Thermite, Part 1 (6 comments)
It's an extremely exothermic chemical reaction that causes molten iron to pour out of the bottom of a flower pot.
But first things first. You'll need eight parts iron oxide
...to every three parts aluminum.
Once you've got those, combine them and make sure they're mixed thoroughly.
Now consider why you've just made a bag of thermite. In my case, Illinois state law requires that disks be overwritten with at least ten passes before they can be disposed of. I recently had the pleasure of retiring our old kerberos servers. They had especially important data on them, so I'd like to render the disks physically unreadable now that they've been wiped.
Thermite justified, it's time to create a shrine of destruction. The classic chemistry-class thermite demonstration uses nested flower pots: the first one (lined with paper) holds the thermite while it burns and the other holds the first pot together when it inevitably shatters. If all goes well, the molten iron will burn through the paper and pour out of the holes in the bottom of the pots.
But you're not out of the woods yet. Thermite is notoriously tricky to ignite. Fortunately, my dad has all kinds of handy things lying around the house, like igniters for high-powered model rockets. He souped one up a little just to be sure.
Twelve volts across the ignitor is plenty.
Of course we shot video!
20070303-thermite.wmv, 320x240, 22 seconds, 994 kB
We didn't get as much molten iron spilling out the bottom as I'd expected, but the aftermath still looks good.
And the spray left a neat pattern on the brake rotor that I'd picked to hold up the flower pots.
The top disk didn't fare too well, but the three below it were mostly left unscathed, so we can't leave it at this.
Upon video review, it's clear that the thermite burned very quickly and quite a bit of the liquid metal was thrown out the top before the reaction made its way to the bottom of the pot to burn through the paper seal. The speed of the burn indicates that our aluminum powder was too fine, so we'll try again with coarser aluminum powder for a slower, longer burn.
I promise you this: the disks will be slag before we're through.