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| 2008/6/22-23 [ERROR, uid:50328, category id '18005#0' has no name! , , Science/Physics] UID:50328 Activity:high Cat_by:auto |
6/22 Glass' solid/liquid nature explained:
http://preview.tinyurl.com/4rh9ro [new scientist]
\- "John Kerry, is glass a solid or a liquid?"
\_ This article is a joke, right?
"Although glass feels like a solid, its molecules cannot quite
settle into a regular 3D lattice and, given enough time, it flows
like a liquid."
Um, no it doesn't flow like a liquid.
\_ It doesn't?
\- yes it does. have you ever seen multi-hundred year old windows?
without obsessing over the "like a liquid part", glass does flow.
\_ Have you ever seen really old windows? -- ilyas
\_ No, it doesn't. Otherwise all glass bottles over a certain
age would be glass puddles. Yet we have them from the middle
ages. It's a common misconception, most likely due to early
glass pane making techniques that made glass panes thicker on
one end than another. Now, when people point out the thicker
bottom on glass panes they say that's proof that it's a
liquid. They conveniently overlook panes with thicker tops
and sides. The real slowest solid-like liquid is pitch IIRC.
http://www.physics.uq.edu.au/pitchdrop/pitchdrop.shtml
\_ Why not put the whole setup in a centrifuge to accelerate
the process? |
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| preview.tinyurl.com/4rh9ro -> technology.newscientist.com/channel/tech/dn14179-glasss-dual-personality-explained-at-last.html?feedId=online-news_rss20 Advertising Although glass feels like a solid, its molecules cannot quite settle into a regular 3D lattice and, given enough time, it flows like a liquid. Now, however, researchers now say they have found out how it gets its unusual properties. The study could pave the way to developing new materials that combine the best properties of metals and glasses. An international team has used a gel packed with plastic particles just 2 micrometres across to simulate what happens when a glass cools. Unstackable shapes To mimic temperature changes in the gel, Royall's team gradually added in a second polymer, and eventually the colloid flipped into a glass-like state. This geometry is incapable of slotting together, or tessellating, to form the regular 3D lattice characteristic of a solid. But equally they cannot move around freely because they are larger than the original particles. Royall thinks that the molecules of real glass takes on the same icosohedral structure, leaving it unable to crystallise into a solid, but not free enough to have liquid-like properties. "For a long time, no-one has really shown what the structure of glass is," Royall says, "but we have been able to show how the structure of a glass differs from that of a liquid." Creating metals that that form icosahedra structures as they cool could create a new class of "metallic glass" materials, he adds. Without the ordered crystal structures typical of metals, these materials might be more resistant to metal failure that can happen when layers of crystals shear away from one another. That would be useful in situations where metals are subject to high stresses, such as aeroplane wings. By Curious Sun Jun 22 19:40:15 BST 2008 Wow, finally some "consensus" on the properties of glass. Does anyone else find it odd that a "consensus" could have been formed on an even MORE unknown property many years ago? By Karl Sun Jun 22 21:17:28 BST 2008 In other words, you're saying the structure of glass proves global warming is a myth? I wonder how the researchers could have missed such an obvious conclusion. By Devon Buchanan Sun Jun 22 19:53:57 BST 2008 Wait, does this prove glass behaves as it does because of the icosahedral structure, or just that an icosahedral structure can create materials that behave like glass. The article seems to be saying the latter (though the original paper may have had proof of the former). By Don Jennings Sun Jun 22 21:35:37 BST 2008 It did not sound like a proof to me because they have not imaged the actual structure of glass but instead shown that the icosahedral structure acts like glass. It may still lead to new materials like they said, but don't hold your breath, might be a decade down the road before we see anything like that. |
| www.physics.uq.edu.au/pitchdrop/pitchdrop.shtml It is also listed in the Guinness Book of Records as the world's longest running experiment. The first Professor of Physics at the University of Queensland, Professor Thomas Parnell, began an experiment in 1927 to illustrate that everyday materials can exhibit quite surprising properties. The experiment demonstrates the fluidity and high viscosity of pitch, a derivative of tar once used for waterproofing boats. At room temperature pitch feels solid - even brittle - and can easily be shattered with a blow from a hammer (see the video clip below). It's quite amazing then, to see that pitch at room temperature is actually fluid! In 1927 Professor Parnell heated a sample of pitch and poured it into a glass funnel with a sealed stem. Three years were allowed for the pitch to settle, and in 1930 the sealed stem was cut. From that date on the pitch has slowly dripped out of the funnel - so slowly that now, 77 years later, the ninth drop is only just forming. The experiment was set up as a demonstration and is not kept under special environmental conditions (it is actually kept in a display cabinet in the foyer of the Department), so the rate of flow of the pitch varies with seasonal changes in temperature. Nonetheless, it is possible to make an estimate of the viscosity of this sample of pitch ( R Edgeworth, BJ Dalton and T Parnell, Eur. It turns out to be about 100 billion times more viscous than water! In the 77 years that the pitch has been dripping no-one has ever seen the drop fall. Fortunately you can also see students of the University of Queensland milling around outside the cabinet, so it is more exciting than watching grass grow! The audio over the live video is an interview with Professor John Mainstone, who maintains the experiment. |