Indium is a metallic element with the chemical symbol In, belonging to the group IIIA of the periodic table. It has an atomic number of 49 and a relative atomic mass of 114.8. Its melting point is 156.61°C, and its boiling point is 2060°C. It has a relative density of 7.31 g/cm³. Indium was discovered in 1863 by the German scientists Reich and Richter while studying sphalerite using spectroscopy. It is a silver-white metal with a slight bluish luster, characterized by its extremely soft texture, being easily scratched by fingernails, and exhibiting strong malleability and ductility, capable of being pressed into thin sheets. Metallic indium does not oxidize in air at room temperature. Indium is slightly radioactive, and thus contact with skin and ingestion should be avoided. It occurs in the Earth’s crust at a concentration of 1×10^(-5)%, although it exists in independent minerals such as copper indium sulfide (CuInS2), iron indium sulfide (FeInS4), and indium hydroxide (In(OH)3), but in very small quantities. Indium is mainly found in isomorphic substitution in sphalerite (with indium content ranging from 0.0001% to 0.1%), hematite, galena, and other polymetallic sulfide ores. Additionally, it is present in tin ores, wolframite, and common hornblende.
The industrial production of indium began in the early 1920s. In recent years, there has been a rapid growth in global demand for indium, increasing at a rate of 5-10% annually since 2003. Prior to 2008, global refined indium production had been increasing year by year; however, after 2008, due to intensified resource protection efforts by countries worldwide, the supply of indium gradually decreased.
As understanding and research on indium continue to deepen, it plays a significant role in various fields such as information technology, aerospace, energy, military industries, and healthcare. Particularly, in the manufacturing of flat panel displays, alloys, semiconductor data transmission, aerospace products, and solar cells, indium is of great importance. With the rapid development of the IT industry, the demand for various new types of liquid crystal displays such as laptops, televisions, and smartphones, as well as touchscreens and architectural materials requiring ITO (indium tin oxide) thin films or ITO glass, has been increasing. (ITO target production accounts for over 70% of global indium consumption), which significantly influences the market status of indium.
Due to the rapid development of the indium industry and the extremely limited global indium resources, countries have begun to strengthen their reserves of indium in recent years.