Liquid water remains a mystery even after decades of dedicated scientific investigations and researchers still struggle to fully describe its unusual structure and dynamics. At high temperatures and high pressures, water is in the so called supercritical state and exhibits a number of peculiar characteristics that are very unlike from water at ambient conditions.
In this state water is a very aggressive solvent, enabling chemical reactions impossible otherwise, e.g. the oxidization of hazardous waste or the conversion of aqueous biomass streams into clean water and gases like hydrogen and carbon dioxide.
High temperature and high pressure conditions can also be found inside the Earth, in its lower crust and upper mantle. Here, the unique properties of supercritical water have been believed to play a key role in the transfer of mass and heat as well as in the formation of ore deposits and volcanoes. Supercritical water is even thought to have contributed to the origin of life.
Knowledge of the structural properties of water on an atomic scale under these extreme conditions of high temperature and high pressure may become very helpful in understanding these processes, says Christoph Sahle, from the Department of Physics at the University of Helsinki and a member of the research team behind the new results.
Spectroscopic investigations confirm previous theoretical model
Now, a research team of scientists from the Technische Universität Dortmund, Germany, the University of Helsinki, Finland, the Deutsches GeoForschungsZentrum in Potsdam, Germany, and the European Synchrotron Radiation Facility (ESRF), Grenoble, France, have used x-ray spectroscopy to study the structural properties of water in the supercritical state.
Conventional spectroscopic analyses can provide key insights into the atomic structure of a substance, however, these techniques are not well suited to studying water under supercritical conditions because of the complicated sample environments in which supercritical water has to be contained. Using the intense x-ray radiation from the ESRF for inelastic x-ray scattering spectroscopy and a new technique that makes it possible to look at the chemistry of water inside a complex environment together with a quantum mechanical modeling framework known as density functional theory, the group of scientists has made these spectroscopic investigations of water at high temperature and high pressure feasible.
The researchers found that the measured inelastic x-ray scattering spectra evolve systematically from liquid-like at ambient conditions to more gas-like at high temperatures and pressures. To learn more about the local atomic structure of water at the tested conditions, theoretical inelastic x-ray scattering spectra from computer simulations were calculated and compared to the experimental data. All features found in the experimental data and the systematic changes of these features as a function of temperature and pressure could be reproduced by the calculation.
Based on this close resemblance of the calculated and measured data, the authors extracted detailed information about the atomic structure and bonding. They could show that, according to the theoretical model, the microscopic structure of water remains homogeneous throughout the range of examined temperatures and pressures.
The presented findings also implicate means to study unknown disordered structures and samples under extreme conditions on an atomic scale in depth even when other structural probing techniques fail.
Read more: Microscopic Structure of Water at Conditions of the Earth's Crust and Mantle, http://www.pnas.org/content/early/2013/03/07/1220301110
Additional information:Christoph Sahle
Christoph Sahle | EurekAlert!
Water - as the underlying driver of the Earth’s carbon cycle
17.01.2017 | Max-Planck-Institut für Biogeochemie
Modeling magma to find copper
13.01.2017 | Université de Genève
Researchers from the University of Hamburg in Germany, in collaboration with colleagues from the University of Aarhus in Denmark, have synthesized a new superconducting material by growing a few layers of an antiferromagnetic transition-metal chalcogenide on a bismuth-based topological insulator, both being non-superconducting materials.
While superconductivity and magnetism are generally believed to be mutually exclusive, surprisingly, in this new material, superconducting correlations...
Laser-driving of semimetals allows creating novel quasiparticle states within condensed matter systems and switching between different states on ultrafast time scales
Studying properties of fundamental particles in condensed matter systems is a promising approach to quantum field theory. Quasiparticles offer the opportunity...
Among the general public, solar thermal energy is currently associated with dark blue, rectangular collectors on building roofs. Technologies are needed for aesthetically high quality architecture which offer the architect more room for manoeuvre when it comes to low- and plus-energy buildings. With the “ArKol” project, researchers at Fraunhofer ISE together with partners are currently developing two façade collectors for solar thermal energy generation, which permit a high degree of design flexibility: a strip collector for opaque façade sections and a solar thermal blind for transparent sections. The current state of the two developments will be presented at the BAU 2017 trade fair.
As part of the “ArKol – development of architecturally highly integrated façade collectors with heat pipes” project, Fraunhofer ISE together with its partners...
At TU Wien, an alternative for resource intensive formwork for the construction of concrete domes was developed. It is now used in a test dome for the Austrian Federal Railways Infrastructure (ÖBB Infrastruktur).
Concrete shells are efficient structures, but not very resource efficient. The formwork for the construction of concrete domes alone requires a high amount of...
Many pathogens use certain sugar compounds from their host to help conceal themselves against the immune system. Scientists at the University of Bonn have now, in cooperation with researchers at the University of York in the United Kingdom, analyzed the dynamics of a bacterial molecule that is involved in this process. They demonstrate that the protein grabs onto the sugar molecule with a Pac Man-like chewing motion and holds it until it can be used. Their results could help design therapeutics that could make the protein poorer at grabbing and holding and hence compromise the pathogen in the host. The study has now been published in “Biophysical Journal”.
The cells of the mouth, nose and intestinal mucosa produce large quantities of a chemical called sialic acid. Many bacteria possess a special transport system...
10.01.2017 | Event News
09.01.2017 | Event News
05.01.2017 | Event News
17.01.2017 | Earth Sciences
17.01.2017 | Materials Sciences
17.01.2017 | Architecture and Construction