A little aluminum, a little lye, a little water, and quite a bit of fizz. That bubbling looks sedate, but it's blown up a couple of trucks. And someday, who knows? It might be powering cars.
We use aluminum too often in our daily lives to be much impressed by it. For us it's just a light, steady metal used for soda cans and cheap cookware. We can preserve that illusion because aluminum has a special reaction with water. The aluminum yanks one oxygen atom and one hydrogen atom off three atoms of water, leaving the last bits of hydrogen to go free as a gas. The aluminum combines with the oxygen and hydrogen to form aluminum hydroxide. This aluminum hydroxide covers the remaining aluminum atoms, forming a coating that keeps the aluminum from reacting with any more water.
Unless some lye gets dropped into the mix. Lye, or sodium hydroxide, a caustic chemical used to make soap and drain cleaner, breaks things down. When mixed with water and put on aluminum with sodium hydroxide, the lye rips apart the protective coating, allowing more and more aluminum to get together with water and be dissolved. This, incidentally, allows more and more hydrogen to rush off as gas. The reaction is not too violent, and can even be useful. There's even an entry at Instructables that shows you how to run your car on soda cans and lye. There is, however, a dark side to this reaction.
Two different trucks have been exploded by this, both under similar circumstances. In 1986 and 2006, a solution of sodium hydroxide was loaded into a tanker truck for transportation. The tanker trucks were made of, among other metals, aluminum. They were sealed. The sodium hydroxide allowed the water and aluminum to react and produce hydrogen gas until the trucks exploded. Fortunately, no one was hurt, as people noticed the smoking trucks and the area was cleared well before the trucks blew apart. Still, huge shards of metal flew for yards in every direction. A little fizz can go a long way.
[Via Reaction of Aluminum With Water and Sodium Hydroxide, WNDU.]