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Jome
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That would result in a precipation, not a slow polymerisation...The idéa of adding just a small ammount of NaOH/KOH is to dissolve SiO2 and Al(OH)3 a
little at a time and allow for polymerisation. Thats how I interprete whats said on the pages.
Now the water (~800ml) with about 48 grams of colloidal SiO2 in it has turned into a gel. Looks kind of funny 
Guess I'll have to fry it in the oven at about 100 degrees to get rid of the water (as done with silicia dessicant), but how in hell do I remove
the NaCl that was formed in the precipation of silicia from waterglass + hydrochlorid acid... Im worried that the salt might mess with the final
products stability.
[Edited on 2-7-2005 by Jome]
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Pyridinium
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geopolymers
This geopolymer stuff has tremendous madscience potential. It has the association with ancient Egypt, lost technology, a touch of academic
controversy, verifiable results that can (theoretically) be duplicated by amateur chemists, and best of all, association with Imhotep (aka The Mummy).
I didn't have time to read many papers on it yet, but was there a specific one that mentioned sodium amide?
The thing that really intrigues me is that they could make geopolymers of basaltic composition (?). I am going to lose sleep tonight over this one.
I now foresee many nights of working at 3 AM with the neighbours wondering whether I'm up to something shady, when in fact I'm just trying
to cast a basaltic urn. "A 5000-year old mummy commanded me to do it."
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Jome
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Well, Im only 200ml of water and a few grams of salt away from testing my geopolymer mix.
How do I remove water from a sludge that "stops" the filtration? (the Al(OH)3) and how do I remove salt from salt mixed with silicia gel?
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12AX7
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Last time I made some Al(OH)3 (same method as a matter of fact), it settled just fine. You must've precipitated it too quick.
Can always boil the water out (vacuum or heat), but that doesn't remove the salts stuck in it.
AFAIK, acid + silicate solution always causes a gel. I would think it would be possible to grow quartz crystals of any size with a solution and slow
enough acidification, but...who knows.
Heh, can always get some 325 mesh flint from a pottery supply, if that's fine enough. I have a 50 pound bag of such concentrated silicosis in
the basement.
Tim
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Tacho
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I used to think that the solid I got from mixing sodium silicate with common mineral acids was silica gel.
Recently I mixed dilute boric acid with dilute neutral sodium silicate. Initially there was just a haze in the liquid solution but, after a couple of
days, there was a true gel formed. Gelatin like. After completelly dry it shrank to and insoluble mass.
I'm testing this as a silicate based binding for graphite powder. Since it remains liquid for a long time, it can be mixed with fillers to obtain
all kinds of solid, insoluble materials.
Hey pyro people, maybe it could be used to bind lead oxide in electrodes.
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Cyrus
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What would the reaction be?
I'm guessing sodium borate would be formed (NaB4O7 IIRC).
Sounds interesting enough, I'll try it on a test tube scale. But I don't know if it would make a good binder for PbO2 if it shrinks a lot.
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Tacho
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I think it's just the classic silica gel formation. That's why it was called gel. I tried boric acid because I read somewhere that a (true)
gel would be formed using weak organic acids in dilute solutions. Boric is not organic but it's weak and I was interested in it's insect
killing properties.
The fact that is shrinks doesn't mean much. The filler should make a paste with the silicate-acid solution, so, just enough gel should be left to
bind the dry particules, keeping electric contact between them.
EDIT: in fact, the shrinking may compress the particles, improving electrical conductivity.
I had a reasonable sucess with powdered graphite after 24h. The resulting solid conducts VERY well, just a few ohms p/ cm. After immersion in water
it broke in larger pieces, but didn't dissolve completely. Not bad for a first try. I believe I should use more concentrate solutions and prevent
drying for a couple of days, so that the gel has time to form.
I know i'm a bit off-topic, but not much if you think about it.
[Edited on 12-7-2005 by Tacho]
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Cyrus
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I tried this reaction with very dilute boric acid and very dilute sodium silicate. It does make a wierd gel after a day or so. I think my solution was
too dilute because the gel is weak and watery. Nothing like Jello. What was the consistency of your gel, Tacho?
I'll see how it changes over the next few days.
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Tacho
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I think you can get all sorts of consistencies, depending on concentrations.
I made a "standart" solution of 2g of boric acid in 40 ml of water.
My sodium silicate bottle does not state it's concentration, but I guess is a industry standard, viscous like thick oil.
A mix of 1 ml SS, 2 ml water and 3 ml of the standart solution of boric acid yiels a gel in a few minutes. The gel is like jello, but more fragile.
As you add more water to this mix, the gellification takes longer to happen. At about 7ml water, it takes many hours.
Gellification also happen with borax solution and ascorbic acid (vitamin C)solution. It takes days though. Sorry, but I can't give you numbers.
Did those in a hush, with chemicals at hand.
I made a solid graphite piece, mixing the powder with the liquids before gellification, keeping it humid for a couple of days, and letting it dry. I
have dismolded it, but I'm waiting one more day to let it dry more completelly. Maybe some reaction with air CO2 will also happen. I'll
break it in two pieces, one goes in an acid solution that, hopefully, will make it more water resistant. The other will be tested "as is" in
water.
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Cyrus
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I used, perhaps, 0.3 g of borax to 8 ml H2O. The gel wasn't displaying much activity or potential, so I threw it away. Perhaps I'll try a
more concentrated one.
[Edited on 18-7-2005 by Cyrus]
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Tacho
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My borax experiment took about 4 days to gellify. Maybe it gellified because part of the water evaporated. I'll try more concentrated solutions.
Anyway, the borax rendered a milky gel, much less transparent than the boric acid one, although the latter was not transparent at all when was a gel,
becoming more transparent as it dryied.
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Tacho
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Just for the record: I meant "borax solution + sodium silicate solution" and "ascorbic acid solution + sodium silicate solution".
I don't think there is easy method of making silica gel without sodium silicate.
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trilobite
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In case you guys missed one of the original patents, US4349386, I think answers some of your questions. The reference was found in http://www.geopolymer.org/davidovits/milestones_geopolymer.h....
Maybe FR2512805 holds the key to refractory materials. It apparently describes expansion of these materials to foams with sodium perborate.
[Edited on 31-7-2005 by trilobite]
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trilobite
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Here's some information on refractory geopolymer materials. It seems metakaolinite is the typical mineral used in making geopolymers but the
patents tell us that kaolin aka china clay could be used as well. Metakaolinite can be made by heating kaolin at 700°C for 6 hours but then you need
a furnace anyway, kinda defeats the advantage of curing at low temperatures. It would be awesome if worked with kaolin.
Synthesis and thermal behaviour of potassium sialate geopolymers
Materials Letters, 57, 1477-1482 (2003)
http://www.geocities.com/tatssnart/Materials_Letters_57_1477...
Fire-resistant Aluminosilicate Composites
Fire and Materials, 21, 67-73 (1997)
http://www.geocities.com/tatssnart/Fire_and_Materials_21_67-...
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Baluuuu
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Hi
I'd like to ask for any subject-matters, technical literature, references, recepts or any help from you to my diploma work.
My theme is the Industrial use for Geopolymers and one of concrete geopolymer's research.
abaluuuu@gmail.com
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franklyn
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I must be missing something , for how does this differ from a zeolite ?
Also the Al - O - Si cross bonding is found in a machinable sintered ceramic
made of silicon nitride and alumina trade name Sialon. What appears new
here is that this is formed without firing. I'm reminded too of a mention
some years ago of a discovery called Beer stone. It was a mix of pearlites
and other minerals that when wetted with beer ( apparently serving as a
blowing agent does for expanded polymers ) foamed and quite rapidly
solidified into a light porous pumice like material with superior strength.
This is the most comprehensive explaination I found on Geopolymer _
http://composite.about.com/library/weekly/aa030529.htm
All I could find on Beer stone _
http://en.wikiquote.org/wiki/Talk:Beer
Perhaps it's related to this ?
http://www.birkocorp.com/brewing/beerstone.asp
burp !
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ShadowWarrior4444
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Rise up, ancient thread! And carry with you a slight request--someone change the title of the thread so that it is spelled correctly. *sigh*
Geopolymers have captivated my interest lately for their potential to create high-quality crucibles for aluminum casting, as well as their superiority
to concrete in most if not all applications. They have interesting ties to ancient times, specifically the theories that Roman fortifications were
constructed from geopolymers, as well as the limestone in Egyptian pyramids.
Video by a French university showing the formula, process, and construction of Egyptian limestone: http://youtube.com/watch?v=znQk_yBHre4
Do try to ignore the comments on it, the sheer amount of fanaticism and religious raving began to wear on me, and I read alchemical texts for fun.
I believe the more professional way of creating geopolymers is to simply mix a white aluminosilicate clay (usually simply Kaolin, occasionally
metakaolin,) a bit of sodium or potassium silicate, then add KOH as the catalyst. Any home/lab formulations would be appreciated--I would very much
like to create molds and crucibles for the casting of aluminum.
[Edited on 5-6-2008 by ShadowWarrior4444]
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