indium

 

(ĭn'dēəm) , a metallic chemical element; symbol In; at. no. 49; at. wt. 114.82; m.p. 156.6°C; b.p. about 2,080°C; sp. gr. 7.31 at 20°C; valence +1, +2, or +3. Indium is a soft, malleable, ductile, lustrous, silver-white metallic element; it crystallizes in a face-centered tetragonal structure. Its properties are similar to those of gallium, the element directly above it in Group 13 of the periodic table. Like gallium, it remains in the liquid state over a wide range of temperatures. It wets glass and can be used to form a mirror surface that is more corrosion-resistant than, and reflects as well as, one of silver. It is also used in low-melting fusible alloys and as a protective plating for bearings and other metal surfaces. Although indium resists oxidation at room temperature, when heated above its melting point it ignites and burns with a violet flame; the oxide that is formed is used in glassmaking to give a yellow color. Indium reacts readily with the halogens and (when warm) with other nonmetals, e.g., phosphorus, selenium, and sulfur. It has trivalent compounds that are similar to those of gallium and aluminum. Indium salts color the Bunsen flame a deep blue-violet. Indium phosphide, arsenide, and antimonide are semiconductor materials used in photocells, thermistors, and rectifiers. Indium is found in very low concentrations in many ores and minerals; it was first found in zinc blende and is produced commercially as a byproduct of the smelting of zinc. Indium was discovered in 1863 by Ferdinand Reich and H. T. Richter, using spectroscopic analysis; it was named for a brilliant indigo line in its spectrum.

49 cadmium ← indium → tin Ga ↑ In ↓ Tl Periodic Table - Extended Periodic Table
General
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 (more)	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
Miscellaneous
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
Main article: Isotopes of indium 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
References

Indium (IPA: /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.

Applications

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. ^[1]
• 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 of a wire it is used as a vacuum seal in cryogenics applications.
• Used as a calibration material for thermogravimetric analysis devices.

History

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

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. 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 typically over 300 tonnes per year, but demand has risen rapidly with the increased popularity of LCD computer monitors and televisions. 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 average indium price for 2005 was US$900/kg.

Precautions

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."^[2] For example, indium trichloride anhydrous (InCl₃) is quite toxic, while indium phosphide (InP) is both toxic and a suspected carcinogen.

See also

• Indium compounds

References

1. ^ Journal of Crystal Growth doi:10.1016/j.jcrysgro.2004.09.006
2. ^ http://www.webelements.com/

• Los Alamos National Laboratory – Indium

External links

• WebElements.com – Indium
• The Indium Corporation
• Reducing Agents > Indium low valent

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