Note:  Contact The Fire Systems Group at Michael.Mari@colorado.edu and John.Humphrey@colorado.edu (email both) ahead of time to have the smoke alarms disabled during the class period when thermite will be performed.

Introduction

Igniting a mixture of Fe2O3 and Al with a magnesium ribbon fuse produces molten iron and aluminum oxide in an impressive exothermic reaction.

Thermite reaction in lab

Equations

2Al(s) + Fe2O3(s) → Al2O3(l) + 2Fe(l) + ∆

For Fe2O3, ∆Hfo = -824 kJ/mole

For Al2O3, ∆Hfo = -1673 kJ/mole

∆Hrxn = -849 kJ/mole

Heat produced raises the products to the melting point of iron (1530oC / 2790oF).  For 50g Fe2O3 and 15g Al, ∆T is approximately 5744oC.

Supplies

Short List

  • Thermite apparatus of sand filled glass container on a metal cart (permanently  devoted to thermite)
  • Safety shield
  • Two nested flower pots with small piece of Kimwipe over bottom hole
  • Self-lighting propane torch assembly
  • Long Tongs
  • Heat protective gloves
  • Empty aluminum beverage can
  • Goggles
  • Lab coat
  • Broom and dust pan

Chemicals

    • Weigh out and mix 50g (0.31mole) Fe2O3 (ferric oxide) and 15g (0.56 mole) finest mesh Al (aluminum) in an ointment jar. Mix very well.  Mix again right before demo.  (More than a single recipe is needed to fill the pot.  Unless there is significant mixture already in the jar, make at least a double batch.)
    • Magnesium ribbon:  Create a wick by cutting three lengths of ribbon, sanding well with sand paper, and barely entwining them so they just hold together (allowing air to get to the most surfaces).

Prior to Lecture  (prep time 5 min.)

    1. Wheel cart with empty flower pots into place in the lecture hall.
    2. With flower pots in place in the ring holder, in the lecture hall, pour the aluminum/ferric oxide mixture into the inner flowerpot so that mixture is light and fluffy and fills the pot to within ½ inch of the top.  (Note: aluminum ferric oxide mixture will stain clothing)
    3. Insert the wicks carefully into the thermite mixture (there should be little or no resistance) and gently, without packing the thermite, create a well around the wicks to allow air access to them.

To Conduct Demonstration

    1. Pick the beverage can up to show the students.  Place the can under the drainage hole in the flower pots.
    2. Ignite the propane torch using the mechanical self-lighter.
    3. Ignite the magnesium ribbon wick until it is white hot, then step quickly back.
    4. After the thermite burns, pick the soda can up with the tongs and show the students the hole burned through it.

Demo Time: 5 - 10 minutes

Safety and Disposal

  1. Have a fire extinguisher handy and place the safety shield between the reaction and the audience. 
  2. Keep the reaction cart a safe distance (at least 6ft) from the front row. 
  3.  Wear goggles and heat-protective gloves.
  4. Do not use water to extinguish flames or to cool products (explosive hydrogen gas can be produced when water comes into contact with molten iron).
  5. Perform in a well-ventilated room. 
  6. Check floor and sweep if it is slippery due to tiny iron balls.  Once cooled, the soda can and iron metal can be disposed in the trash.