Indium: bringing liquid-crystal displays into focus

Abstract

Introduction Indium is rare in the Earth’s crust. The continental crust contains an average of about 50 parts per billion of indium, whereas the oceanic crust contains about 72 parts per billion, which is similar to meteoritic abundances and comparable to the crustal abundance of silver. Indium minerals are rare in nature and only 12 indium minerals are known. In its elemental form, indium is a soft, lustrous, silver-white metal with a low melting point relative to other metals. It is ductile and malleable, even at temperatures approaching absolute zero, making it ideal for cryogenic applications. Indium was discovered in the mid-1800s by two German chemists who were investigating zinc ores from Freiberg, Saxony. They named it after the distinctive indigo-blue color observed in its emission spectrum. For years indium remained only a scientific curiosity and early applications of indium were few, but included manufacturing of light-emitting diodes and coatings for bearings used in aircraft engines. Indium-bearing nuclear control rods became more widely used in the 1970s, and today the major application of indium is in manufacturing liquid-crystal displays. Compared to more abundant industrial metals such as lead and zinc, information about the behavior and toxicity of indium in the environment is limited. However, many indium compounds have been proven to be toxic to animals.