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Thread: melting point soft glass

  1. #11
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    This is from a UC Riverside physics FAQ 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. In terms of its material properties we can do little better. There is no clear definition of the distinction between solids and highly viscous liquids. All such phases or states of matter are idealisations of real material properties. Nevertheless, from a more common sense point of view, glass should be considered a solid since it is rigid according to everyday experience. The use of the term "supercooled liquid" to describe glass still persists, but is considered by many to be an unfortunate misnomer that should be avoided. In any case, claims that glass panes in old windows have deformed due to glass flow have never been substantiated. Examples of Roman glassware and calculations based on measurements of glass visco-properties indicate that these claims cannot be true. The observed features are more easily explained as a result of the imperfect methods used to make glass window panes before the float glass process was invented.

  2. #12
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    The key characteristic of glass and glass-like substances is that they show no large-scale order in their atomic structure. This is unlike crystals, for example, which do show large-scale order. I agree that the characteristic is generally of interest only to scientists. For the rest of us, basically if it seems solid, it is solid and if it seems liquid then it is liquid. Most materials can be in either state given the application of the proper temperature although some skip the liquid phase altogether and go directly from being a solid to being a gas. All the other things we describe, such as viscosity, COE, strain point, working point and so on are best left to those who really care about such matters because they have a vested interest in doing so. Manufacturers of glass are one class of interested parties because they want their various different offerings to be "compatible" - or not, as the case may be.

    The discussion about what to call glass in the technical sense will go on for a very long time but the outcome will not matter to any of us as artists and I doubt that the nomenclature has any cosmological consequences.

    Vince

  3. #13
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    Quote Originally Posted by Vince
    I doubt that the nomenclature has any cosmological consequences.

    Vince
    God will get you for that

  4. #14
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    Wink !

    I am so glad I had 6 years of latin, :-)

    O and chemistry, but that was my weakest point.

    Thank you al for explaining and making me understand more about glass. It is almost cristal clear now (unlike MOretti's clear).

    Cheers,
    Marlein

  5. #15
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    Marlein,

    yes, the Latin is handy. I had seven years of it and it keeps being useful.

    Mike, If I thought God really cared about the inflationary period I'd be really worried, but the neutrinos didn't appear until it was over, so the solid/liquid argument would not have existed until very much later. Besides if that's the worst thing I need to be concerned about I'm in really good shape with God.

    Vince

  6. #16
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    "How did the "glass is a supercooled liquid" urban legend originate? It is possible it began with an erroneous reading of an influential book by Gustav Tammann (1861-1938), a German physicist who was among the first to study glass as a thermodynamic system (Tammann, 1933). I was unable to locate a copy of Tammann's book to verify this, so the following is speculation. One or two papers I consulted attributed to Tammann the statement "Glass is a supercooled [or undercooled] liquid." But, from other papers, it appears that what Tammann actually wrote was "Glass is a frozen supercooled liquid" [my emphasis]. My speculation is that an author misquoted Tammann, and this misquotation was repeated by later authors who, since copies of Tammann's book are rather rare, did not refer directly to Tammann"

    I have always known glass as an "amorphous solid" this quotation might help some of you who are still under the influence of high scool definitions.
    B

  7. #17
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    Vince - heh..........

  8. #18
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    Yep, "Amorphous Solid" basically says it all. It's a good term that describes the substance correctly. Now, let's see how fast our fellow beadmakers pick that one up.

    I think the colloquial terms we use like "Crystal" to describe a very clear, usually lead containing, glass has added to the confusion since any glass is by definition not "crystal"; but you would be amazed how firmly the concept that glass can be crystal is entrenched in the artistic mind.

    Isn't language wonderful?

    Vince

  9. #19
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    Quote Originally Posted by Vince
    (...)
    Mike, If I thought God really cared about the inflationary period I'd be really worried, but the neutrinos didn't appear until it was over, so the solid/liquid argument would not have existed until very much later. Besides if that's the worst thing I need to be concerned about I'm in really good shape with God.

    Vince
    Hi Vince!

    ROTF.... That's a go(o)d statement!

    Dietmar


    PS: The "Story of the flowing windowglass" is a legend: I saw stress optical photos from roman cage cups (Diatret Glass). The glass is allmost 2000 jears old and the stress from the manufactoring process is still there.

  10. #20
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    The whole business of glass flowing after set was debunked by Harvey Littleton Sr. Look to his work for a complete discussion of this rather murky topic. The real question here, beyond simple curiosity, is does it mean anything to the artist?

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