Notable exceptions to this rule exist, the most famous one being the melting of ice. Recently, some experimentalists have discovered a number of other materials that have anomalous melting properties.
Measurements realized at a synchrotron facility (a ring in which electrons are accelerated) on a sodium crystal, which is archetype of a so-called ‘simple’ metal, have indicated that above a certain compression the sample begins to contract upon melting. This effect is so pronounced that it causes the melting temperature to decrease all the way down to room temperature! [Gregoriantz, et al., Physical Review Letters 2005]
Thanks to computer simulations of solids and liquids and to quantum mechanics calculations, an international research group from Belgium (Jean-Yves Raty, FNRS-University of Liège), Canada (Prof. Stanimir Bonev, Dalhousie University) and California (Dr Eric Schwegler, Lawrence Livermore National Laboratory), managed to reproduce the results of the experiments.
Researchers were surprise to discover that not only the sodium atoms were modified under pressure with a modification of their arrangement, but that the electrons themselves were transformed: the electronic cloud gets modified, the electrons sometimes get trapped into interstitial voids of the liquid and the bonds between atoms adopt some specific directions. This behavior is totally new in a liquid as one expects that metals get compacter with pressure, the ‘harder’ nuclei behaving as billiard balls in a quasi-uniform sea of electrons. Thanks to our simulations, we have shown that this new liquid is not a perfect metallic anymore and thus, even its color should change. Today, evidence is building from other calculations in the scientific group as well as experiments underway in various labs that the other seemingly simple metals in the periodic table may exhibit unusual melting as well.The results are published in next issue of Nature magazine (September 27th). "Electronic and structural transitions in dense liquid sodium"
Jean-Yves Raty , Eric Schwegler & Stanimir A. Bonev.
Didier Moreau | alfa
Gamma rays will reach beyond the limits of light
23.10.2017 | Chalmers University of Technology
Creation of coherent states in molecules by incoherent electrons
23.10.2017 | Tata Institute of Fundamental Research
Salmonellae are dangerous pathogens that enter the body via contaminated food and can cause severe infections. But these bacteria are also known to target...
University of Maryland researchers contribute to historic detection of gravitational waves and light created by event
On August 17, 2017, at 12:41:04 UTC, scientists made the first direct observation of a merger between two neutron stars--the dense, collapsed cores that remain...
Seven new papers describe the first-ever detection of light from a gravitational wave source. The event, caused by two neutron stars colliding and merging together, was dubbed GW170817 because it sent ripples through space-time that reached Earth on 2017 August 17. Around the world, hundreds of excited astronomers mobilized quickly and were able to observe the event using numerous telescopes, providing a wealth of new data.
Previous detections of gravitational waves have all involved the merger of two black holes, a feat that won the 2017 Nobel Prize in Physics earlier this month....
Material defects in end products can quickly result in failures in many areas of industry, and have a massive impact on the safe use of their products. This is why, in the field of quality assurance, intelligent, nondestructive sensor systems play a key role. They allow testing components and parts in a rapid and cost-efficient manner without destroying the actual product or changing its surface. Experts from the Fraunhofer IZFP in Saarbrücken will be presenting two exhibits at the Blechexpo in Stuttgart from 7–10 November 2017 that allow fast, reliable, and automated characterization of materials and detection of defects (Hall 5, Booth 5306).
When quality testing uses time-consuming destructive test methods, it can result in enormous costs due to damaging or destroying the products. And given that...
Using a new cooling technique MPQ scientists succeed at observing collisions in a dense beam of cold and slow dipolar molecules.
How do chemical reactions proceed at extremely low temperatures? The answer requires the investigation of molecular samples that are cold, dense, and slow at...
23.10.2017 | Event News
17.10.2017 | Event News
10.10.2017 | Event News
23.10.2017 | Life Sciences
23.10.2017 | Physics and Astronomy
23.10.2017 | Health and Medicine