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Planes with glass wings?

June 22, 2008
Courtesy University of Bristol
and World Science staff

Airplanes with glass wings might become a possibi­lity, thanks to a new in­sight into the na­ture of glass, some sci­en­tists say.

Al­though it looks sol­id, glass is ac­tu­ally a “jammed” state of mat­ter, ac­cord­ing to re­search­ers at the Uni­ver­s­ity of Bris­tol, U.K. and else­where. Un­like or­di­nary sol­ids, whose mo­le­cules crys­tal­lize in­to sta­ble grid-like ar­range­ments, atoms in a glass can’t reach their des­tina­t­ion be­cause the route is blocked by their neigh­bors. Thus glass nev­er quite be­comes a “prop­er” sol­id.

Colloidal particles mi­mick­ing atoms form a gel that sci­ent­ists say has the same struc­ture as glass. (Cour­tesy Pad­dy Roy­all)


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 the uni­ver­s­ity’s Pad­dy Roy­all, with col­leagues in Aus­tral­ia and Ja­pan, found that the prob­lem really lies with the des­tina­t­ion, not with the jam.

The sci­en­tists con­clud­ed that glass fails to be a true sol­id be­cause of spe­cial atom­ic struc­tures that form in a glass when it cools, as it the atoms ap­proach their des­tina­t­ions.

“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 that you can’t watch what atoms do as they cool be­cause they are just too small, Roy­all ex­plained. So he worked with spe­cial par­t­i­cles called col­loids that mim­ic atoms, but are just large enough to be vis­i­ble with newer mi­cro­scopes. Roy­all cooled some of the corp­us­cules down and watched. 

He found, he said, that the par­t­i­cles formed a gel that al­so “wants” to be a crys­tal, but fails to do so due to the forma­t­ion of icosahedra-like struc­tures—just as Frank had pre­dicted. The forma­t­ion of these struc­tures is what leads to “jammed” ma­te­ri­als and ex­plains why a glass is nei­ther liq­uid nor sol­id, he added.

The find­ings are pub­lished in the June 22 is­sue of the re­search jour­nal Na­ture Ma­te­ri­als.

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.


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Imagine a plane with glass wings. Thanks to a new analysis of the nature of glass, scientists say this is a possibility. Although it looks solid, glass is actually a “jammed” state of matter, according to the University of Bristol, U.K., researchers. Unlike ordinary solids, whose molecules crystallize into stable grid-like arrangements, atoms in a glass can’t reach their destination because the route is blocked by their neighbors. Thus glass never quite becomes a “proper” solid. 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 the university’s Paddy Royall, with colleagues in Australia and Japan, found that the problem really lies with the destination, not with the jam. The scientists concluded that glass fails to be a true solid because of special atomic structures that form in a glass when it cools, as it the atoms approach their destinations. “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 that you can’t watch what atoms do as they cool because they are just too small, Royall explained. So using special particles called colloids, that mimic atoms, but are just large enough to be visible with newer microscopes, Royall cooled some down and watched. What he found, he said, was that the gel these particles formed also “wants” to be a crystal, but fails to do so due to the formation of icosahedra-like structures—just as Frank had predicted. The formation of these structures is what leads to “jammed” materials and explains why a glass is neither liquid nor solid, he added. The findings are published in the June 22 issue of the research journal Nature Materials. 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 claims. In other words, he added, “metallic glasses” could be suitable for a whole range of products that need to be flexible such as aircraft wings, golf clubs and engine parts.