Posts Tagged‘dry ice’

Dry Ice Screaming.

Dry ice is a very interesting substance, both from a scientific and “it’s just plain cool” point of view. Many are familiar with the billowing clouds of smoke it can produce when placed in water, seemingly a staple of anything that needs to be made to look spooky. Others will know it for its culinary applications, able to cool things down far more rapidly than any fridge or freezer. However whats less understood is the mechanisms of how dry ice actually works which is what can produce some rather interesting effects like those shown below.

Dry ice is the solid form of carbon dioxide which, thanks to its useful properties, has found many everyday applications. It’s also quite easy to manufacture as carbon dioxide is a byproduct of many other processes. This gas is then trapped and pressurized, changing it into a liquid form. Then the pressure is released, causing some of the liquid to boil off which rapidly cools down the remaining liquid. This then forms a kind of carbon dioxide snow which can then be compressed into blocks or small pellets. Industrial applications often use the large blocks whilst the pellets are used in more everyday applications.

The video above demonstrates a property of dry ice that’s not completely obvious if you don’t know what to look for. Carbon dioxide doesn’t have a liquid state at atmospheric pressures which means that it transitions directly from a solid to a gas, bypassing the liquid phase. This process is called sublimation and means that the entire surface of dry ice is constantly emitting carbon dioxide gas. When you put something on top of it, like a large metal part shown above, the gas has to squeeze past the surface in order to escape. This is akin to pulling the ends of a balloon apart to make that loud screeching noise which is why this part appears to “scream”.

There are many other videos of people producing similar effects with dry ice and other metal objects like spoons and pennies. One interesting thing I noted from some of the other ones that the screaming effect would often stop after a short period of time. I believe this is due to the metal’s temperature approaching that of the dry ice which means that the dry ice no longer sublimates. The part in the video above is likely carrying quite a bit of heat which is why the screaming continues on for so long.

Quite fascinating, if I do say so myself.

Dry Ice on Mars (and Earth).

Mars doesn’t have much of an atmosphere and the little it does have is rather hostile to life, being composed almost entirely of carbon dioxide with only small percentages of other gasses detectable. Due to the freezing temperatures that grip it constantly -60°C in summer and -125°C in winter a lot of this carbon dioxide ends up in its solid form, usually buried in the permafrost. Last year NASA even confirmed that Mars experiences dry snow a phenomena where frozen carbon dioxide falls to the surface in the form of snow not unlike the water based version we have on Earth. These are all mightily cool in their own regard but there was one particular interaction that came to my attention recently that’s just so much cooler because I realized I had first seen it for myself in my backyard.

I had heard about these gullies before and had always wondered how the heck they formed. It’s not like Mars is a completely dead planet, we’ve caught crazy things like avalanches happening on it, but things that look like they require surface water (or some other liquid) in order to create them are usually out of the question (at least for new features anyway). They’re even reminiscent of the sailing stones in Death Valley, although we’ve probably solved that mystery, but the lack of something at the end of them was the thing that was really puzzling.

Where I saw this in my backyard was a chance encounter with a couple blocks of dry ice that came with a delivery of frozen meals. They weren’t as big as the blocks in the movie above, although you can get them pretty easily if you know where to look, but of course the science nerd in my wife and I couldn’t resist playing with them in the kid pool we had set up. The result wasn’t exactly surprising since we’ve all seen this kind of stuff before but it was rather interesting to see the same principles at work on Earth just as they are on Mars.

The effect isn’t nearly as dramatic but you can definitely see the same carbon dioxide cushion at work which makes the block appear to glide on the surface rather than bobbing in it like water ice does. Another cool thing (which I didn’t show in the video) is when it’s placed just below the surface that same cushion will actually propel it straight to the bottom where it will pin itself and bubble like crazy until it’s all melted away.

I’d recommend doing this for yourself as it’s one thing to see it in a video and a completely different thing altogether to play around with it. Of course there’s a whole host of other things you can do, some which I’d probably not recommend (anything that involves a pressure vessel contains a certain amount of danger), but just watching it interact with other things is pretty satisfying.