In probing mysteries of glass, researchers find a key to toughness

Feb 26, 2013

Glass doesn't have to be brittle. Scientists propose a way of predicting whether a given glass will be brittle or ductile—a property typically associated with metals like steel or aluminum—and assert that any glass could have either quality.

In a paper published online Feb. 26 in the journal Nature Communications, a Yale University team and collaborators propose a way of predicting whether a given glass will be brittle or ductile—a desirable property typically associated with metals like steel or aluminum—and assert that any glass could have either quality.

Ductility refers to a material's plasticity, or its ability to change shape without breaking.

"Most of us think of glasses as brittle, but our finding shows that any glass can be made ductile or brittle," said Jan Schroers, a professor of and at Yale, who led the research with Golden Kumar, a professor at Texas Tech University. "We identified a special temperature that tells you whether you form a ductile or brittle glass."

The key to forming a ductile glass, they said, is cooling it fast. Exactly how fast depends on the nature of the specific glass.

Focusing on a new group of glasses known as bulk metallic glasses (BMGs)—, or blends, that can be extremely pliable yet also as strong as steel—researchers studied the effect of a so-called critical fictive temperature (CFT) on the glasses' at .

When forming from liquid, there is a temperature at which glass becomes too viscous for reconfiguration and freezes. This temperature is called the glass transition temperature. Based on experiments with three representative bulk metallic glasses, the researchers said there is also, for each distinct alloy, a that determines the brittleness or plasticity of the glass. This is the CFT.

Researchers said it's possible to categorize glasses in two groups—those that will be brittle because in liquid form their CFT is above the glass transition temperature, and those that will be ductile, because in liquid form their CFT is below the .

They previously thought a liquid's chemical composition alone would determine whether a glass would be brittle or ductile.

"That's not the case," Schroers said. "We can make any glass theoretically ductile or brittle. And it is the critical fictive temperature which determines how experimentally difficult it is to make a ductile glass. That is the major contribution of this work."

The finding applies theoretically to all glasses, not metallic glasses only, he said.

"A glass can have completely different properties depending on the rate at which you cool it," Schroers said. "If you cool it fast, it is very ductile, and if you cool it slow it¹s very brittle. We anticipate that our finding will contribute to the design of ductile glasses, and in general contribute to a deeper understanding of glass formation."

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rah
1 / 5 (2) Feb 26, 2013
So how long will it be until they can start hammering or pressing glass into different shapes?
nkalanaga
1 / 5 (1) Feb 26, 2013
Instead of Star Trek's transparent aluminum, maybe we'll have glass spaceships, and simply paint the parts we don't want to look through?
RichTheEngineer
5 / 5 (4) Feb 26, 2013
ref: Larry Niven's Known Space series, General Products spaceship hulls.
Shootist
2.4 / 5 (5) Feb 26, 2013
ref: Larry Niven's Known Space series, General Products spaceship hulls.


Are a single molecule grown to the shape desired, transparent to unharmful amounts of EM radiation, 100% opaque to neutrinos and which evaporates when exposed to minute quantities of antimatter.
ODesign
3 / 5 (2) Feb 26, 2013
very exciting news.

it's a bit hard to believe, so I look forward to seeing physical objects instead of just equations predicting their possibility. Or maybe I'm misunderstanding the potential for a metallic glass with custom chosen range of ductility/brittleness. in theory this sounds like a replacement for steel that doesn't corrode and might even be self healing to some degree like window pane glass can self heal fine scratches. But in practice, maybe cooling metal glass uniformly to the specs requires heat dissipation scaffolding inside the glass to keep temperture uniform and at the right rate. Lots of other possible engineering hurdels might come up even if the potential is to replace steel.
ValeriaT
1 / 5 (2) Feb 26, 2013
very exciting news.
Only for those, who know physics from popular TV shows only - as this finding is not new at all. The so-called "Prince Rupert's drops" are very hard. Once they're broken at some place though, the fracture propagates across whole bulk of material - which is the price for their toughness before fracture. The increasing of ductility of glass with fast cooling is already used industrially in production of hardened ductile glass. Everyone of you has it in your car already. The question rather is, why you're so surprised with it. It's evident, due the overspecialization the modern kids are separated from technologies, which are surrounding them. They remember number of cheat codes for computer games, but they don't know anything about real world, which is surrounding them.
Static
1 / 5 (1) Feb 26, 2013
Researchers said it's possible to categorize glasses in two groups—those that will be brittle because in liquid form their CFT is above the glass transition temperature, and those that will be ductile, because in liquid form their CFT is below the glass transition temperature.
So...there are two types of glasses: One, which will freeze before it reaches the CFT temperature, and it is the strong glass. The other type reaches the CFT temperature before freezing, which changes its internal structure significantly enough to cause it to be brittle.
They previously thought a liquid's chemical composition alone would determine whether a glass would be brittle or ductile.

"That's not the case," Schroers said. "We can make any glass theoretically ductile or brittle."
Therefore...it's somehow possible to freeze the glass fast enough to avoid the viscous reconfiguration? Wouldn't our efforts be better suited to look at WHY the reconfiguration happens?
Grallen
5 / 5 (1) Feb 26, 2013
I think this means glass that can literally be reformed through mechanical force, not like the glass in the car that will still shatter if you attempt that.

Anyways. I look forward to seeing a cold bar of glass bent in half. I wonder if it would remain clear.
nkalanaga
not rated yet Feb 27, 2013
Grallen: That's the way I read it too. Glass that can actually be handled like a metal, not something super-hard but very fragile.

Rich and Shootist: I though of General Products as well, but as Shootist says, their hulls have at least one drawback. For our near-term purposes ductile glass would be more useful. For one thing, it's possible to cut a hole in one AFTER it's built if you want to make changes!