“Amorphous ice”: scientists discovered a new type of ice with properties similar to liquid water

For the find, the team implemented a process using steel balls in a container at about -200 degrees (Credit: University College London)

A new discovery raises many questions about the very nature of liquid water. The new form of ice, which has been discovered in new research just published in Science, is amorphous. Unlike ordinary crystalline ice where the molecules are arranged in a regular pattern, in “amorphous ice” the molecules are in a disorganized shape that resembles the structure of a liquid.

The discovery team created a new form of amorphous ice in an experiment and achieved an atomic-scale model in computer simulation. The experts used a technique called ball milling, which grinds crystalline ice into small particles using metal balls in a steel bowl.

The ball mill is regularly used to make amorphous materials, but it had never been applied to ice.

It has been suggested that amorphous ices are models for liquid water (istock)

The professionals also discovered that ball milling created an amorphous form of ice that, unlike all other known ice, had a density similar to that of liquid water and whose state resembled that of water in solid form.

They called it medium-density amorphous (MDA) ice. To understand the process on a molecular scale, the team used computer simulation. By mimicking the ball milling procedure through repeated random cutting of crystalline ice, the team successfully created a computational model of MDA.

“Our discovery of MDA raises many questions about liquid water, so it is very important to understand the precise atomic structure of MDA. We found striking similarities between MDA and liquid water,” explained co-author Michael Davies, who carried out the computational modelling.

Bottle with amorphous ice of medium density inside, with steel balls and liquid nitrogen. Credit: University College London

Until now, there have been two main types of amorphous ice: high-density and low-density. As the names suggest, there is a large density gap between them. This, combined with the fact that the density of liquid water is in the middle, has been the cornerstone of understanding liquid water. It has led in part to the suggestion that water consists of two liquids: one of high density and one of low density.

Lead author Professor Christoph Salzmann explained: “The accepted wisdom has been that no ice exists within that density gap. Our study shows that the density of MDA is precisely within this density gap, and this finding may have far-reaching consequences for our understanding of liquid water and its many anomalies.”

The discovery of MDA raises the question of where it might exist in nature. In this study, shear forces were found to be key to creating MDA. The team suggests that ordinary ice could experience similar shear forces on ice moons due to tidal forces exerted by gas giants like Jupiter. Additionally, MDA displays a remarkable property not found in other forms of ice.

This new research could help change our understanding of this fluid and its abnormalities.

Using calorimetry, they found that when MDA is recrystallized from ordinary ice, it releases an extraordinary amount of heat.

The heat released by the recrystallization of MDA could play a role in triggering the tectonic movements. More generally, this discovery shows that water may be a high-energy geophysical material that can drive reactions in the Earth’s layers.

Professor Angelos Michaelides, lead author from Cambridge’s Yusuf Hamied Department of Chemistry, said: “Amorphous ice in general is said to be the most abundant form of water in the universe. Now the path to understanding how much MDA is and how geophysically active this newly discovered form is has begun,” he concluded.

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