Is Graphite Powder Flammable? (A comprehensive overview)

Is Graphite Powder Flammable?

Graphite finely divided (graphite powder) suspended in the air can catch on fire if an ignition source is applied. Meaning it may act as a flammable material under some circumstances. Graphite in bulk form is much harder to set on fire than graphite in powder or dust from.

Graphite can be natural or synthetic, and its chemical structure and morphology is variable, but any form of graphite is combustible. 

In this article combustible means capable of undergoing a combustion reaction and in the processes produce heat or fire. Furthermore, graphite can react violently with very strong oxidizing substances such as fluorine (F2), chlorine (Cl2) and potassium peroxide (K2O2).

Even though graphite is combustible, it can withstand very high temperatures, particularly in conditions absent from oxygen.

Chemically, graphite is composed of carbon atoms bonded to each other by single and double bonds. The carbon atoms bonded to each other form a planar layer of carbon atoms, the layers are near each other but they are not chemically bonded to each other.

The individual layers are called graphene and they can move in relation to each other. It is possible for gas molecules such as oxygen gas (O2) to be present in the space between the layers. And the presence or absence of oxygen within graphite influences its ability to catch on fire.

How Likely Can Graphite Catch on Fire?

Graphite in bulk form does not easily catch on fire. For it to catch on fire significant heat needs to be applied to it. The amount of heat depends on some factors such as the exact morphology of the graphite and the amount of oxygen gas present.

Overall, under ordinary conditions, bulk graphite would need to be heated to at least 400 ºC (752 ºF) for it to possibly catch on fire. Graphite finely divided suspended in the air can catch on fire if an ignition source is applied, possibly causing an explosion.

The main reason for the difference between graphite in bulk form and finely divided is the difference in surface area to volume ratio, which is far higher for finely divided particles of graphite.

The higher the surface area to volume ratio is, the more susceptible to chemical reactions. For graphite to catch on fire it must be oxidized and for that to happen an oxidizing agent must approach and chemically react with the carbon atoms in the graphite molecules.

Graphite molecules in the bulk form of graphite are much harder to be approached by an oxidizing agent (oxygen gas for example) in comparison to finely divided graphite. That is because they are surrounded by more graphite molecules.

Meanwhile, finely divided graphite has its molecules more accessible to an oxidizing agent. So it is ‘easier’ for an oxidizing agent to approach and oxidize them. This translates to less heat being necessary to combust graphite in this form.

However, not every oxidation of graphite will result in a fire. Graphite can be oxidized in a mild manner and in fact the partially oxidized graphite or graphene is a very interesting material.

Some Combustion Reactions of Graphite

Considering a combustion reaction, one in which one substance is oxidized (in this case graphite molecules) and another acts as the oxidizing agent which releases heat. Sometimes the heat released is enough to produce fire.

Graphite can be oxidized by oxygen under high temperatures, forming graphene oxide. Graphene oxidation often leads to the formation of epoxides in the graphene layer. Epoxides are believed to be one of the reasons graphene-oxide has a significant risk of catching on fire.

Fumes Released From Burning Graphite

If graphite does catch on fire in air it will mostly produce carbon dioxide (CO2) and possibly carbon monoxide (CO). Carbon dioxide has a relatively low toxicity to humans as long as it does not stack up in the ambient air.

Carbon monoxide is highly dangerous if inhaled and it can lead to severe health conditions.

Some Of Graphite Physical Properties

Graphite can be natural or synthetic and both variations have further variations which depend on the form and chemical modifications. Both natural and synthetic graphite gave a series of interesting properties such as high resistance and electrical conductivity.

The physical properties of graphite are very dependent on the morphology and any chemical modifications it may have gone through. Some physical properties of natural graphite are listed in the table below.

Density2.0 to 2.2 g/cm3
Melting point~3,600 ºC (6,512 ºF) at 1 atm
Boiling point~4,800 ºC (8,672 ºF) at 1 atm
Hardness1 to 2 in the Mohs scale
Solubility Not soluble in: water, organic solventsSoluble in molten nickel (Ni)

Graphite Thermal Stability And Conductivity

One of the useful properties of graphite is its potentially high thermal conductivity, its capacity to transfer heat from one object to another.

The thermal conductivity of natural graphite,, is between 25 and 470 watt per meter per kelvin (W/m.K) under ordinary temperature and pressure. For comparison under similar temperatures the thermal conductivity of iron is around 80 W/m.K.

Graphite Electrical Conductivity

Graphite is considered electrically conductive, that is electrons can ‘travel’ through graphite from one point to another.

Even though graphite is made only of carbon, and many carbon based materials are not electrically conductive (e.g. wood, paper, cotton, gasoline, plastics), graphite can conduct electricity because in its molecules there are altered single and double carbon bonds.

These altered single and double bonds, also called conjugated bonds, make it possible for charges to move. Since these bonds are in the layers of graphene, the electrical conductivity can only take place in the plane of the layers and not from one layer to the other.

Graphite Applications

Graphite diverse properties has led to many applications, such as:

  • Batteries
  • Brake linings
  • Lubricants
  • Pencils
  • Electrodes (synthetic graphite)
  • Neutron moderator (synthetic graphite)

Further detail on some of the applications are presented below.

Graphite In Lubricants

Graphite and graphite powder are valued in industrial applications for their self-lubricating and dry lubricating properties.

Graphite-moderated Reactor

Synthetic graphite can have very high thermal and nuclear stability. These properties make graphite useful in nuclear reactor designs. Graphite-moderated reactors are used in uranium nuclear reactors.

A graphite-moderator rector was used in the first nuclear reactor in history, the Chicago Pile-1.

The Windscale disaster in 1957 involved graphite control blocks (graphite itself did not catch on fire). In the Chernobyl disaster, a graphite fire increased the spreading of radioactive material.

Diamond From Graphite

If graphite is submitted to high pressures the graphene layers will undergo a chemical transformation in which double bonds are broken and new single bonds are formed. After enough time under high pressure this chemical transformation leads to the formation of diamond.

Diamonds are also made of only carbon atoms, but unlike graphite the carbon atoms in this case are not disposed in planar layers but in a fully linked ‘network’ of carbon atoms. Diamonds can be made synthetically or naturally occur.

Graphite Health Hazards

Overall graphite has mild toxicity if ingested or inhaled. However, in situations of long exposure to graphite dust or powder there is the risk of damage to the lungs. The possible symptoms include black sputum, cough, chest tightness, pain, and shortness of breath

Is Graphene Flammable?

Graphene is often chemically modified from natural graphene. Natural unmodified graphene is more easily ignited than graphite because it is less bulky and therefore has a higher surface area to volume ratio.

Graphene-oxide, graphene which has some oxidized sites in its molecules can be highly flammable. This flammability is attributed to epoxides that can be present in the carbon frameworks.

Conclusion

Every form of graphite is at least combustible (it can catch on fire) but in most situations graphite does not pose an immediate risk of fire. Some forms of graphite are somewhat easily ignited while other forms are extremely resistant to high temperatures.

Frequently Asked Questions (FAQ): Is Graphite Powder Flammable?

Is graphite from a pencil flammable?

Pure graphite does not easily catch on fire unless it is very finely divided. Graphite from a pencil is generally even less likely to catch on fire given the possible presence of chemicals that can reduce the flammability of graphite even further.

Does graphite explode?

Graphite is combustible, meaning it can catch on fire, so it is possible for graphite to explode but very unlikely. The conditions (temperature, pressure, presence of reactive chemicals) for graphite to explode would need to be very extreme

Can you light a pencil on fire?

If it is a pencil made of wood or a combustible plastic, yes a pencil can be set on fire. Many pencils are made with materials that have some resistance to fire.

Is graphite a combustible dust?

Graphite is combustible in either bulk, powder or dust form. In dust or powder form, however, it is more likely to catch on fire than in bulk form. So, yes graphite can be a combustible dust.

Can graphite be used as fuel?

Using graphite as fuel would probably be very impractical. But, graphite is used in many applications related to power generation. For instance, graphite is used in batteries and in nuclear reactors.

Is diamond flammable?

Both synthetic and natural diamonds are harder to ignite than graphite but at extremely high temperatures diamond can combust.

References

Maria Cristina Tanzi, Silvia Farè, Gabriele Candiani, Chapter 1 – Organization, Structure, and Properties of Materials, Editor(s): Maria Cristina Tanzi, Silvia Farè, Gabriele Candiani, Foundations of Biomaterials Engineering, Academic Press, 2019, Page 41, ISBN 9780081010341, https://doi.org/10.1016/B978-0-08-101034-1.00001-3. (Accessed June 19th, 2022)

Kedar Hippalgaonkar, Jae Hun Seol, Dongyan Xu, Deyu Li, Chapter 12 – Experimental Studies of Thermal Transport in Nanostructures, Editor(s): Gang Zhang, In Micro and Nano Technologies, Thermal Transport in Carbon-Based Nanomaterials, Elsevier, 2017, Pages 319-357, ISBN 9780323462402, https://doi.org/10.1016/B978-0-32-346240-2.00012-1. (Accessed June 19th, 2022)


Hulusi Turgut, Z. Ryan Tian, Fengjiao Yu, and Wuzong Zhou. Multivalent Cation Cross-Linking Suppresses Highly Energetic Graphene Oxide’s Flammability. The Journal of Physical Chemistry C 2017 121 (10), 5829-5835. https://doi.org/10.1021/acs.jpcc.6b13043 (Accessed June 19th, 2022)

https://www.cdc.gov/niosh/topics/pneumoconioses/ (Accessed June 18th, 2022)

https://www.cdc.gov/niosh/pel88/7782-42.html (Accessed June 18th, 2022)

https://www.britannica.com/event/Windscale-fire (Accessed June 18th, 2022)

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