It is, however, in FPDs—whether liquid crystal displays (LCDs), plasma display panels (PDPs) or screens employing OLEDs (organic light emitting diodes)—that indium finds its primary application.
Indium-tin oxide (ITO)—by weight 90 percent In2O3, 10 percent SnO2—when deposited (by evaporation, vapor deposition or by using a sputtering target) as a thin film on either clear glass or plastic becomes, typically, a transparent electrical conductor.
As such, ITO thin films are found in the LCDs used in, among other places, TVs, cellphones, tablets and computers. They are also still used to make the touch screen cathode ray tubes (CRTs) found, e.g., in some banks’ ATMs, although these are slowly being phased out. And since ITO is good for both de-icing and de-misting, thin films of it are also applied both to car and aircraft windshields.
In addition to having both the highest optical transparency and lowest electrical resistance, ITO thin films are:
- Stable and long-lived
- Accurately and quickly etched
- When applied by physical vapor deposition (PVD), uniform over wide areas—especially important on such appliances as large-screen TVs
No Indium Shortage
Whatever you might read (or hear) to the contrary, there is plenty of indium around. In fact, in relative terms, it is three times more abundant than its look-alike silver. So when you see pieces like touch-and-go tablet and computer screens published, e.g., by the BBC on March 8, 2012, treat them with the skepticism they deserve. When we first looked at the metal back in December 2009, a study undertaken by Indium Corp. (its first such) indicated that Western world indium reserves (“proven and probable, measured and indicated, and inferred”) in “identified base metal mines” were some 26,000 tons, with combined reserves in China and the former Soviet Union amounting to some 23,000 tons.
Their latest such study, undertaken in 2012, “concluded that there were approximately 30,000 tonnes of indium reserves contained in zinc mines in the west.” This is some 15 percent more than first estimated for the West alone. (The figure for China, Russia and the former CIS remains unchanged.) And this does not even address the fact that indium is also to be found in copper, iron, lead, silver and tin ores.
A figure for global indium reserves of only some 6,000 tonnes should, therefore, be treated with some caution, even disbelief.
Using feedstock either produced domestically or imported from abroad, China is the world’s largest refiner of “primary” indium, closely followed (according to figures from the U.S. Geological Survey (USGS)) by Canada, Japan and Korea.
Estimated Global Refinery Production 2008-2012 (Tonnes)