Glass - Liquid or Solid

It's mostly a word game.

(Or maybe a practical versus technical difference in usage.)

It A high huge viscosity liquid

Here in my conutry we can find glass windows that are thick on the bottom and thin at the top , maybe 250 years old.

I think that choice of example not good is galileo not in space without any load since gravity is small as stress ?

In old glass panes more often is a cristalisation to be noticed or the water effect which takes off some chemical components at surface and brings "rainbows"locally.

What I noticed on a almost horizontal glass panel was a flexion but i cannot say that it was not from the beginning.

'...I think that choice of example not good is galileo not in space without any load since gravity is small as stress ?...'

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Er.....what? Where exactly do you think Galileo's telescopes are? It sounds like you are saying that someone bundled them all up and launched them into orbit to experience microgravity.....

As all other post put in doubt my point of view , i did a search , and it seem to be I´m in a error.

See here please

http://math.ucr.edu/home/baez/physics/General/Glass/glass.html

Didn't look at the link I posted?

Ahem, it is your link, lyn.

_{I can only give you the one GA, not that it matters in the big picture.}

GA's come, and they go.

I think somebody ought to put an 8 foot piece of glass on a couple of broom handles and measure the center deflection over 50 years.

I learned in school that glass was a "supercooled liquid".

Is glass liquid or solid?

I still don't know.

A very cool (pun intended) link, lyn. A very good explanation of the ambiguous state that is glass will be found at your link.

One thing I've been told to support the concept that glass is actually a liquid is that a glass cutter actually rolls (as opposed to cutting) a groove in the glass surface; if the glass is not broken but just left for an extended period of time- 250 years?- the surface tension of the glass will cause the groove to level out & disappear, or at least change significantly to a more rounded depression.

I've never had the time or inclination to verify this! Does anyone else know if it is factual? P.S. in my opinion the difference is essentially semantics anyways.

Just can't help remembering this:

in the good old days silicon chips were not sawn apart from the wafer. You scribed the edges with a diamond and then you would brake the chips apart with a roller or a wedge.

monocrystalline silicon is as close to a classical solid as I can think of, so the diamond really cuts a very small groove (no rolling). However, if you wait for the next day breaking will not occur at the scribe lines.

brgds

Snel

The answer to your question is that the two choices you presented are not mutually exclusive. Glass is both a highly viscous liquid and an amorphous solid. The answer to the second part of your question is, yes different glass compositions have different flow characteristics. Pure fused silica (SiO2) is much more viscous at room temperature than lead glass, or window glass.

'....Pure fused silica (SiO2) is much more viscous at room temperature than lead glass, or window glass.....'

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Care to share the logic or references that lead you to this assertion?

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I'm pretty sure that fused silica, lead glass and window glass all share a similar characteristic in response to stress at room temperature: exhibiting elastic deformation right up to the point that it fractures.

If there isn't appreciable plastic deformation then talking about viscosity is a non sequitur.

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I don't think glass at room temperature exhibits appreciable plastic deformation, so I don't think it qualifies as a viscous flowing fluid.

I certainly could be wrong, and would be eager to learn of examples of glasses like silica, window or leaded glass exhibiting plastic deformation at room temperature.

To quote sources such as "Glass" by G.O. Jones, ".....glass behaves as a Newtonian fluid" The reason that most people think glass is a solid is because without stress, it doesn't flow very much. However, add stress and your windows, roman glass, and Hubble telescope mirrors will all flow like water.

And you are most certainly wrong. All materials exhibit unrecoverable plastic deformation at some time and stress level. Even fused silica springs that were once touted to be the perfect weighing scale, exhibit creep when stressed beyond certain limits.

"...However, add stress and your windows, roman glass, and Hubble telescope mirrors will all flow like water"..."Even fused silica springs...exhibit creep when stressed beyond certain limits."

Okay fine but so does steel and aluminum once you exceed the yeild stress and get into to the plastic deformation range...so what's your point? That doesn't make them Newtonian fluids. Newtonian fluids by definition have constant viscosity regardless of stress or forces acting upon them. If glass is Newtonian then by definition zero stress would make it flow but you're saying add stress to make it flow so your contradicting yourself.

I'm no expert but if glass flows under it's own weight then by definition it can't be a Newtonian fluid because self weight induces stress in everything regardles of how minute the stress is.

"...exhibit creep when stressed beyondcertain limits."

Well, in that case, perhaps if we add enough heat, glass can be defined as a liquid, yes? Add even more heat: a gas. Even more, a plasma! Oh wouldn't that simplify things, yes? The point being, if we're going to change the conditions under which the thing is defined, why not go for broke? If want it to be a liquid, just melt the damn thing and be done with it!

When I open a faucet, I don't need to perform deformation tests on what comes out to know if it's a liquid. It does that on its own just fine. Nor do I need to test what comes out of bottle of molasses when I pour it on my pancakes, just to be sure. It is more viscous than water, but it flows. On a cold, Yukon winter's day? It'll take for-bluddy-ever, but it still flows. It's a liquid. Not rocket science.

Extending this increasing-viscosity bit to that 2000-year-old Roman glass vase sitting there in the British Museum - a vase which has been subject to the continuous tug of gravity for over twenty centuries and yet shows no sign of deformation whatsoever, do I conclude that it's a liquid simply because Dr. Glass says so? That vase has had twenty centuries to do what liquids do - flow - and it hasn't done it. Not even a little, so what should we conclude? I don't think it's all that much of a stretch to consider it a solid, quite honestly. Same for that Egyptian glassware in the Corning Glass Museum, New York. Dates back to the time of the pharaohs, it does. Signs of flow? Nope. Nary a bit.

Dr. Glass, PhD can call it Newtonian, Einsteinian, George Orwellian, Mickey Mousian or whatever else he wants to call it, and that's his prerogative, but it doesn't mean he's necessarily correct (and just because he's got a bluddy 'PhD' tacked on after his name doesn't mean diddly squat. I know plenty whose PhDs dilute the value of the degree to that of a high-school diploma. Oh don't get me started on that one!).

I do know at the very least - like most people, I suppose - that liquids flow and solids do not. If one must change the conditions to something else in order to justify one's particular definition, it kind of goes without saying that the definition in isolation isn't saying much. One must also state the conditions under which the definition holds.

Yeah, windows, Roman glass and Hubble telescope mirrors will also incinerate everyone within pissing distance when heated to 200 million degrees, but it doesn't necessary mean glass is a plasma.

Change the conditions and you can define anything any way you bluddy like.

No need to get your panties in a knot.The reason we study material science is to learn how the properties of materials are affected by different conditions. Lava flowing down a volcano is a natural condition; we didn't create it. As the lava solidified, it turned into glass and a prehistoric man made a spear point out of it. It took a significant temperature change to melt the volcanic glass, but not all materials require a large temperature change to exhibit large property changes. Your glue gun adhesive is one example. Hold a solid clump of gallium metal in your hand and it will turn into liquid. It's not cheating to change conditions. We do it to learn what would happen to the steel support beam if it became hot in a fire. If you study high power circuit interruption, you are very interested in the plasma state and its properties. We change the conditions to predict properties at various conditions.

The rationale for the study of materials was never called into question, but thank you for your edifying intro, all the same (even if the main thrust of my post was missed wholesale).

Back in high school (contrary to what you may have been told, the great lakes had already been formed) a phisics the teacher told me the difference between a crystaline solid and a supercooled liquid (which is also called an amorphous solid) is a well defined melting point. Water at 1 degree C is liquid, no question. Water at -1 degree (normal atmospheric pressure) is solid. Most other crystaline solids are not even affected by pressure. Glass makes a very gradual transition so that at 500 degree it still flows noticably and at 200 degree it may be flowing inpreceptably.

I wish everything my teachers had told me in school was true and correct. They said I would be rich and famous.

I'd call what your physics teacher said hearsay evidence. Got any proof to back it up?

When melted, Glass is a liquid. As it cools it slowly transitions to a disorganized non-crystalline solid. Over very long periods of time it develops some crystal structure but does not revert to a liquid unless its temperature is raised to near its melting point.

I guess you could say, it depends on the temperature.

Glass behaves like a liquid - no gaps between atoms and does not exhibit porosity. Let me give you specific application of glass being used in lighting. All lamps- incandescent, sodium, mercury, fluorescent, CFL etc are all made using glass - as the lamps are evacuated and filled ti different pressure levels using different gases. The content never leaks out - unless glass is broken/ cracked. Now compare this with any other new transparent solids- polypropylene or polyester or acrylic sheets / tubes etc. Man has not yet developed any transparent material which is as good as glass. It may also be noted that glass is 100 % recycled.

"Glass behaves like a liquid - no gaps between atoms and does not exhibit porosity."

You're suggesting that liquids trap gasses but that's not true. Gasses pass through liquids quite easily.

Try farting in a bathtub and you'll know what I mean!

Oh, come on! That helium doesn't just leak out. You guys just like to suck it out and sound like a duck when you're bored.

Sssssh! You'll spoil the effect! Look, I've tried and, well, I sound more like a goose. Canadian goose. Mating season.

What's remarkable about the helium leaking through the glass is that the pressure inside the envelope is very low and yet the helium leaks to the side of much higher pressure. It's really not so remarkable when you look at the mechanism. The helium diffuses through the glass and only meets the high-pressure (atmospheric) side at the very last minute, where the emerging He atoms are knocked away from the surface. Until then, they don't feel any pressure at all - it's pure diffusion and not pressure-related at all.

Not remarkable- osmotic.

Yep.

Yes, boys and girls, that's why we do Helium leak testing before we launch stuff that's supposed to be sealed into outer space.

It is also why ultra-high vacuum chambers are also Helium leak checked.

Dalton's Law of partial pressures....

Would this osmotic/diffusion process apply to hydrogen as well? Or, since it's not an inert gas, given enough time would it react with one or more of the other elements in the glass -- or whatever substance is containing it? If so, would very high pressure make more of the hydrogen react with such substances? (Am I asking if pressure would act as a catalyst? Not sure.)

Hydrogen does diffuse through glass. The effect is deleterious on optical fibers but is the basis for at least one proposed method for safely storing hydrogen at elevated pressures.

Neat post! Never seen that before.

As the smallest molecule there is, hydrogen is worse than helium for leakage. Inertness or lack thereof does not make any difference to this; what matters are the partial pressures involved, the constitution and the thickness of the barrier wall (kind of funny thinking of a pipe or bottle wall as a membrane, but that's really what it is!).

There is sufficient diffusive pressure in this process that hydrogen is capable of cracking steel! This is the reason for low hydrogen electrodes.

I'm not so sure which gas will be more difficult to contain. H2 is the smallest molecule but He being a noble gas is only one atom in unit size. H2 does not have a permanent dipole moment but can exhibit a dipole moment under some conditions. Lets not forget that H2 liquefies at 33K while He liquefies at about 4K. At the same time H2 is flammable while He is not flammable. So a H2 leak can quickly be a more critical problem than He.

I agree that both gasses are difficult to contain. I suspect it would be tricky to configure a balanced experiment to settle which has more leakage.

I worked in a shop that rebuilt cryogenic dewars to ship liquid helium across the world. The dewer had 2 sections, one big one for He cargo, and another smaller liquid nitrogen one that kept the He cool(ish).

DrewK

Wrong. The partial pressure of helium on outside(for all practicle purposes zero) is lower than the partial pressure inside (of helium). Gasses tend to act as if other gasses are not present so pressure of nitrogen, oxygen, argon, etc. on outside of tube does not impede flow of helium out. Nitrogen is also difusing in but at a very slow rate because molecules are so large.

Please cite the place in my post where I said the atmospheric gasses outside the tube impeded anything?

Is there an echo in the room? See 30↑.

GA from me but the experiment I suggested is by far more entertaining and educational !!

Does this fall under the heading of good, clean family fun, and will you have one of the kids pull your finger to start?

Only if you light them. Best with bubble bath as it tends to trap aforesaid emissions efficiently for mass detonation later on (should your little ones invade the bath with you in it). How do think FAEs were invented! By engineers? Try again: A rogue accountant, farting in the bath whist lighting a cigarette!

Guess that was a problem he couldn't work out with his pencil....

The neon leaks out too, albeit at a much slower rate.

Besides neon and helium, deuterium and hydrogen have well established non-negligible diffusion rates through many common types of glass.

Notwithstanding any word games, it doesn't matter for all practical purposes.

What about fiber optics? How do they contribute to this debate?

How close are ceramics to glass, I have heard about ceramic bearings used in industry...are there any glass bearings? How do the ceramic (if glass-like) or glass bearings deal with the stresses?

Drew K

How about lead? and creep in concrete?

Edit. Should have been OT.