Thermite – How Iron Oxide Reacts With Aluminium to Produce Molten Metal

Thermite is a powerful and impressive experiment that shows how iron oxide reacts with aluminium to produce molten metal. It is also an excellent demonstration of how different metals react differently with oxygen. Iron and aluminum are both very common elements and both are very reactive, however they react quite differently with oxygen. Aluminum reacts to form a very hard, dense metallic substance called aluminium oxide and is relatively inert, while iron oxidizes quickly to become rusty iron oxide and dissolves easily in water.

In the thermite reaction, powdered iron oxide and aluminum are mixed together in a ceramic container and ignited using a magnesium strip. This is a highly exothermic reaction and the resulting molten metal is extremely hot, over 2000 degC. Be very careful when working with thermite and always stand well back once the reaction starts, even if you are using a ceramic container as it can crack or break from the heat of the reaction. It is important to wear a welding mask or welder’s glasses and never look directly at the flame, as this can cause severe eye damage.

The thermite reaction illustrates the principle of single-displacement, whereby a more reactive metal replaces a less reactive one in an oxide and produces a new oxide with a higher specific heat. It is also an excellent example of how the rate at which a molten metal cools influences its magnetism; a slower cooling allows for microscopic atomic ordering and therefore magnetic properties, while a rapid cooling results in randomly oriented atoms that do not form a prevailing magnetism.