Indium is one of the least abundant minerals on Earth, typically it is found associated with zinc minerals and iron, lead and copper ores. It is commercially produced as a by-product of zinc refining. Indium is a moderately toxic metal by inhalation and mildly toxic by ingestion. Indium is a soft, malleable metal with a brilliant lustre. The name Indium originates from the Indigo blue it shows in a spectroscope. It has the unusual property of remaining soft and workable at very low temperatures. Indium conforms to many irregular surfaces and has a characteristic “stickiness”. Indeed, when pure, it sticks strongly to itself or to other metals. This property makes it useful as a solder – it reduces the melting point of some solders, strengthens others, and prevents some solders from breaking down. Indium has been called a “metal vitamin” in alloys, which means that very small amounts of indium can make big changes in an alloy. Some aircraft parts are made of alloys that contain indium and it prevents them from reacting with oxygen in the air or wearing out. At higher temperatures, it combines with oxygen to form Indium Oxide, where it becomes a transparent conductive oxide. When applied as a thin coating onto glass or plastic films, it is both transparent to visible light as well as electrically conductive. It is actually Indium Tin Oxide or “ITO” which is applied in solar cells and flat panel displays (LCDs – liquid crystal displays). If coated onto aircraft or automotive windshields, it allows the glass to be electrically de-iced, reducing the air conditioning requirement. It has also been used to coat ball bearings in Formula 1 racing cars because of its low friction.
The availability of indium has been questioned since the demand has risen rapidly in recent years with the popularity of LCD televisions and computer monitors. Currently, increased recycling and manufacturing efficiency maintain a good balance between demand and supply.