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Indium
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Indium 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). 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).
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Encyclopedia
Indium 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). 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 is also used for making particularly low melting point alloys, and is a component in some lead-free solders.
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 has a half-life is 4.41 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.
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 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.
Electronics
Alloys and Metal
- For manufacture of low-melting-temperature alloys. An alloy consisting of 24% indium and 76% gallium is liquid at room temperature.
- 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.
- Very small amounts used in aluminium alloy sacrificial anodes (for salt water applications) to prevent passivation of the aluminium.
- To adhere 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 applications.
- Used as a calibration material for Differential scanning calorimetry.
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.
- 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 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 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.
History
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 was 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. Richter went on to isolate the metal in 1864.
Occurrence and consumption
Indium ranks 61st in abundance in the Earth's crust at approximately 0.25 ppm, which means it is more than three times as abundant as silver, which occurs at 0.075 ppm.
Less than 10 indium minerals are known, none occurring in significant deposits. Examples are the dzhalindite (In(OH)3) and indite (FeIn2S4).
Production
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 the zinc production the main source for indium. The indium is leached from slug and dust of zinc production. Further purification is done by electrolysis.
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, 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. Demand has risen rapidly in recent years with the popularity of LCD computer monitors and televisions, which now account for 50% of indium consumption. 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. 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.
Resources
Based on content of indium in zinc ore stocks, there is a worldwide reserve base of approximately 6,000 tonnes of economically-viable indium. This figure has led to estimates suggesting that, at current consumption rates, there is only 13 years' supply of indium left. However, such estimates are called alarmist and scaremongering by some. 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.
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, which is 40 times greater than current indium mining rates.
On the other hand, replacements for indium tin oxide are already on the horizon. According to recent research, mass production of transparent conductors made from graphene, a modification of the virtually inexhaustible element carbon discovered in 2004, may be just years away.
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. For example, an anhydrous indium trichloride (InCl3) is quite toxic, while indium phosphide (InP) is both toxic and a suspected carcinogen.
See also
Indium compounds
Footnotes
Notations
External links
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