Thermite


Background

The thermite reaction was discovered by Hans Goldschmidt in 1895. When it burns it leaves behind very pure iron and so was used in the welding of steel and in the production of carbon free metals.

This is an extremely dangerous reaction where the aluminium burns, using the iron oxide as an oxidizer. It burns at between 2000 and > 3000º C, spits and should not be looked at directly because of the brightness and UV light emited.

Composition

Ingredient Formula Proportion
iron (III) oxide (rust) Fe2O3 8
aluminium powder Al 3

Thermite would work using any non-reactive metal oxide and any reactive metal, with varying degrees of efficency.

Equations

2Al(s) + Fe2O3(s) => Al2O3(g) + 2Fe(l)

Ignition

Thermite is extremely difficult to ignite because a very high temperature is required and the two powders are separate. It may ignite more easily if the two powders were melted together to achieve an alloy, similar to the one which can be bought as rods in welding stores.

When the military uses thermite as an incendiary device it is held in a magnesium casing which is ignited, causing its contents to be ignited.

As a laboratory experiment, it is often ignited with magnesium ribbon or a common party sparkler. Another method which I have seen suggested is to place some potassium chlorate on the thermite and then add a small amount of sulfuric acid. This method should not, however, be used as what happens is chloric acid is formed which explodes spontaneously, which may or may not ignite the rest of the chlorate mix.

Other Information

Thermite is not classified as an explosive and is not really used as a firework either. It is used by the military as an incendiary weapon.

Please Note: I have had to remove a lot of information on this page. See the bottom of the contents page.