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Name, Symbol, Number indium, In, 49
Chemical series Poor metals
Group, Period, Block 13 (IIIA), 5, p
Density, Hardness 7310 kg/m3, 1.2
Appearance silvery lustrous gray
Atomic properties
Atomic weight 114.818 amu
Atomic radius (calc.) 155 (156) pm
Covalent radius 144 pm
van der Waals radius 193 pm
Electron configuration [Kr]4d10 5s2 5p1
e- 's per energy level 2, 8, 18, 18, 3
Oxidation states (Oxide) 3 (amphoteric)
Crystal structure Tetragonal
Physical properties
State of matter solid
Melting point 429.7485 K (156.5985 ?C)
Boiling point 2345 K (2072 ?C)
Molar volume 15.76 ×10-6 m3/mol
Heat of vaporization 231.5 kJ/mol
Heat of fusion 3.263 kJ/mol
Vapor pressure 1.42 E-17 Pa at 429 K
Speed of sound 1215 m/s at 293.15 K
Electronegativity 1.78 (Pauling scale)
Specific heat capacity 233 J/(kg?K)
Electrical conductivity 11.6 MS/m
Thermal conductivity 81.6 W/(m?K)
1st ionization potential 558.3 kJ/mol
2nd ionization potential 1820.7 kJ/mol
3rd ionization potential 2704 kJ/mol
4th ionization potential 5210 kJ/mol
Most stable isotopes
iso NA half-life DM DE MeV DP
113In 4.3% In is stable with 64 neutrons
115In 95.7% 4.41 E14 y Beta- 0.495 115Sn
SI units & STP are used except where noted.

Indium 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 also widely used in thin-films to form lubricated layers (during World War II it was widely used to coat bearings in high-performance aircraft).

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Notable characteristics

Indium is a very soft, silvery-white true metal that has 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 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, 4 x 1014 years, many thousands of times longer than the estimated 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 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 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.


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Indium metal

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 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. Canada is a leading producer of indium, producing more than 1,000,000 troy ounces (31,100 kg) in 1997.


Pure indium in metal form is considered non-toxic by most sources. This may not be the case with indium compounds: there is some unconfirmed evidence that suggests that indium has a low level of toxicity. However, in the welding and semiconductor industries, where indium exposure is relatively high, there have been no reports of any toxic side-effects. 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.


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