Ice - a Hot Research Topic

There are 18 different types of ice and one of them was only recently discovered in a project supported by the Austrian Science Fund FWF. This project was done at the University of Innsbruck and it got a lot of attention because it precisely determined the temperature and pressure required for creating a wide variety of ices. This allows the production of ultra-pure ice for subsequently analysing its structure.

Snow flakes are only one of 18 possible forms of frozen water © Use of this photo for editorial purposes is free of charge, subject to attribution: "The Snowflake" by K. Libbrecht, P. Rasmussen, www.snowcrystals.com

Hoar frost, snow and frozen lakes - from the point of view of research, this is a boring winter idyll since all of these forms of frozen water have the same crystalline structure. Altogether, there are 13 types of crystalline ice known to science. In addition, depending upon temperature and pressure, there are also non-crystalline forms of ice known as amorphous ice. Until recently, our understanding of how various structures are created was extremely limited making it very difficult to produce them. However, the studies done by the research group around Professor Andreas Hallbrucker at the Institute for General, Inorganic and Theoretical Chemistry at the University of Innsbruck have brought about a radical change and led to the discovery of a new form of amorphous ice.

Ice - a Quick-Change Artist
In this FWF project, the team of researchers was successful at defining the precise conditions for creating a wide variety of crystalline forms of ice, although originally this analysis was "only" planned for one form. The initial material was high density amorphous ice (HDA) that develops from "normal" ice when very high pressure is exerted at -200 degrees Celsius. The Innsbruck-based research team used an experimental apparatus they developed themselves to precisely control pressure and temperature during the production process so that they were able to transform various types of ice into one another. Altogether, they were able to create six forms of crystalline ice (ice IV, V, VI, IX, XII and "normal" ice) and two amorphous forms of ice (HDA and LDA - low density amorphous).

But, that wasn't enough for them, as Dr. Ingrid Kohl from Hallbrucker's team explains: "We even discovered an unknown form of amorphous ice with a high degree of density. It is designated as very high density amorphous ice (VHDA) because we observed a reduction in volume and hence an increase in density when we heated HDA under high pressure. This is now the fifth form of amorphous ice". Dr. Kohl's colleague, Dr. Thomas Loerting, analysed VHDA very precisely in co-operation with an English group. This was only made possible in the first place by the knowledge developed on the precise conditions for creating it. This makes it possible to produce ice at a degree of purity that is essential for making a structural analysis with X-ray diffraction, neutron diffraction and Raman spectroscopy. In contrast to HDA, neutron diffraction indicated that each water molecule of VHDA is surrounded by six water molecules instead of five in a local unit of order, which also explains the loss in volume observed and therefore also its high density.

Ice in Space
Ice has been a hot topic for research ever since ice was discovered on Ganymede, one of the moons of Jupiter. And indeed, measurements made by space probes indicate that there is water in the form of amorphous ice on a number of celestial bodies. We have the team around Professor Hallbrucker to thank for having improved experimental data that explain what forms of ice exist under what given temperature and pressure conditions and what structural transformations ice goes through if conditions change, for instance if a meteor falls.

There are also other reasons why solid amorphous water is interesting to research. In contrast to crystalline ice, the water molecules are arranged in an irregular pattern, meaning that amorphous ice is similar to liquid water. It is something akin to flowing water in frozen form. This means that solid amorphous water figures prominently in researching various processes in water that are not fully understood even today. FWF has been supporting this project for a number of years and it has made a fundamental contribution to the international debate with more than 20 publications while calling upon one of the project team members to work in an American Nobel Prize laboratory.

Contact
Dr. Ingrid Kohl
Institute for General, Inorganic and Theoretical Chemistry
University of Innsbruck
Innrain 52
A 6020 Innsbruck
T +43/512/507 5109
Ingrid.Kohl(at)uibk.ac.at

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Vienna, January 19, 2004