Indium was discovered in 1863 by Ferdinand Reich and Hieronymus Richter in Freiberg, Germany.
Indium is a soft, silvery-white metal and has one of the longest liquid ranges of all the other elements. It is stable in air and water, but dissolves in acids.
It occurs in a zinc blend and some iron ores and is obtained from zinc flue dust. Naturally occurring indium consists of 4.23% indium 113 (stable) and 95.77% indium 115, (half-life 14 Gigayears).
With only 3 electrons in its valency shell (electronic configuration 5s25p1), indium is an electron acceptor and is used to dope pure germanium and silicon. It forms stable indium (I)/(II)/(III) compounds.
The metal is tetragonal with a distorted close-packed structure. Small additions of this metal into gold and platinum strengthen the main metal without detracting from their other properties.
Relative Atomic Mass
Think of a flat screen such as you might see at an airport check-in desk, in designer corporate headquarters or, even perhaps the screen on which you are now viewing this website. You have now reached the locations where you may find the latest and most dynamic uses of Indium!
So, to understand this market a little bit, let us take a look at exactly what makes it possible to dispense with the cathode-ray tube, its bulky transport, and that space-consuming heavy object eating up your desk.
To actually look where Indium comes from, you must look at where another metal – Zinc – is mined, concentrated and refined. It is here at the refinery stage that Indium is recovered from either flue dusts, slags & lead drosses produced as a by product of electrolytic zinc plant residues.
It is easier to understand the principle behind a flat screen and how it became a commercial reality by looking at how the two main problems confronting researchers had to be solved – that is to say, how to create a circuit without wire. It was to do this that a rather special material was required – and scientists alighted on an oxide of Indium.
Leading producers of Zinc in Belgium, France, China, Peru, Canada and Russia cast either 1 kgs or 3 kgs ingots of 4N’s (99.99% purity) or greater which are the staple of our minor metal trade.
Indium oxide is doped with tin to form Indium Tin Oxide (ITO). The two absolutely essential properties of ITO are that it is the only material which, in the form of thin films (typically only one hundreth of a micron thick!) has a very high electrical conductivity and is nearly completely transparent over the whole visible spectrum – ie it is colour-neutral. This can consequently be used in touchscreens.
Lipmann Walton & Co Ltd is proud to specialise in this part of the supply chain, taking its supply mainly from the CIS (Commonwealth of Independent States). This, we deliver to manufacturers worldwide who create the Indium Tin Oxide (ITO) sputtering targets, which are then used to coat onto the flat screens or onto transparent glass and plastic components to give antistatic or antireflective coatings.
From this thin coated layer, circiuts are etched to form minute electrodes feeding current to the indiviual pixels of the liquid crystal display (LCD). Current flowing between these electrodes and a further layer of ITO on the reverse side of the display controls intensity and colour to produce an image.
The world usage of Indium has risen to circa 700-750 metric tons per year (from circa 300-350 mt/y in 2001) and is still rising. Other more traditional uses include the mature industry of low melting point solders used in electronics and coatings for shell bearings in the automotive industry. (It is only thanks to Indium that your may drive away your brand new car away from the showroom at 60 mph – always abiding by the speed limit of course – without the one time inconvenience of ‘running in’ which was the norm for vehicles of yesteryear.
But, as with so many other special metals, it is a long journey from mine to Microsoft…