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The AFU and Urban Legend Archive Science Glass Flow glass flow the thread
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The AFU and Urban Legend Archive Science Glass Flow glass flow the thread
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From: rrd@fc.hp.com (Ray Depew)
Newsgroups: alt.folklore.urban
Subject: Glass does flow and old windows prove it
Date: 6 Nov 1995 20:49:25 GMT
Perhaps I can forestall the rest of this discussion by posting a summary of what transpired last time the "glass flow" discussion went through alt.folklore.urban.
If you're thinking of posting "yes it does, and yes they do, and how do you know they don't?" or any thing similary, please take the time to read the next 1200 lines.
I would have put this on Cathouse, but the best parts of it are already there, and our cries of "Read all about it on Cathouse" seem to have fallen on deaf ears.
I would have shortened it for the benefit of our NZ colleagues, but I was afraid I'd leave something out -- and besides, it takes up less room, all told, than the lameoid "I'm better than snopes" flame wars and the utterly moronic "best bumper sticker" threads going on elsewhere in AFU.
Regards
Ray Depew
rrd@fc.hp.com
Chairman, Curator and Headmaster of The Axeman Institute
From: twcaps@tennyson.lbl.gov (Terry Chan)
Newsgroups: alt.folklore.urban
Subject: Glass Flow [Was Re: OBJECTIONS to afu faq (v.2.50 1/194) ]
Date: 30 Jan 1994 04:15:56 GMT
As part of a series of off-the-cuff objections to various points in the FAQ, cee1@Ra.MsState.Edu (Charles Evans) objected to the following:
RE "F. You can see glass flow in the windows of old buildings."
and wrote:
>I will have to disagree.. in (at least) the Old Wavery Mansion >near Columbus, MS
[...details involving information from a "Lady" deleted...]
>I had heard/seen that before I learned in school that glass is >amorphic (no crystals.. right).. just very very viscous "but >would flow over time".. always stuck in my mind.
Others, such as prolific poster boy dbd@martha.utcc.utk.edu (David "Soon to be a Pud Boy Near You" DeLaney) cautiously casts his lot against the FAQ and writes:
>This discussion I wasn't around for the first time; I will put my >1.87 cents in on the T. side, as I'm pretty sure I've *seen* very >old, wavy windows at several points.
Well, since Punk Papai's credibility may have been eroded somewhat since he didn't request address and plane fare when he had the opportunity, I dug some junk of out my files and present the following.
In a 4 Oct 1993 post, surprisingly informative poster (for someone who's affected by Coriolis as much as those in Oz are) paul@mercury.chem.csiro.au (G. Paul Savage) gave some pertinent information:
[...]
>By the same token, this does not mean that
>we can observe the flow of glass by simple
>empirical methods such as looking at the
>thickness of window panes. See for example
>the following: "Antique windowpanes and the
>flow of supercooled liquids" by Robert C.
>Plumb (Worcester Polytech. Inst.)in the Journal
>of Chemical Education, 66(12), 994-6, 1989.
Paul provided the abstract of that paper, which read:
In an attempt to dispel the notion that colonial window panes are
thicker at the bottom than at the top because the glass is a
supercooled liq. that has slowly flowed downward over the hundreds
of years since it was installed, a discussion is presented on the
properties of glass. A historical account is also given on the
manuf. of window pane glass using the Crown glass process which
produced glass of fairly uniform thickness.
Now, this may have no meaning to some parties, so Paul dug out the paper and summarized it in the following post:
>From: paul@mercury.chem.csiro.au (G. Paul Savage)
>Newsgroups: alt.folklore.science,alt.folklore.urban
>Subject: Re: Non-flow of glass - final proof
>Date: 4 Oct 1993 23:52:12 -0500
>Organization: UTexas Mail-to-News Gateway
>Lines: 58
>Sender: daemon@cs.utexas.edu
>Message-ID: <199310050452.AA27417@shark.mel.dit.csiro.au>
>NNTP-Posting-Host: cs.utexas.edu
>Xref: dog.ee.lbl.gov alt.folklore.science:8135 alt.folklore.urban:94929
>
>In article <199310050310.AA25843@shark.mel.dit.csiro.au>, I write:
>>I will try to get hold of the full paper and relate its findings.
>
>And indeed I have. Some interesting points arise in the article "Antique
>windowpanes and the flow of supercooled liquids" by Robert C. Plumb
>(Worcester Polytech. Inst.)in the Journal of Chemical Education, 66(12),
>994-6, 1989.
>
>1)Robert Brill of the Corning Museum has records of the stories
> [of window panes 'flowing' over the years] dating back sa far
> as high school chemistry class in 1947. [surely enough to qualify
> as UL]
>2)The glassy state resembles a liquid in having short-range [molecular]
> order without long-range order ,but differs in that the entire network
> is rigid, whereas in the liquid state enough energy is available to
> break and reform bonds continuously.
>3)The temperature at which a rigid glass becomes a supercooled liquid is
> called the glass transition temperature, Tg. For window glass, Tg
> (measured) is 550 degrees C. For the limiting case of infinite time
> the thermodynamically calculated ideal glass transition state Tg(0)
> for window glass is 270 degrees C. For Pyrex the values are 550 and
> 350 deg., respectively. [This allone should be enough to put to rest
> any argument for the liquid properties of glass at room temperature
> (which rarely gets above 50 degrees C).]
>4)If a rod of glass is twisted it will return to its original shape.
> If it is twisted and held for a period it will retain its twisted
> shape BUT will gradually return to its original zero-twist state over
> time. This 'delayed elastic recovery effect' is explained in the paper
> but is too technical to go into here. Suffice to say, this experiment
> debunks any 'deformation of glass under pressure = glass flows' type
> experiments.
>5)Those who are convinced that glass flows like a viscous liquid under
> its own weight sometimes cite the Corning Glass Co. instructions
> printed on boxes of tubing, "Lay flat, do not stand on end". According
> to R. Lemker (Operations Manager, Fallbrook Plant, Corning Glass,
> Corning, NY) the instructions are to avoid damage to the ends of the
> tubing, not to keep it from sagging.
>6)The paper then goes into a long discussion of how glass windows were
> manufactured in the 1800's (the Crown glass process) and essentially
> comes to the conclusion (already offered in AFU) that antique window
> panes are thicker at the bottom because of variations in the thickness
> of the glass (which at the time were less important than other defects
> such as blisters, dust, lines, curves and scratches) produced during
> manufacture. The author surmises that glaziers would tend to put the
> thick end of the glass at the bottom for stability.
>Okay, does that end the issue? One thought mentioned at the end of the
>paper was interesting. If someone could find a copy of a window glazier's
>instruction book from the 1800's there might be mention of putting the
>thick end of the pane at the bottom. That would be conclusive evidence.
>
>
>Paul.
>----------------------------------------------------------------------------
>paul.savage@mercury.chem.csiro.au ....................... Australian Science >CSIRO, Division of Chemicals & Polymers ................. Australia's Future
>----------------------------------------------------------------------------
Terry "so I went ahead and built that glass house" Chan
[Here's one from David Bloomberg, who has a degree in materials science and does/did research in glass science.]
From: David.Bloomberg@f2112.n2430.z1.fidonet.org (David Bloomberg)
Date: 15 Jun 95 06:41:08 -0500
Subject: My dog ate your homework
To: rrd@hpfcla.fc.hp.com
For what it's worth, glass did used to be commonly referred to as a super-cooled liquid. However, as Doremus points out in _Glass Science_ (incidentally a book Copyrighted in 1973), "the difficulty with this view is that glasses can be prepared without cooling from the liquid state. Glass coatings are deposited from the vapor or liquid solution, sometimes with chemical reactions. Thus sodium silicate glass can be made by evaporating an aqueous solution of sodium silicate (water glass) and baking the deposit to remove water. The product of this process is indistinguishable from sodium silicate glass of the same composition made by cooling from the liquid." (p. 1)
Interestingly, while he doesn't speak specifically of the supposedly flowing windows, he does say the following, also on p. 1:
"Glass is an amorphous solid. A material is amorphous when it has no long-range order, that is, when there is no regularity in the arrangement of its molecular constituents on a scale larger than a few times the size of these
groups. ... A solid is a rigid material; IT DOES NOT FLOW WHEN IT IS SUBJECTED TO MODERATE FORCES. More quantitatively, a solid can be defined as a material with a viscosity of more than about 10^15 P (poises)." [Emphasis mine]
From: David.Bloomberg@f2112.n2430.z1.fidonet.org (David Bloomberg)
Date: 15 May 95 12:35:05
Newsgroups: alt.folklore.urban
Subject: Re: Old windows thickening at the base?
In a msg to All on <May 09 14:30>, Ray Depew of 1:2619/599 writes:
RD> : Colored panes of glass have significant amounts of metallic impurities, RD> : which can create more ordered crystalline structure in the glass.
RD> Whoa, wait, back up. "Metallic impurities?" You mean salts of gold,
RD> copper, sodium or cobalt? Okay. Let's add some of those "metallic
RD> impurities" to other liquids. Take molten metal, for example, or molten
RD> sodium chloride, or even plain old water. Add a handful of copper
RD> sulfate. Now, lower the temperature. Is the "freezing point" higher
RD> or lower than it was before?
RD> It's lower, right? So we could say that adding impurities to the
RD> liquid lowers the freezing/melting point. That's freshman chemistry.
Sorry, Ray, but glass science is anything BUT "freshman chemistry." Considering the impressive-looking signature you ended this message with, I'm quite surprised you would make such a statement. When you add those things to water, they don't modify the structure in a way which may either strengthen or weaken the bonds overall -- that's because glass is NOT simply a liquid -- it is an amorphous _solid_.
RD> Hence, the impurities in stained glass should lower the glass RD> transition temperature of the glass, making colored glass flow MORE RD> easily than regular glass, right?
Not necessarily, no. Some impurities raise the glass transition temperature, some lower it.
RD> Your suggestion about "more ordered crystalline structure in the glass" RD> is meaningless if you insist that glass is an "amorphous solid". RD> Either it's amorphous, or it isn't. The "metallic impurities" do not RD> impart a crystalline structure to the glass; by your own definitions, if RD> they did, it would cease to be a glass.
It is amorphous in long-range order, but its short-range order may become "more crystalline" as he has said. Perhaps he could have better phrased it by saying that the bonds would become stronger.
RD> : Keith Gerritsen, a student of Materials Science and Engineering
RD> Ray Depew, BSChE, MSEE, amateur mineralogist and geologist, working in RD> chemical engineering and materials science for nigh onto 14 years
David Bloomberg, BS Ceramic Engineering, Did Master's project on the varying effects of additives to phosphoborosilicate glasses (haven't finished writing thesis).
Newsgroups: alt.folklore.urban
From: jg94au@badger.ac.BrockU.CA (JASON J GILL)
Subject: Re: Old windows thickening at the base?
Date: Thu, 18 May 1995 00:48:06 GMT
So, then, to recap:
Hope this clears everything up,
JG.
Newsgroups: alt.folklore.urban
From: ctf2m@kelvin.seas.Virginia.EDU (Chris Fishel)
Subject: Re: Old windows thickening at the base?
Date: Thu, 18 May 1995 16:50:48 GMT
s9244816@cs.sun.ac.za (David Richfield) writes:
>
> When you heat glass up, it doesn't reach a temperature where it suddenly
> starts to flow. It just gets more and more fluid. When you use a diamond
> to score a sheet of glass (Glass cutter) and crack it along the mark, it
> works noticeably better if you do it while the cut is fresh, as the fine
> edge of the cut flows into a rounder shape within seconds, and doesn't
> concentrate the stress so well.
>
And how fast is it flowing during those critical seconds? Let's say it flows at 1 angstrom per second (seems to me as if anything much slower wouldn't seriously affect the edges enough to screw up your ability to cut it). Applying that rate to a really old (500 yrs) cathedral window gives [(500x365x24x60x60)sec] x (10^-10 m/sec) = 1.58 m. Obviously, then the real question isn't why windows are thick at the base, it's why are any old windows still in palce at all.
Chris "There may be a few mistakes in these calculations, but I'll
leave it to the inevitable gangs of malcontents to point
them out" Fishel
From: rrd@fc.hp.com (Ray Depew)
Newsgroups: alt.folklore.urban
Subject: Re: Old windows thickening at the base?
Date: 18 May 1995 16:53:54 GMT
David Bloomberg (David.Bloomberg@f2112.n2430.z1.fidonet.org) wrote:
: In a msg to All on <May 09 14:30>, Ray Depew of 1:2619/599 writes:
: weaken the bonds overall -- that's because glass is NOT simply a liquid -- it
: is an amorphous _solid_.
: RD> Hence, the impurities in stained glass should lower the glass
: RD> transition temperature of the glass, making colored glass flow MORE
: RD> easily than regular glass, right?
: Not necessarily, no. Some impurities raise the glass transition temperature,
: some lower it.
Cool. So the previous poster was correct in stating that colored glass (*some* colored glass) could have a higher Tg. Can you give us an educated guess about some of the additives in colored glasses? For example, gold salts (red glass), cobalt salts (blue), copper (blue and green) and iron-I-think (yellow/brown)?
I stand happily corrected by someone with more real knowledge on the subject. Speaking of which:
: David Bloomberg, BS Ceramic Engineering, Did Master's project on the varying
: effects of additives to phosphoborosilicate glasses (haven't finished writing
: thesis).
Maybe *you* can definitively answer the question for us -- okay, three questions:
(1) As an "amorphous solid," does glass flow?
(2) What's the "flow rate" of glass at room temperature?
(Okay, assume a pane of ordinary soda-lime window glass, mounted
vertically in a frame. The only force acting on it is its own
weight -- gravity, if you will.)
(3) What evidence of this "flow" would we be able to see over, say,
a few centuries?
(No micrometers or calipers here. We want things like: bulging
at the bottom; voids; weeping; dendrites or nodules; oozing out
over the frame. You know, stuff that can be easily observed with
the unaided senses.)
Regards
Ray "will defer to anyone who writes their thesis on glass" Depew
rrd@fc.hp.com
From: D.A.G.Gillies@bradford.ac.uk (David Gillies)
Newsgroups: alt.folklore.urban
Subject: Re: Old windows thickening at the base?
Date: Thu, 18 May 1995 17:43:53 GMT
In article <D8oL6J.BE@ez0.ezlink.com> rdepew@ez0.ezlink.com (Ray Depew) writes:
>Going around this circle for the one hundred and fifty-third time,
>P.J. Hendrick (u3pjh@csc.liv.ac.uk) wrote:
>
>: Glass is a liquid not a solid, but only shows it is a liquid over a long period
>: of time when it flows, hence thicker glass at the bottom of the pane.
>
>I just love it when people don't stop to read all the postings on a
>subject before they jump in with both feet. This was the very assertion
>that started this discussion, less than two weeks ago. And that
>unfounded assertion was offered as evidence in an idential discussion
>that had ben started by an identical assertion sometime in teh past
>six weeks. Get it?
>
>Okay, Mr. Hendrick, if what you say is really true,, then we should
>see old glass oozing out over the windowframes, shouldn't we? Not
>only that, but we should see some bulging -- saggin, even -- in the
>larger pieces of stained glass in the churches, shouldn't we? And
>we should see some "weeping," voids or other deformation in some of
>the older pieces of glassware in museums and royal residences,
>shouldn't we? At least in the glassware as old as these "flowing"
>windows.
>
>Guess what? WE DON'T! There must be some other explanation for old
>windowpanes being thicker at the bottom. "Glass is a liquid" doesn't
>work.
>
>--
>Getting tired of this "glass flows and old windows prove it" crap,
>Ray Depew
>rdepew@ezlink.com
Sorry to pop yer bubble, Ray, but guess what - we do! There was even a bit in New Scientist a while back about a ghost image formed by a 200-yearold mirror that had flowed downwards. The mirror was thicker at the bottom than at the top. Due to a fairly complex optical phenomenon this caused a ghost image to hover a few mm off the surface.
The sad fact is that glass *is* a liquid, but of a type known as a nonNewtonian fluid. It has astonishingly high viscosity, but it's a liquid nonetheless.
I would suspect that the impurities introduced into glass to colour it raise the 'melting' point (i.e. raise the viscosity). Also, remeber that most pieces of glassware in museums have been buried until fairly recently. You do get voids in glass panes that are sufficiently old. Take a look at some of the glass in Canterbury Cathedral if you're in the UK.
Right, lets kill this thread now.
[David & I corresponded re: this article in NS. Unfortunately, I don't have access to the article, but I'd love to read it. -- rrd]
Newsgroups: alt.folklore.urban
From: ctf2m@kelvin.seas.Virginia.EDU (Chris Fishel)
Subject: Re: Old windows thickening at the base?
Date: Thu, 18 May 1995 17:46:46 GMT
ctf2m@kelvin.seas.Virginia.EDU (myself) wrotes:
> s9244816@cs.sun.ac.za (David Richfield) writes:
> >
> > When you heat glass up, it doesn't reach a temperature where it suddenly
> > starts to flow. It just gets more and more fluid. When you use a diamond
> > to score a sheet of glass (Glass cutter) and crack it along the mark, it
> > works noticeably better if you do it while the cut is fresh, as the fine
> > edge of the cut flows into a rounder shape within seconds, and doesn't
> > concentrate the stress so well.
> >
> And how fast is it flowing during those critical seconds?
Or for an alternative way of looking at it: If the thickening of windows in old buildings is from glass flow [Not that I buy that it is, mind you] and if the rate of flow for that thickening is, at maximum, 1 cm over 500 years, that gives a flow rate equivalent to 0.0063 angstroms per second. Meaning that it would require 2-1/2 minutes for that cut's fine edges to flow an angstrom out of shape.
Chris "Either way, something doesn't seem to add up" Fishel
Newsgroups: alt.folklore.urban
From: hsm@unislc.slc.unisys.com (Helge Moulding)
Subject: Re: Old windows thickening at the base?
Date: Tue, 30 May 1995 17:11:33 GMT
Someone had asked,
: : Could the egyptians have found an extremely efficient way of blowing
: : glass or found aditives which stengthened the molecular bonds in
: : their glass?
And I quipped,
: >Sure. The famous glass pyramids of Bizet are proof of that.
: >(Where the hell have you seen man-made glass more than a few hundred
: >years old????!!!)
GryphonSus wrote,
: Try the Grand Rapids (MI) Public Museum, on Jefferson St.
Ah, yes. I did some reading on this business in the past few days. Glass has been around a while, indeed. Egyptians made mostly glass beads, although they did manage to pour glass vessels in sand molds. The folks in Carthage apparently came up with glass blowing, and did try their hand at slab pouring. The problem with slab pouring is, of course, that the glass isn't all that transparent...
I described an earlier version of producing crown glass, and my supposition of how window glass was produced without modern tech was all wrong. (They slab poured, and polished like the dickens. The pouring process was nothing like even, and resulted in a thickened edge on the side of the slab that had longer to cool as they used a roller to press the glass flat.)
I also found that glass coloring has been around forever. In fact, colorless glass is a lot more difficult to make than colored glass. Mostly, colorless glass is made by adding colorants that reduce existing, obvious color to a sort of gray, which is no longer noticable.
Glass flowing is a matter of silliness. Glass viscosity is around 10^13 poise, which amounts to forces several orders of magnitude greater than what is needed to break glass, should it flow perceptibly at room temperature -- even over several centuries.
Someone mentioned diamond on this subject, claiming it was a liquid because it evaporates. Was he trolling? --
Helge "True, they aren't forever." Moulding
(Just another guy with a simple .sig)
From: peter@cara.demon.co.uk (Peter Ceresole)
Newsgroups: alt.folklore.urban,alt.folklore.science
Subject: Re: tornado shoves straw thru 2by4
Date: 15 Jun 1995 07:17:44 +0100
In article <ufkaap6ps6.fsf@hrlib.brooks.af.mil>, tjm@hrlib.brooks.af.mil (SrA Tim Miller) wrote:
> I'm sorry, but glass *does* flow. I work with stained glass,
>and I can show you pieces of 50-year-old glass that *has* flowed; the
>vertically hanging pieces are noticably thicker on the bottom.
GREAT! I enjoyed this one last year...
I seem to remember that this was due to glaziers, when dealing with uneven glass, instinctively putting the thicker section at the bottom. A materials scientist pointed out that, under its own weight, the changed thickness from glass flow would be unmeasurable after 10,000 years.
Peter
Newsgroups: alt.folklore.urban
From: ctf2m@kelvin.seas.Virginia.EDU (Chris Fishel)
Subject: Re: Glass flows. Angus is wrong.
Date: Fri, 16 Jun 1995 18:47:34 GMT
dave@mercury.utb.edu writes:
>
> What is a solid? Something with a definate crystalline structure. Glass
> has no crystalline structure, hence it is NOT a solid. I'm sorry, guys.
>
Well, since I don't see any of the official troll clues, I'll assume this was meant seriously. Please explain the following comments from _Physics of Amorphous Materials_ by S. R. Elliott (London: Longman Group Ltd, 1983; ISBN 0-582-44636-8), both from the definitions section, p. 5:
Although 10^14.6 poise is a semi-arbitrary cutoff point for the solidliquid transition, it perhaps should be noted that common silicalite glasses have this viscosity at temperatures greater than 1100 C (p. 32). At room temp., the viscosity is even larger.
Chris "Of course if you have an actual source to back up your
claims about glass *really* being a liquid, by all means bring
'em out." Fishel
From: s-sehlhorst@ds.mc.ti.com (Scott Sehlhorst)
Newsgroups: alt.folklore.urban,alt.folklore.science
Subject: Glass Blows! was re:wit, pith, tornado(e)s, straw and 2x4's
Date: Mon, 19 Jun 1995 17:11:36
In article <waterrd.26.000DD1E2@mins2.msfc.nasa.gov> waterrd@mins2.msfc.nasa.gov (Ronald D. Waters) writes: [...battling snip quips continue...]
>>If the glass did flow, then it maintained a constant volume. Also, it would
>>flow 'towards' becoming first a cone, and then a pool of molten glass.
> The shape it flowed toward would depend heavily on the manner in which it
>was supported. *If* it was only supported at the bottom (i.e., sitting
>loosely in a window pane), your suggestion would be accurate. If it was
>supported *around* its perimeter (via caulking or some other method), I would
>expect it to flow towards another shape (in particular, the thickness at
>corners would be expected to be greater than that in the center, in this case).
I agree with your assessment, _if_ there is chemical bonding between the glass and the supporting members. _If_ that premise were true, not only would the shape be as you described, but, more importantly, the glass would be slightly thicker at the very top, in the immediate vicinity of the supporting member, than it would slightly less close (a little below). This would also follow in your toothpaste analogy.
According to J.A. Pask, in
Chemical Bonding at Glass-To-Metal Interfaces, presented at the Winter Annual
Meeting of the American Society of Mechanical Engineers, Boston, MA, Dec 13-18,
1987.,
regarding glass to metal chemical bonding,
"Compatibility of electronic structures of the two phases is required but
not easily acquired because of the incompatibility of the metallic and ioniccovalent
bonding."
He basically says that a chemical bond, although achievable is unlikely without the presence of an oxide layer (today generated by a redox reaction with air on the metal, prior to attachment to the glass), which is probably beyond the technology of 'old' glass manufacturers.
> [...remainder deleted...]
The remainder you deleted was the point I was trying to obfuscate. If a time period sufficient to allow glass to flow (if it could flow) were to pass, then mechanical bonding would have long since broken down, unless the glass were loaded under a compressive stress. Now some science references...
First, one that I do not have, but should serve as a cathouse-caliber-answer... Shay, R.M. Jr., Ph.D. dissertation, Purdue University, West Lafayette, IN (1989) : An ideal glass analysis, referenced in... The Effect of Thermal History on the Mechanical Behavior of Amorphous Polymers, R.M. Shay, Jr., and J.M. Caruthers, Purdue University, School of Chemical Engineering, presented at the Winter Annual Meeting of the American Society of Mechanical Engineers, San Francisco, CA Dec 10-15, 1989.
In all of the references (6 or 7 that I just checked), although not at all conclusive, the researchers treat glass as a brittle amorphous structure (at least below about 600C) with no dissenting arguments in favor of other models.
Perhaps if we identify the glass in question (soda-lime-silica glass, used in window glass, for those 'old factory on the Allegheny' arguments, or a pressed glass, for the '400 year old monastary' argument), we can get some specific data on the bonding to support structures.
***
this is probably the important paragraph for those interested only in
conclusions
***
Clearly, we've reached an academic point regarding the potential mechanism
of flow (if it exists), as we concur that any flow will result in specifically
measureable non-prismatic characteristics, not just "duh...thicker at the
bottom...", through analysis of edge effects in the glass, whether surface
tension held them to the supports, or an unsupported existance resulted.
> Regards,
> R.W.
I'm afraid I don't have the familiarity with the Bingham model needed to show that it is inapropriate (or validate your hypothesis). I hope I have supplied some fodder for actual analysis, and the end of an undying thread.
Scott "maybe some garlic and a stake driven through it (by a tornado)" Sehlhorst
From: s-sehlhorst@ds.mc.ti.com (Scott Sehlhorst)
Newsgroups: alt.folklore.urban,alt.folklore.science
Subject: Re: Glass flows... [was: Tornado shoves straw through 2x4]
Date: Tue, 20 Jun 1995 07:54:13
In article <3s66un$2n5@nnrp2.primenet.com> btrosko@primenet.com (Brian Trosko) writes:
>J.Young (ccjy@sun.cse.bris.ac.uk) wrote:
[...coments of pinhead dancing on head of angel deleted...]
>And here we go yet again, dammit. Once more, for the folks who have
>missed it.
>From the archives at Cathouse:
> >And indeed I have. Some interesting points arise in the article "Antique
> >windowpanes and the flow of supercooled liquids" by Robert C. Plumb
> >(Worcester Polytech. Inst.)in the Journal of Chemical Education, 66(12),
> >994-6, 1989.
[...familiar summary deleted...]
>Brian "And wood is also a liquid, right?" Trosko
More ammo Brian! The Mark's Standard Handbook for Mechanical Engineering also supports the cathouse data, although 594C is Tg for silica lime glass.
Also,
Regarding discussions of bonding keeping glass from 'gaping' at the top...
According to J.A. Pask, in
Chemical Bonding at Glass-To-Metal Interfaces, presented at the Winter Annual
Meeting of the American Society of Mechanical Engineers, Boston, MA, Dec
13-18,1987.,
regarding glass to metal chemical bonding,
"Compatibility of electronic structures of the two phases is required but
not easily acquired because of the incompatibility of the metallic and ioniccovalent
bonding."
He basically says that a chemical bond, although achievable is unlikely without the presence of an oxide layer (today generated by a redox reaction with air on the metal, prior to attachment to the glass), which is probably beyond the technology of 'old' glass manufacturers.
Shay, R.M. Jr., Ph.D. dissertation, Purdue University, West Lafayette, IN (1989) : An ideal glass analysis, referenced in... The Effect of Thermal History on the Mechanical Behavior of Amorphous Polymers, R.M. Shay, Jr., and J.M. Caruthers, Purdue University, School of Chemical Engineering, presented at the Winter Annual Meeting of the American Society of Mechanical Engineers, San Francisco, CA Dec 10-15, 1989.
Shay, btw, treats glass as a solid.
Scott "but if a tree flows in the forest, will anyone hear it?" Sehlhorst
From: spindler@alcoa.com (Doug Spindler)
Newsgroups: alt.folklore.urban
Subject: Re: Glass does not flow. David is wrong.
Date: 20 Jun 1995 13:37:11 GMT
Brian Trosko (btrosko@Primenet.Com) wrote:
> Greg Stevens (stevens@prodigal.psych.rochester.edu) wrote:
> : Uh, actually, it's liquid because it has no crystal structure.
> >... Some interesting points arise in the article "Antique
> >windowpanes and the flow of supercooled liquids" by Robert C. Plumb
> >(Worcester Polytech. Inst.)in the Journal of Chemical Education, 66(12),
> >994-6, 1989.
> > [standard good glass/liquidity points]
Although we're all a bit glazed over on this topic, I thought I would pile on with a semi-pertinent aggressively pro-rigidity statement I found in the literature a year or so ago.
If I am desciphering my notes correctly this was quoted in a book by Reiner, _Deformation, Strain and Flow_, from an article on glass in J. Appl. Phys. (13) pp623-654, 1942 by Preston(?).
[Describing a use of glass in a particular telescope] We use glass in this case, not because it is transparent, but because its rigidity and permanence of shape are better than steel or concrete.
Doug "rigid assets" Spindler
From: btrosko@primenet.com (Brian Trosko)
Newsgroups: alt.folklore.urban
Subject: Re: Glass does not flow. David is wrong.
Date: 20 Jun 1995 20:15:32 GMT
Doug Spindler (spindler@alcoa.com) wrote:
: [Describing a use of glass in a particular telescope]
: We use glass in this case, not because it is transparent, but
: because its rigidity and permanence of shape are better than steel
: or concrete.
And so is its elasticity. I'm not familiar with too many elastic liquids.
Brian "Mr. Bubble?" Trosko
From: scharle@lukasiewicz.cc.nd.edu (scharle)
Newsgroups: alt.folklore.urban,alt.folklore.science
Subject: Re: Glass flows... [was: Tornado shoves straw through 2x4]
Date: 20 Jun 1995 13:41:34 GMT
People have been making refracting telescopes with large glass
lenses for some time. These are precision instruments, and a 50
or 100 year old telescope would surely show signs of glass flow
more dramatically than a piece of window glass. I don't know
whether this is a problem with old refractors. Perhaps some
astronomer or historian of astronomy can tell us.
--
Tom Scharle
Room G003 Computing Center |scharle@lukasiewicz.cc.nd.edu
University of Notre Dame Notre Dame, IN 46556-0539 USA
Newsgroups: alt.folklore.urban,alt.folklore.science
From: nathan@pact.srf.ac.uk (Nathan Sidwell)
Subject: Re: Glass flows... [was: Tornado shoves straw through 2x4]
Date: Tue, 20 Jun 1995 14:09:49 GMT
J.Young (ccjy@sun.cse.bris.ac.uk) wrote:
: Confirmed information.
: Glass IS a supercooled LIQUID.
A super cooled liquid is a substance which remains in a liquid state
below its freezing point. Given a nucleation center it will immediately
freeze.
Glass does not show this phenonmenon. (doesn't undergo a phase transition when scratched)
As others have pointed out it is an amorphous solid. The atoms have the same ordering as the molecules of a liquid (ie no long range order), so in certain ways glass resembles a liquid. *but* the bonds between the atoms are covalent (ie strong) not weak inter-molecular bonds as in acetone, or the hydrogen bonding which occurs in water.
In order to flow, these bonds must be broken (and then reform). The energy required to do so is much higher than the thermal energy available at room temperature -- an additional source of energy must be provided (such as stress).
nathan
From: mbartels@efn.org (Mel Bartels)
Newsgroups: alt.folklore.urban,alt.folklore.science
Subject: Re: Glass flows... [was: Tornado shoves straw through 2x4]
Date: 21 Jun 1995 05:46:23 GMT
>>> old telescopes showing glass movement
I am a 25 yr avid student of amateur astronomy and specifically telescope making over the ages. I have never heard of any scope either refractor reflector or a combination that has shown glass movement. Glass movement in the amateur professional world is fairly easily detected to 1/10 wavelength of visible light. In all these years, I have come across only one story of glass changing shape, and that was an anecdotal story of a mirror that sat on a shelf for years that was tested to a different figure than the original maker had described - hardly convincing evidence.
Regards,
Mel Bartels
From: s-sehlhorst@ds.mc.ti.com (Scott Sehlhorst)
Newsgroups: alt.folklore.urban
Subject: Glass flow, the answer.
Date: Wed, 21 Jun 1995 17:06:49
NNTP-Posting-Host: 157.87.224.38
X-Newsreader: Trumpet for Windows [Version 1.0 Rev Final Beta #11]
Enough already.
Here's the bottom line.
File it at cathouse. Also reference my other posts, which pointed towards
but did not include the solution.
From:
_Elastic-Plastic Problems_, B.D. Annin and G.P. Cherepanov, c 1988,
The American Society of Mechanical Engineers, 345 East 47th St, NYNY 10017
Translation of:Uprugo-plasticheska[i]a zadacha.
QA931.A613 1988 531'.3823'015 88-70032
ISBN 0-7918-0000-8
Note: The equations are nearly unintelligible in ascii, so I will only reference them by author/eq# in the derivation of the solution, and will only try and asciify the bottom line.
Discussion is of elastic-plastic and pure plastic behavior of materials.
Guber-Mises condition (eq#1.3.12) defines shear type plastic deformation in metals and polymers.
Schleiher-Mohr condition is best applicable to granular materials and rocks, (like amorphous solids, like glass), and describes the onset of plastic deformation.
An example of the Guber-Mises is carried through, with support of the equations put forth by Reuss (1930) for pure shear, and Prandtl (1924) for plane stress, resulting in Prandtl-Reuss eq's.
Further discussion of boundary problem definitions and references to Melan's work (1939) lead to the formulation of the Mises maximum principle (1974), leading to the incremental theory of plasticity, and then the associated law, which is recognized as "the most general and substantiated theory."[p11]
In section 1.4, the Haar-Karman principle further goes on to define the conditions under sufficiently smooth surfaces. As everyone knows, the H-K principle becomes the Castigliano principle of linear elasticity once the entire body deforms elastically. That of course is not relevant to this thread, but does serve to define the scope of the theory. I digress.
In equations (#1.4.8), known as Hencky's relations, the tensor fields are defined. The Tresca plasticity condition (1.3.11) is applied, where tau-s is the yield limit for pure shear, and this is continued in the solution of "eq#1.4.6 under conditions (1.4.2), (1.2.4)", returning to the HaarKarman series of equations.
Again, common knowledge, the Haar-Karman equations have different forms depending upon the number of principle stresses that meat or exceed tau-s.
Since gravity is the only vector, I am taking the liberty of assuming that a single stress (that caused by gravity) is relevant. This state is called a "semi-plastic state". If two principle stresses are greater that or equal to tau-s, then we have a state of "total plasticity", but gravity can't create that, so I don't get the simplified equation.
Eq#1.4.12 is what I'm trying to type in ascii as follows:
s2=Ev E
-----------(e1+e2+e3) +---e2
(1+v)(1-2v) 1+v
where s2 = the principle stress due to gravity
E = The Young's Modulus for glass is 4 to 14 e10^3 kg/mm^2
(today's glass falls in the range of 5.5 to 9 e10^3 kg/mm^2)
(so don't use that old impure glass crap to disprove!)
en = the principle strains
v = Poisson's ratio (0.244 for glass)
Stress concentration factors (from cracks, etc) impact measures of glass strength, but not the material properties relevant to flow calculations, so don't waste your breath. I'll get back to it, just wait.
Glass material yield stress is around 3500 kg/mm^2. Glass would have to be subjected to stresses IN EXCESS of that amount, in a sustained fashion for this to begin to occur.
Because of material flaws and crack propogation principles, and the breakdown of crystal bonds (in localized ways) as a mechanism of crack propogation, you can't ever load the glass to its yield stress.
The highest observed macro stress level acheived is only 20% of that, and was done to a glass fiber (as close to flawless as we can get).
Therefore, we can not apply a yield stress to the glass that could cause it to flow without first breaking our sample.
If, somehow, magically, you could apply a stress to an unflawed sample, then the observed plastic deformation (e2) would be roughly 1/15000 the magnitude of the applied stress (in kg/mm^2).
So even if you could magically apply a yielding stress, then you would not be able to measure the deformation.
This applies to glasses below 600C (or 270C for infinite time lengths).
This should be enough for the FAQ!
Scott "A fortune teller told me I'd be famous someday" Sehlhorst
From: schumach@convex.com (Richard A. Schumacher)
Newsgroups: alt.folklore.urban,alt.folklore.science
Subject: Re: Glass flows... [was: Tornado shoves straw through 2x4]
Date: 21 Jun 1995 20:02:21 -0500
Ahem. Speaking as the resident amateur astronomer:
Glass does not flow. People who think that "non-crystalline = liquid" need to re-read their physics or materials texts. There are telescope lenses and mirrors 150 years old. None of these have changed shape by as much as a nanometer. Any such change due to flow would be obvious, even ruinous.
Glass optics do *sag* enough to degrade images if not they
are not supported carefully. But this is not flow; restore
the supports and the mirror etc. regains its shape. (A steel
rod will sag, too, if not adequately supported. Does anyone
call that "flow"?) The size limit for refractor lenses is because
they cannot be supported adequately from their edges.
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