Iridium

Iridium is a chemical element classified as a Transition metals, and known by the chemical symbol Ir. It is perhaps best known for its extraordinary density and high melting point. It is the second densest element after Osmium, melting only at an incredible 2447 °C.

A majority of people do not even realize how many uses it offers. The element can be found in simple, everyday materials such as pens and jewelry. However, Iridium is rarely found in its pure substance. It is found mainly in alloys and acts as a hardening agent. All in all, scientists have Iridium to thank because it has brought forth chemical advancements ever since its discovery in 1803. Its stability is outstanding when combined with other elements.

Properties
As a metal of the Platinum group, Iridium is hard, lustrous and brittle. It is the second densest element after Osmium. It is a silver-white metal with a yellowish cast and very low toxicity and has a face centered cubic structure. Its density is 22.65 grams per cubic centimeter with an atomic radius of 135.7 pm.

Iridium contains seventy-seven protons, 77 electrons. It is most famous for its resistance against acid attacks, making it a corrosion resistant metal. Unfortunately, Iridium is not completely indestructible. When it comes to affecting this particular element, heat is an essential factor. At red heat (the temperature or state of something so hot that it emits red light), fluorine and chlorine have the ability to attack the element. It can also dissolve in hydrochloric acids with sodium perchlorate when intense heat is added. Under high temperatures, Iridium can react with Oxygen in the air and oxidizes. It can also react greatly with halogens, thus creating Iridium trihalides. At room temperature, Iridium remains a solid and is considered chemically unreactive at SATP (Standard Ambient of Temperature and Pressure). However, at high temperatures, it reacts vigorously. Iridium’s ductility also increases, resulting in the ability to shape it.

Occurrences
Iridium rarely occurs in nature. Its abundance in the earth’s crust is .4 parts per billion by weight and, in the solary system at 2 parts per billion by weight. The element is usually found, however, in natural alloys. These alloys normally contain Iridium mixed with Platinum and Osmium (or any other Platinum group metal) and can be found in alluvial deposits. Examples of those alloys are Iridosmine, Platiniridium, and Aurosmiridium.

Ores that contain iridium can be found in South Africa, Alaska, Myanmar, Russia, and Australia. Of all these areas, South Africa is considered Iridium’s major producer. Although the amount of Iridium on earth is quite small, the element can be found in sources beyond the earth's atmosphere. Asteroids and meteors, such as the Iron meteors, contain three parts per billion of Iridium by weight. The more stony meteorites have a slightly smaller concentration of .64 per million. Meteors and asteroids contain more Iridium than the earth's crust.

Uses
Since pure Iridium is very rare in nature, its principal use is usually in alloys (especially Platinum alloys). For example, combined with Osmium, Iridium forms an alloy that is found in pen tips and compass bearings. Some surgical pins and jewelry are made of alloys containing Iridium as well. Being the second densest metal, it also acts as a hardening agent for certain elements when combined. Because Iridium is extremely corrosive and chemical attack resistant, it is used in electrical contacts such as sparkplugs and electrical wires. It is also used in crucibles and other instruments that deal with high temperatures.

Iridium plays a significant role in advancements of modern day science and everyday life. It can reach expensive prices and is used only for special purposes. The International Standard Kilogram bar is made of a platinum alloy, 90% Platinum and 10% Iridium. In 1960, the same alloy was used in the standard meter bar. Iridium metal is also being successfully used as catalysts that capture sunlight and convert it into chemical energy (similar to that of photosynthesis). Utilizing Iridium, scientists have been able to find a way to cause artificial photosynthesis to occur.

History
Smithson Tennant made a huge discovery in London in 1803. While dissolving Platinum in aqua regia (a mixture of nitric acid and hydrochloric acid) a black residue, thought to be graphite at first, remained every time. This residue was eventually discovered to be the element Iridium combined with Osmium. The name Iridium is derived from the Greek word for rainbow, Iris, because of its variety of colors.

While Tennant did discover Iridium, Antoine Fourcroy, Louis Vanquelin, and Hippolyte Collet-Descotils were going through the same steps as Tennant in France. They utilized aqua regia and observed the black residue left from the native Platinum as well. Unlike Fourcroy, Vanquelin, and Collet-Dscotils, Tennant additionally discovered that diamonds were composed of pure carbon.

Humphrey Davy, shortly after Iridium’s discovery in 1803, discovered that Iridium actually did have the ability to be melted. It melted when exposed to the powerful current run by large batteries. A powerful source had to be used to melt the “indestructible” Iridium.

Video
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