Indium

Indium (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 wet glass.

One unusual property of indium is that its most common 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 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:

• For manufacture of low-melting-temperature liquid at room temperature.
• Some indium compounds such as indium antimonide, semiconductors with useful properties.
• Component required for synthesis of the semiconductor Copper indium gallium selenide (CIGS), which is used for the manufacture of thin film solar cells.
• Used in MOVPE) technology.
• The ultrapure 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 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 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 thallium. Richter went on to isolate the metal in 1867.

Occurrence and consumption

  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 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 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.

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 carcinogen.