The Nature Of The Metal
As with a number of the strategic metals, indium was not only quite a late addition to the table, it was also not used for much until the early part of this last century. The metal was only “discovered” in 1863 by the duo of German chemists Ferdinand Reich and Hieronymous Richter. It is appropriately named after the indigo blue line that appears when the element is subjected to spectroscopic analysis.
As for its physical characteristics, the metal is a shiny silver color and very soft. Like some of the other strategic metals such as gallium, indium is solid at room temperature but has a relatively low melting point: 313.88 °F (156.6 °C). (Indeed, when indium is alloyed with gallium in the proportions indium 24 percent and gallium 76 percent, the resulting eutectic alloy is liquid at room temperature—quite useful in situations when you don’t want to use a toxic metal like mercury.)
Although it had already been used to coat mirrors (equal in quality to those made with a coating of silver), indium really only came into its element during World War II, when it was used to coat bearings in fighter aircraft. But, in the last 20-30 years, commercial use of indium has taken off, particularly with the development of flat-panel displays, semiconductors and photovoltaic cells. Production of the metal, too, has increased over this period: In 1989, the U.S. Geological Survey estimated indium refinery production was 115 tonnes; in 2008, that figure had risen to 568 tonnes.
Whence The Indium
With an abundance in the Earth’s continental crust of 0.05 parts per million (ppm) and its oceanic crust of 0.072 ppm, indium is somewhat more abundant than its lookalike, silver. However, since it does not occur in the same concentrations as silver, indium is never mined in its own right.
Instead, like many other strategic and minor metals, indium is mined as a by-product of the production of other ore. Commercially, “virgin” indium is extracted primarily as a by-product of zinc and tin mining. However, it can be extracted also as a by-product from the production of other metals, including lead, copper and, less extensively, bismuth, cadmium and silver.
Even when it occurs most liberally, indium is an impurity whose concentration can be measured only in ppm. But the technology used to extract the metal has improved so much that it can now be produced from “concentrations as little as 100 ppm of indium per ton material.” However, extraction rates remain medium: Historically, less than 20 percent of the indium content in concentrates could be extracted, and even with modern technological improvements, producers still can only extract 30 percent of the “1,500 mt of indium mined every year worldwide,” says the Indium Corporation of Utica, N.Y.
As far as refining indium is concerned, according to the USGS, China is the world’s largest refiner of the metal, using feedstock either produced domestically or imported from abroad.
Indeed, China, followed by Japan, has held this position for at least the last five years.
Secondary indium, of which around twice as much as the virgin metal is produced each year, is sourced predominantly from recycling the indium-tin oxide [ITO] sputtering targets used to make liquid crystal display [LCD] flat-panel screens. The figure given by the Indium Corporation for such reclaimed indium is some 1,000 tonnes per year.
Recycling takes place mainly in China, Japan and Korea where, according to the USGS, “ITO production and sputtering take place.”
The Many Uses of Indium
By far the major use of indium is in flat-panel displays and, in particular, LCDs. After that, its most important uses are in various compounds, alloys and semiconductors, respectively.
Aside from its use in thin films, especially in the ITO form, indium is important in a number of other applications, including:
Solder: Indium is an important ingredient in lead-free solders, as it improves the solder’s resistance to thermal fatigue and lowers its tendency to crack. Since lead-based solder has been banned in many countries, indium has been found increasingly useful for this purpose.
Low-Temperature Alloys: With its low melting point, indium in alloy form can be used to hold high-value items while they are being worked on; for example, turbine blades, or glass lenses as they’re being ground. The alloy can then be melted away at a low temperature with no resulting damage to the item it held.
Lighting: Indium can be used as a light filter in low-pressure sodium vapor lamps.
Nuclear Control Rods: In nuclear reactors, there are four general methods of controlling either the power or flux of neutrons. In addition to the temporary addition or removal of fuel, and using a moderator or reflector, a neutron absorber can also be used. When indium is alloyed with silver and cadmium (silver: 80 percent, indium: 15 percent, cadmium: 5 percent), the resulting material serves as an effective neutron absorber, particularly in pressurized water reactors.
The films are also used to make touch screens found on cell phones, tablet computers, and gambling machines in Las Vegas (and worldwide). ITO films are used to make self dimming rear view mirrors in automobiles, self darkening windows in new high-tech buildings, and in CIGS solar cells. And, since ITO can also generate heat when enough electricity is applied, it is used in aircraft cockpit windows as a high tech defroster, as well as being used by the military as an infra-red reflector on vehicle windows.
In addition to being both electrically conductive and optically transparent, thin films of ITO are ideal for the job as they are also:
- Both stable and long lived;
- Efficiently, rapidly and uniformly etched; and,
- Uniform over wide areas when applied by physical vapor deposition (PVD) using, for example, a sputtering target.
Of the world’s estimated indium reserves still in the ground, it has been estimated that of the indium in such concentrates, 30 percent is lost because it never reaches a smelter that can (or will) extract the metal. Of the remaining 70 percent, the final average rate of extraction of the metal is only around 50 percent.
Prospects For Indium
For the last couple of decades, indium has experienced not only some extreme pricing volatility, but also, at times, various supply concerns. These last have in turn affected the metal’s price. Over the last 15 years in particular, we’ve seen some significant swings in pricing.
Raw Indium Price for 100kg (220 pound) Manufacturing Quantities:
1995 – November 2009 (US$/Kg)
In particular, recent supply concerns have focused on China. In the past couple of years, various revisions in export quotas and tariffs have led certain major consumers of indium, especially Japan, to reach out to other sources of the metal to secure supply predictability.
In 2008, in addition to the effects from the global economic downturn, matters were not made any easier for Chinese producers when the government canceled “the tolling trade of indium metal.”
According to sources, “the output of reclaimed indium ingot fell from 120tpy to zero,” and the major Chinese recycler of indium had to set up business in neighboring Laos to compensate for the ban. Various other Chinese indium producers have also been affected by further government moves to protect the environment—moves which look set to continue.
One interesting side effect of the Chinese authorities’ actions has been the significant smuggling of indium from China to Japan. From January to October 2008 alone, the differences between Japanese and Chinese statistics appear to indicate that some 21.2 tonnes of indium were smuggled into Japan from China. The smuggled amount accounted for some 41.2 percent of the total volume of the metal coming into the country from China.
While it is understandable that supply concerns may be leading certain major indium users to seek substitutes for ITO, it is far less likely that the price of the metal itself has that much to do with such a decision. It has been pointed out that, “In terms of the cost structure of an LCD panel, the cost of ITO per panel is insignificant. [At a price of $600/kg], the cost of indium that is applied to a 32″ LCD panel would be US$0.55.”
Concerns about neither pricing nor supply appear to be affecting too greatly some of those companies that are currently looking to use indium in new and innovative ways.
In the world of solar cells, companies producing thin films using copper, indium, gallium and selenium (CIGS) are still betting that their product will win out against not only traditional crystalline solar panels, but also thin films using cadmium telluride (CdTe) and silicon. And for those involved in photovoltaics, the stakes appear to be quite significant. According to an October 2009 article in The Economist, “…thin film’s share of the market has continued to rise: it is now almost half, compared with just 10% in 2004.”
Researchers at Purdue University in Indiana are developing a new type of transistor (called a fin-type field effect transistor—finFET—after its finlike, as opposed to flat, design) using indium, which, if it works, could lead to mediumer, faster computer chips. Using indium gallium arsenide instead of the more traditional silicon, the team at Purdue claims to be the first to have produced such a new transistor which is a potential replacement for aging silicon technology used in computer CPUs.
For those involved in chips used in ultra high speed fiber-optic communications, photonic integrated circuits [PICs] appear extremely promising. Indium phosphide (InP) can be used to create Microdisk Lasers. PICs made of the stuff, therefore, are ideal for use in fiber-optic telecoms networks. The newest such chips have been loaded with as many as 200 devices and can transmit data at speeds of up to 1.6 terabits per second. And when it comes to compound semiconductors, an article in The Financial Times in early 2009, “Intel has been actively experimenting with compound semiconductor technology at its research labs in Santa Clara, California. It has talked about recent breakthroughs in bonding compound semiconductor-based chips onto silicon chips, using indium antimonide (InSb) and indium gallium arsenide (InGaAs).”