Sunday, 18 September 2011

Argon, the inert gas

So the guy was talking about high-quality windows filled with argon, and how they get worse at insulating as they get older, and I suggested that this was because the argon steadily leaked out and eventually became air.

No, no, he denied, it loses its edge because of a chemical reaction. 

I think we were in his house at the time, and it's rude to tell people they are talking nonsense when you are their guest, but this did make me suspicious of his grasp of science. Maybe it's just the English name, I thought, but Argon is one of the inert gases. "Inert" as in "does not react with anything".

I checked on Wikipedia later, just to make sure. After all, I don't know everything. In fact I thought I was wrong once. I thought I was wrong, but I was mistaken.

Anyway, according to Wikipedia, "Argon" is from the Greek αργόν (which, for anyone who is not a classical buff is exactly the same word, but in Greek letters). It means "inactive", "not working the land" or "lazy". Bit of a giveaway there too!

The reason it is used in windows is because it is monatomic. While gases like Oxygen and Nitrogen have two atoms in each molecule, Argon, and it's friends Krypton and Xenon, just have the one. Because heat is a function of the movement of atoms, this means that the inert gases hold a lot less heat, because the motion is just going on within the atom rather than between atoms in bi-atomic molecules. Because they hold less heat, they conduct less heat between the inside and outside window pains. Triatomic molecules, like CO2 and Ozone have even more movement between atoms, and can hold a lot more heat, which is one reason they are green house gases. 

With a little further investigation, I found that Argon is not strictly inert. In 2000, a group of Finnish researchers led by Markku Räsänen discovered that it combined with other substances to make Argon fluorohydride under UV light, but this substance is only stable below −265°C.

So, it seems unlikely that chemical reactions are causing the argon in windows to stop insulating.