The discovery of new ice may change our understanding of water

New ice discovery may change understanding of water

Part of the preparation to create medium density amorphous ice. Credit: Christoph Salzmann

Researchers at UCL and the University of Cambridge have discovered a new type of ice that looks more like liquid water than any other known ice, and may rewrite our understanding of water and its many anomalies.

The newly discovered ice is amorphous – that is, its particles are in a disordered shape, not as neatly arranged as they are in regular crystalline ice. Amorphous ice, although rare on Earth, is the main type of ice found in space. This is because in the colder environment of space, ice does not have enough heat energy to form crystals.

For the study published in the journal SciencesThe research team used a process called ball milling, vigorously shaking regular ice with steel balls into a jar chilled to -200 degrees Celsius.

They found that rather than ending in small chunks of regular ice, the process resulted in a new, amorphous form of ice that, unlike all known ice, had the same density as liquid water Which is similar to water in solid form. They called the new ice “medium density.” amorphous ice(The red star of David).

The team suggested that MDA (which looks like a fine white powder) may be present within the ice moons of the outer solar system, such as tidal forces Gas giants such as Jupiter and Saturn may exert similar shearing forces on plain ice as those produced by ball milling. In addition, the team found that when MDA was heated and recrystallized, it released an unusual amount of heat, meaning it could trigger tectonic movements and “ice quakes” in the kilometer-thick ice sheets on moons like Ganymede.

Fresh snow looks like a shot of liquid water

The new form of ice is very similar in molecular structure to liquid water (left), compared to regular crystal snow (right). Credit: University of Cambridge

Senior author Professor Christoph Salzmann (UCLA Chemistry) said: “Water is the basis of all life. Our existence depends on it, and we launch space missions to look for it, but from a scientific point of view it is poorly understood.

We know of 20 crystalline forms of ice, but only two major types of amorphous ice have been discovered previously, known as High density And amorphous snow has a low density. There is a large density gap between them and the accepted wisdom is that there is no ice within this density gap. Our study shows that the density of MDA falls precisely within this density gap, and this finding may have far-reaching consequences for our understanding of liquid water and its many anomalies.”

The density gap between known amorphous ices has led scientists to propose that water does in fact exist as two liquids at very cold temperatures and that theoretically, at a certain temperature, both of these liquids could coexist, with one type floating on top of the other, as when mixing Oil and water. This hypothesis has been demonstrated in computer simulations, but not confirmed by experiment. The researchers say their new study may raise questions about the validity of this idea.

Professor Salzmann said, “Existing models of water must be retested. They must be able to explain the existence of amorphous ice of medium density. This may be the starting point for finally explaining liquid water.”

The researchers suggested that the newly discovered ice may be the true glassy state of liquid water – that is, an exact replica of liquid water in solid form, in much the same way that the glass in windows is Solid form of liquid silicon dioxide. However, another scenario is that MDA is not glassy at all, but is in a highly refractive crystalline state.

Co-author Professor Andrea Sella (UCLA Chemistry) said: “We have shown that it is possible to create what looks like a kind of standing water. This is a very unexpected and surprising discovery.”

The lead author, Dr. We realized we had come up with a whole new kind of thing, with some cool properties.”

New ice discovery may change understanding of water

Part of the preparation to create medium density amorphous ice. Credit: Christoph Salzmann

By simulating the ball milling action by randomly repeated shearing of the crystal ice, the team also created a computational model for MDA. Dr. Michael Davies, who performed computer modeling while earning his Ph.D. A student in the ICE (Interfaces, Catalytic and Environmental) Laboratory at UCL and the University of Cambridge said, “Our discovery of MDA raises many questions about the nature of liquid water, and therefore understanding the precise atomic structure of MDA is very important.”

The water contains many anomalies that have puzzled scientists for a long time. For example, water is at its highest density at 4°C and becomes less dense as it freezes (hence ice floats). Also, the more you squeeze liquid water, the easier it becomes to compress it, a deviation from the correct principles of most other substances.

Amorphous ice was first discovered in its low-density form in the 1930s when scientists condensed water vapor on a metal surface cooled to -110 degrees Celsius. Its high-density state was discovered in the 1980s when normal ice was compressed at around 200°C. While common in space, on Earth, amorphous ice is only thought to occur in the colder upper reaches of the atmosphere.

Ball milling is a technique used in many industries to grind or blend materials, but has never before been applied to ice. In the study, liquid nitrogen was used to cool a grinding jar to -200 °C and the density of ball-crushed ice was determined from its buoyancy in liquid nitrogen. The researchers used a number of other techniques to analyze the structure and properties of MDA, including X-ray diffraction (looking at the pattern of X-rays reflected off ice) and Raman spectroscopy (looking at how light scatters off ice) at UCLA. Chemistry as well as small angle diffraction at UCL’s Nature-inspired Engineering Center to explore its long-range structure. They have also successfully replicated the medium-density ice production process in a computer simulation, using the UCL Kathleen high-performance computing facility.

Moreover, they used thermometry to examine the heat released whendensity Recrystallization of ice warmer temperatures. They found that if they compress MDA and then heat it, it releases a surprisingly large amount of energy as it recrystallizes, which indicates that H2O could be a high-energy geophysical substance that may drive tectonic movements in the solar system’s icy moons.

more information:
Alexandre Rousseau-Vinsen et al., Amorphous medium-density ice, Sciences (2023). DOI: 10.1126/science.abq2105.

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