Is Iridium Flammable? (A 5-point guide)

This article will answer the following question: “Is Iridium Flammable?”. We will show what iridium is, where it comes from, what is it used for, and rather it can catch fire or not.

Is Iridium Flammable?

The best answer is: it depends. Iridium can suffer combustion if has the right conditions to do so, but only in powder form. Iridium alloys and pure iridium can’t ignite if we’re talking about a metal bar or pellets. It only becomes flammable if has a high surface area.

What is iridium?

Iridium is a chemical element that can be found in the periodic table with the symbol Ir. It is a tough, friable, and silver-white metal, somewhat similar to platinum.

The metal presents one of the highest densities of all natural compounds, losing only to Osmium. The material is one of the most corrosion-resistant materials and less reactive ones.

It can, although, react more easily when in powder form, even with oxygen. Only a few molten salts and halogens are corrosive enough to react with a bar of iridium, even in temperatures high as 2000ºC.

The abundance of iridium is really low, so it’s not easy to come across it naturally. Normally, the metal is mixed with other ores in small quantities, and only 3 tonnes are mined globally each year.

Iridium was discovered in the early’s 1800, as an impurity in natural platinum, by a Cambridge chemistry professor named Smithson Tennant. He named the metal after Iris, the Greek goddess of the rainbow, thanks to the iridescent colors that iridium salts present.

The British chemist tried to dissolve platinum using a very acidic solution called aqua regia (a mixture of nitric and hydrochloric acid). 

But he realized there was a black residue remaining, and ended up discovering iridium and osmium, two metals with very low reactivity.

Is iridium rare?

Iridium is one of the rarest elements in the Earth’s crust. Only 0.0000001% of the ground is made of the metal. But the ground is only part of our planet.

It is so rare that whenever a big amount of iridium is found naturally, it means that the source is not from our planet. This means that the metal must have come from an extraterrestrial source.

Iridium is a common element in outer space. It can be found in meteors, so every time lots of it is found somewhere on Earth, we know that there was a meteor impact.

One of the evidences that support the idea that the dinosaurs were extinct by a meteor is the Chicxulub crater, a 180km (110 miles) long hole, with a depth of 20km. The iridium concentration there was about 160 times above the background level.

At the same time, iridium is only so rare in Earth’s crust. There’s more of it deep down the planet’s core. This happens because Iridium is very dense and has an affinity to bond with iron atoms (is siderophilic). 

So when our planet was forming (around 4.5 billion years ago), iridium melted and bonded with iron. The surface of the planet eventually cooled down, and iridium stayed in Earth’s core. Life started as microorganisms around 1 billion years later.

What is iridium used for?

Iridium has many industrial, medical, and scientific applications.

Alloys made by adding a bit of iridium present much higher hardness and corrosion resistance. Most iridium applications are meant to create metals with special properties. Here’s a list:

  • Spinnerets crafting (a device used to craft some polymers by extruding a hot plastic mass through a small hole);
  • Compass bearings;
  • Aircraft engine parts;
  • Crucibles (a container that must endure high temperatures);
  • Catalysts in chemical reactions;
  • Radiography (using radioactive isotopes);
  • Cancer treatment (again, by using radioactive isotopes. In this case, it’s used a type of iridium that can be a source of gamma radiation);

Thanks to iridium anti-corrosion properties, the metal was used as a standard for the measuring of two important metrics: the meter and kilograms. This was effected between 1889 and 1960.

An iridium bar has the ability to sustain lots of chemical attacks, including oxidation with the air and other reactants. So it was safe to use it as a standard in the measure of length and mass.

What are the Iridium properties?

In this section, we will point out some important chemical, physical and overall properties of iridium atoms.

It’s the second most dense atom. Has a very high melting and boiling point

  • Appearance: silvery-white
  • Atomic number (Z): 77
  • Group (periodic table): 9
  • Period: 6
  • Electron config.: [Xe] 4f14 5d7 6s2
  • Electrons per shell: 2, 8, 18, 32, 15, 2
  • Phase at STP: solid
  • Melting point: 2446 °C, ​4435 °F
  • Boiling point: ​4130 °C, ​7466 °F
  • Density: 22.56 g/cm3
  • when liquid: 19 g/cm3
  • Heat of fusion: 41.12 kJ/mol
  • Heat of vaporization: 564 kJ/mol
  • Molar heat capacity: 25.10 J/(mol·K)

Iridium oxidation states and compounds

Iridium is one of the less reactive atoms in the periodic table, but it can still react and form new compounds if specific conditions are applied to it (normally, really high temperatures or strong reactants).

You can check some oxidation states and compounds in the list below:

−3[Ir(CO)3]3−
−1[Ir(CO)3(PPh3)]
0Ir4(CO)12
+1[Ir(CO)Cl(PPh3)2]
+2IrCp2
+3IrCl3
+4IrO2
+5Ir4F20
+6IrF6
+7[(η2-O2)IrO2]+
+8IrO4
+9[IrO4]+

Can iridium catch fire?

We spoke about how iridium is a corrosion-resistant material and can endure many kinds of attacks. But can it catch fire? Fire is the result of a chemical reaction, in which iridium can participate.

Although, it depends on how available the metal molecules are. Iridium as a metal bar or in an allow will not present any flammability, because it’s not reactive. Hence why it was used as a standard for the measure of 1 meter and 1 kilogram.

But finely divided iridium is flammable, similar to iron. Its molecules can react with the air’s oxygen to produce iridium oxides in the right conditions, and this reaction liberates heat.

This is essentially how combustion happens. A material (fuel) suffers ignition, oxidation (bonding with oxygen) starts and its particles liberate heat. This heat creates a chain reaction, and the fuel burns until runs out.

But not all forms of heat are fires, and not all burnings have flames.

When wood burns in a fireplace, the fire sustains itself as long as it has oxygen, heat, and fuel available. These 3 are the ingredients for every fire and the components of the fire triangle below.

Fuels are always organic stuff. Every time we burn something we are actually using the molecules of something that once lived. We are using their carbon and hydrogens to produce energy.

But this doesn’t mean that other things cannot provide heat upon burning, as happens with iridium, iron, and a few other metals.

Is iridium safe?

The best way to discover a material’s safety is to assess its Safety Data Sheets. Overall, we can say that Iridium is one of the safest metals, as long as it’s not in powder form.

When finely divided it is a flammable solid. It can also cause serious eye irritation and present long-lasting harmful effects to aquatic life, being hazardous to the environment in the long term.

By evaluating its safety data sheets we can have a better understanding of how flammable iridium products are. Here we list a few:

  • Iridium Black: Considered a highly flammable solid. Also presents health hazards and some reactivity. Metal oxide fumes can be released in case of a fire.
  • Iridium powder 99.9%: also a highly flammable solid, with potential health effects. This material can be considered pyrophoric at normal or slightly elevated temperatures.
  • Iridium (pieces): made for exterior surface coating. According to the manufacturer, the product presents no flammability and no other relevant health hazard.
  • Iridium(IV) oxide: this iridium oxide does not present any flammability as expected, but it is considered very toxic and shouldn’t be left anywhere near a fire or intense heat even so.

Conclusion

Iridium can be considered flammable or highly flammable but it depends on how big its particles are. Iridium bars and pieces present no flammability because can’t suffer combustion, but finely divided, powder and dust forms can even be considered pyrophoric.

Frequently Asked Questions (FAQS): Is Iridium Flammable?

is iridium a metal?

Iridium is a hard and silvery metal. It has the second largest density and a high melting point. Iridium is the most corrosion-resistant natural material known. Iridium belongs to the same group as Cobalt in the periodic table.

is iridium magnetic?

Iridium can be weakly attracted to a magnet but does present some level of magnetism.

The oxides of iridium lose their magnetization when pressure is applied to them. Science is still trying to figure out how these properties exactly work.

Is iridium toxic?

It presents some level of toxicity to humans and the environment but only when its particles are very thin, like in a dust/ powder form. Otherwise, the metal is not much reactive and plays no role in live systems.

Citations

https://researchoutreach.org/articles/origin-life-conditions-sparked-life-earth/
https://en.wikipedia.org/wiki/Chicxulub_crater
https://en.wikipedia.org/wiki/History_of_Earth
https://en.wikipedia.org/wiki/Iridium
https://en.wikipedia.org/wiki/History_of_the_metre
https://pubchem.ncbi.nlm.nih.gov/compound/Iridium#section=GHS-Classification
https://www.rsc.org/periodic-table/element/77/iridium

http://www.chemspider.com/Chemical-Structure.22367.html

https://rsc.aux.eng.ufl.edu/_files/msds/2/Iridium.pdf
https://www.acialloys.com/wp-content/uploads/msds/ir.html
https://www.periodictable.one/element/77
https://www.mining-technology.com/analysis/five-most-expensive-metals-and-where-they-are-mined/#:~:text=Iridium,production%20of%20just%20three%20tonnes.
https://cpb-us-e2.wpmucdn.com/sites.utdallas.edu/dist/a/1208/files/2018/10/Ir-MSDS.pdf

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