal ore in large quantities, its supply is closely tied to the health of zinc and related mining operations, which in turn matters for industries dependent on indium‑rich materials such as transparent conductors and certain semiconductors. Global production and refining involve complex supply chains, with recycling of electronic waste increasingly viewed as an important supplementary source of indium for industry.

Applications

Transparent conductors: Indium tin oxide (Indium tin oxide) is the principal transparent conductor used in touch screens, flat‑panel displays, and some solar modules. The combination of electrical conductivity with optical transparency makes ITO essential for modern visual interfaces and photovoltaics.
Solders and alloys: Indium forms low‑melting‑point alloys and solder materials used in electronics assembly, affording reliable joints at relatively low temperatures.
Semiconductors and photonics: Indium is a key element in compounds such as Indium phosphide and in indium‑based alloy systems like InGaAs, which enable high‑speed electronics, infrared detectors, and fiber‑optic communications.
Coatings and plating: Indium or indium‑containing alloys are used for specialty coatings and corrosion‑resistant platings on specific components.
Other uses: The metal has applications in certain high‑reliability components and niche aerospace or industrial contexts, often tied to the properties of low‑temperature processing or unique dielectric/semiconducting characteristics.

Health and safety

Exposure to indium and its compounds is primarily a concern in industrial settings, such as during mining, refining, or manufacturing of indium‑containing materials. Indium metal itself is generally considered of low acute toxicity, but inhalation of indium compounds (notably in dust or aerosol forms found in some industrial processes) has been associated with lung and other occupational health risks in some cases. Protective equipment, proper ventilation, and adherence to industrial hygiene practices are important to minimize exposure. In the context of electronics manufacturing, handling of indium tin oxide powders and related materials requires appropriate controls to reduce inhalation risk.