Just how does one go about recycling an old Etch-A-Sketch? To Jesse, it’s just another piece of junk cluttering up his garage, but to Walt it’s a source of aluminium powder. An Etch-A-Sketch is quite simple in operation – there’s a thin coating of fine aluminium powder sticking to the plastic screen, and the knobs move a stylus that scrapes it off. The lines we see are therefore areas without aluminium powder, which allow us to see through to the dark interior. When the Etch-A-Sketch is shaken, polystyrene beads help to redistribute the powder evenly over the surface of the screen again.
Why is aluminium powder so important? As Walt later explains, he’s making thermite – a mixture of a metal powder and a metal oxide. Such a mixture is not explosive, but will create extremely high temperatures around a small area – it’s often used to weld sections of railway line together in locations inconvenient for conventional welding equipment. The reaction requires some kind of heat source to get started (Walt and Jesse use a gas torch), and then the metal powder is simply oxidised by the oxygen in the metal oxide in a classic redox reaction.
In this episode, Walt is probably using iron(III) oxide due to its easy availability:
Fe2O3 + 2Al → 2Fe + Al2O3 + heat
This reaction would reach around 2500 °C, easily enough to melt through the steel padlock on the storeroom door. Too bad the guys didn’t bring a trolley along.
