[neilep (OP)]

I have heard that glass is a liquid but is frozen at room temperature.

Is this true..?...what about rubber ?

If Glass IS a liquid...why is it a liquid ?

[Heliotrope]

It's not a liquid.
It's a crystal.
Glass can relax and distort which is why it's sometimes thicker at the bottom than at the top in very, very old windows.

[neilep (OP)]

It's not a liquid.
It's a crystal.
Glass can relax and distort which is why it's sometimes thicker at the bottom than at the top in very, very old windows.

THANK YOU Chum,

So...aren't crystals solid though !!....I never seen a liquid one !!

[JimBob]

Glass is a metastable substance called a mineraloid. It is metastable, i.e., it will break down into small stable crystals of "sand." Glass, along with granite and rhyolite, are all metastable substances. Glass is just the shortest lived - lasts less than about 250,000,000 years. The answer to Question 1 is TRUE. Glass is frozen liquid because not all - only part - of the atoms are not in a crystal matrix.

As for rubber - go ask a rubber tree. Then rubber changes when it is combined with sulfer and heated and than there are a couple (at least) of types of artificial rubber so I do not have a clue.

[neilep (OP)]

Glass is a metastable substance called a mineraloid. It is metastable, i.e., it will break down into small stable crystals of "sand." Glass, along with granite and rhyolite, are all metastable substances. Glass is just the shortest lived - lasts less than about 250,000,000 years. The answer to Question 1 is TRUE. Glass is frozen liquid because not all - only part - of the atoms are not in a crystal matrix.

As for rubber - go ask a rubber tree. Then rubber changes when it is combined with sulfer and heated and than there are a couple (at least) of types of artificial rubber so I do not have a clue.

I'm gonna knock knock knock on wood !!


*walks up to Rubber tree...knocks to see if anybody is in......bounces back !!...end of inquisition*

THANK EWE JIMBOB....I appreciate your clarification.

[daveshorts]

Rubber has a structure which is not really either. It is made up of long protein polymers (a bit like a bowl of spaghetti), which are occasionally interlinked (the red dots)
[diagram=50_0]

This means that they can move past each other for a bit, and you can stretch the molecules out.
[diagram=51_0]

But eventually you reach a point where some of the molecules are straight, so the only way you can stretch it any more is by breaking it.

When you release the rubber band because the straight molecules get vibrated and wobbled, as if something is warm it's molecules are vibrating.

[diagram=52_0]
A diagram of one of the billions of molecules being buffeted by other molecules

they tend to get less straight over time and hence the whole thing gets shorter.

[diagram=53_0]

[Heliotrope]

Hmmmmm.
Looks like there isn't a lot of consensus regarding the liquid/solid/amorphous solid etc...

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

Glass as a liquid
One arguably justifiable belief is that glass is a liquid of practically infinite viscosity at room temperature and as such flows, though very slowly, similar to pitch. Glass is generally treated as an amorphous solid rather than a liquid, though different views can be justified since characterizing glass as either 'solid' or 'liquid' is not an entirely straightforward matter [3]. However, the notion that glass flows to an appreciable extent over extended periods of time is not supported by empirical evidence or theoretical analysis.

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.

So it's dificult to classify.
And it seems like the flowing thing is rubbish too.
I should have read the article first.
Ah well.

No day in which you learn something is a complete loss.

[]

[JimBob]

Hmmmmm.
Looks like there isn't a lot of consensus regarding the liquid/solid/amorphous solid etc...

That is right - it is all of these things at the same time. It is a liquid when very hot, as it cools slightly before it sets it forms small crystals (solids) and then when completely cool the other forms crystals and some not, leaving an amorphous solid as compared to the amorphous liquid. An amorphous solid such as glass will flow unless it has been cooled very slowly which creates larger crystals that form a more solid matrix. This is exactly analogous to concrete. Concrete is a metastable substance but we put in sand and gravel, as well as rebar, provide a matrix in which the cement hydrates into amorphous chemical compounds binding the portland cement particles, the gypsum hydrate and the matrix bound together by mainly the gypsum  hydrate.

 



It is the 'bridging' by small crystalline (solids) in the amorphous surrounding materials that make glass, concrete, obsidians, granites and rhyolites into solids but technically metastable substances. (See the article on obsidian at http://en.wikipedia.org/wiki/Obsidian)

THUS: 'A metastable state may thus be considered a kind of temporary energy trap ... ' (Britanica Online)

[jysk]

Could a metastable substance behave hydraulically in a state of confinement? That is, if it can no longer be compressed, can if flow?

Mike

[eric l]

Could a metastable substance behave hydraulically in a state of confinement? That is, if it can no longer be compressed, can if flow?

Mike

Is bread dough (before baking) solid or liquid ?  You can not really compress it to a smaller volume, but you can press it into any shape you want, and it will not restore itself like an elastic body (= ideal solid) would do.
Classifying matter into solids, liquids and gasses is a poor representation of all the states possible !

[JimBob]

THAT'S AN AFFIRMATIVE, jysk!  The flow is what happens when granite, rhyolie, obsidian (glass) are involved in tectonic activity. Glass , even table ware will flow slowly over time if weight is applied.

Of course, the elastic (or plastic, depending on your thing), bulk and Young's moduli are out of sight for the flow.

[DoctorBeaver]

I thought all substances had 4 states - solid, liquid, gaseous & plasma. Or is that just elements?  []

[JimBob]

Good day, Herr Doktor,

Yes, matter has 4 states but these states are not mutually exclusive - thus metastability.

Also, molecules can exist in a plasma form as all that is required is to have an ionized particle to have a plasma. Low temperature solid plasmas, such as a candle flame, are know to all of us. Ultra cold plasmas are also possible. Then thee are things like the Sun and other cosmic and/or quantum stuff.

What is most interesting to me are all the triple point phase charts that at one time permeated beginning text books (But are now block diagrams with P,V,T as the axies. No one ever says "OK, this diagram represents the system under IDEAL conditions. Add another variable - the existence of two phases of the same substance at the same P,V,T conditions (metastability) - and the ordinary person says "See, Melvin, I told you them people were idjits!" 



                                                                                                                                                                                                               

[BillJx]

Glass does not flow.  Not at a rate fast enough to be observable over a period of billions of years.  The idea that it does is an urban legend, probably due to old glass windows being thicker at the botton than at the top.  There are a couple of explanantions for that.  Ancient glass wasn't flat, and was installed thick side down to start with.  And according to Wikipidia,  the lead that holds it in place bends.
A web search will bring up many reliable sites to debunk this old myth.
http://glassnotes.com/Resources/No,%20It%20Doesn't%20Flow.pdf
http://www.phschool.com/science/science_news/articles/cathedral_glass_myth.html
http://en.wikipedia.org/wiki/Glass

[neilep (OP)]

Excellent links  and post.......... thank ewe BillJx

[paul.fr]

By Dr Karl S. Kruszelnicki

"It has been suggested that, "glass is a liquid that flows very slowly, and to prove it, just look at old windows that are thicker at the bottom". Well, this story has been around for a long time, but only recently have we got the definitive answer.

Glass is mostly silicon dioxide, which you get from sand. The trouble is the melting point of sand is up around 1700°C and it takes a lot of expensive energy to get up there. But if you add sodium carbonate, you drop the melting point down to a more reasonable 850°C. Unfortunately, a glass made from sand and sodium carbonate will actually dissolve in water - in fact, they're called water glasses. So adding limestone (which gives you calcium oxide) makes the glass insoluble in water.

This process was discovered a long time ago, and some of the earliest totally-glass objects that we have are glass beads from Egyptian tombs, some 4,500 years ago.

But it was the stained glass in old cathedrals that probably led to the story that glass would flow like a very thick liquid. The oldest pieces of stained glass, according the Guinness Book Of Records, are dated before AD 850, from St. Paul's Church in Jarrow, Ireland. And if you look at stained glass around the world, and even glass from old windows, you'll find that some of it is in fact thicker at the bottom.

But it's nothing to do with the glass flowing, and all to do with how the glass was made into a flat sheet. It turns out that it's fairly difficult to make plate window glass, that's smooth and flat. The Romans would "cast" or pour molten glass into a mould, and then polish it. Their plate glass had many defects. Later on came the "crown glass" method. Here a gob of molten glass would be blown to make a large sphere, and then the sphere would be rapidly spun until it eventually turned into a large disc - spinning vertically. Then, while it still quite soft, the glass would be flipped from vertical to horizontal and plonked onto a flat surface. Even after it was polished, it was still a fairly wavy sort of glass.

Another way to make plate glass was the "cylinder" method. The glass blower would blow molten glass into a cylinder, which would be then cut open to make a glass plate. Once again, the finish and smoothness weren't very good.

A more recent method was "mechanical rolling", when molten glass was rolled between rollers in the same way that sheet metal is rolled. Once again, it needed to be polished and there was still obvious waviness in the glass. Finally, in 1959, Alistair Pilkington of the Pilkington Glass Company invented the "float glass" method. Molten glass is poured onto a bath of molten tin - the glass spreads and cools to be perfectly flat on both sides, with no need of further polishing. So now you have the answer to those who say that "glass flows, and old windows prove it".

Practically all plate glass made before 1959 had some degree of waviness in it. It was uneven in thickness. When the glaziers would install it in a window, they would normally do it like you build a building - with the bigger bits at the bottom and the thinner bits at the top. But, Stephen Hawkes from Oregon, who has dedicated his life to dismantling and repairing medieval glass windows, says that while most of the glass that he has seen was bottom-heavy, he has seen hundreds of pieces of old plate glass that were thicker at the top.

Astronomers have been making and using telescopes, with large glass lenses, for well over a century. They would have noticed if glass flowed. Lenses need a shape that is accurate to about one tenth of a wavelength of visible light - roughly 50 billionths of a metre. But not one astronomer has ever complained that their old lens is unusable because the glass had changed shape.

But according to Edgar Zanotto, from the Federal University of São Carlos in Brazil, glass can flow - but very slowly. In May 1998, he wrote an article in the American Journal of Physics, where he worked out how fast glass can flow. According to his calculations, if you heated the glass to 450°C, it would flow a decent amount in only 800 years. But if you wanted to see glass flow at room temperature, you would have to wait at least 10,000 million million million times the age of the universe! Getting glass to flow at room temperature? It's enough to make your eyes glaze over. "