PeriodicExperiments: #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.