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Post by tileman2 on Jul 31, 2015 18:22:44 GMT -6
I have been reading some mineralogical studies in regards to silica transformation phases. The ceramic industry teaches about the quartz inversion that occurs at 573C: A quartz becoming B Quartz at the temperature. This temperature as taught in our books comes from mineralogical studies of how various minerals are formed in the earth: under the conditions of heat plus time. The temperature that is not discussed is 870C; when B quartz converts to A phase tridymite. From there to B-crystobalite at 1470C: and finally a complete melt at 1705C: which our text books teach as the melting temperature of silica. The 1470C and 1705C do not concern us we never come close to those temperatures. The 870C temperature however very well may affect us: it is within the range of our firings.
Upon further study: some articles suggest that the transformation from B-quartz to B-tridymite can be more unstable than the quartz inversion at 573C (1032F). If in fact, this holds out to be applicable: it might help to explain why reduction and strike firings seem to heal crazing. In both applications; the firing temperature usually does not exceed 870C (1566F). The glass in the glaze would be affected by this temperature: but a vitrified clay body would not go through the radical changes it does in the initial firing. Only a thought at this point, perhaps even a possible theory of why reduction and strike firing heals glaze. In addition, if memory serves in the glass arts: slumping is used to round off sharp cuts and fuse multiple pieces together below the 1566F temp. Someone familiar with glass techniques would have to expound on that portion. It has to be applicable on some level; 50% or more of our glaze starts with frit. Throwing it out there for consideration.
Tom
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Post by Koz on Jul 31, 2015 20:34:23 GMT -6
Tio2,
So what exactly are you trying to say?
Koz
P.S.
And who cares?
I blow through that whole quartz inversion phase like a tornado hittin' a double wide in Oklahoma.
Just get some $hit hot and let's see what you got besides all your looked up stuff.
We aren't sending rockets into space.
Blah blah blah blah blah.
Keep it real huh?
Nice try on the Kiln Song post by the way.
Been there done that too.
Once.
Not twice, nor thrice.
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Post by mohawkpiper on Aug 1, 2015 1:54:30 GMT -6
Hi Tom!
Don't forget, you also have to add 32° when converting from C to F!
G
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Post by jfox on Aug 1, 2015 8:45:25 GMT -6
Tom you posted this page in a previous conversation its about as clear as it gets ,but still dosnt discuss some of the latest high pressure polymorphs they have discovered www.quartzpage.de/gen_mod.html dunting is really the biggest challenge and the hard limit when you go for a really big pot then of coarse its more complicated than that, cause there are actually at least seven forms of tridymite en.wikipedia.org/wiki/Tridymite |
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Post by Arnie Benton on Aug 1, 2015 9:42:52 GMT -6
Jim -
I've been assuming that the alpa to beta crystabolite conversion was the one most involved with the dunting problem - and have been cooling at 40 degrees F from 600 down to 400F - and still have had some breakage with 12 inch or larger plates and bowls. Cooling very slowly doesn't solve the problem.
Arnie
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Post by jfox on Aug 1, 2015 10:39:57 GMT -6
in glass production the annealing process involves holding at around 450 C for several hours to give the glass time to relax maybe that approach would work www.cmog.org/article/annealing-glassthey use a polariscope to visualize strain in glass but i dont think it would work with just reflected light |
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Post by tileman2 on Aug 1, 2015 10:46:23 GMT -6
Greg: Thank you for the reminder; I always manage to forget that even though I know it.
Jim: bringing this up for two reasons primarily. 1. Is it possible that 1566F is the cut off point for reduction and strike firing before the clay starts reacting? Not asserting that it is, but this temperature reaction has not been discussed that I am aware of: if it has, I have missed it; then the point is moot. The quartz inversion temp we use is from mineralogical data: so is this second temp applicable? Jim, if I would have started discussing polymorphic variations: I would have been stoned to death by the Koz. 2. The fact remains that 50% (median) of our glaze recipe is glass (frit), so are some of the principles used in the glass arts applicable on some level? The primary point being; is this 1566CF temp a cut off point we should observe in order to avoid possible expansion issues? 3. Should we observe the slumping temperatures used in the glass arts as a guide to heal crazing? Finally there is a difference between how flat surfaces and vertical surfaces react to glaze cooling. Obviously from an engineering stand point; an ovoid form will exert equal pressure across the entire surface purely due to the design. Reason the Romans and modern engineers use that shape to build bridges: even distribution of weight and pressure. So the plates Arnie makes are prone to unequal pressures regardless of the glaze used because of the design. (mechanics)
Koz: not sure what is going on in your life: but the pressures are coming out in every post. If blowing steam at me makes you feel better: then blow away before you pop. The cool kids in here are in fact pretty cool; inventive, intelligent, creative, curious, pushing boundaries.
Greg: I have stared at your vase several times: impressive piece of work, excellent symmetry in form. Glad to see you are doing a teaching gig; you have the experience and credentials for it. Glad to see your knowledge is being passed to the next generation.
Tom
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Post by tileman2 on Aug 1, 2015 10:50:55 GMT -6
Jim: By the way, the temps posted are from normal room pressures: obviously those temps change as pressure is exerted. Not sure anyone in this room cares besides you and I about tridymite variations below the earths mantle and inside magma chambers. Tom Koz: the whole point of the kiln song was to reflect the emotions of using crystalline glaze. One time you open the kiln and it's stunning, the next time it is: what the  Happens to every crystallier: not to mention the pressures and demands that being a production potter brings. |
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Post by tileman2 on Aug 1, 2015 11:03:33 GMT -6
Jim:
As we have discussed: can crawling be caused by a chemical reaction as well?
Tom
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Post by jfox on Aug 1, 2015 12:46:23 GMT -6
no one really understands phase change, its explained by thermodynamics experimentally but nobody can really predict or explain the specifics but those constants define the nature of the world we live in en.wikipedia.org/wiki/Phase_transition |
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Post by tileman2 on Aug 1, 2015 13:45:00 GMT -6
Jim:
NOTE TO ALL READERS: BORING TOPICS AHEAD!!!!
You just had to post that link; didn't ya. Now I have to spend all weekend reading it and the numerous definitions; thank you for that. Which in turn will spark a topic that will require those reading to tune us out or take No Doz. Case in point:
"The transition between different molecular structures (polymorphs, allotropes or polyamorphs), especially of solids, such as between an amorphous structure and a crystal structure, between two different crystal structures, or between two amorphous structures."
and
"A eutectic transformation, in which a two component single phase liquid is cooled and transforms into two solid phases. The same process, but beginning with a solid instead of a liquid is called a eutectoid transformation."
and
"Phase transitions often involve a symmetry breaking process. For instance, the cooling of a fluid into a crystalline solid breaks continuous translation symmetry: each point in the fluid has the same properties, but each point in a crystal does not have the same properties (unless the points are chosen from the lattice points of the crystal lattice)."
Pick one?
Tom
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Post by jfox on Aug 1, 2015 14:06:38 GMT -6
If you can do the math it almost makes sense(I hear)
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Post by tileman2 on Aug 1, 2015 17:15:17 GMT -6
Jim:
Sure, bait me with links knowing I will jump into the fire. Then fall back on math: may a noreaster blow your dress up next time your in the air.
Or the Arabic version: may the fleas from a thousand camels infect your head. I know about the equations; my trig buddy has looked at them. Problem is he requires determined values to run them: and seeing as though I lack the millions in testing equipment: its back to M>A>G>
Tom
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Post by Koz on Aug 1, 2015 21:11:51 GMT -6
TiO2,
The pressures in my life are minimal.
My game is dialed in, and I wake up feelin' no pain.
I'm always dirty, but my conscience is always clean.
Don't analyze me.
The Kiln Song was just a rip off to me of my own 'Twas The Night Before Crystals , which was my 1000th post on the old forum. Look it up.
Folks have tried to copy me before.
Oh who cares. Go ahead and try.
I'd like to see some of your Useable Art instead of your tests and theories and regurgitated information.
But keep on spewin' and you'll be way ahead of my 2000 plus posts, most of which were very usable, transferable, real world information that helped folks out.
Truth, not theories beyond any tangible application.
I'll stay on my side of The River from now on.
I've been up and down it too many times to get hung up in a whirlpool that goes nowhere.
Koz
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Post by mohawkpiper on Aug 2, 2015 0:28:30 GMT -6
unless im doing large platters or sinks i pretty much blow through quartz inversion also both up and down and haven't really noticed any problems.
G
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Happens to every crystallier: not to mention the pressures and demands that being a production potter brings. 