Scientists discover a strange new form of ice that could change the way we think about water

Scientists discover a strange new form of ice that could change the way we think about water

  • Post category:Technology

Scientists vibrating ordinary frozen water in a jar with ultra-cold steel balls have discovered a previously unknown form of ice that is closer to liquid water than any other ice to date.

This is amorphous ice, a form not found naturally on Earth. This is because its atoms are not arranged in a clean, repeating crystalline pattern, but blended together, an atomic omnishamble.

But the amorphous ice that results from the team’s experiments, a process called ball milling, is unlike any amorphous ice ever seen before.

Amorphous ice typically has a low density, around 0.94 grams per cubic centimeter, or a high density, starting at 1.13 grams per cubic centimeter. The new ice has a density of 1.06 grams per cubic centimeter, which is incredibly close to the density of water at 1 gram per cubic centimeter.

Researchers led by chemist Alexander Rosu-Finsen, formerly of University College London in the UK, have dubbed the new form medium-density amorphous (MDA) ice.

“Water is the basis of all life. Our existence depends on it, we launch space missions to look for it, but from a scientific point of view it is misunderstood,” explains chemist Christoph Salzmann of University College London.

“We know of 20 crystalline forms of ice, but so far only two main types of amorphous ice, known as high-density and low-density amorphous ice, have been discovered. No ice exists in this density gap,” says Salzmann.

“Our study shows that the density of MDA falls exactly within this density gap, and this finding may have far-reaching implications for our understanding of liquid water and its many anomalies.”

Water, don’t beat around the bush, it’s just weird. Because it’s so ubiquitous and necessary for our survival, we don’t think much about it, but it doesn’t follow the same rules as other liquids.

It is a universal solvent; that is, many other substances dissolve in it very easily. Its surface tension is unusually high compared to other liquids, as is its boiling point.

And its density under refrigerated conditions is perhaps the strangest of all: when most liquids freeze, their density increases. Water does the opposite: it becomes less dense, which means that water ice is generally less dense than water. That’s why ice cubes float in your drink.

But not all ice cream is the same. Here on Earth, ice naturally takes on a crystalline form, with its atoms arranged in a repeating hexagonal pattern. This is why snowflakes are usually hexagonal. In the near-vacuum of space, however, ice is generally amorphous because the atoms do not store enough thermal energy to coil themselves into a crystalline structure.

The density gap in amorphous ice has been quite fundamental to our understanding of water. In fact, previous research and simulations have suggested that the split could mean that at very cold temperatures, water exists as two separate liquids, coexisting even like oil and water, rather than mix if the conditions are met. Hey, the water did some weird things.

Part of the experimental apparatus for crushing ice. (Christoph Salzman)

But then Rosu-Finsen and his colleagues grabbed some steel balls. Ball milling is an industrial technique for grinding or mixing materials. Researchers cooled a grinding jar to -200 degrees Celsius (-328 degrees Fahrenheit) with liquid nitrogen, added plain water ice, and shook things up.

“We shook the ice like crazy for a long time and destroyed the crystal structure,” says Rosu-Finsen. “Rather than ending up with smaller pieces of ice, we realized we had found something completely new with remarkable properties.”

The meaning of these properties is still not entirely clear. MDA could be a “glassy” state of liquid water, the researchers suggest. Although amorphous ice does not form naturally, other amorphous solids exist; Glass is one of them, and it is simply a solid form of liquid silicon dioxide. But MDA could also just be highly sheared crystalline ice.

This suggests that our existing water models need to be revisited to see where MDA fits into the picture. But it already looks promising for explaining some of the behaviors of water ice in the Universe.

The researchers experimented to see what happens when MDA is recrystallized, compressed and heated. They found that this process releases a surprising amount of energy, suggesting that MDA may play a role in tectonic activity on ice-covered worlds like Jupiter’s moon Ganymede.

And the discovery also shows potential for future experiments and studies of the special properties of water.

“We have shown that it is possible to produce water that looks like a sort of stop-motion water,” says chemist Andrea Sella from University College London.

“This is an unexpected and quite surprising finding.”

The research has been published in Science.


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