Introduction
Many believe that a colossal asteroid collision about 65 million years ago left behind a distinctive layer rich in iridium, a rare and precious element. This event is often linked to the mass extinction of the dinosaurs. While some consider this a myth, iridium’s scarcity and unique properties make it a fascinating subject of scientific study. In this article, we explore whether iridium is magnetic, its electrical conductivity, radioactivity, natural occurrence, and various applications.
Is Iridium Magnetic or Non-magnetic?
Iridium is classified as a paramagnetic metal, which means it exhibits a weak attraction to magnetic fields but is primarily known for its tendency to repel magnets at both poles. This behavior is due to the presence of unpaired electrons in its atomic structure, specifically three of the nine valence electrons that are unpaired. These unpaired electrons generate a magnetic moment through their orbital motion and intrinsic spin, producing a subtle magnetic response when exposed to an external magnetic field. Like most transition metals, iridium displays paramagnetic properties, which increase with the number of unpaired electrons. As a member of the platinum group metals, iridium shares similar magnetic characteristics, placing it between osmium and platinum on the periodic table. Its position in period six and group nine underscores its classification within the platinum metals family.
Does Iridium Conduct Electricity?
Iridium is an excellent conductor of electricity, making it a valuable component in various electrical and electronic devices. Its high electrical conductivity stems from its atomic structure, which allows multiple free electrons to move rapidly through its face-centered cubic (FCC) crystal lattice. These free electrons facilitate efficient electrical current flow. When an electric field interacts with iridium, the electrons respond by pushing against each other, enabling the passage of electric charge. The FCC crystal structure significantly contributes to this high conductivity, as it provides a uniform, closely packed framework for electron mobility.
Watch the video below to understand the Face-Centered Cubic Crystal System (FCC) – Bravais Lattice
Is Iridium Radioactive?
While iridium is largely stable in its natural state, it can exist in radioactive forms under specific conditions. Naturally occurring iridium comprises primarily two stable isotopes: iridium-193 (about 62.7%) and iridium-191 (approximately 37.3%), both of which are non-radioactive. However, there are about ten known radioactive isotopes of iridium, with iridium-192 being the most notable due to its relatively short half-life of approximately 74 days. This isotope is artificially produced by bombarding stable iridium-191 with neutrons in a nuclear reactor, transforming it into iridium-192.
Iridium-192 decays by emitting gamma rays and beta particles, making it useful in medical and industrial applications despite its radioactivity. Its applications include:
- Use in brachytherapy for cancer treatment.
- Non-destructive testing (NDT) for industrial quality control.
- As a radiotracer in the oil industry for tracing flow paths.
- Medical implants, such as in head and breast cancer treatments.
Where is Iridium Found?
Pure iridium rarely occurs naturally in its elemental form. Instead, it is predominantly found embedded within alloys with noble metals such as platinum and osmium, often associated with volcanic activity. The Earth’s crust contains only trace amounts of iridium, but meteorites and extraterrestrial materials tend to be richer sources. Commercially, iridium is obtained as a byproduct during the refining of nickel, copper, and platinum group metals. Countries with significant iridium deposits include Australia, Brazil, Myanmar (Burma), and particularly South Africa, which is the primary producer of mined iridium.
Historically, iridium was discovered in 1803 by Smithson Tennant while analyzing residues left after dissolving platinum ores in aqua regia. He identified iridium as a distinct element after processing the residues with acids and alkalis. Today, iridium is produced and processed into various forms for industrial use.
Forms and Commercial Products of Iridium
- Discs: Cast into flat discs for use in scientific instruments and high-precision applications.
- Granules: Ground into small particles used in paints, coatings, and specialized manufacturing.
- Wire: Fabricated into fine wires for jewelry, electrical contacts, and thermocouples.
- Sheets or Slabs: Flat, thin pieces used in electronics, industrial processes, and scientific research.
- Powders: Utilized in chemical synthesis, glass manufacturing, and water treatment, though it is costly to produce.
- Pellets: Used in medical radiation sources and jewelry applications.
Properties of Iridium
Iridium is a dense, hard, and brittle transition metal with the symbol Ir and atomic number 77. Its physical and chemical properties are as follows:
| Physical | Iridium appears as a shiny, silvery-white metal. When alloyed with other metals, it retains a metallic luster. It is notable for its high density of 22.56 g/cm3. Its melting point is approximately 4,436°F (2,446°C), and it boils at around 8,002°F (4,428°C). Iridium is hard and brittle, making it resistant to deformation but challenging to machine. It exhibits high electrical conductivity, suitable for electrical contacts and high-temperature applications. |
| Chemical | Iridium is highly resistant to corrosion and does not react readily with water or most acids, including aqua regia. It reacts with cyanide salts in the presence of oxygen and forms brightly colored salts with various acids. When heated in air, iridium forms iridium (IV) oxide, which is a stable, insoluble compound. It also reacts with fluorine gas at high temperatures to produce iridium hexafluoride, a highly corrosive compound. Iridium’s chemical stability makes it ideal for demanding chemical environments. |
Major Uses of Iridium
The etymology of ‘iridium’ traces back to the Greek word “iris,” meaning rainbow, referring to its colorful salts. Although rare and expensive, iridium’s unique properties make it valuable in specialized applications:
- As an antiferromagnetic layer in magnetic storage devices due to its stability at high temperatures.
- Manufacturing of durable pen tips, compass bearings, surgical pins, and pivots in alloys with osmium.
- In the creation of standard meter bars, typically composed of 10% iridium and 90% platinum.
- Production of high-performance spark plugs for aircraft engines, leveraging its high melting point and durability.
- Fabricating crucibles and containers capable of withstanding extreme temperatures in metallurgy and scientific experiments.
- In the manufacturing of LED panels and backlit displays for electronic devices like smartphones and tablets.
- As a component in the chloralkali process, crucial for chlorine production.
- Utilized in jewelry, where only small amounts are needed to produce long-lasting, corrosion-resistant pieces due to its scarcity and cost.
Conclusion
Iridium’s unpaired electrons confer paramagnetic properties, with a tendency to weakly repel magnets while also exhibiting slight attraction. Its face-centered cubic crystal structure allows free electrons to traverse efficiently, facilitating high electrical conductivity. Despite its stability, man-made radioactive isotopes like iridium-192 are created through nuclear reactions for medical and industrial purposes. Understanding iridium’s properties and applications underscores its significance as a rare, valuable transition metal with extraordinary resilience and functionality.
Frequently Asked Questions
Is iridium harmful to humans?
In its metallic form, iridium is generally non-toxic because it does not react with biological tissues. However, handling iridium powder can be hazardous due to its irritant and flammable nature. Most iridium compounds are insoluble, making absorption into the body difficult, but exposure to radioactive iridium-192 poses serious health risks, including increased cancer risk. External radiation exposure can cause burns, radiation sickness, or even fatal injuries.
How do you identify iridium?
Chemical identification of iridium is complex; advanced techniques such as X-ray fluorescence (XRF) spectroscopy or inductively coupled plasma (ICP) analysis are typically employed. A more involved method involves melting powdered iridium in zinc and subsequently dissolving it in hydrochloric acid, followed by ICP testing of the solution after boiling off excess acids.
Does iridium react with water?
Under normal conditions, iridium does not react with water or moisture. It also remains unreactive with most acids, including aqua regia, unless heated. When heated in air, iridium forms iridium (IV) oxide. It can react with salts like potassium and sodium cyanide at high temperatures, and when combined with fluorine gas, it forms highly corrosive iridium hexafluoride. Additionally, iridium reacts with halogen elements to form trihalides.
How can you separate gold from iridium?
One method involves alloying iridium with silver, typically in a ratio of three parts iridium to one part silver, then melting the mixture in large crucibles made of black lead. Due to its higher density, iridium granules sink to the bottom, allowing for separation from gold, which remains above or can be extracted through further refining processes.