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.