Is iron oxide flammable?

This article will answer the following question: “Is iron oxide flammable?”. We will discuss the nature of oxidized iron compounds, how fire happens and rather iron oxides can present flammability or not.

Is iron oxide flammable?

Iron oxides are not expected to be flammable. When pure iron burns it liberates iron oxides as byproducts, and the oxides can’t burn again. Some incomplete forms of oxide such as iron II may present some flammability, but only in a powder of wool form.

What is iron oxide?

Iron oxide is a chemical compound made of iron, oxygen, and sometimes, water. There are currently sixteen iron oxide forms known, each presenting its own uses and properties.

An iron atom can present itself in many oxidation states, which makes it suitable for creating different kinds of oxides.

Iron(III) (ferric) oxides are one of the three main species, which have the general chemical formula of Fe2O3, the same formula as the mineral hematite, the source of iron for the steel industry.

There’s also Iron(II) (ferrous) oxide, which can be found naturally but more rarely, and has the formula FeO. It’s used as a pigment and in cosmetics.

Ultimately, we also have iron(II, III) oxide, a kind of material that has both forms of oxidation states. This is the chemical specie presented in the mineral magnetite.

But what is iron?

Iron is a solid metal that can be found naturally in the form of ores or crafted into many kinds of alloys. Pure iron is normally obtained through chemical reactions.

It can’t melt until reaches at least 1500ºC/ 2738ºF.

Iron is tough, friable, and quite fusible. It is used to produce other alloys, including steel. Forged iron contains only a few percent of carbon, but it enhances its durability, fracture resistance, and strength.

Pure forms of iron can’t really be found naturally, not originally. Although iron is common in meteorites, so we can find pure forms of iron that “naturally” came from extraterrestrial sources.

Iron has the ability to form many kinds of ores. Its chemistry is wide.

Steel is an alloy made with the addition of other minor compounds like manganese, nickel, sulfur, titanium, phosphorous, tungsten, cobalt, and niobium.

Stainless steel is typically made with an additional 11% chromium, making the material oxidation-resistant.

Iron is known since prehistoric times, at least 5 thousand years ago. It is the cheaper and most abundant of all metals. 

Iron chemistry

Before we proceed we must explain a few important properties of iron and some chemistry. We promise it won’t be long.

Iron is a chemical element, an atom. All atoms humanity has found or created are expressed in the periodic table. 

The periodic table is just a convenient way humans found to write about atoms. Every atom there has a neutral charge, meaning that they have no excess or lack of electrons.

In the picture above you can see an atom of iron and its place in the periodic table. The way an atom is written there is not exactly the best, more common, or stable. It’s just a representation.

But iron can be found in a pure form, just like in the table, bonded with other twin irons. These are the forms that can burn, they react with air’s oxygen to produce iron oxides.

All those green balls are the 26 electrons that iron has. These are the particles that participate in chemical reactions. An atom nucleus is never touched unless there’s a nuclear fusion going on.

When for some reason an iron loses two or three electrons, it becomes a cation named Iron(II) or Iron(III) [Fe+2 or Fe+3]. This can happen in an aqueous solution (the cations become a free species), or in a molecule, especially oxides.

Is iron flammable?

Iron oxide is a chemical quite different from pure iron, but we still need to assess how flammable iron is before we can understand if iron oxides would catch fire.

You can jump to the other topics right away, but the explanation might become incomplete.

For something to become flammable, it must catch fire easily and generate heat, in conditions considered mild. But before that, it must be combustible.

Our common sources of fuel are always organic compounds, something that can burn, liberates lots of energy, and flames. 

In fuels, this energy unleashed is the flames themselves.

This kind of fire can only happen with sources of carbon (C) and hydrogen (H), which liberates carbon dioxide (CO2) and water (H2O) as the main byproducts of oxidation with the air’s oxygen (O2).

Therefore, can iron even burn?

Well, it can’t burn like other fuels because it’s a metal. Iron (Fe) only has Fe atoms to participate in the chemical reaction that provokes a fire. But iron can burn because it does oxides, in certain conditions.

But pure iron can only burn if its particles are finely divided, like iron powder. A high surface area is required so the chemical reaction can take place fast, so we can witness heat being liberated.

When pure iron oxidates it loses electrons to oxygen and forms iron oxides. This reaction liberates energy in the form of heat and light, so we can say that iron is flammable. But it doesn’t produce flames.

And is iron oxide flammable?

As we saw, something can only burn if it can oxidate and liberate energy. Iron oxides are already oxidized, so we can’t expect much flammability from them.

Iron oxide can still burn if it still has some space left to oxide.

Thus, we can’t answer this question for all iron oxides at once. 

Well, any iron oxide will present a certain level of flammability if it can still react and bond with other oxygens and if this event liberates energy. They are all less flammable than iron alone.

Under normal conditions, an oxide compound that has iron(III) species wouldn’t be flammable because it already has lots of oxygens in its molecules. 

Trying to add more oxygen to it would be a really hard task, would require thousands of degrees Celsius or Fahrenheit, and perhaps wouldn’t even generate heat. 

An oxide of iron(II), although, can still oxidize until the iron(III) form. If you possess a solid material made with iron(II) and its particles are very thin, it can become flammable if you toss it into a fire.

But it wouldn’t exactly mean that the compound has a fire hazard. Iron(II) wouldn’t liberate much heat unless you burn a big amount of it. At the same time, it might serve as an ignition for other fuels.

So just be careful where you store iron powder materials. If we are talking about a metal bar or pellets, they present no fire risk whatsoever.

Remember that fire is all about liberating energy in the form of heat.

What is fire?

We did speak briefly about how fuels burn, and how iron doesn’t really generate flames. But why is that? How can something be burned but have no flames? The answer lies in a fuel’s chemistry.

Have you ever wondered why a stove’s fire is blue, while a fire pit is something between red and yellow?

The fuel is in the form of gas. The particles are much simpler and smaller than wood, for example. The gas is burned all the way to the form of carbon dioxide and water.

The combustion of hydrocarbon gases such as butane occurs much more readily, and evenly. It doesn’t produce many byproducts because the combustion is more or less complete.

Incomplete combustion happens when the ingredients of fire (fuel, oxygen, and heat) are not in an ideal form. Smoke, carbon monoxide, and fumes are examples of byproducts from an incomplete reaction.

Flames themselves are also part of incomplete combustion. There are countless intermediate products in any kind of flame. The different colors in a fire are the result of different stages of burning.

You may have noticed that charcoal produces much fewer flames than wood when burning. Charcoal is produced for this end, the fuel is made to burn more evenly and generate fewer unwanted byproducts.

But when pure (and let’s say, powdered) iron burns, there are any other byproducts, only iron oxides. The burning is much cleaner because of that, so there’s no reason to see flames appearing.

But one of the results of the combustion is irradiating heat, which warms up the unburned pieces of iron and the iron oxides, making them incandescent. 

But as you can see from the picture above, there won’t be any flames arising from the material, unless it contains impurities.

Conclusion

Combustion is a chemical reaction between something and oxygen. When iron burns it produces iron oxides due to oxidation with oxygen. The oxides can’t burn (oxidize) again, so they’re not flammable unless they’re in a lower oxidation state like iron (II).

But even so, the iron oxide wouldn’t be much flammable, and much less than pure iron.

Frequently Asked Questions (FAQS): Is iron oxide flammable?

is iron oxide rust?

Yes. Rust is formed when ferrous metals corrode. The chemical reaction that takes place is called oxidation, it happens mostly between the iron in the ore, oxygen, and water.

Rust is the name we give for the mixture of several kinds of oxides that arise from oxidized metals. Most of them appear red or red-brown, are made of hydrated iron (III) oxides, and have the formula  Fe2O3·H2O.

is iron oxide magnetic?

Yes. Iron oxides are still magnetic, but less than other iron ores. This is because iron oxides have fewer electrons to interact with a magnetic field.

is iron oxide soluble in water?

Iron oxides are not soluble in water, alcohol, and alkali solutions. They are soluble in strong acids.

Citations

https://en.wikipedia.org/wiki/Iron_oxide
https://en.wikipedia.org/wiki/Iron(II)_oxide
https://en.wikipedia.org/wiki/Iron(III)_oxide
https://en.wikipedia.org/wiki/Iron(II,III)_oxide
https://pubchem.ncbi.nlm.nih.gov/element/Iron
https://pubchem.ncbi.nlm.nih.gov/compound/16211978
https://www.reliance-foundry.com/blog/what-is-rust#:~:text=Rust%20is%20the%20term%20we,when%20iron%20is%20left%20exposed.

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