Thursday, June 17

Ice freezes thanks to heat


Ice freezes thanks to heat

Ice freezes thanks to heat

The first step in the formation of ice requires that the water is heated: it is essential to achieve an extra dose of energy that harmonizes the activity of water molecules, according to new research led by scientists from the Graz University of Technology ( TU Graz) in Austria.

It sounds strange if we think about the temperature of the ice, but the specialists came to this conclusion after analyzing in detail the microscopic conditions of the ice formation, a process that until now is difficult to understand in depth because conventional microscopes are too slow. to follow the movement of water molecules.

Now, the scientists responsible for the new study, published in the journal Nature Communications, believe from their observations that water molecules repel each other and need to gain enough energy to overcome that repulsion before ice formation occurs: in others words, water has to heat up before turning to ice.

The paradox of heat and ice

Water is known to freeze and turn to ice when it interacts with a cold surface. How does that process happen concretely on a microscopic scale? That’s the question the Austrian scientists asked themselves, collaborating with colleagues from the British universities of Cambridge and Surrey.

The specialists explained in a Press release that this initial moment of ice formation is called “nucleation.” The first step to freeze water it occurs in a negligible time: it happens in a fraction of a billionth of a second.

Because it takes place in such a short time, it is impossible to observe the process with conventional microscopes, as indicated above. In this way, in order to appreciate the combination of water molecules when they come into contact with surfaces at low temperatures, it was necessary to use a new technology.

Observations and process control

The scientists used a device called the Helium Spin-Echo (HeSE), created at the Cavendish Laboratory at the University of Cambridge. It allows to follow the movement of atoms and molecules, by analyzing the dispersion of helium on a specific surface.

The researchers placed water molecules on an icy graphene surface, observing how they repel each other because their hydrogen atoms are oriented in the same direction.

The phenomenon is similar to what could be observed when joining two magnets with the same polarity, which will immediately tend to separate. Under these conditions, the water could not turn into ice crystals.

The results of the observations and tests indicated that an essential step for the transformation of the Water in ice it is the rearrangement of dispersed molecules, which in principle collide and cannot unite to generate “nucleation.” To achieve that goal you need additional energy, which precisely comes from the heat.

Along with the observations made, the specialists carried out computer simulations that made it possible to verify the characteristics of the phenomenon. They even managed to control it, activating or deactivating the onset of icing by adding a slight addition of heat or removing it.

Related topic: Boiling water can be turned into ice without power consumption.

The applications of discovery

According to the researchers, the finding will make it possible to advance towards the development of new applications and technologies capable of controlling and managing ice production. It is not a minor issue: these advances could prevent the freezing of the engines of an aircraft in mid-flight or the paralysis of a power generation system for the same reasons.

Furthermore, as ice is present in different contexts both on our planet and in the rest of the universe, an in-depth understanding of the mechanics of its formation can have implications in multiple fields of research.

Reference

Motion of water monomers reveals a kinetic barrier to ice nucleation on graphene. Anton Tamtögl, Emanuel Bahn, Marco Sacchi, Jianding Zhu, David J. Ward, Andrew P. Jardine, Stephen J. Jenkins, Peter Fouquet, John Ellis and William Allison. Nature Communications (2021).DOI:https://doi.org/10.1038/s41467-021-23226-5

Photo: The results of the study lead to a completely new understanding of ice formation: water molecules require additional energy in the form of heat before freezing. Credit: Lunghammer – TU Graz.


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