Is Carbon Flammable? Why it Burns…

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The fundamental building block of most organic life and all organic chemicals is carbon. This is due to its unusual chemistry which allows carbon to form four bonds with other elements (or with other carbon atoms) and thus it has unparalleled chemical flexibility. But does that mean carbon is flammable and burns easily and if so, what makes that happen? 

Carbon can be flammable, though it will depend on the type and physical state of the carbon as to how flammable it will be. Carbon can ignite between 300 and 450 degrees Celsius (572 and 842 Fahrenheit).

Carbon is abundant in our world, but its form can really vary and that affects its behavior around heat and fire. Let’s take a closer look at why. 

Also read: What Makes Something Flammable?

An Introduction To Carbon And Its Many Forms

carbon coals burning

Pure carbon can exist in many different forms. 

The two naturally occurring forms of pure carbon are graphite and diamond. 

You will be familiar with both of these forms in real life, and you’ll know that they have very different properties. 

Graphite is so soft that it can be used to write with, diamond, on the other hand, is so hard that it can be used to drill oil wells. 

There are also three other forms of carbon that can be created in the lab (and possibly, by natural processes somewhere else in the universe, though this is not certain): fullerene, amorphous carbon, and Q-carbon.

There are also other sources of pure carbon which appear to be some sort of mixture of other types of carbon such as coke, charcoal, soot, lampblack, etc. 

This means that carbon can behave in a myriad of ways depending on the form it takes and how it is treated with heat or, indeed, other elements. 

Chemical Properties of Carbon - Combustion - Part 2 | Don't Memorise

Also read: Is Carbon Monoxide Flammable? Should You Be Worried?

Is Carbon Flammable? (Gas, Liquid, Solid)

All elemental forms of carbon, that is pure carbon, are solids at temperatures up to 199.4 degrees Fahrenheit and that means that carbon is not, by standard definition, flammable, according to OSHA.

However, in common usage, the term “flammable” means “burns easily” and in that context, some forms of carbon will burn easily despite not being flammable in the strictest context. 

Carbon can’t easily be made into a gas and that’s because it burns very easily in the air once it melts, thus you will not encounter carbon as a gas at all. 

In theory, if you could get carbon gas, and keep it at a temperature below 199.4 degrees, it would be flammable but as carbon solidifies long before it reaches temperatures this low – in practice, carbon gas is not going to be flammable, even if you could make some. 

Also read: Is Carbon Dioxide Flammable? (CO2) 

Are Carbon Compounds Flammable?

There is nearly an unlimited number of carbon compounds on the planet and many more can easily be created in laboratory conditions. 

That means there are almost no rules which govern the behavior of carbon compounds. 

Many carbon compounds are very flammable, think methane gas or butane, the popular lighter fuel, or ethanol (the alcohol that humans drink socially), etc.

Even coal, used for its heat-generating capabilities as it burns, is made up mostly of carbon and hydrocarbons.

The same is true for Mazut, the heavy oil from Russia, which can be used as a vehicle fuel but is not at all flammable. 

Can You Ever Burn Carbon?

However, despite the fact that carbon is usually not flammable (technically), it will burn, and, in some cases, it will burn very well, indeed. 

Soot is the most easily burned form of carbon.

This is because soot is carbon dust and dust has a very large surface area when compared to its volume, this means that it takes less heat to set it on fire than say a lump of coal which has a much smaller surface area when compared to its volume. 

A cloud of soot can explode over a naked flame and will burn very easily in most circumstances. 

Diamond, on the other hand, will burn but you’ll need to get it up to very high temperatures to do so. 

This is because the internal bonds between atoms in diamond are very strong, they give a diamond its hardness too, and in order to get the carbon to burn, you need to break these bonds down. 

You would need to raise diamonds to temperatures of thousands of degrees to break these bonds and enable it to burn. 

Other forms of carbon will burn at some point between these two extremes. 

Coke, for example, is an essential fuel in coal-fired power plants and though it won’t catch light too easily (though Coke dust will), it will burn very well once it has caught fire. 

What Happens When You Burn It?

Assuming that you are burning pure carbon and that you are doing so in the presence of oxygen, then burned carbon will react with the oxygen to produce two gasses.

Carbon dioxide is produced when the carbon atom burns completely and the reaction with oxygen progresses to a finish. 

In this end product, there is one carbon atom and two oxygen atoms and there is a double bond formed between each oxygen atom and the carbon atom. 

Carbon dioxide is the gas that human beings exhale and it is caused by the “burning” of carbon within the body, though there are no flames involved in this chemical process, thankfully. 

The other potential end product is carbon monoxide. 

In this case the carbon atom bonds with only one oxygen atom. 

Carbon monoxide can be further burned in oxygen to create carbon dioxide, though it requires higher temperatures to do so. 

Carbon monoxide is a problem for human beings and many living organisms. 

If we inhale carbon monoxide it bonds to our red blood cells in the same way that oxygen does, unfortunately, unlike oxygen, it will not break off and be used in the body, instead, it stays stuck on the red blood cell and cannot be dislodged.

Thus, carbon monoxide poisoning occurs, when our red blood cells have bonded with so much carbon monoxide that we can no longer bond any oxygen to those cells, and it causes us to suffocate. 

This is why it’s important to have a carbon monoxide detector in your home as carbon monoxide poisoning is irreversible and fatal. 

Both the production of carbon dioxide and carbon monoxide by burning carbon are exothermic reactions.

That is, they produce light and heat. 

The heat is sufficient that it will continue to propagate the burning reaction and explains why carbon burns so easily once the fire begins. 

Does Carbon Melt?

In theory, both graphite and diamond can be melted (as can other forms of carbon) but in practice, this has only been achieved in computer simulations. 

The issue is that the melting point of the natural forms of carbon is very, very high, indeed.

Graphite requires a temperature of around 6,000-7000 degrees to melt and so does diamond. 

These temperatures are not found anywhere on earth naturally and would require extraordinary efforts to generate.

And as graphite and diamond began to melt, the carbon, assuming that there was an oxygen source, would catch fire and burn rather than melt. 

So, the only way to melt carbon would be to place it in a vacuum and subject it to incredibly intense heat. 

This is not terribly practical and wouldn’t, as far as we are aware, provide any particular benefit, so, for now, at least, it remains a theoretical process to melt carbon rather than a practical one.

This is good news though.

It means that graphite can be used as heat-shielding for spacecraft (it is easy to shape, low cost, and absorbs temperatures that would melt most metals) and thus allows us to better explore the universe around us.

Diamond, on the other hand, is commonly used for drill bits due to its hardness and drilling creates immense heat through friction. 

And while it is debatable that the ability to drill for oil is a “good thing”, it is the fact that diamond doesn’t melt that enables us to easily drill for oil. 

Sources

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