The "glass isn't a solid" is, apparently, a myth. For example,
http://math.ucr.edu/home/baez/physics/General/Glass/glass.html wheich
ends with " 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."
Also, there's
http://dwb.unl.edu/Teacher/NSF/C01/C01Links/www.ualberta.ca/~bderksen/florin.html
http://www.scientificamerican.com/article/fact-fiction-glass-liquid/
http://chemistry.about.com/od/matter/a/Is-Glass-A-Liquid-Or-A-Solid.htm
And finally, from Dow-Corning:
http://www.cmog.org/article/does-glass-flow
Kim N5OP
On 1/24/2015 10:38 AM, donroden@hiwaay.net wrote:
I just went out and measured a 100 year old pane of glass on my
grandfather's shop. No appreciable thickness change from top to bottom.
I wouldn't spend to much time watching for glass flow.
Don W4DNR
Quoting greg greene <greg.greene74@gmail.com>:
Actually, there is something wrong with that. Glass, technically, is a
liquid and flows very slowly under pressure, even at room temperature
over long periods of time. I believe this is the main reason glass
tubes are prone to become gassy after years of storage. I can't prove
it, but I believe this is why ceramic tubes are much less prone to
this problem since ceramic is a rigid crystalline solid.
That's just my theory - comments welcome.
Bill W6WRT
*************************************
You are correct Bill, if you exam glass windows that are several
years old
you will find the bottoms thicker than the tops from the flow of the
glass
due to gravity. Add heat from using the tube to accelerate the
process and
one can see how glass tubes could be more prone to failure than ceramic.
I'm not aware of the formula for the glass used in tubes off shore
but we
can hope they are taking this into account when they manufacture
them, but
probably not.
Greg VE7GPG
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--
Kim Elmore, Ph.D. (Adj. Assoc. Prof., OU School of Meteorology, CCM, PP
SEL/MEL/Glider, N5OP, 2nd Class Radiotelegraph, GROL)
/"In theory there is no difference between theory and practice. But, in
practice, there is." //– Attributed to many people; it’s so true that it
doesn’t matter who said it./
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