Iridium Today And Yesterday

Iridium was unknown until it was separated from platinum by Smithson Tennant in 1803. He and his associate, William Hyde Wollaston, had been working with platinum for some time, attempting to find out whether it had properties that could be used in industry. As he reduced the platinum time and again, Tennant found that a residue was left after his final reduction. When this residue was dissolved in a solution of hydrochloric acid, it produced a lovely rainbow of colors. Tennant named the metal iridium, after the Greek goddess Iris, the god's messenger and goddess of rainbows. Iridium is one of rarest elements on earth, but is still more common than its sister noble metal, rhodium.

This noble metal was found to be extremely hard, resistant to corrosion, and able to withstand high heat. Widespread application of iridium into industry proved to be impossible given the limited resources at the time, although it was incorporated into the nibs of fountain pens to make them more durable, as was the case with rhodium. Iridium also found a use, when combined with platinum, in the touch holes of cannons.

Not only is iridium extremely hard, the fact that its melting point is 4,424 F (2410 C) has made it valuable in many industrial and scientific applications. However, although it is hard, heat resistant, and resistant to corrosion by chemicals, it is extremely brittle and has almost no ductility. Generally, when iridium is used, it is not used in a solid form, but rather as a powder. Other than pen nibs and touch holes in cannons, there was little practical use for iridium until the latter part of the 19th century when iridium contributed to the invention of the incandescent light bulb. Thomas Edison, a young telegraph operator in 1863, discovered some batteries that had been used by the telegraph company then discarded. He was able to remove the platinum from the old batteries and use an alloy of iridium and platinum to make the filaments for his first light bulbs. The excellent heat resistance of iridium made it perfect for this use.

The early decades of the 20th century were also important for this metal when a German researcher made thermocouples using iridium that were capable of withstanding temperatures in excess of 2,000 C. Thermocouples are an important part of any industry that must operate using extreme amounts of heat, such as foundries or glass works. The ability of iridium and its alloys to withstand high temperatures has also made it valuable when producing parts for spacecraft, where deformation by extreme heat or corrosion would have serious consequences. Iridium is also used to fabricate parts for airplane engines, where durability and dependability are necessary.

Part of the platinum group of metals, iridium is often refined out of copper and nickel ore when these are processed. By a technique called electro-refining of the above common metals, iridium, platinum, rhodium, and gold will often settle out at the bottom of the refining chamber in what is called anode mud.

The synthetic fiber industry is dependent upon iridium spinnerets to produce such fabric as nylon. These spinnerets are long lasting, and help to keep the price of manufacture down. As the price of iridium, as with all the platinum derivatives, is extremely volatile, the ability of machinery made with iridium to be long lasting is extremely important.

Over the last several decades, computers have come to dominate nearly every facet of our lives. Most of us have at least one computer, either for leisure or working at home, and companies of all sizes make use of them for myriad tasks. And, once again, iridium has proven itself to be important in the computer industry. High quality, pure crystals are needed to make the semiconductors used not only in computers, but also in cell phones, solar cells, light emitting diodes, and transistors, among other things. These crystals are formed from silicon with the addition of various chemicals, such as boron. As a great deal of heat is needed for the production of the crystals, it is essential that the crucible in which they are formed will be able to retain its integrity during the process. Iridium crucibles are generally the preferred receptacle for the task, as these crucibles are able to withstand temperatures up to 2,000 C without problem and can resist corrosion from the materials being melted.

Another use for iridium has been found in the x-ray field, especially as concerns x-ray telescopes. As part of the United States space program, this time in collaboration with India, the Chandra X-ray Observatory has been sent into space in 1999. The mirrors for the x-ray telescope in the Chandra Observatory were plated with iridium, in part because of the superior reflective power of the metal and also for durability. Since its launch, the observatory has returned data relating to super novae, black holes, neutron stars, and dark matter, all of which would have been impossible or difficult without the use of the iridium coating on the telescope mirrors.