Our knowledge of glass is steadily improving and it appearsmanufacture using a vapor deposition method could be used to doublecurrent strength specifications. This takes it to the half way marktoward the theoretical limit.
All good stuff and adds to the persistent improvements we havewitnessed in the technology.
It is also nice to know that we have plenty of room for going muchfurther. A doubling of strength takes it way beyond mostspecifications and plausibly allows for items that are trulyunbreakable in terms of real application.
Glass half full:Double-strength glass may be within reach
MIKE WILLIAMSSEPTEMBER 20, 2012
Rice University studysuggests possible method for increasing the strength of glass
http://news.rice.edu/2012/09/20/glass-half-full-double-strength-glass-may-be-within-reach-2/
Glass is strong enoughfor so much: windshields, buildings and many other things that needto handle high stress without breaking. But scientists who look atthe structure of glass strictly by the numbers believe some of thelatest methods from the microelectronics and nanotechnology industrycould produce glass that’s about twice as strong as the bestavailable today.
Rice Universitychemist Peter Wolynes is one of them. Wolynes and Ricegraduate student Apiwat Wisitsorasak determined in a new study that aprocess called chemical vapor deposition, which is usedindustrially to make thin films, could yield a glass that withstandstremendous stress without breaking.
Wolynes, a seniorscientist with the Center for Theoretical Biological Physics atRice’s BioScience Research Collaborative, and Wisitsorasakreported their results this week in the Proceedings of theNational Academy of Sciences. Their calculations were based on amodified version of a groundbreaking mathematical model that Wolynesfirst created to answer a decades-old conundrum about how glassforms. With the modifications, Wolynes’ theory can now predictthe ultimate strength of any glass, including the common varietiesmade from silica and more exotic types made of polymers and metals.
If metal glass soundsodd, blame it on the molecules inside. Glass is unique because of itsmolecular structure. It freezes into a rigid form when cooled. Butunlike ice, in which water molecules take on regular crystallinepatterns — think of snowflakes — the molecules in glass aresuspended randomly, just as they were as a liquid, with no particularpattern. The strong bonds that form between these randomly-arrayedindividual molecules are what hold the glass together and ultimatelydetermine its strength.
All glasses share theability to handle a great deal of strain before giving way, sometimesexplosively.
Exactly how muchstrain a glass can handle is determined by how much energy it canabsorb before its intrinsic elastic qualities reach theirlimitations. And that seems to be as much a property of the way theglass is manufactured as the material it’s made of.
Materials scientistshave long debated the physics of what occurs when glass hardens andcools. In fact, the transition is one of their last greatpuzzles of the field. Cooling temperatures for particular kinds ofglass are well defined by centuries of experience, but Wolynes arguesit may be possible to use this information to improve upon glass’sultimate strength.
The elastic propertiesof the finished product and the configurational energy (the positiveand negative forces between the molecules) held in stasis by the“freezing” process determine how close a glass gets to thetheoretical ideal — the most stable glass possible, he said.
“The usualimpression of glass is that, relative to other materials in yourlife, it seems easy to break,” said Wolynes, Rice’s Bullard-WelchFoundation Professor of Science and a professor of chemistry. “Thereality is that when it’s freshly made and not scratched, glass isvery strong.”
Wolynes, whospecializes in how molecular systems move across microscopic “energylandscapes,”particularly as they relate to protein folding inbiology, has an interest in glass that goes back many years.His random first-order transition theory of glasses, whichquantifies the molecules’ kinetic properties as they cool, helpedset the stage for decades of debate among theorists over howglass actually forms.
But the theory, basedon work by Wolynes and collaborators that goes back to 1989, didnot consider the strength of glass.
“You can come upwith a theory of something and ignore one of the most practicalimplications because you just don’t think about it,” Wolynesexplained.
A chance encounterwith a metallurgist last year made Wolynes think again about just howstrong glass could be. “We had never worked on that kind ofproperty, and the problem struck me as intriguing – and relativelysimple in the framework of the theory we already had. We just hadn’tthought to calculate it,” he said.
Traditional glass isso ubiquitous that people rarely think about it (until it breaks).“Even though we now have Gorilla Glass and othertempering developments, they’ve been developed in a somewhatEdisonian fashion,” he said, noting that such hardened glassescommonly used in cell phones have a self-healing surface treatmentthat protects the glass itself from scratching. “Our paper is aboutwhat determines the limits on the strength of the glass, if there isno surface problem.”
Wolynes noted thestrength of materials has been studied since the 1920s, when Russianscientist Yakov Frenkel ”calculated how strong somethingcould be if we just take into account the direct forces betweenatoms. He made a simple calculation: If you have a row of atoms andpull it over another row of atoms, when would it go from one way ofaligning to the next?” Wolynes said that determines a material’selastic modulus — “how springy the material is” — an easyconcept to understand in metals that bend before they break.
“The elastic modulusis related to the thermal vibrations in the material,” he said.“Basically, if you have a material that has a very high meltingpoint, its elastic modulus is also very high. According to Frenkel,the strength should also be very high.
“That overall trendis true. That’s why fighter jets are made of titanium, one thehighest-melting metals, and low-melting aluminum, which is not asstrong but lighter, is used for other things.”
The theory didn’tseem to relate to glasses, however. “In the early days, when peoplefirst measured the properties of glasses, they found they were easilybreakable. Silica glass is very high-melting, so you’dexpect it to be strong,” Wolynes said. “Then they did finallyfigure out this was because cracks at the surface were propagatingin. If they could eliminate the cracks, they would get much higherstrengths.”
Current metallicglasses like the Liquidmetal famously licensed byApple for consumer electronics “come to be about a quarter ofthis theoretical Frenkel strength,” Wolynes said. “So what is itthat limits their strength? We ask whether the collective motionsthat go on in liquids as they’re becoming glasses are the samemotions that are being catalyzed when we stress the material.
“Basically, weapplied our theory for what determines how the liquid rearranges asit’s becoming glass. Add to that the extra driving force when youapply stress, and see what that predicts for the limit of how much itcan be pushed before the atoms roll over each other” and the glassbreaks, he said.
He noted thetheoretical results closely match experimental ones for mostmaterials. “The good news is, according to this theory, if youcould make a material that is much closer to ideal glass – theglass you would get if you could make it infinitely slowly – thenyou would be able to increase its strength.”
That may not bepossible through traditional cooling of silica, metal and polymerglasses, which Wolynes’ and Wisitsorasak’s calculations indicateare approaching their limits.
But it might bepossible through vapor deposition of atoms, akin to the chemicalvapor deposition process used in microelectronics and nanotechnologyto make thin films. “It would require tuning the deposition rate tothe liquid/glass transition properties,” he said.
“Our theory says thebest you can do with this is get about halfway to ideal glass,”which he said some experimentalists have demonstrated. “It’spossible there’s some loophole we don’t yet see that will let usget even closer to the ideal,” Wolynes said. “But at least, atthis point, we can get halfway there.
That means it would bepossible, in principle, to get glass with at least twice theintrinsic strength of current glasses.”
Wolynes’ theorycomes with a caveat, though. Glass hardened even to the point of nearindestructibility can still be destroyed, and with dramatic effect.“If you could have something infinitely strong, then you’d neverneed to worry about it,” he said. “But there’s a little bit ofa problem if you make something that’s very strong but caneventually break. It contains a huge amount of energy, so when itbreaks, it fails catastrophically.”
Hiç yorum yok:
Yorum Gönder