 |
 |
A breakthrough discovery in the nature of glass |
|
For over 50 years scientists have tried to understand just what glass is. Work so far has focused on trying to understand the traffic jam, but now Dr Paddy Royall from the University of Bristol, with colleagues in Canberra and Tokyo, has shown that the problem really lies with the destination, not with the traffic jam. Publishing in june in Nature Materials, the team has revealed that glass ‘fails’ to be a solid due to the special atomic structures that form in a glass when it cools (ie, when the atoms arrive at their destination).
“Some materials crystallize as they cool, arranging their atoms into a highly regular pattern called a lattice. But although glass ‘wants’ to be a crystal, as it cools the atoms become jammed in a nearly random arrangement,” said Royall. “Back in the 1950s, Sir Charles Frank in the Physics Department at Bristol University suggested that the arrangement of the ‘jam’ should form what is known as an icosahedron, but at the time he was unable to provide experimental proof. We set out to see if he was right.”
The problem is you can’t watch what happens to atoms as they cool because they are just too small. So using special particles called colloids that mimic atoms, but are just large enough to be visible using state-of-the-art microscopy, Royall cooled some down and watched what happened. What he found was that the gel these particles formed also ‘wants’ to be a crystal, but it fails to become one due to the formation of icosahedra-like structures – exactly as Frank had predicted 50 years ago. It is the formation of these structures that underlie jammed materials and explains why a glass is a glass and not a liquid – or a solid.
Knowing the structure formed by atoms as a glass cools represents a major breakthrough in our understanding of so-called “meta-stable” materials like glass, Royall said. It will also allow further development of new materials such as metallic glasses, he added.
Metals normally crystallize when they cool. Unfortunately, stress builds up along the boundaries between crystals, which leads to metal failure. The world’s first jetliner, the British built De Havilland Comet, fell out of the sky due to metal failure. If a metal could be made to cool with the same internal structure as a glass and without crystal grain boundaries, it would be less likely to fail, Royall said: such “metallic glasses” could be suitable for a range of products that need to be flexible such as aircraft wings, golf clubs and engine parts.
Illustration :
Colloidal particules, that mimic atoms, form a gel with the structure of glass
Credit : Paddy Royall, University of Bristol, UK
|
| http://www.nature.com/nmat/journal/v7/n7/full/nmat2219.html |
|
|
|
|
|
 |
|
|
Solidification is one of the oldest processes for procuding useful implements and remains one of the most important modern commercial processes. Since the 1980s, rapid and fundamental developments in the understanding of solidification have come from both analytical theories and from the widerspread availability of powerful computational techniques. This book describes the fundamentals of the technology in the context of these recent developments, presenting them in a coherent way, using consistent notation.
|
 |
|
|
Nouvelle édition augmentée de deux nouveaux chapitres, l’un consacré à la détermination structurale, l’autre aux éléments de structures cristallines.
|
 |
|
|
Cet ouvrage est le premier en langue française consacré aux matériaux verre et céramique depuis près de 35 ans.
|
 |
|
|
Ce livre fera voyager le lecteur de la métallurgie aux derniers développements en cryobiologie ou des technologies verrières au domaine agroalimentaire en passant par la science des polymères.
|
|
