It sounds paradoxical but scientists say they have discovered that an element can be both liquid and solid at the same time.
In a study soon to be published in the Proceedings of the National Academy of Sciences, scientists have achieved a very particular state of matter whereby potassium atoms display properties of both a liquid and a solid simultaneously.
So, how exactly does this work? It all comes down to the structure of potassium.
In its solid form, potassium has a pretty basic crystal lattice-type structure. But put the element under extremely high pressure and that structure will shift. It will become more complex, reshuffling so that five cylindrical tubes made up of atoms form an X-shape while four long chains assemble between them.
The two arrangements are loosely connected – so much so that when the temperature is turned up, the chains start to disappear as the tubes stay intact. The researchers describe it as a “chain-melting transition”.
“It would be like holding a sponge filled with water that starts dripping out, except the sponge is also made of water,” Andreas Hermann, study co-author and a condensed matter physicist at the University of Edinburgh, told National Geographic.
To find out what is going on here, Hermann and his colleagues employed a neural network, a type of AI based on the human brain and nervous system that “learns” from a bank of previous examples.
In this case, it was taught quantum mechanics using computer simulations of small groups of potassium atoms. Post-training, it was able to create simulations involving 20,000 atoms and confirmed that under the right circumstances, potassium can achieve this chain-melted state.
This occurs at pressures between 20,000 and 40,000 times higher than atmospheric pressure and only when temperatures have reached 400 to 800 Kelvin (127-527°C or 260-980°F). At this point, the weaker chains in the potassium dissolve but the stronger tubes remain solid – creating this bizarre part solid, part liquid state.
According to National Geographic, this is the first time scientists have been able to show it is possible to achieve this state and for it to be stable – for any element, which is very exciting stuff. There are over half a dozen other elements (including sodium and bismuth) that, like potassium, are thought to be able to achieve this strange state under the right circumstances.
“Potassium is one of the simplest metals we know, yet if you squeeze it, it forms very complicated structures,” Hermann said in a statement.
“We have shown that this unusual but stable state is part solid and part liquid. Recreating this unusual state in other materials could have all kinds of applications.”
This is just the latest experiment to show things aren't always as simple as they seem, particularly when it comes to states of matter. Despite what most of us learned at school, materials can exist in states other than solid, liquid, and gas. As well as plasma, scientists have discovered dropletons, the Jahn-Teller metal, Bose-Einstein condensate – even supersolids and superfluids.