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Fluids

Triple point of carbon dioxide


Under normal atmospheric pressure (1 atm) frozen carbon dioxide (dry ice) has a temperature of below its melting point of -78^oC. However, it does not melt at room temperature. The reason is that under 1 atmosphere of pressure liquid carbon dioxide can not exist. As a consequence carbon dioxide sublimates directly from its solid phase into its gas phase.
However, under a pressure of about 5 atmosphere liquid carbon dioxide can exist. A nice video from MI Streamnet shows that phenomenon.
The video shows this in two different ways. The idea of the experiment is simply that frozen carbon dioxide, while sublimating into carbon dioxide gas inside a closed container, builds up sufficient pressure in the interior of the container for it to turn into liquid carbon dioxide.

critical point