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Indium (pronounced /ˈɪndiəm/) is a chemical element with chemical symbol In and atomic number 49. This rare, soft, malleable and easily fusible post-transition metal is chemically similar to aluminium or gallium but more closely resembles zinc (zinc ores are also the primary source of this metal).

Indium's current primary application is to form transparent electrodes from indium tin oxide in liquid crystal displays, and this use largely determines its global mining production. It is widely used in thin-films to form lubricated layers (during World War II it was widely used to coat bearings in high-performance aircraft). It is also used for making particularly low melting point alloys, and is a component in some lead-free solders. Radioactive indium-111 is used in nuclear medicine as a imaging agent to follow the movement of leukocytes in the body.

Characteristics
Indium wetting the glass surface of a test tubeIndium is a very soft, silvery-white, relatively rare true metal with a bright luster. As a pure metal indium emits a high-pitched "cry", when it is bent/ Both gallium and indium are able to wet glass.

One unusual property of indium is that its most common isotope is slightly radioactive; it very slowly decays by beta emission to tin. This radioactivity has a half-life is 4.41 × 1014 years, four orders of magnitude larger than the age of the universe and nearly 50,000 times longer than that of natural thorium. Unlike its period 5 neighbor cadmium, indium is not a cumulative poison.

Applications
The first large-scale application for indium was as a coating for bearings in high-performance aircraft engines during World War II. Afterward, production gradually increased as new uses were found in fusible alloys, solders, and electronics. In the 1950s, tiny beads of it were used for the emitters and collectors of PNP alloy junction transistors. In the middle and late 1980s, the development of indium phosphide semiconductors and indium tin oxide thin films for liquid crystal displays (LCD) aroused much interest. By 1992, the thin-film application had become the largest end use.

 Electronics
Indium oxide (In2O3) and indium tin oxide (ITO) are used as a transparent conductive coating applied to glass substrates in the making of electroluminescent panels.
Some indium compounds such as indium antimonide, indium phosphide, and indium nitride are semiconductors with useful properties.
Indium is used in the synthesis of the semiconductor copper indium gallium selenide (CIGS), which is used for the manufacture of thin film solar cells.
Used in light-emitting diodes (LEDs) and Laser Diodes (LDs) based on compound semiconductors such as InGaN, InGaP that are fabricated by Metalorganic Vapor Phase Epitaxy (MOVPE) technology.
The ultrapure metalorganics of indium, specifically high purity trimethylindium (TMI) is used as a precursor in III-V compound semiconductors, while it is also used as the semiconductor dopant in II-VI compound semiconductors.

Alloys and Metal
For manufacture of low-melting-temperature alloys. An alloy consisting of 24% indium and 76% gallium is liquid at room temperature.
Can also be plated onto metals and evaporated onto glass which forms a mirror which is as good as those made with silver but has higher corrosion resistance.
Very small amounts used in aluminium alloy sacrificial anodes (for salt water applications) to prevent passivation of the aluminium.
To bond gold electrical test leads to superconductors, Indium is used as a conducting glue and applied under a microscope with precision tweezers.
In the form of a wire it is used as a vacuum seal in cryogenics and ultra-high vacuum applications.
Used as a calibration material for Differential scanning calorimetry.

Other uses
Indium tin oxide is used as a light filter in low pressure sodium vapor lamps. The infrared radiation is reflected back into the lamp, which increases the temperature within the tube and therefore improves the performance of the lamp.
Indium's melting point of 429.7485 K (156.5985 °C) is a defining fixed point on the international temperature scale ITS-90.
Indium's high neutron capture cross section for thermal neutrons makes it suitable for use in control rods for nuclear reactors, typically in an alloy containing 80% silver, 15% indium, and 5% cadmium.
In nuclear engineering, the (n,n') reactions of 113In and 115In are used to determine magnitudes of neutron fluxes.
111In emits gamma radiation and is used in scintigraphy, a technique of medical imaging. Scintigraphy has many applications, including early phase drug development, and monitoring the activity of white blood cells. A blood test is taken from the patient, white cells removed and labeled with the radioactive 111In, then re-injected back into the patient. Gamma imaging will reveal any areas of high white cell activity such as an abscess.
Indium is also used as a thermal interface material by personal computer enthusiasts in the form of pre-shaped foil sheets fitted between the heat-transfer surface of a microprocessor and its heat sink. The application of heat partially melts the foil and allows the indium metal to fill in any microscopic gaps and pits between the two surfaces, removing any insulating air pockets that would otherwise compromise heat transfer efficiency.