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silvery lustrous gray
General properties
Name, symbol, number indium, In, 49
Element category post-transition metal
Group, period, block 135, p
Standard atomic weight 114.818g·mol−1
Electron configuration [Kr] 4d10 5s2 5p1
Electrons per shell 2, 8, 18, 18, 3 (Image)
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 429.7485 K, 156.5985 °C, 313.8773 °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
Specific 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
Oxidation states 3, 2, 1 (amphoteric oxide)
Electronegativity 1.78 (Pauling scale)
Ionization energies 1st: 558.3 kJ·mol−1
2nd: 1820.7 kJ·mol−1
3rd: 2704 kJ·mol−1
Atomic radius 167 pm
Covalent radius 142±5 pm
Van der Waals radius 193 pm
Crystal structure tetragonal
Magnetic ordering diamagnetic[1]
Electrical resistivity (20 °C) 83.7 nΩ·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
Most stable isotopes
Main article: Isotopes of indium
iso NA half-life DM DE (MeV) DP
113In 4.3% 113In is stable with 64 neutrons
115In 95.7% 4.41×1014 y β 0.495 115Sn

Indium (pronounced /ˈɪndiəm/, IN-dee-əm) 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 touchscreens, 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 an imaging agent to follow the movement of leukocytes in the body.



Indium wetting the glass surface of a test tube

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.[2] 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 of 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.


In 1863 the German chemists Ferdinand Reich and Hieronymous Theodor Richter were testing ores from the mines around Freiberg, Saxony. They dissolved the minerals pyrite, arsenopyrite, galena and sphalerite in hydrochloric acid and distilled the raw zinc chloride. As it was known that ores from that region sometimes contain thallium they searched for the green emission lines with spectroscopic methods. The green lines were absent but a blue line was present in the spectrum. As no element was known with a bright blue emission they concluded that a new element was present in the minerals. They named the element with the blue spectral line indium, from the indigo color seen in its spectrum.[3][4] Richter went on to isolate the metal in 1864.[5] At the World Fair 1867 an ingot of 500g was presented.[6]

Occurrence and consumption

Indium ranks 61st in abundance in the Earth's crust at approximately 0.25 ppm,[7] which means it is more than three times as abundant as silver, which occurs at 0.075 ppm.[8] Fewer than 10 indium minerals are known, none occurring in significant deposits. Examples are the dzhalindite (In(OH)3) and indite (FeIn2S4).[9]



Based on content of indium in zinc ore stocks, there is a worldwide reserve base of approximately 6,000 tonnes of economically viable indium.[10] This figure has led to estimates suggesting that, at current consumption rates, there is only 13 years' supply of indium left.[11] However, the Indium Corporation, the largest processor of indium, claims 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.[12]

This conclusion also seems reasonable in light of the fact that silver, three times less abundant than indium in the earths crust,[13] is currently mined at approximately 18,300 tonnes per annum,[14] which is 40 times greater than current indium mining rates.


The lack of indium mineral deposits and the fact that indium is enriched in sulfidic lead, tin, copper, iron and predominately in zinc deposits, makes zinc production the main source for indium. The indium is leached from slag and dust of zinc production. Further purification is done by electrolysis.[6]

Indium is produced mainly from residues generated during zinc ore processing but is also found in iron, lead, and copper ores.[2] Canada is a leading producer of indium. The Teck Cominco refinery in Trail, British Columbia, 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.[12] Demand has risen rapidly in recent years with the popularity of LCD computer monitors and television sets, which now account for 50% of indium consumption.[15] 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.[10] Demand for indium may increase with large-scale manufacture of CIGS-based thin film solar technology starting by several companies in 2008, including Nanosolar and Miasole, although zinc oxide is often used instead.


A magnified image of an LCD screen showing RGB pixels. Individual transistors are seen as white dots in the bottom part.

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.[16][17]


Metal and alloys

Ductile indium wire
  • 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. For example, to manufacturing gaskets which deform to fill gaps.[22]
  • Used as a calibration material for Differential scanning calorimetry.
  • It is an ingredient in the alloy Galinstan, which is liquid at room temperature while not being toxic like mercury.

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.[17]
  • 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.


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. For example, anhydrous indium trichloride (InCl3) is quite toxic, and indium phosphide (InP) is both toxic and a suspected carcinogen.[23][24]

See also


  1. ^ Magnetic susceptibility of the elements and inorganic compounds, in Handbook of Chemistry and Physics 81th edition, CRC press.
  2. ^ a b Alfantazi, A. M.; Moskalyk, R. R. (2003). "Processing of indium: a review". Minerals Engineering 16 (8): 687–694. doi:10.1016/S0892-6875(03)00168-7.  
  3. ^ Reich, F.; Richter, T. (1863). "Ueber das Indium" (in German). Journal für Praktische Chemie 90 (1): 172–176. doi:10.1002/prac.18630900122.  
  4. ^ Venetskii, S. (1971). "Indium". Metallurgist 15 (2): 148–150. doi:10.1007/BF01088126.  
  5. ^ Reich, F.; Richter, T. (1864). "Ueber das Indium" (in German). Journal für Praktische Chemie 92 (1): 480–485. doi:10.1002/prac.18640920180.  
  6. ^ a b Schwarz-Schampera, Ulrich; Herzig, Peter M. (2002). Indium: Geology, Mineralogy, and Economics. Springer. ISBN 9783540431350.  
  7. ^ "The Element Indium". It's Elemental. Retrieved 2007-12-26.  
  8. ^ "The Element Silver". It's Elemental. Retrieved 2007-12-26.  
  9. ^ Sutherland, J. K. (1971). "A second occurrence of dzhalindite". The Canadian Mineralogist 10 (5): 781–786.  
  10. ^ a b "Mineral Commodities Summary 2007: Indium" (pdf). United States Geological Survey. Retrieved 2007-12-26.  
  11. ^ "How Long Will it Last?". New Scientist 194 (2605): 38–39. May 26, 2007. ISSN 0262-4079.  
  12. ^ a b "Indium and Gallium Supply Sustainability September 2007 Update" (pdf). 22nd EU PV Conference, Milan, Italy. Retrieved 2007-12-26.  
  13. ^ "Indium Price Supported by LCD Demand and New Uses for the Metal". September 6, 2009.  
  14. ^ "Top World Silver Producers" (pdf). World Silver Survey 2007.  
  15. ^ "Indium Price Supported by LCD Demand and New Uses for the Metal" (pdf). Retrieved 2007-12-26.  
  16. ^ Tolcin, Amy C.. "Mineral Yearbook 2007: Indium" (pdf). United States Geological Survey. Retrieved 200-02-03.  
  17. ^ a b Downs, Anthony John (1993). "Chemistry of Aluminium, Gallium, Indium, and Thallium". Springer. pp. 89 and 106.  
  18. ^ Bachmann, K. J. (1981). "Properties, Preparation, and Device Applications of Indium Phosphide". Annual Review of Materials Science 11: 441–484. doi:10.1146/  
  19. ^ Bhuiyan, Ghani; Hashimoto, Akihiro; Yamamoto, Akioare (2003). "Indium nitride (InN): A review on growth, characterization, and properties". Journal of Applied Physics 94: 2779. doi:10.1063/1.1595135.  
  20. ^ Powalla, M.; Dimmler, B. (2000). "Scaling up issues of CIGS solar cells". Thin Solid Films 361-362: 540–546. doi:10.1016/S0040-6090(99)00849-4.  
  21. ^ Shenai, Deodatta V.; Timmons, Michael L.; DiCarlo Jr., Ronald L.; Marsman, Charles J. (2004). "Correlation of film properties and reduced impurity concentrations in sources for III/V-MOVPE using high-purity trimethylindium and tertiarybutylphosphine". Journal of Crystal Growth 272: 603–608. doi:10.1016/j.jcrysgro.2004.09.006.  
  22. ^ ed. by G. L. Weissler ... (1990). Vacuum physics and technology. San Diego: Acad. Press. p. 296. ISBN 9780124759145.  
  23. ^ Tanaka, A.; Hirata, M.; Omura, M., (2002). "Pulmonary toxicity of indium-tin oxide and indium phosphide after intratracheal instillations into the lung of hamsters". Journal of the Occupational Health 44: 99–102. doi:10.1539/joh.44.99.  
  24. ^ Blazka, ME; Dixon, D., Haskins, E., Rosenthal, G. J. (1994). "Pulmonary toxicity to intratracheally administered indium trichloride in Fischer 344 rats". Fundamental Applied Toxicology 22: 231–239. doi:10.1006/faat.1994.1027.  

External links

1911 encyclopedia

Up to date as of January 14, 2010

From LoveToKnow 1911

INDIUM (symbol In, atomic weight 114.8), a metallic chemical element, included in the sub-group of the periodic classification of the elements containing aluminium, gallium and thallium. It was first discovered in 1863 by F. Reich and Th. Richter (Journ. fiir prak. Chem., 1863, 89 by means of its spectrum.

, P 444) It occurs naturally in very small quantities in zinc blende, and is best obtained from metallic zinc (which contains a small quantity of indium) by treating it with such an amount of hydrochloric acid that a little of the zinc remains undissolved; when on standing for some time the indium is precipitated on the undissolved zinc. The crude product is freed from basic zinc salts, dissolved in nitric acid and the nitric acid removed by evaporation with sulphuric acid, after which it is precipitated by addition of ammonia. The precipitated indium hydroxide is converted into a basic sulphite by boiling with excess of sodium bisulphite, and then into the normal sulphite by dissolving in hot sulphurous acid. This salt on strong ignition leaves a residue of the trioxide, which can be converted into the metal by heating in a current of hydrogen, or by fusion with sodium (C. Winkler, Journ. fit?' prak. Chem., 1867, 102, p. 273). Indium is a soft malleable metal, melting at 155° C. Its specific gravity is 7.421 and its specific heat 0.05695 (R. Bunsen).

Indium oxide, In203, is a yellow powder which is formed on ignition of the hydroxide. It is readily reduced on heating with carbon or hydrogen, and does not pass into an insoluble form when ignited. The hydroxide, In(OH) 3j is prepared, as a gelatinous precipitate, by adding ammonia to any soluble indium salt. It is readily soluble in caustic potash, but insoluble in ammonia.

Three chlorides of indium are known: the trichloride, InC13j a deliquescent salt, formed by heating a mixture of the oxide and carbon in a current of chlorine; the dichloride, InCl2, obtained by heating the metal in hydrochloric acid gas; and the monochloride, InCl, which is prepared by distilling the vapour of the dichloride over metallic indium. The monoand dichlorides are decomposed by water with the formation of the trichloride, and separation of metallic indium. Indium Sulphate, Ine(SO 4) 3, is obtained as a white powder very soluble in water by evaporating the trioxide with sulphuric acid. Concentration of the aqueous solution in a desiccator gives a deposit of crystals of a very deliquescent salt, H21n2(S04)4.8H20. An indium ammonium alum, In2(S04)3 (NH4)2S04.24H20 is known.

The atomic weight of indium has been determined by C. Winkler and by R. Bunsen by converting the metal into its oxide. Thiel (Ber., 1904, 37, p. 1135) obtained the values 115.08 and 114.81 from analyses of the chloride and bromide, whilst F. C. Mathers (Abst. J.C.S., 1907, ii. 352) obtained 114.88 and 114.86. Indium salts can be recognized by the dark blue colour they give in the flame of the Bunsen burner; and by the white beads of metal and the yellow incrustation formed when heated on charcoal with sodium carbonate.

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Up to date as of January 15, 2010

Definition from Wiktionary, a free dictionary

See also indium


Chemical Element: In (atomic number 49)



Indium n

  1. indium

Simple English

Indium is a chemical element. It has the chemical symbol In. It has the atomic number 49. It is a rare metal. It is a soft, malleable and poor metal. Indium looks like zinc. Pieces of indium can easily be joined together by pushing one piece into another. The chemistry of indium is quite like aluminium or gallium. Zinc ores are the main source of indium.

The main use of indium is in the chemical compound Indium tin oxide in liquid crystal displays. It is also used in very thin layers as a lubricant. In World War II it was used a lot to coat bearings in aircraft.


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