Indium
Indium is a chemical element with the symbol In and atomic number 49. Indium is a malleable, blue-white metal. It is one of the least common elements in the Earths crust, and it is a fussy element that has no practical uses apart from traces in some very specialized alloys and materials. It melts at a comparatively low temperature of 156.6° Celsius, and is liquid in range up to 2000° Celsius.
Indium was discovered in 1863 by Ferdinand Reich and Hieronymous Theodor Richter, two German researchers. They were analysing the content of a zinc ore near Freiberg in central Germany called Zincblende, when the Indium was first noticed.
Indium is rarely found in its pure metallic form, and is usually located in sulfide ores in combination with zinc, tin and lead. Its major sources are zinc-lead ores and also recovered from sphalerite ore in which it replaces zinc in small amounts. In addition, indium is recovered from residues of copper, tin and lead refining processes. When zinc ore is processed, indium is one of several waste products.
Under protection from the atmosphere, metallic indium has an indefinite shelf life. In heavier atmospheric conditions, finely divided indium reacts very rapidly to form indium oxide. Indium oxide is a white powder and is largely used in the electronics industry to form indium tin oxide or ITO. ITO is a transparent thin-film coating used in many applications, such as plasma and LCD screens.
Indium is also used in alloys known as fusible alloys, alloyed also with bismuth, lead and tin. These alloys have a lower melting point and sprays as aerosols or foams. Other uses of indium include bearing materials, thin film components on glass, and solders for electronic materials.
Indium is trivial and found at an estimated concentration of about 0.25 milligrams per kilogram (mg/kg) in the Earths crust. The primary commercial production of indium from ore concentrates is undertaken by leaching and solvent extraction. Its derivatives are increasingly being used in the manufacture of a range of different products such as capacitors, transistors, and semiconductor devices. Despite its rarity, indium is one of the most overlooked and underestimated of all metals, and its current and future uses are yet to be fully championed.
Recent developments in the technology have led to a major rise in indium applications and its production. Today, approximately 15,000 to 20,000 tonnes of indium is produced worldwide primarily in the form of indium oxide, and later chemically reduced to the metal. Indium is a silvery-white metal and has some of the highest thermal and electrical conductivities of any metal. It is thought that its properties make it more suitable for use in a number of consumer product applications.
The main source of commercial indium is zinc smelting by-products and residues, derived by leaching of zinc and concentration of indium through solvent extraction. This is the most economical and environment friendly way to produce indium, with the vast majority of indium now produced in this way. The global demand of indium is largely cyclical and is determined by the level of technological advancement, with the application of indium in the technology industry having the most significant impact in the demand.
Indium is a relatively rare element and will continue to remain so in the future, with current estimates indicating that it is only produced in quantity equal to approximately 0.2 ppm in the Earths crust. As a result, its supply is highly dependent on the price for which it is sold, and it is therefore very much in demand on the global market. Despite its rarity and the cost of production, its current and future applications make it an important element to study and understand.
