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|Name, Symbol, Number||indium, In, 49|
|Chemical series||poor metals|
|Group, Period, Block||13, 5, p|
|Appearance||silvery lustrous gray
|Standard atomic weight||114.818(3) g·mol−1|
|Electron configuration||[Kr] 4d10 5s2 5p1|
|Electrons per shell||2, 8, 18, 18, 3|
|Density (near r.t.)||7.31 g·cm−3|
|Liquid density at m.p.||7.02 g·cm−3|
|Melting point||429.75 K
(156.60 °C, 313.88 °F)
|Boiling point||2345 K
(2072 °C, 3762 °F)
|Heat of fusion||3.281 kJ·mol−1|
|Heat of vaporization||231.8 kJ·mol−1|
|Heat capacity||(25 °C) 26.74 J·mol−1·K−1|
|Electronegativity||1.78 (scale Pauling)|
|1st: 558.3 kJ·mol−1|
|2nd: 1820.7 kJ·mol−1|
|3rd: 2704 kJ·mol−1|
|Atomic radius||155 pm|
|Atomic radius (calc.)||156 pm|
|Covalent radius||144 pm|
|Van der Waals radius||193 pm|
|Magnetic ordering||no data|
|Electrical resistivity||(20 °C) 83.7 n Ω·m|
|Thermal conductivity||(300 K) 81.8 W·m−1·K−1|
|Thermal expansion||(25 °C) 32.1 µm·m−1·K−1|
|Speed of sound (thin rod)||(20 °C) 1215 m/s|
|Young's modulus||11 GPa|
|Brinell hardness||8.83 MPa|
|CAS registry number||7440-74-6|
Indium (IPA: /ˈɪndiəm/) is a chemical element in the periodic table that has the symbol In and atomic number 49. This rare, soft, malleable and easily fusible poor metal, is chemically similar to aluminium or gallium but looks more like zinc (zinc ores are also the primary source of this metal). Its current primary application is to form transparent electrodes from indium tin oxide in liquid crystal displays. 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's also used for making particularly low melting point alloys, and is a component in some lead-free solders.
 Notable characteristics
One unusual property of indium is that its most common isotope is very slightly radioactive; it very slowly decays by beta emission to tin over time. This radioactivity is not considered hazardous, mainly because its decay rate is nearly 50,000 times slower than that of natural thorium, with a half-life of 4.41×1014 years, four orders of magnitude larger than the age of the universe. Also, indium is not a notorious cumulative poison like its neighbor cadmium, and is relatively rare.
The first large-scale application for indium was as a coating for bearings in high-performance aircraft engines during World War II. Afterwards, 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 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. Other uses:
- Used in the manufacture of low-melting-temperature alloys. An alloy consisting of 24% indium and 76% gallium is liquid at room temperature.
- Some indium compounds such as indium antimonide, indium phosphide, and indium nitride are semiconductors with useful properties.
- Used in light-emitting diodes (LEDs) and Laser Diodes (LDs) based on compound semiconductors 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. 
- 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.
- Indium oxide (In2O3) is used as a transparent conductive glass substrate in the making of electroluminescent panels.
- Used as a light filter in low pressure sodium vapor lamps.
- Indium's freezing 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 is used in medical imaging to monitor the activity of white blood cells. A blood test is taken from the patient, white cells removed and labelled 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.
- Very small amounts used in aluminium alloy sacrificial anodes (for salt water applications) to prevent passivation of the aluminium.
- In the form a wire it is sometimes used as a vacuum seal.
Indium (named after the indigo line in its atomic spectrum) was discovered by Ferdinand Reich and Hieronymous Theodor Richter in 1863 while they were testing zinc ores with a spectrograph in search of thallium. It is interesting to note that most elements were discovered while searching for other elements. Richter went on to isolate the metal in 1867.
Indium is produced mainly from residues generated during zinc ore processing but is also found in iron, lead, and copper ores. The amount of indium consumed is largely a function of worldwide LCD production. Increased manufacturing efficiency and recycling (especially in Japan) maintain a balance between demand and supply. The average indium price for 2005 was US$900 per kilogram. This is unusually high. Demand increased as the metal is used in LCDs and televisions, and supply decreased when a number of Chinese mining concerns stopped extracting indium from their zinc tailings. In 2002, the price was US$94/kg.
Up until 1924, there was only about a gram of isolated indium on the planet. The Earth is estimated to contain about 0.1 ppm of indium which means it is about as abundant as silver, although indium is in fact nearly three times more expensive by weight. Canada is a leading producer of indium. The Teck Cominco refinery in Trail, BC, is the largest single source, with production of 32,500 kg in 2005, 41,800 kg in 2004 and 36,100 kg in 2003. Worldwide production is typically over 300 tonnes per year, but demand has risen rapidly with the increased popularity of LCD computer monitors and televisions.
Pure indium in metal form is considered non-toxic by most sources. In the welding and semiconductor industries, where indium exposure is relatively high, there have been no reports of any toxic side-effects.
This may not be the case with indium compounds: there is some unconfirmed evidence that suggests that indium has a low level of toxicity. Other sources are more definite about indium compounds' toxicity - for example, the WebElements website states that "All indium compounds should be regarded as highly toxic. Indium compounds damage the heart, kidney, and liver, and may be teratogenic." For example, indium trichloride anhydrous (InCl3) is quite toxic, while indium phosphide (InP) is both toxic and a suspected carcinogen.