#17: Gallium Infiltration of Aluminum

In my 10th post, I talked about some of the incredible properties of gallium (the 31st element). Recently, I decided to check out another one of gallium's unique aspects. This time, I wanted to see how it would interact with a similar metal: aluminum. As you probably know, when two metals come together they form an alloy. The interesting thing about alloys is that they often take on different characteristics than their composite metals. In this experiment, I created and explored an alloy of gallium and aluminum. The results were pretty fascinating.

To start, I cut out two identical squares of aluminum sheet metal. I then positioned one of the sections above my butane burner and began heating it. As it warmed, I selected a few small bits of gallium. When the aluminum became hot enough (over 86 ℉), I placed the pieces of gallium on top of it. After a little while, the gallium chunks melted into shiny globs. I then used a toothpick to spread the molten metal across the aluminum. As minutes went by, the gallium started to disappear. The silver liquid simply sank right into the aluminum. When the gallium was gone, I turned off the heat and removed the sheet metal. Now came the test.

In order to understand what was different about my newly-created alloy, I first had to examine my aluminum control sample. I bent it around a few times and found it to be rather sturdy. Next, I picked up the sample that I had previously treated with gallium. Without trying very hard, I was able to rip the piece straight in half. I then continued to tear up the subsequent sections as if they were made of cardboard. The once-tough sheet metal felt like a cereal box. The sensation was freaky.

Similar to most chemistry experiments, the explanation for what happened here can be found by looking at the chemicals involved. The first thing to keep in mind is that gallium and aluminum lie in the same column of the periodic table. Thus, it is no surprise that they share some traits. One of these being that both chemicals have fairly similar molecular structures. It is partly because of this that gallium atoms are able to diffuse into aluminum's molecular lattice. However, while gallium atoms can take their place among aluminum, they don't necessarily act the same. As they infiltrate the aluminum, the gallium atoms greatly weaken its structural integrity. This is exactly why I was able to tear apart the metal so easily. It is also the reason why gallium is not allowed on airplanes.

Here you can see the tiny portions of liquid gallium as they infiltrate a heated piece of aluminum sheet metal. 

After exposing it to the gallium, I was able to effortlessly tear apart the aluminum as if it were cardboard.

Another version of the demonstration using an aluminum soda can...

http://www.youtube.com/watch?v=FaMWxLCGY0U

To learn more about gallium...

http://en.wikipedia.org/wiki/Gallium

#16: Ammonium Dichromate Volcano

For a bit of pyrotechnic fun, I burned some ammonium dichromate ([NH4]2Cr2O7).

#15: Leidenfrost Effects

What if I told you that you could safely stick your fingers in molten lead (621 ℉). Or that you can submerge your hand in liquid nitrogen (-321 ℉) without being harmed. Better yet, what if I said that water can flow uphill? Remarkably, all of these things are possible thanks to a certain scientific concept. That concept: force fields. While they can't deflect giant laser beams, force fields actually exist in real life. However, they go by a different scientific name: Leidenfrost effects.

Discovered in 1756 by Johann Gottlob Leidenfrost, the Leidenfrost effect is a little-known phenomenon of science. Since I discovered it about a week ago, the concept has fascinated me. My interest in it eventually led me to perform some experiments. Seeing as I didn't have any molten metal or liquid nitrogen to play with, I had to settle for some simpler demonstrations. My first experiment involved dropping a red-hot steel ball into water. While the procedure was easy, it took a couple tries to film it right. When I did get a good shot, the results were amazing.

Upon examining my amateur slow-motion footage, I noticed something peculiar about the metal ball as it entered the water. The sphere became surrounded by a bubble. As you have probably seen, water evaporates when it comes in contact with a heated surface. However, if a surface is extremely hot, things get a little strange. Sometimes, if a liquid is vaporizing faster than it can escape, the gas builds up and forms a barrier. The thing to note here is that gases can't transfer heat nearly as well as liquids can. It is for this reason that the gas bubble slows down further evaporation. This is the essential idea behind the Leidenfrost effect.

In my second experiment I did something quite different. To show the Leidenfrost effect once again, I started by heating an empty frying pan. As it sat over the stove flame, I used a small pipette to shoot water at it. Initially, the water quickly boiled away as expected. However, after about five minutes, something very interesting happened. The water drops from the pipette stopped vaporizing. Upon landing on the skillet, each droplet began to skitter around wildly. While they did evaporate eventually, the droplets seemed impervious to the pan's extreme heat.

Similar to the steel ball, the metal pan was beyond hot enough to vaporize any water that touched it. Surprisingly, this is exactly what kept the pipette drops around for so long. As soon as the droplets hit the pan, their underside instantly evaporated. Due to the fact that this happened so quickly, their own vapor became trapped beneath them. And just like before, their vapor insulated them from the hot skillet. As a result, they were able to ride around on a cushion of air like miniature hovercrafts. To see more Leidenfrost magic, click the links below!

Although the photo isn't great, you can clearly see the force-field-like bubble surrounding the heated steel ball.

Despite the pan's extreme heat, the water droplets continued to skitter around thanks to the Leidenfrost effect.

For more information about the amazing Leidenfrost effect...

http://en.wikipedia.org/wiki/Leidenfrost_effect

Watch Leidenfrost droplets as they go uphill and navigate a maze...
http://www.youtube.com/watch?v=vPZ7sx3EwUY

The MythBusters demonstrate the effect by dipping their hands in molten lead...
http://www.youtube.com/watch?v=yTOCAd2QhGg

This guy shows the Leidenfrost effect by plunging his hand into liquid nitrogen...
http://www.youtube.com/watch?v=gjsMV1MglA4