A collaborative team of scientists from the University of Cambridge and University College London discovered a new type of ice that resembles water more than any other. This type of ice may be vital to understanding the most well-known liquids, according to an institutional press release.
Unlike ordinary crystalline ice, the new form is amorphous, in which the molecules are disorganized, like in liquid.
The research team produced this new amorphous ice in the experiment and generated an atomic-scale model in a computer simulation. In the trials, crystalline ice was ground into tiny particles using the ball-milling process in a steel jar. Although it is frequently employed to create amorphous materials, ice has never been subjected to ball-milling.
MDA: Unlike all other ice
The researchers discovered that ball-milling produced an amorphous type of ice with a density comparable to liquid water and a condition that resembled water in solid form, unlike all other known ice. Their novel ice was given the term medium-density amorphous ice (MDA).
“Our discovery of MDA raises many questions on the very nature of liquid water, and so understanding MDA’s precise atomic structure is very important,” said co-author Dr. Michael Davies, who carried out the computational modeling. “We found remarkable similarities between MDA and liquid water.”
It has been proposed that amorphous ice serves as a model for liquid water. Amorphous ice has historically been divided into two primary categories: high-density and low-density ice.
“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,” senior author Prof. Christoph Salzmann.
Besides, MDA exhibits a stunning quality unique from other types of ice. They discovered via calorimetry that MDA releases a remarkable amount of heat as it recrystallizes to common ice. The heat produced by MDA’s recrystallization may contribute to the tectonic motions. This finding demonstrates that water can be a high-energy geophysical substance more generally.
The study was published in Science on February 2.
Study abstract:
Amorphous ices govern a range of cosmological processes and are potentially key materials for explaining the anomalies of liquid water. A substantial density gap between low-density and high-density amorphous ice with liquid water in the middle is a cornerstone of our current understanding of water. However, we show that ball-milling “ordinary” ice Ih at low temperatures gives a structurally distinct medium-density amorphous ice (MDA) within this density gap. These results raise the possibility that MDA is the true glassy state of liquid water or, alternatively, a heavily sheared crystalline state. Notably, the compression of MDA at low temperatures leads to a sharp increase of its recrystallization enthalpy, highlighting that H2O can be a high-energy geophysical material.
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