Indium
Symbol: In
Atomic Number: 49
Atomic Mass: 114.818 amu (atomic mass units)
Melting Point: 156.61°C (429.76 K, 313.898°F)
Boiling Point: 2000.0°C (2273.15 K, 3632.0°F)
Number of Protons: 49
Number of Electrons: 49
Number of Neutrons: 66
Classification: Metal
Crystal Structure: Tetragonal
Density @ 293 K: 7.31 grams per cubic centimeter
Color: Silver/white
Indium was discovered in 1863, by two German scientists Ferdinand Reich and Hieronymus Theodor Richter. These two chemists were using spectroscopic analysis to look for the presence of the element thallium in zinc ores. They found an intense indigo colored band within the spectrum for the ore indicating the presence of an unknown element within the ore sample. This characteristic indigo colored band was used to give the element its name indium. They continued working on the element and were the first to isolate the pure metal.
Indium is a very soft metal with a high luster. When bent a sample of the pure metal produces a high pitched “scream”. It can wet glass, a property it shares with the element gallium. It can be used to make alloys with low melting points, an alloy containing 24% indium and 76% gallium is liquid at room temperature. The element has two naturally occurring isotopes indium-113 which is stable and indium-115 which has an extremely long half life of 441 trillion years. In addition over seventy man-made isotopes of indium have been identified. These man-made isotopes have half lives ranging from 150 nanoseconds to 49.51 days.
In addition to being obtained from zinc ores, indium is also found in the ores from which lead and copper are produced. It is as about as abundant as the element silver in the earth crust. Currently Canada is the major producer of indium for the world market.
Indium has a number of industrial uses. A coating of indium on the bearings of motors enables an even distribution of lubricating oils. Indium is used in the electronics industry to dope the element germanium to produce transistors. Other uses within the electronic industry include the production of photoconductors, photocells, rectifiers and thermistors. Its low melting point makes it useful in the production of solders.
Indium produces mirrors of a similar quality to those produced by silver when it is either plated on to metal or evaporated onto glass. These mirrors have an added advantage over the traditional silvered mirrors in that they resist being tarnished.
