Thermite Reaction Chemistry Demonstration

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Thermite Reaction
The thermite reaction is an exothermic redox reaction between a metal and a metal oxide. (photo: Kingfisher; CC 3.0)

The thermite reaction is a spectacular exothermic chemical reaction that makes an exciting chemistry demonstration. As a demonstration, the reaction illustrates the metal reactivity series, oxidation, and exothermic reaction. Of course, the thermite reaction has practical applications, too, including welding, pyrotechnics, military uses, making diamonds, and ore extraction.

Thermite Reaction Materials

All you need for the thermite reaction demonstration is finely-divided aluminum metal, iron oxide, and an ignition source.

  • 50-55 g iron(III) oxide powder (Fe2O3)
  • 15 g aluminum powder (Al)

For a smaller demonstration:

  • 9 g iron(III) oxide powder
  • 3 g aluminum powder

Aluminum filings or powder are available online, or you can harvest the material inside an Etch-a-Sketch toy. For the iron oxide, use either rust or magnetite. One source of rust is residue scraped from an intentionally rusted iron skillet or rusted ball bearings. If you live near a beach, collect magnetite by running a magnet through sand repeatedly. Alternatively, order iron oxide online.

  1. Mix the iron oxide and aluminum and pour the mixture into a pile on a heat-safe surface. Examples include a cookie sheet on concrete or a terra cotta flower pot.
  2. Ignite the mixture.

You have several ignition options:

  • Large sparkler (essentially burning magnesium)
  • MAPP or propane torch
  • Magnesium strip fuse ignited using a lighter
  • Instant fire chemical reaction

For the instant fire chemical reaction, press a depression into the mixture of aluminum and iron oxide. Pour 20 to 25 grams of potassium permanganate (KMnO4). Start the reaction by pouring about 5 ml of glycerol [glycerine, C3H5(OH3)] onto the potassium permanganate. The reaction ignites the thermite within about 15 seconds.

Once the thermite reaction begins, expect smoke, heat, and sparks. Have a large clear area around the demonstration, as sparks may eject a few meters outward from the reaction.

How the Thermite Reaction Works

The thermite reaction occurs between a metal and a metal oxide, where the metal is higher on the reactivity series than the one in the oxide. So, technically any two metals work. However, aluminum is almost always the metal of choice because it’s affordable and readily available. For chemistry demonstrations, the oxide is usually iron(III) oxide or iron(II) oxide, for the exact same reasons. In practical applications, several oxides are common. These include iron oxide, manganese oxide (MnO2), chromium oxide (Cr2O2), and copper(II) oxide (CuO).

Aluminum replaces the metal in the oxide. This is because aluminum is more reactive than iron. In the reaction between aluminum and iron(III) oxide, this forms iron and aluminum oxide and releases a lot of heat:

2 Al(s) + Fe2O3(s) → 2 Fe(s) + Al2O3(s) ΔH° = -850 kJ

So, the reaction illustrates combustion of iron oxide, oxidation, and also oxidation-reduction because one metal becomes oxidized as the other is reduced.

Thermite Reaction and Dry Ice

Dramatic variations of the reaction surround thermite with either ice or dry ice and igniting it. In either case, the reaction often explodes rather than burns. You’re better off watching a video of the effect rather than trying it yourself.

Ice is solid water (H2O), while dry ice is solid carbon dioxide (CO2). Looking at the chemical formulas, you can see they contain oxygen. But, the extra oxygen isn’t the only reason for the amped-up reaction. Rapid heating vaporizes the ice or dry ice, causing a pressure wave.

Safety Information

  • As with all chemistry demonstrations, wear eye protection, a lab coat, and close-toe shoes.
  • Practice performing the reaction so you know what to expect.
  • The best location for this demonstration is indoors on an open lab bench. Seat the audience some distance away from the reaction. Make sure the immediate area is clear of combustible materials. Some people prefer doing the reaction outdoors, but only do so if there is no wind.
  • Bigger is not better for this reaction! Do not use more metal and metal oxide. Doing so produces a larger reaction and more heat, potentially damaging surfaces or throwing out debris. While the reaction is not explosive, particle size of the reactants affects whether or not it throws off sparks or bits of metal.
  • You can’t extinguish the thermite reaction using water or carbon dioxide. Options include liquid nitrogen or covering the reaction with alumina.

References

  • Goldschmidt, Hans; Vautin, Claude (30 June 1898). “Aluminium as a Heating and Reducing Agent“. Journal of the Society of Chemical Industry. 6 (17): 543–545.
  • Kosanke, K.; Kosanke, B. J.; Von Maltitz, I.; Sturman, B.; Shimizu, T.; Wilson, M. A.; Kubota, N.; Jennings-White, C.; Chapman, D. (2004). Pyrotechnic Chemistry. Journal of Pyrotechnics. ISBN 978-1-889526-15-7.
  • Swanson, Daren (2007). “Method For Creating Diamonds“. Patent CA 2710026. Canadian Intellectual Property Office.