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Author Topic: Why is glass said to be a liquid?  (Read 3357 times)

Offline science_guy

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Why is glass said to be a liquid?
« on: 21/01/2007 07:41:08 »
I heard recently from a friend of mine that glass is classified as a liquid.  Is this true?

if it is true, how is this possible?
« Last Edit: 05/04/2008 10:46:03 by chris »


 

Offline bigtim

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Re: Why is glass said to be a liquid?
« Reply #1 on: 21/01/2007 10:52:10 »
It is indeed true, but it has such a high viscosity that it's properties are very much like that of a solid. For example, If you study a piece of glass from an old window, it will be thicker at the bottom than at the top since it has kinda re-moulded itself over time.
 

Offline Soul Surfer

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Re: Why is glass said to be a liquid?
« Reply #2 on: 21/01/2007 11:24:14 »
Glasses are essentially very viscous supercooled liquids.  Most conventional solids have a crystalline structure on a very small scale and this can be seen by their X-ray diffraction pattern even if the crystals are very small because the atoms have a fixed separation and show clear lines.  Glasses do not show this fixed separations between the atoms but a much more fuzzy separation like the X-ray diffraction pattern of liquids
 

Offline daveshorts

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Re: Why is glass said to be a liquid?
« Reply #3 on: 21/01/2007 22:48:08 »
However the panes of glass thing is apparently somewhat of a myth. Glass ought to behave like a liquid but it is so viscous that there would be no discernable difference over the sort of time period that we have been able to make it. The reason that the bottom is often thicker than the top is that window glass was made by blowing a big flat bottle, and then cutting it up. the middle of the bottle would be thicker than the outside. The glaziers would then tend to put the thick end at the bottom, as you want to have a system or it will look silly, and that feels more stable.
 

Offline science_guy

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Re: Why is glass said to be a liquid?
« Reply #4 on: 22/01/2007 07:57:52 »
I see.

So If i were to conduct an experiment with x-raying two surfaces, glass and some metal, than the metal would show different structure than glass?
 

Offline daveshorts

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Re: Why is glass said to be a liquid?
« Reply #5 on: 22/01/2007 09:27:11 »
Yes, because a crystal structure repeats, over a relatively large scale, but a glass is much more random, if you make an X-ray diffraction pattern the crystal will produce lots of well defined spots, but the glass's diffraction pattern would be much more blurry.
 

Offline lightarrow

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« Last Edit: 02/04/2008 08:10:17 by lightarrow »
 

lyner

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Re: Why is glass said to be a liquid?
« Reply #7 on: 03/04/2008 10:50:22 »
However the panes of glass thing is apparently somewhat of a myth. Glass ought to behave like a liquid but it is so viscous that there would be no discernable difference over the sort of time period that we have been able to make it. The reason that the bottom is often thicker than the top is that window glass was made by blowing a big flat bottle, and then cutting it up. the middle of the bottle would be thicker than the outside. The glaziers would then tend to put the thick end at the bottom, as you want to have a system or it will look silly, and that feels more stable.
That make a lot of sense - there is always a risk when you don't actually do the whole experiment yourself!
 

lyner

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Re: Why is glass said to be a liquid?
« Reply #8 on: 03/04/2008 11:03:09 »
But the whole of elementary Science seems obsessed with categorising. Why does any material 'have' to be called a liquid or a solid? It just exhibits properties.
We show kids ice, water and steam and then they ask us about mud, foam etc. Thermoplastics can't be classifiable as solid or liquid, either.
Kids are so inclined to want a simple, taxonomical, view of things and the Science curriculum has always encouraged this. It gives credence to the complaints of 'rote learning' which we read so frequently in these forums. In fact, many kids just want to know whether it's A or B and not to think about the in between situation.
It's difficult for a teacher to say "It's not as simple as that" but they should always point it out because it never is.
 

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Re: Why is glass said to be a liquid?
« Reply #8 on: 03/04/2008 11:03:09 »

 

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