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Author Topic: Why is glass not really a solid, or is it?  (Read 5066 times)

Offline Seany

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Why is glass not really a solid, or is it?
« on: 01/04/2008 23:06:11 »
Apparently Glass isn't solid.

Say you have a lots of glass pieces in a bowl. In millions of years time, it will be all in a straight line in the bowl, like frozen water or something.

Also in windows.. Very old windows, the glass at the bottom is slightly thicker than the top.


What makes glass have this weird property??
« Last Edit: 05/04/2008 10:47:48 by chris »


 

another_someone

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Re: Why is glass not really a solid, or is it?
« Reply #1 on: 02/04/2008 02:22:41 »
This is a common misconception, but I have been assured (possibly on this site, but maybe elsewhere - I cannot recollect right now) that it is incorrect.

Glass is not crystalline, but is an amorphous solid, but it is solid.

The argument about very old windows being thicker at the bottom is correct, but not for the reason given.  Old glass makers were not competent to make absolutely flat glass, so glass tended to be made inevitably thicker on one end than the other.  When fitters came to fit the glass in the windows, it was inevitable that they would put the heaver (i.e. thicker) bit on the bottom, because it was more stable that way.
 

Offline science_guy

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Re: Why is glass not really a solid, or is it?
« Reply #2 on: 02/04/2008 05:20:34 »
i've been told that the structure is semi-liquid, semi-solid, but closer to liquid, so they classify it that way...

some things you hold in your memory for about a year, for it to come crashing down (no topic-related pun intented) suddenly...
 

Offline Seany

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Re: Why is glass not really a solid, or is it?
« Reply #3 on: 02/04/2008 09:12:23 »
i've been told that the structure is semi-liquid, semi-solid, but closer to liquid, so they classify it that way...

some things you hold in your memory for about a year, for it to come crashing down (no topic-related pun intented) suddenly...

Yup.. I just found your post.. On the first page!
 

Offline Seany

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Re: Why is glass not really a solid, or is it?
« Reply #4 on: 02/04/2008 09:12:43 »
This is a common misconception, but I have been assured (possibly on this site, but maybe elsewhere - I cannot recollect right now) that it is incorrect.

Glass is not crystalline, but is an amorphous solid, but it is solid.

The argument about very old windows being thicker at the bottom is correct, but not for the reason given.  Old glass makers were not competent to make absolutely flat glass, so glass tended to be made inevitably thicker on one end than the other.  When fitters came to fit the glass in the windows, it was inevitable that they would put the heaver (i.e. thicker) bit on the bottom, because it was more stable that way.
So it's actually not a crystal or a liquid but a solid?
 

Offline techmind

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Re: Why is glass not really a solid, or is it?
« Reply #5 on: 02/04/2008 10:49:58 »
Glass is amorphous (i.e. it's molecules are randomly aligned as in a liquid, with no long-range order), but also "solid" - in as much as it doesn't flow (at least definitely not noticeably over time periods of weeks or months).

Yes Seany, glass is definitely not a crystal. Crystals are defined by having regular geometric arrangements of atoms, like diamond, sugar, salt etc. Crystal is the absolute opposite of amorphous.

Solid is a bit harder to clarify: a "normal" material goes through solid-liquid-gas phase transistions (water is far from normal in many respects, but demonstrates this effect well), where the melting and boiling temperatures are well defined, and a significant amount of energy is needed to go from solid-to-liquid (and later, liquid-to-gas) at a constant temperature.

I understand (ie I'm not 100% certain) that regular glass does not have a well-defined melting temperature, but tends to just progressively soften as the temperature is raised. Anyone know better?

So when does an extremely viscous ("thick") liquid become a "solid"?

There's lots of interesting-looking material here:
http://en.wikipedia.org/wiki/Viscosity    
...but I'm not sure it helps us very much!    ???
« Last Edit: 02/04/2008 10:59:51 by techmind »
 

another_someone

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Re: Why is glass not really a solid, or is it?
« Reply #6 on: 02/04/2008 14:24:14 »
And gets even more interesting when you get to liquid crystals.  The lines between solid and liquid can get quite ambiguous.
 

Offline that mad man

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Re: Why is glass not really a solid, or is it?
« Reply #7 on: 02/04/2008 15:33:20 »
I was in the glass industry for some time and visited many glass blowing factories and at Whitefriars even had a go at blowing. I was always told, and read also that glass was a "supercooled fluid". I was told it a myth that in olden days the glass was made thicker at one end, uneven and a bit thicker in places yes. No glass making records exist (as far as I know) that show that stained glass was ever made that way.

I dealt in high quality cut crystal glass and again was told it was not "crystal" but it was given that generic name because of its brilliance when cut.

So, beware of people selling cut crystal as "healing crystal" as that's what its not.
 

Offline neilep

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Re: Why is glass not really a solid, or is it?
« Reply #8 on: 02/04/2008 16:07:25 »
There must be something about the phenomena that is the Seany hurricane that has him asking some rather klevur questions....here ,for instance, is a link to a similar question asked by an equally klevur fella !! ;)

http://www.thenakedscientists.com/forum/index.php?topic=6232.0
 

Offline Seany

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Re: Why is glass not really a solid, or is it?
« Reply #9 on: 02/04/2008 16:18:06 »
That is a very clever fellow!! ;)
 

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Re: Why is glass not really a solid, or is it?
« Reply #9 on: 02/04/2008 16:18:06 »

 

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