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49 cadmiumindiumtin


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
Physical properties
Phase solid
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
Vapor pressure
P(Pa) 1 10 100 1 k 10 k 100 k
at T(K) 1196 1325 1485 1690 1962 2340
Atomic properties
Crystal structure tetragonal
Oxidation states 3
(amphoteric oxide)
Electronegativity 1.78 (scale Pauling)
Ionization energies
1st:  558.3  kJ·mol−1
2nd:  1820.7  kJ·mol−1
3rd:  2704  kJ·mol−1
Atomic radius 155pm
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
Mohs hardness 1.2
Brinell hardness 8.83  MPa
CAS registry number 7440-74-6
Selected isotopes
iso NA half-life DM DE (MeV) DP
113In 4.3% In is stable with 64 neutrons
115In 95.7% 4.41×1014y Beta- 0.495 115Sn

Indium (pronounced /ˈɪndiəm/) is a chemical element with chemical symbol In and atomic number 49. This rare, soft, malleable and easily fusible poor metal is chemically similar to aluminium or gallium but more closely resembles 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

Indium 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 is not considered hazardous, mainly because its 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 notorious cumulative poison.


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:


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. Richter went on to isolate the metal in 1867.

Occurrence and consumption

File:Indium wire.jpg
Ductile Indium wire

Indium ranks 61st in abundance in the Earth's crust at approximately 0.25 ppm [2], which means it is more than three times as abundant as silver, which occurs at 0.075 ppm [3]. Up until 1924, there was only about a gram of isolated indium on the planet. Indium is produced mainly from residues generated during zinc ore processing but is also found in iron, lead, and copper ores. 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.

The amount of indium consumed is largely a function of worldwide LCD production. Worldwide production is currently 476 tonnes per year from mining and a further 650 tonnes per year from recycling [4]. Demand has risen rapidly in recent years with the popularity of LCD computer monitors and televisions, which now account for 50% of indium consumption [5]. Increased manufacturing efficiency and recycling (especially in Japan) maintain a balance between demand and supply. 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 per kilogram. The recent changes in demand and supply have resulted in high and fluctuating prices of indium, which from 2005 to 2007 ranged from US$700/kg to US$1,000/kg [6]. Demand for indium is likely to continue to increase with large-scale manufacture of CIGS-based thin film solar technology starting by several companies in 2008, including Nanosolar and Miasole.

Based on content of indium in zinc ore stocks, there is a world-wide reserve base of approximately 6,000 tonnes of economically-viable indium [7]. This figure has led to estimates suggesting that, at current consumption rates, there is only 13 years' supply of indium left [8]. However, such estimates are often regarded as alarmist and scaremongering [9]. The Indium Corporation, the largest processor of indium, claim that, on the basis of increasing recovery yields during extraction, recovery from a wider range of base metals (including tin, copper and other polymetallic deposits) and new mining investments, the long-term supply of indium is sustainable, reliable and sufficient to meet increasing future demands [10]. This conclusion also seems reasonable in light of the fact that silver, a less abundant element, is currently mined at approximately 18,300 tonnes per annum [11], which is 40 times greater than current indium mining rates.


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."[12] For example, indium trichloride anhydrous (InCl3) is quite toxic, while indium phosphide (InP) is both toxic and a suspected carcinogen.

See also


  1. Journal of Crystal Growth doi:10.1016/j.jcrysgro.2004.09.006
  2. "The Element Indium". It's Elemental. Retrieved 2007-12-26.
  3. "The Element Silver". It's Elemental. Retrieved 2007-12-26.
  4. "Indium and Gallium Supply Sustainability September 2007 Update" (pdf). 22nd EU PV Conference, Milan, Italy. Retrieved 2007-12-26.
  5. "Indium Price Supported by LCD Demand and New Uses for the Metal" (pdf). Retrieved 2007-12-26.
  6. "Indium (Mineral Commodities Summary 2007)" (pdf). USGS Minerals Information. Retrieved 2007-12-26.
  7. "Indium (Mineral Commodities Summary 2007)" (pdf). USGS Minerals Information. Retrieved 2007-12-26.
  8. "How Long Will it Last?". New Scientist. 194 (2605): 38–39. May 26, 2007. ISSN 0262-4079. Check date values in: |date= (help)
  9. "Find More Ore". New Scientist. 194 (2608): 26. June 16, 2007. ISSN 0262-4079. Check date values in: |date= (help)
  10. "Indium and Gallium Supply Sustainability September 2007 Update" (pdf). 22nd EU PV Conference, Milan, Italy. Retrieved 2007-12-26.
  11. "Top World Silver Producers" (pdf). World Silver Survey 2007.

External links

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