Not all ice is the same. The arrangement of the actual molecules varies considerably based on the pressure and temperature conditions under which it forms.
We already know 18 of the distinct stages of ice, some occurring naturally, some only seen under laboratory conditions.
To find out, three years ago a team of researchers edited one of the existing ice structures, turning it into a form they called β-XV ice .
Just now, members of the new research team claim to have determined its exact crystal structure, answering questions about how it was formed and naming ice XIX .
This discovery could help us better understand how ice forms and behaves under conditions very different from those found on Earth.
The new tape is called β-XV tape.
The ice you see in the freezer, or fall from the sky as snowflakes or hail, is the most common natural ice on Earth. This is called band I , and its oxygen atoms are arranged in a hexagonal lattice. However, the structure is geometrically different, with the hydrogen atoms being much more disordered.
When ice I is cooled in a certain way, the hydrogen atoms can be cyclically arranged, in addition to the oxygen atoms. This is how scientists in the lab were able to create different types of ice that have a much more ordered molecular lattice than their disordered parent form.
A team of physical chemists at the University of Innsbruck in Austria has been studying band VI for some time. This is one of the forms of ice that can be found in nature, but is only subject to very high pressures, 10,000 times more than atmospheric pressure at sea level (about 1 gigapascal), such as ice found in Earth’s mantle, or wrapped around the core of Saturn’s moon Titan.
Arranged in order of hydrogen, the XV ice was discovered only about a decade ago. It is made by cooling ice to less than 130 Kelvin (-143 degrees Celsius, -226 degrees Fahrenheit) at a pressure of about 1 gigapascal.
A few years ago, by altering this process, researchers created a different type of ice. They slow down cooling and lower the temperature below 103 Kelvin, while increasing the pressure by 2 gigapascals. This creates a second arrangement of hydrogen molecules distinct from the XV band, which they named the β-XV band.
To figure out the order of the atoms in the crystal lattice, scientists need to scatter neutrons from the nuclei, so normal hydrogen atoms won’t cut it.
“Unfortunately, this also changes the time scale in ice production,” said physical chemist Thomas Loerting of the University of Innsbruck.
But doctoral student Tobias Gasser then had the more important idea of adding a few percent of normal water to heavy water. This turned out to be a huge speed boost.
Specifically, it allowed the team to obtain the neutron data they needed to piece together the crystal structure. It differs from band XV, which became an official position as the nineteenth known period, band XIX.
“This also means that for the first time, it is possible to realize an ordered transition between two ice forms in experiments,” says Loerting.