Not to stick my head in the proverbial lion's mouth of PM flame wars but I have noticed in several (at least five) other current threads the topic of whether or not glass is a liquid or not at room temperature has come up and has lots of credible arguments for it NOT being a liquid at room temperature.

So in the interest of having the discussion in one place I'm starting this thread.

Looking at some of the links, though, with lots of scientific-types chiming in on other sites and referencing studies, it seems that the jury is still out, to some degree.

While I appreciate that even if we reached a consensus here glass will not start behaving differently because we tell it to, but I would be really interested to hear if anyone has a link or information relating to a modern composition of glass "flowing" detectably...

Is glass a liquid at room temperature? Is it really just an urban legend?

Thanks!

If you fully read the article posted earlier at http://math.ucr.edu/home/baez/physic...ass/glass.html I think it will answer that question as well as it can be answered.

Whether glass is a liquid or not depends on the physical properties of the glass itself, the temperature, and the definition of "liquid" which generaly refers to "flow" or the ability of a substance to assume the shape of its container. I dimly recall hearing of a delicate and sensitive apparatus (a galvanometer, I think)which had glass springs as part of its design. After two centuries the apparatus still performs to 4 digit repeatability.

The "fluidity" of glass is not a subject for debate by people using apocryphal stories as a substitute for verifiable experimental data. One might as well dispute over a different value for Pi or to advocate Aristotelean cosmology. If you want to determine the flow rate for various glasses (there are thousands of varieties) under specified conditions, look up the physical properties.

The fluidity of glasses is not a topic for debate where a preponderance of opinion prevails. Fluidity of glass is a matter of well established and independantly verified technical fact - in brief words: Generally glasses used in modern technology are not liquids and they do not flow within the accepted meaning of the term. They are non-crystaline isotropic elastic solids.

Let it go at that and discontinue the pointless dissent.

I would tend to believe that typical glass of all types anyone ever encounters in day-to-day life are solid.

The definition of a fluid from fluid mechanics class is:

a substance that deforms continually under any applied shear force, no matter how small

there is a subclass of liquids called "bingham plastics" (sp?) that are things like toothpaste or mayonnaise where you have to push a certain amount and then they start deforming and behave as liquids after that.

but per the basic definition I would contend that typical glass is not a liquid at all. amorphous crystalline solid is a perfect description IMO.

but I posted the thread because there seems to be tremendous disagreement on this point and wanted to know if anyone had a reference to anything that definitively showed glass "flow" under controlled conditions.

i think by the shear force definition of liquids it can be stated with certainty that glass is not a liquid. it may not be a "solid" but I don't think you can say it's a liquid unless you can show that you can apply a force to it and have it plastically deform, which certainly there would be evidence of everywhere like where those little mirror hooks hold on to your mirrors, bottlecaps, etc etc.

agreed, as in the first post.

That means it flows VERY slowly at room temperature, but appears solid for the most part. Here is a better explanation than I could hope to give. It does flow very slowly kinda like a liquid. It's not technically a liquid or a true solid. So, it's an amorphous solid.

http://en.wikipedia.org/wiki/Amorphous_solid

Junkyard, your own link does not support your assertion. Maybe I missed something. Could you post the relevant passage?

For instance, common window glass is an amorphous ceramic, many polymers (such as polystyrene) are amorphous, and even foods such as cotton candy are amorphous solids.

look at very old houses , and you can see the old window glass has wrinkled and sagged over time .

-It's wrinkled, yes, but it didn't sag over time. It was simply made prior to the advent of "float" glass, meaning it was essentially hand-blown and hand-rolled. Variations in thickness were very common.

On the other hand, we've recovered glass pitchers, urns and other pieces, from the Greek or even Egyptian eras- closer to 1,200 to 1,500 years old, or many times that of windowglass in old houses.

Even after being broken and buried under many meters of dirt, sand or even volcanic ash for whole millennia, the pieces still fit perfectly, with no distortion or misalignment.

No, glass is an interesting substance all right, we we can argue phase trnasformations all night long. But the fact is, it's an immutable solid at room temperature. It does not flow, will not floe, will not distort, it is not a liquid.

Unless you also want to define steel as a "supercooled liquid" or describe mercury as "low-temperature molten solid".

Doc.

I don't buy that, our old house had some windows that would make you wonder. It was built by my great uncle before WWI on Braile in Detroit (near Braile and 6 mile). The windows in the upstairs bedrooms were so thin at the top, and were so wavy, I couldn't see that glass passing ANY QC they might have had in the day. My grandfather worked for Hess Glass (@ the corner of Braile and 6 mile), and his uncle (my great uncle also worked for Hess Glass) was the one who glazed the original windows. My grandpa said the windows didn't look like that when he was a kid. He also told me that they'd replace windows that got so thin they'd just shatter due to somebody slamming a door in the house, and they looked more distorted than those windows. The one window had an air bubble in it that actually stretched until it opened up! It got some condensation in it, then it froze in the winter time and cracked. Glass was made in such a way that it was thicker on one edge. It was installed thick side down, which I beleive, but I DO NOT beleive they would have EVER used glass that looked like the glass in our old house for windows.

On my mom's side of the family, my grandparents had a BEAUTIFUL anitque bookshelf from the 1700's with glass window/door things that lifted open, and slid in. The bottom window thing was stuck open for MANY YEARS. When they got it unstuck (after my grandparents died, and it was being auctioned off ) the glass had a visible sag to it. The other original glass that spent most of it's time closed (3 of 4 were original) was just thicker on the bottom, and wavy. There were some other things in the house that also looked like the glass sagged.

Maybe there are differences in glass that make some types "flow" more than others, but after seeing it first hand, I beleive it flows very slowly. Perhaps the roman and egyptian glass was different, and didn't flow as easily. I dunno, I suppose if I live to be 100, I MIGHT be able to confirm it.

Wikipedia, as is often the case, has not got it quite right again;

Actually the reverse is true. Polymers in the solid state are either amorphous or semi-crystalline, but in the molten state all polymers (apart from LCP) change to an amorphous structure.
If you cool them quickly, the crystalline polymers will lock-in the amorphous structure, if you cool them slowly, they will re-crystallise.

As far as material flow, amorphous materials are more resistant than crystalline structures. In polymers, the long-chain molecular structure of an amorphous material is somewhat akin to a plate of sphagetti or a tangled ball of wool.
This very entanglement prevents movement and slippage. In semi-crystalline materials the very ordered structure of the chains allows these to slip over each with much greater ease.

Peter

They have say polymers cooled slowly become amorphous, then ceramics and glass cooled quickly become amorphous. That didn't make any sense to me either, everythign I read talked about cooling quickly to become amorphous.

I wish I had a picture of that glass in the old bookshelf, that would have removed all doubt that glass can flow a bit. It was sagging a good 1/8" toward the top where it was thinner, and it was straight near the edges! I remember my dad pointing out to me, it was probably the most extreme case I've EVER seen. It probably was probably open for 100 years or more, because my grandpa (mom's side) said his parent's never remembered it being able to close, and it came from one of THEIR parents. They gave it to him when he got the house in Pleasant Ridge (30 ridge road). It was in that house since the '40s, then it went to their house in Marshall in the late '70s where it sat until the early '90s.

I will weigh in on the side of glass being a liquid at room temeperature albeit highly supercooled below it's glass transition temperature. Forget the viscosity it is high enough to neglect, even highly stressed glass fibres have very low creep. For anybody who has worked glass you will notice that on cooling it just becomes more viscous until it is unworkable. Metal displays different properties.

For those who haven't worked glass honey and corn syrup are very similar, cool them and they eventually become almost unworkable. They can be stored well below thier glass transition temperature for quite some time before crystallising.

Some polymers are amorphous some are crystalline and some are somehere in between. Acrylic and polycarbonate are amorphous, polyethylene is somewhere in between.

Could go into more detail but I think the Flu is coming on.

I've been in restorations for years, and have to say that while I -have- seen glass that has apparently 'sagged' or 'settled', it can easily be explained if you understand the manufacturing techniques used for some glass in the dim past.
One method was to collect a glob of molten glass on a rod or blow pipe and spin it causing t to stretch into a thin disk, the disk was spun till it cooled, then the 'best' sections were cut out and used as panes. Because of the hand spinning you were limited in the size you could do, and in the actual control of thickness. this is also the reason they used muntins in windows, it was too hard to make large panes of glass that were clear, and didn't have the 'bullseye' in the center from the spinning process, so they made windows using many small panes.

If glass, as hard as it is, is able to sag, why don't metal objects which have much better 'flow' characteristics at common 'human comfortable' temps flow?

My gramma has an old corner cabinet that has 16 panes of handblown glass in it, made using the same methods, looking at it you can see the curved ridges and the thicker bottoms on each pane. A couple of the panes have 'dents' in them.

ken.

Glass at room temperature is a solid, period. As Forrest said, there are a lot of things that can be debated, but this one has been proven over and over through careful scientific experiment. If people honestly want to know the proof is not hard to find. I just ask that you look in Journals and Books, peer reviewed literature, not some random internet site.

You all are fools arguing whether glass is solid or liquid. The way to settle this is to use a Diving Rod. Therein you will find the truth to your quest.

Yes, if it was accompanied by a piece of paper where someone had carefully measured the thickness of the glass to the thousandths at a large number of points when it was made so it can be measured today for comparison.

By the way, Wikipedia is information posted with minimal review by people of unknown qualifications making it a questionable choice for a reference. But you know that right?

Steve.

http://math.ucr.edu/home/baez/physic...ass/glass.html

Conclusion

There is no clear answer to the question "Is glass solid or liquid?". In terms of molecular dynamics and thermodynamics it is possible to justify various different views that it is a highly viscous liquid, an amorphous solid, or simply that glass is another state of matter which is neither liquid nor solid. The difference is semantic.
Philip Gibbs




I was taught that it is a fluid you just have to wait 10,000 years to see it move.
Tim

I may have missed something, not having taken the time to open all the links, but in all the supposed instances of window glass flowing, has anyone actually come up with a documented example of a window pane that has flowed over its bottom rail, or bunched up adjacent to it? If this phenomenon is measurable, then shouldn't you see, in such windows, a definable ridge, however tiny, where the unsupported pane enters the rail? Can anyone come up with a photograph of this?