#22: Another Liquid Metal

Mercury is an awesome element. In addition to being a liquid at below room temperature, it has an extremely high density and surface tension. In fact, a solid steel ball placed in it will actually float. Unfortunately, mercury is also quite toxic. This, coupled with its high cost, means that I probably won't be getting my hands on it. However, it doesn't mean that there isn't an alternative.

If you've read my previous posts, you might recognize the element gallium. Gallium has a relatively low melting point of 86 ℉. While that's low enough for it to melt in my hand, the metal solidifies rather quickly. Plus, gallium forms a pesky oxide layer which prevents it from flowing freely. Some alkali metals such as cesium also have low melting points. However, they are extremely reactive to say the least. There are a few other low-melting metals but they are either too dangerous or too expensive. Fortunately, pure metals aren't the only option.

A while back, I explored an alloy of gallium and aluminum. The alloy was interesting because it took on different characteristics than its two components. In general, alloys are useful because they have properties that aren't found in pure metals. For example, bronze was important because, unlike copper or tin, it was both strong and resistant to corrosion. Similarly, many alloys have lower melting points than the metals that form them. These alloys are often used as solders. But is there a low-melting alloy to replace mercury? The answer is yes.

The alloy is called Galinstan. Its name is derived from the three metals that are used to make it: gallium, indium, and stannum (the latin word for tin). Galinstan's melting point is about -2 ℉. It is also nontoxic, which makes it a fantastic replacement for mercury in many devices such as thermometers. The fact that it is safe also means it can be explored by people like me. So after buying the necessary materials online, I went ahead and made the alloy for myself. To do so, I melted down 7 grams of gallium (86 ℉), 2 grams of indium (314 ℉), and 1 gram of tin (450 ℉). When the liquid metal cooled, I removed any unalloyed bits which had solidified. After purifying the alloy, I had my liquid Galinstan metal.

If you noticed, all three of the metals that I used had relatively high melting points. So how did their combined melting point end up so much lower? To figure this out, we must understand what determines a substance's melting point. To do that, let's first look at the concept of temperature itself. Temperature is actually a measure of kinetic energy. On the molecular level, kinetic energy is the constant movement or "jigglyness" of the atoms in a substance. So when something is getting hot, it means that the atoms inside are moving around more. And when a substance's atoms are moving around more, that substance begins to move around more as well. Eventually, that substance begins to melt, or in the case of a liquid, it evaporates. The important thing to note here is that different types of substances require different amounts of energy in order to melt or evaporate. This amount of energy is often determined by the molecular structure of the substance. So in the case of Galinstan, its molecular structure simply requires minimal energy to melt. Thus, it is able to remain a liquid at low temperatures.

Here you can see the shiny, mercury-like globs of my Galinstan alloy. 

Here are samples of my gallium, indium, and tin (from left to right).

For more information about Galinstan and its properties...
http://en.wikipedia.org/wiki/Galinstan