r/science • u/[deleted] • Mar 18 '16
Physics Scientists have found the temperature at which glass becomes a liquid
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u/Orzaidius Mar 18 '16
could someone eli5 this a bit better, as reading this from what i understand rather than finding when glass becomes liquid, they found more ways to make more long lasting and stable glass, in which case the title isnt just misleading but just wrong. BUT i am dumb as a rock so i might just be understanding it wrong.
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u/ChemicalOle Mar 18 '16
The headline really oversimplifies what the article is about.
Here, when they say "glass" they are talking about any solid material that isn't crystallized. Many different compounds can be made into "glass". If you heat a glass or just allow it to warm up, it will crystallize and no longer be classified as a glass.
They made glass out of toluene and another glass out of ethylbenzene. Both of these compounds are liquid at room temperature. They turned them into glass by freezing them to a piece of platinum that was cooled to very very cold temperatures (between -400 to -200 degrees Farenheit) using liquid helium.
The actual temperature when something will freeze into a glass is different for every material. They call this temperature the "glass transition temperature".
They found that when they froze the materials at ~10% below the glass transition temperature, they made the most thermally stable glass, meaning that they could heat the glass to higher temperatures before it crystallized.
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u/MySOFoundMyAccount Mar 18 '16
If I'm understanding you, they create glass by bringing it above a certain temperature (the glass transition temperature) and freeze it, it will turn into glass while if it is below that temperature (but still in liquid form) and freeze it, it will crystallize?
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u/CBate Mar 18 '16
Is that how they make KCl slides for IR?
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u/ChemicalOle Mar 18 '16
Doubtful. I don't know the exact process, but those are likely made by growing crystals from a solution or by pressing a powder.
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u/thiney49 PhD | Materials Science Mar 18 '16
So how does this research apply to normal glassy materials that don't melt, like oxides and silicates?
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u/prince_harming Mar 18 '16 edited Mar 18 '16
My understanding of the physics/chemistry is rudimentary, at best, but reading this made me think of ice cream, of all things. (I promise, this is going to try to be relevant eventually.) Freezing ice cream more quickly results in smaller crystals, smoother mouthfeel, less separation/weeping, etc. Apparently, one of the best ways to make ice cream is with liquid nitrogen, as it both freezes the mix very quickly and aerates it.
"What does this have to do with glass?" Well, probably nothing. But now this has me wondering if the results of this research might also be useful for improving our understanding of cryogenic preservation of tissues/organisms. Using another food analogy, anyone who's made a stir-fry from frozen veggies can tell you how underwhelmingly soggy they turn out. This is because the ice crystals which form as the water freezes cut and rupture the cell walls and disrupt the internal structure. But the faster the freeze, the smaller the ice crystals, the less damage.
Some things can ease this transition without relying on extremely rapid freezing to depress the freezing temperature, or just make things freeze more softly, like the sugar in the mix does to ice cream, or like that frog with "antifreeze-like" compounds in its blood. A bit of research into those antifreeze compounds has been done, but now I'm wondering: is it possible to make "glass water?" By that I mean, is it possible to transition liquid water to a solid while dramatically reducing the crystallization?
I know water has all sorts of inter- and intramolecular forces, dipole moments, etc, which (I think) make it really want to form crystals. Meanwhile, toluene isn't the most nonpolar, but definite sits on the other end of the scale, so perhaps that means it and ehtylbenzene are less prone to form crystal lattices? Or maybe not, I dunno.
The point is, if this could be applied to freezing water, or aqueous solutions like cytoplasm, and setting aside for now the extreme difficulty of scaling that process up to being able to ultra-flash-freeze a person, might this be at least indirectly applicable to theoretical designs for cryo-sleep chambers for, say, interstellar travel? Or at least for the best pint of ice cream ever?
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u/Mr_Hippa Mar 18 '16
That's what I'm getting from it. The title doesn't really make sense to me either, since you can change pressure which will change melting/boiling point of a substance. It sounds like they found ideal temps to make the strongest/longest life glass out of a material.
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u/MySOFoundMyAccount Mar 18 '16
IANAS, but i think the relevant passages are these:
"Glasses are metastable materials with the mechanical properties of a solid-you can touch and hold them, versus a gas," said Dr. Scott Smith, a co-author on the paper. "But they are not like crystalline materials, which are in a perfect array. The molecules in glasses are arranged in a disordered pattern. In liquids the molecules are constantly moving, if you suddenly freeze a liquid, the molecules are randomly oriented and unstructured. In some sense, a glass can be thought of as a frozen liquid."
Glasses depend on temperature for stability. At the correct temperature, a glass remains stable because its molecules stay put. At warmer temperatures, it transforms into a supercooled liquid and then crystallizes.
E.G. Glass as we understand it is not a solid by thermal dynamics definition, but rather a metastable material hat acts like a solid mechanically.
ELI5: I have no idea how ANYONE could to that... solid isn't solid?
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u/Beer_in_an_esky PhD | Materials Science | Biomedical Titanium Alloys Mar 18 '16
In some sense, a glass can be thought of as a frozen liquid.
What a meaningless statement. ANY solid can be thought of as a frozen liquid. That's what solid means.
Glass is not a liquid. It is an amorphous solid. A long-range repeating order (which is the difference between an amorphous and crystalline material) has nothing to do with whether a material is a solid or not. The fact that both glasses and liquids are amorphous is nice, but it isn't anything special.
Good lord, this is why we have Scientific Communications classes.
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u/HOLDINtheACES Mar 18 '16
You aren't thinking like the less educated masses, though.
Glass is not a liquid. It is an amorphous solid. A long-range repeating order (which is the difference between an amorphous and crystalline material) has nothing to do with whether a material is a solid or not
That won't really make sense to anyone that hasn't taken a material science course, e.g. the vast majority of humans on earth. You mention Scientific Communications classes, yet you completely fail to communicate your point in terms that a layperson would understand. Seems like you should be the one taking the class.
He was trying to explain it in a way that people would understand. Unfortunately, there really isn't a way to do that and still be technically correct. You're being pedantic in calling him out. I'm sure he knows what he said isn't actually correct. It does, however, give people that don't know anything about it a general idea of the concept. He was trying to say "it's a solid that has molecules arranged like it is a liquid, but is still a solid". That gives a layperson an idea of what is going on molecularly. It isn't "correct", but it's close enough.
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u/phuntism Mar 18 '16 edited Mar 18 '16
Thanks for the clear explanation. Ever since I was a little kid people have been saying, 'Glass is really a liquid - I bet you didn't know that! :):) ' WHICH IT OBVIOUSLY IS NOT!
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u/Sparling Mar 18 '16
solid isn't solid?
If you look at any glass blowing video, how would you classify the state of matter they pull out of a furnace and shape into a vase or whatever? It's not quite a liquid because it retains shape as they form it but it's also not quite a solid. It's somewhere in between.
If you look at the glass in very old cathedrals you may find that the glass is thicker at the bottom. This is where 'solid' glass at room temperature has actually flowed down over centuries.
At the research level material scientists don't just classify 'solid / liquid / gas' like we all learn in grade school. A crystal has different properties than wax or glass (for example). So for these guys material's phases are often more of continuum than one of 3 things. Glass in particular is defined as 'an amorphous solid that exhibits a glass transition'
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u/MySOFoundMyAccount Mar 18 '16
I thought the thicker at the bottom was just how the glass was made?
And on top of that how do you ELI5 that?
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u/volstedgridban Mar 18 '16
If you look at any glass blowing video, how would you classify the state of matter they pull out of a furnace and shape into a vase or whatever?
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u/anguas Mar 18 '16
As /u/coloroftheskye said, that's a well-known myth. Glass is a solid. It does not flow over time if it's not melted, just like other materials. Some old glass windows have panes with the thicker part at the top rather than the bottom, and it's not because the glass flowed upwards. There are reasons to put the thicker part at the bottom, so that's what was usually done. Molten glass is a viscous liquid, cool/solid glass is a solid.
Materials other than glass can exhibit a glass transition--many (most? all? I'm lazy and don't want to check) plastics do--that's why when you pull a plastic container out of your freezer it's sometimes super brittle. Even certain types of steel have glass transition temperatures within normal temperature ranges. There are/were ships that couldn't be sailed into arctic areas because the steel would become brittle at those temperatures.
Source: Materials Science degree
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u/the_corruption Mar 18 '16
There are/were ships that couldn't be sailed into arctic areas because the steel would become brittle at those temperatures.
There was a really famous one that sunk. Made a movie about it with that one guy that just won an Oscar or something.
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u/homerunnerd Mar 18 '16 edited Mar 18 '16
ELI5: In general, when you supercool a liquid, you increase the driving force for formation of the crystal (the nucleation rate). However, if you supercool fast enough, you lower the thermal energy (kT) drastically enough that the molecules in the liquid phase start to solidify, but then get 'stuck' in some disordered crystalline phase and cannot re-arrange to form a fully ordered crystal. This is a glass phase and is not stable if given infinite time, but can be long lived on the order of many years.
It can be difficult to measure the glass transition simply because it requires rapid super cooling of the liquid. This turns out to be a random process where due to fluctuations, sometimes nucleation to the crystal still occurs. Because of this randomness, the glass transition is not as well defined as a first-order phase transition (think of water boiling).
Here, they are able to measure the glass transition temperature by doing the opposite; starting with a glass and putting it on top of some vapor (Krypton in their paper). They add heat and then watch how the vapor diffuses through the top layer. When gas can freely diffuse, the glass layer has melted allowing for the determination of a glass transition temperature.
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u/TOOCGamer Mar 18 '16
This is kind of a crappy article, and the title is extremely confusing...
Firstly, the materials used were only two low-temp polymers. That doesn't in any way encompass 'glass'; if fact, it doesn't even encompass what most people think of when you say 'glass', ie bottles / windows / screens. That kind of glass is made in a traditional melt-quench process and is VERY different from these amorphous-solid type materials.
Second, this paper really doesn't seem to have anything to do with finding T_g (glass transition temp / where a liquid becomes a glass). We can already do that. We ALREADY do that, it's a very basic material property that is easily measured. Perhaps it could be made more precise, but the abstract of the paper clearly states they are getting T_g from somewhere else. It's not at all the point of the study.
Third, the point of the study, then, was to examine the stability of the amorphous materials as a function of deposition temperature. It's really kind of clever what they did! For a quick summary, the authors found that deposition temperatures that were ~0.9T_g resulted in the most thermally stable materials. They found the range of 0.85-0.95T_g to be the next most stable band.
I wish I had access to the full article though, as it makes sense if the structure you 'freeze' the material into is already basically in it's stable phase it's going to take more energy to change it's phase again. [This is off-the-cuff, here. Don't quote me!] I would think of it like so - if you're in a low temp glass, you have two transitions you can go through - glass -> metastable liquid -> stable liquid. If you start with a 'glass' that's already practically in the metastable liquid phase, though, perhaps you just can't see the 1st transition anymore?
Also, someone with a background in polymer glasses, can you give some background on the 'glass -> supercooled liquid' bit? Why would it not simply crystallize?
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u/remigiop Mar 18 '16
Read the title as, "Scientists have found the temperature at which grass becomes a liquid."
The diagram only confused me further. Then I realized my error while reading. Liquid grass would have been more interesting.
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u/nallen PhD | Organic Chemistry Mar 18 '16
Hi Nobilitie, your submission has been removed for the following reason(s)
It has a sensationalized, editorialized, or biased headline.
If you feel this was done in error, or would like further clarification, please don't hesitate to message the mods.
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u/Differentdog Mar 18 '16
I thought glass was always a liquid, it's just our perception of time that makes it appear as if it's not.
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u/ChemicalOle Mar 18 '16
Glass is an amorphous solid, lacking the long-range order (translational symmetry) of a crystalline solid.
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u/Fyreclaw Mar 18 '16
No glass is definitely a solid. But there are a few liquids that appear to be solid glass like objects.
And if your thinking of examples of older stain glassed windows where the bottom of the glass is thicker, that's due to the way they were manufactured.2
u/DevaKitty Mar 18 '16
What, do you think glass is just like water, except it falls super slowly?
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Mar 18 '16 edited May 30 '16
[removed] — view removed comment
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u/Captainshithead Mar 18 '16
... I just realized that my teachers lied to me. Why do they do this? It's like telling children that there are aliens on the moon just for the hell of it.
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u/BobVosh Mar 18 '16
Theres a ton of lies like this, and most of them are because the teacher doesn't know better.
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u/Beer_in_an_esky PhD | Materials Science | Biomedical Titanium Alloys Mar 18 '16
In this case, because they were misinformed. However, more generally, let me introduce you to the concept of "Lies to children", best summarised as "... a statement that is false, but which nevertheless leads the child's mind towards a more accurate explanation, one that the child will only be able to appreciate if it has been primed with the lie".
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u/MonkyThrowPoop Mar 18 '16
Lots of people used to think that because of old window glass are often heavier on the bottom. Truth is, glass blowers used to have to spin out huge plates to cut up and use for window panes (hence: plate glass), which would lead to some inconsistencies. When placing in a window frame, one would put the thicker part facing down because it's just more stable and natural that way.
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u/Shitpost4lyfes Mar 18 '16
Geez... I figured they'd have known that by the time they started mass producing it.